The BGP Tunnel Encapsulation Attribute
draft-ietf-idr-tunnel-encaps-11
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9012.
|
|
|---|---|---|---|
| Authors | Eric C. Rosen , Keyur Patel , Gunter Van de Velde | ||
| Last updated | 2019-02-22 | ||
| Replaces | draft-rosen-idr-tunnel-encaps, draft-vandevelde-idr-remote-next-hop | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
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| Stream | WG state | WG Consensus: Waiting for Write-Up | |
| Document shepherd | John Scudder | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | John Scudder <jgs@juniper.net> |
draft-ietf-idr-tunnel-encaps-11
IDR Working Group E. Rosen, Ed.
Internet-Draft Juniper Networks, Inc.
Obsoletes: 5512 (if approved) K. Patel
Intended status: Standards Track Arrcus, Inc
Expires: August 26, 2019 G. Van de Velde
Nokia
February 22, 2019
The BGP Tunnel Encapsulation Attribute
draft-ietf-idr-tunnel-encaps-11
Abstract
RFC 5512 defines a BGP Path Attribute known as the "Tunnel
Encapsulation Attribute". This attribute allows one to specify a set
of tunnels. For each such tunnel, the attribute can provide the
information needed to create the tunnel and the corresponding
encapsulation header. The attribute can also provide information
that aids in choosing whether a particular packet is to be sent
through a particular tunnel. RFC 5512 states that the attribute is
only carried in BGP UPDATEs that have the "Encapsulation Subsequent
Address Family (Encapsulation SAFI)". This document deprecates the
Encapsulation SAFI (which has never been used in production), and
specifies semantics for the attribute when it is carried in UPDATEs
of certain other SAFIs. This document adds support for additional
tunnel types, and allows a remote tunnel endpoint address to be
specified for each tunnel. This document also provides support for
specifying fields of any inner or outer encapsulations that may be
used by a particular tunnel.
This document obsoletes RFC 5512.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on August 26, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Brief Summary of RFC 5512 . . . . . . . . . . . . . . . . 3
1.2. Deficiencies in RFC 5512 . . . . . . . . . . . . . . . . 4
1.3. Brief Summary of Changes from RFC 5512 . . . . . . . . . 5
1.4. Impact on RFC 5566 . . . . . . . . . . . . . . . . . . . 6
2. The Tunnel Encapsulation Attribute . . . . . . . . . . . . . 6
3. Tunnel Encapsulation Attribute Sub-TLVs . . . . . . . . . . . 8
3.1. The Remote Endpoint Sub-TLV . . . . . . . . . . . . . . . 8
3.2. Encapsulation Sub-TLVs for Particular Tunnel Types . . . 10
3.2.1. VXLAN . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2.2. VXLAN-GPE . . . . . . . . . . . . . . . . . . . . . . 12
3.2.3. NVGRE . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2.4. L2TPv3 . . . . . . . . . . . . . . . . . . . . . . . 14
3.2.5. GRE . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2.6. MPLS-in-GRE . . . . . . . . . . . . . . . . . . . . . 15
3.3. Outer Encapsulation Sub-TLVs . . . . . . . . . . . . . . 16
3.3.1. IPv4 DS Field . . . . . . . . . . . . . . . . . . . . 16
3.3.2. UDP Destination Port . . . . . . . . . . . . . . . . 16
3.4. Sub-TLVs for Aiding Tunnel Selection . . . . . . . . . . 17
3.4.1. Protocol Type Sub-TLV . . . . . . . . . . . . . . . . 17
3.4.2. Color Sub-TLV . . . . . . . . . . . . . . . . . . . . 17
3.5. Embedded Label Handling Sub-TLV . . . . . . . . . . . . . 17
3.6. MPLS Label Stack Sub-TLV . . . . . . . . . . . . . . . . 18
3.7. Prefix-SID Sub-TLV . . . . . . . . . . . . . . . . . . . 20
4. Extended Communities Related to the Tunnel Encapsulation
Attribute . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.1. Encapsulation Extended Community . . . . . . . . . . . . 21
4.2. Router's MAC Extended Community . . . . . . . . . . . . . 22
4.3. Color Extended Community . . . . . . . . . . . . . . . . 23
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5. Semantics and Usage of the Tunnel Encapsulation attribute . . 23
6. Routing Considerations . . . . . . . . . . . . . . . . . . . 27
6.1. No Impact on BGP Decision Process . . . . . . . . . . . . 27
6.2. Looping, Infinite Stacking, Etc. . . . . . . . . . . . . 27
7. Recursive Next Hop Resolution . . . . . . . . . . . . . . . . 28
8. Use of Virtual Network Identifiers and Embedded Labels when
Imposing a Tunnel Encapsulation . . . . . . . . . . . . . . . 29
8.1. Tunnel Types without a Virtual Network Identifier Field . 29
8.2. Tunnel Types with a Virtual Network Identifier Field . . 29
8.2.1. Unlabeled Address Families . . . . . . . . . . . . . 30
8.2.2. Labeled Address Families . . . . . . . . . . . . . . 30
9. Applicability Restrictions . . . . . . . . . . . . . . . . . 32
10. Scoping . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
11. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 33
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34
12.1. Subsequent Address Family Identifiers . . . . . . . . . 35
12.2. BGP Path Attributes . . . . . . . . . . . . . . . . . . 35
12.3. Extended Communities . . . . . . . . . . . . . . . . . . 35
12.4. BGP Tunnel Encapsulation Attribute Sub-TLVs . . . . . . 35
12.5. Tunnel Types . . . . . . . . . . . . . . . . . . . . . . 36
13. Security Considerations . . . . . . . . . . . . . . . . . . . 36
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 37
15. Contributor Addresses . . . . . . . . . . . . . . . . . . . . 37
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
16.1. Normative References . . . . . . . . . . . . . . . . . . 38
16.2. Informative References . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
1. Introduction
This document obsoletes RFC 5512. The deficiencies of RFC 5512, and
a summary of the changes made, are discussed in Sections 1.1-1.3.
The material from RFC 5512 that is retained has been incorporated
into this document.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.1. Brief Summary of RFC 5512
[RFC5512] defines a BGP Path Attribute known as the Tunnel
Encapsulation attribute. This attribute consists of one or more
TLVs. Each TLV identifies a particular type of tunnel. Each TLV
also contains one or more sub-TLVs. Some of the sub-TLVs, e.g., the
"Encapsulation sub-TLV", contain information that may be used to form
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the encapsulation header for the specified tunnel type. Other sub-
TLVs, e.g., the "color sub-TLV" and the "protocol sub-TLV", contain
information that aids in determining whether particular packets
should be sent through the tunnel that the TLV identifies.
[RFC5512] only allows the Tunnel Encapsulation attribute to be
attached to BGP UPDATE messages of the Encapsulation Address Family.
These UPDATE messages have an AFI (Address Family Identifier) of 1 or
2, and a SAFI of 7. In an UPDATE of the Encapsulation SAFI, the NLRI
(Network Layer Reachability Information) is an address of the BGP
speaker originating the UPDATE. Consider the following scenario:
o BGP speaker R1 has received and installed UPDATE U;
o UPDATE U's SAFI is the Encapsulation SAFI;
o UPDATE U has the address R2 as its NLRI;
o UPDATE U has a Tunnel Encapsulation attribute.
o R1 has a packet, P, to transmit to destination D;
o R1's best path to D is a BGP route that has R2 as its next hop;
In this scenario, when R1 transmits packet P, it should transmit it
to R2 through one of the tunnels specified in U's Tunnel
Encapsulation attribute. The IP address of the remote endpoint of
each such tunnel is R2. Packet P is known as the tunnel's "payload".
1.2. Deficiencies in RFC 5512
While the ability to specify tunnel information in a BGP UPDATE is
useful, the procedures of [RFC5512] have certain limitations:
o The requirement to use the "Encapsulation SAFI" presents an
unfortunate operational cost, as each BGP session that may need to
carry tunnel encapsulation information needs to be reconfigured to
support the Encapsulation SAFI. The Encapsulation SAFI has never
been used, and this requirement has served only to discourage the
use of the Tunnel Encapsulation attribute.
o There is no way to use the Tunnel Encapsulation attribute to
specify the remote endpoint address of a given tunnel; [RFC5512]
assumes that the remote endpoint of each tunnel is specified as
the NLRI of an UPDATE of the Encapsulation-SAFI.
o If the respective best paths to two different address prefixes
have the same next hop, [RFC5512] does not provide a
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straightforward method to associate each prefix with a different
tunnel.
o If a particular tunnel type requires an outer IP or UDP
encapsulation, there is no way to signal the values of any of the
fields of the outer encapsulation.
o In [RFC5512]'s specification of the sub-TLVs, each sub-TLV has
one-octet length field. In some cases, a two-octet length field
may be needed.
1.3. Brief Summary of Changes from RFC 5512
In this document we address these deficiencies by:
o Deprecating the Encapsulation SAFI.
o Defining a new "Remote Endpoint Address sub-TLV" that can be
included in any of the TLVs contained in the Tunnel Encapsulation
attribute. This sub-TLV can be used to specify the remote
endpoint address of a particular tunnel.
o Allowing the Tunnel Encapsulation attribute to be carried by BGP
UPDATEs of additional AFI/SAFIs. Appropriate semantics are
provided for this way of using the attribute.
o Defining a number of new sub-TLVs that provide additional
information that is useful when forming the encapsulation header
used to send a packet through a particular tunnel.
o Defining the sub-TLV type field so that a sub-TLV whose type is in
the range from 0 to 127 inclusive has a one-octet length field,
but a sub-TLV whose type is in the range from 128 to 255 inclusive
has a two-octet length field.
One of the sub-TLVs defined in [RFC5512] is the "Encapsulation sub-
TLV". For a given tunnel, the encapsulation sub-TLV specifies some
of the information needed to construct the encapsulation header used
when sending packets through that tunnel. This document defines
encapsulation sub-TLVs for a number of tunnel types not discussed in
[RFC5512]: VXLAN (Virtual Extensible Local Area Network, [RFC7348]),
VXLAN-GPE (Generic Protocol Extension for VXLAN,
[I-D.ietf-nvo3-vxlan-gpe]), NVGRE (Network Virtualization Using
Generic Routing Encapsulation [RFC7637]), and MPLS-in-GRE (MPLS in
Generic Routing Encapsulation [RFC2784], [RFC2890], [RFC4023]).
MPLS-in-UDP [RFC7510] is also supported, but an Encapsulation sub-TLV
for it is not needed.
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Some of the encapsulations mentioned in the previous paragraph need
to be further encapsulated inside UDP and/or IP. [RFC5512] provides
no way to specify that certain information is to appear in these
outer IP and/or UDP encapsulations. This document provides a
framework for including such information in the TLVs of the Tunnel
Encapsulation attribute.
When the Tunnel Encapsulation attribute is attached to a BGP UPDATE
whose AFI/SAFI identifies one of the labeled address families, it is
not always obvious whether the label embedded in the NLRI is to
appear somewhere in the tunnel encapsulation header (and if so,
where), or whether it is to appear in the payload, or whether it can
be omitted altogether. This is especially true if the tunnel
encapsulation header itself contains a "virtual network identifier".
This document provides a mechanism that allows one to signal (by
using sub-TLVs of the Tunnel Encapsulation attribute) how one wants
to use the embedded label when the tunnel encapsulation has its own
virtual network identifier field.
[RFC5512] defines a Tunnel Encapsulation Extended Community, that can
be used instead of the Tunnel Encapsulation attribute under certain
circumstances. This document addresses the issue of how to handle a
BGP UPDATE that carries both a Tunnel Encapsulation attribute and one
or more Tunnel Encapsulation Extended Communities.
1.4. Impact on RFC 5566
[RFC5566] uses the mechanisms defined in [RFC5512]. While this
document obsoletes [RFC5512], it does not address the issue of how to
use the mechanisms of [RFC5566] without also using the Encapsulation
SAFI. Those issues are considered to be outside the scope of this
document.
2. The Tunnel Encapsulation Attribute
The Tunnel Encapsulation attribute is an optional transitive BGP Path
attribute. IANA has assigned the value 23 as the type code of the
attribute. The attribute is composed of a set of Type-Length-Value
(TLV) encodings. Each TLV contains information corresponding to a
particular tunnel type. A TLV is structured as shown in Figure 1:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tunnel Type (2 Octets) | Length (2 Octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Value |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Tunnel Encapsulation TLV Value Field
o Tunnel Type (2 octets): identifies a type of tunnel. The field
contains values from the IANA Registry "BGP Tunnel Encapsulation
Attribute Tunnel Types".
Note that for tunnel types whose names are of the form "X-in-Y",
e.g., "MPLS-in-GRE", only packets of the specified payload type
"X" are to be carried through the tunnel of type "Y". This is the
equivalent of specifying a tunnel type "Y" and including in its
TLV a Protocol Type sub-TLV (see Section 3.4.1) specifying
protocol "X". If the tunnel type is "X-in-Y", it is unnecessary,
though harmless, to include a Protocol Type sub-TLV specifying
"X".
o Length (2 octets): the total number of octets of the value field.
o Value (variable): comprised of multiple sub-TLVs.
Each sub-TLV consists of three fields: a 1-octet type, a 1-octet or
2-octet length field (depending on the type), and zero or more octets
of value. A sub-TLV is structured as shown in Figure 2:
+--------------------------------+
| Sub-TLV Type (1 Octet) |
+--------------------------------+
| Sub-TLV Length (1 or 2 Octets) |
+--------------------------------+
| Sub-TLV Value (Variable) |
+--------------------------------+
Table 1: Tunnel Encapsulation Sub-TLV Format
o Sub-TLV Type (1 octet): each sub-TLV type defines a certain
property about the tunnel TLV that contains this sub-TLV.
o Sub-TLV Length (1 or 2 octets): the total number of octets of the
sub-TLV value field. The Sub-TLV Length field contains 1 octet if
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the Sub-TLV Type field contains a value in the range from 0-127.
The Sub-TLV Length field contains two octets if the Sub-TLV Type
field contains a value in the range from 128-255.
o Sub-TLV Value (variable): encodings of the value field depend on
the sub-TLV type as enumerated above. The following sub-sections
define the encoding in detail.
3. Tunnel Encapsulation Attribute Sub-TLVs
In this section, we specify a number of sub-TLVs. These sub-TLVs can
be included in a TLV of the Tunnel Encapsulation attribute.
3.1. The Remote Endpoint Sub-TLV
The Remote Endpoint sub-TLV is a sub-TLV whose value field contains
three sub-fields:
1. a four-octet Autonomous System (AS) number sub-field
2. a two-octet Address Family sub-field
3. an address sub-field, whose length depends upon the Address
Family.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Autonomous System Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Family | Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Remote Endpoint Sub-TLV Value Field
The Address Family subfield contains a value from IANA's "Address
Family Numbers" registry. In this document, we assume that the
Address Family is either IPv4 or IPv6; use of other address families
is outside the scope of this document.
If the Address Family subfield contains the value for IPv4, the
address subfield must contain an IPv4 address (a /32 IPv4 prefix).
In this case, the length field of Remote Endpoint sub-TLV must
contain the value 10 (0xa).
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If the Address Family subfield contains the value for IPv6, the
address sub-field must contain an IPv6 address (a /128 IPv6 prefix).
In this case, the length field of Remote Endpoint sub-TLV must
contain the value 22 (0x16). IPv6 link local addresses are not valid
values of the IP address field.
In a given BGP UPDATE, the address family (IPv4 or IPv6) of a Remote
Endpoint sub-TLV is independent of the address family of the UPDATE
itself. For example, an UPDATE whose NLRI is an IPv4 address may
have a Tunnel Encapsulation attribute containing Remote Endpoint sub-
TLVs that contain IPv6 addresses. Also, different tunnels
represented in the Tunnel Encapsulation attribute may have Remote
Endpoints of different address families.
A two-octet AS number can be carried in the AS number field by
setting the two high order octets to zero, and carrying the number in
the two low order octets of the field.
The AS number in the sub-TLV MUST be the number of the AS to which
the IP address in the sub-TLV belongs.
There is one special case: the Remote Endpoint sub-TLV MAY have a
value field whose Address Family subfield contains 0. This means
that the tunnel's remote endpoint is the UPDATE's BGP next hop. If
the Address Family subfield contains 0, the Address subfield is
omitted, and the Autonomous System number field is set to 0.
If any of the following conditions hold, the Remote Endpoint sub-TLV
is considered to be "malformed":
o The sub-TLV contains the value for IPv4 in its Address Family
subfield, but the length of the sub-TLV's value field is other
than 10 (0xa).
o The sub-TLV contains the value for IPv6 in its Address Family
subfield, but the length of the sub-TLV's value field is other
than 22 (0x16).
o The sub-TLV contains the value zero in its Address Family field,
but the length of the sub-TLV's value field is other than 6, or
the Autonomous System subfield is not set to zero.
o The IP address in the sub-TLV's address subfield is not a valid IP
address (e.g., it's an IPv4 broadcast address).
o It can be determined that the IP address in the sub-TLV's address
subfield does not belong to the non-zero AS whose number is in the
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its Autonomous System subfield. (See section Section 13 for
discussion of one way to determine this.)
If the Remote Endpoint sub-TLV is malformed, the TLV containing it is
also considered to be malformed, and the entire TLV MUST be ignored.
However, the Tunnel Encapsulation attribute SHOULD NOT be considered
to be malformed in this case; other TLVs in the attribute SHOULD be
processed (if they can be parsed correctly).
When redistributing a route that is carrying a Tunnel Encapsulation
attribute containing a TLV that itself contains a malformed Remote
Endpoint sub-TLV, the TLV SHOULD be removed from the attribute before
redistribution.
See Section 11 for further discussion of how to handle errors that
are encountered when parsing the Tunnel Encapsulation attribute.
If the Remote Endpoint sub-TLV contains an IPv4 or IPv6 address that
is valid but not reachable, the sub-TLV is NOT considered to be
malformed, and the containing TLV SHOULD NOT be removed from the
attribute before redistribution. However, the tunnel identified by
the TLV containing that sub-TLV cannot be used until such time as the
address becomes reachable. See Section 5.
3.2. Encapsulation Sub-TLVs for Particular Tunnel Types
This section defines Tunnel Encapsulation sub-TLVs for the following
tunnel types: VXLAN ([RFC7348]), VXLAN-GPE
([I-D.ietf-nvo3-vxlan-gpe]), NVGRE ([RFC7637]), MPLS-in-GRE
([RFC2784], [RFC2890], [RFC4023]), L2TPv3 ([RFC3931]), and GRE
([RFC2784], [RFC2890], [RFC4023]).
Rules for forming the encapsulation based on the information in a
given TLV are given in Sections 5 and 8.
For some tunnel types, the rules are obvious and not mentioned in
this document.
There are also tunnel types for which it is not necessary to define
an Encapsulation sub-TLV, because there are no fields in the
encapsulation header whose values need to be signaled from the remote
endpoint.
3.2.1. VXLAN
This document defines an encapsulation sub-TLV for VXLAN tunnels.
When the tunnel type is VXLAN, the following is the structure of the
value field in the encapsulation sub-TLV:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V|M|R|R|R|R|R|R| VN-ID (3 Octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address (4 Octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address (2 Octets) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: VXLAN Encapsulation Sub-TLV
V: This bit is set to 1 to indicate that a "valid" VN-ID (Virtual
Network Identifier) is present in the encapsulation sub-TLV.
Please see Section 8.
M: This bit is set to 1 to indicate that a valid MAC Address is
present in the encapsulation sub-TLV.
R: The remaining bits in the 8-bit flags field are reserved for
further use. They SHOULD always be set to 0.
VN-ID: If the V bit is set, the VN-id field contains a 3 octet VN-
ID value. If the V bit is not set, the VN-id field SHOULD be set
to zero.
MAC Address: If the M bit is set, this field contains a 6 octet
Ethernet MAC address. If the M bit is not set, this field SHOULD
be set to all zeroes.
When forming the VXLAN encapsulation header:
o The values of the V, M, and R bits are NOT copied into the flags
field of the VXLAN header. The flags field of the VXLAN header is
set as per [RFC7348].
o If the M bit is set, the MAC Address is copied into the Inner
Destination MAC Address field of the Inner Ethernet Header (see
section 5 of [RFC7348].
If the M bit is not set, and the payload being sent through the
VXLAN tunnel is an ethernet frame, the Destination MAC Address
field of the Inner Ethernet Header is just the Destination MAC
Address field of the payload's ethernet header.
If the M bit is not set, and the payload being sent through the
VXLAN tunnel is an IP or MPLS packet, the Inner Destination MAC
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address field is set to a configured value; if there is no
configured value, the VXLAN tunnel cannot be used.
o See Section 8 to see how the VNI field of the VXLAN encapsulation
header is set.
Note that in order to send an IP packet or an MPLS packet through a
VXLAN tunnel, the packet must first be encapsulated in an ethernet
header, which becomes the "inner ethernet header" described in
[RFC7348]. The VXLAN Encapsulation sub-TLV may contain information
(e.g.,the MAC address) that is used to form this ethernet header.
3.2.2. VXLAN-GPE
This document defines an encapsulation sub-TLV for VXLAN tunnels.
When the tunnel type is VXLAN-GPE, the following is the structure of
the value field in the encapsulation sub-TLV:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|V|R|R|R|R|R| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VN-ID | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: VXLAN GPE Encapsulation Sub-TLV
V: This bit is set to 1 to indicate that a "valid" VN-ID is
present in the encapsulation sub-TLV. Please see Section 8.
R: The bits designated "R" above are reserved for future use.
They SHOULD always be set to zero.
Version (Ver): Indicates VXLAN GPE protocol version. (See the
"Version Bits" section of [I-D.ietf-nvo3-vxlan-gpe].) If the
indicated version is not supported, the TLV that contains this
Encapsulation sub-TLV MUST be treated as specifying an unsupported
tunnel type. The value of this field will be copied into the
corresponding field of the VXLAN encapsulation header.
VN-ID: If the V bit is set, this field contains a 3 octet VN-ID
value. If the V bit is not set, this field SHOULD be set to zero.
When forming the VXLAN-GPE encapsulation header:
o The values of the V and R bits are NOT copied into the flags field
of the VXLAN-GPE header. However, the values of the Ver bits are
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copied into the VXLAN-GPE header. Other bits in the flags field
of the VXLAN-GPE header are set as per [I-D.ietf-nvo3-vxlan-gpe].
o See Section 8 to see how the VNI field of the VXLAN-GPE
encapsulation header is set.
3.2.3. NVGRE
This document defines an encapsulation sub-TLV for NVGRE tunnels.
When the tunnel type is NVGRE, the following is the structure of the
value field in the encapsulation sub-TLV:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V|M|R|R|R|R|R|R| VN-ID (3 Octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address (4 Octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Address (2 Octets) | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: NVGRE Encapsulation Sub-TLV
V: This bit is set to 1 to indicate that a "valid" VN-ID is
present in the encapsulation sub-TLV. Please see Section 8.
M: This bit is set to 1 to indicate that a valid MAC Address is
present in the encapsulation sub-TLV.
R: The remaining bits in the 8-bit flags field are reserved for
further use. They SHOULD always be set to 0.
VN-ID: If the V bit is set, the VN-id field contains a 3 octet VN-
ID value. If the V bit is not set, the VN-id field SHOULD be set
to zero.
MAC Address: If the M bit is set, this field contains a 6 octet
Ethernet MAC address. If the M bit is not set, this field SHOULD
be set to all zeroes.
When forming the NVGRE encapsulation header:
o The values of the V, M, and R bits are NOT copied into the flags
field of the NVGRE header. The flags field of the VXLAN header is
set as per [RFC7637].
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o If the M bit is set, the MAC Address is copied into the Inner
Destination MAC Address field of the Inner Ethernet Header (see
section 3.2 of [RFC7637].
If the M bit is not set, and the payload being sent through the
NVGRE tunnel is an ethernet frame, the Destination MAC Address
field of the Inner Ethernet Header is just the Destination MAC
Address field of the payload's ethernet header.
If the M bit is not set, and the payload being sent through the
NVGRE tunnel is an IP or MPLS packet, the Inner Destination MAC
address field is set to a configured value; if there is no
configured value, the NVGRE tunnel cannot be used.
o See Section 8 to see how the VSID (Virtual Subnet Identifier)
field of the NVGRE encapsulation header is set.
3.2.4. L2TPv3
When the tunnel type of the TLV is L2TPv3 over IP, the following is
the structure of the value field of the encapsulation sub-TLV:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Cookie (Variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: L2TPv3 Encapsulation Sub-TLV
Session ID: a non-zero 4-octet value locally assigned by the
advertising router that serves as a lookup key in the incoming
packet's context.
Cookie: an optional, variable length (encoded in octets -- 0 to 8
octets) value used by L2TPv3 to check the association of a
received data message with the session identified by the Session
ID. Generation and usage of the cookie value is as specified in
[RFC3931].
The length of the cookie is not encoded explicitly, but can be
calculated as (sub-TLV length - 4).
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3.2.5. GRE
When the tunnel type of the TLV is GRE, the following is the
structure of the value field of the encapsulation sub-TLV:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GRE Key (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: GRE Encapsulation Sub-TLV
GRE Key: 4-octet field [RFC2890] that is generated by the
advertising router. The actual method by which the key is
obtained is beyond the scope of this document. The key is
inserted into the GRE encapsulation header of the payload packets
sent by ingress routers to the advertising router. It is intended
to be used for identifying extra context information about the
received payload.
Note that the key is optional. Unless a key value is being
advertised, the GRE encapsulation sub-TLV MUST NOT be present.
3.2.6. MPLS-in-GRE
When the tunnel type is MPLS-in-GRE, the following is the structure
of the value field in an optional encapsulation sub-TLV:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GRE-Key (4 Octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: MPLS-in-GRE Encapsulation Sub-TLV
GRE-Key: 4-octet field [RFC2890] that is generated by the
advertising router. The actual method by which the key is
obtained is beyond the scope of this document. The key is
inserted into the GRE encapsulation header of the payload packets
sent by ingress routers to the advertising router. It is intended
to be used for identifying extra context information about the
received payload. Note that the key is optional. Unless a key
value is being advertised, the MPLS-in-GRE encapsulation sub-TLV
MUST NOT be present.
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Note that the GRE tunnel type defined in Section 3.2.5 can be used
instead of the MPLS-in-GRE tunnel type when it is necessary to
encapsulate MPLS in GRE. Including a TLV of the MPLS-in-GRE tunnel
type is equivalent to including a TLV of the GRE tunnel type that
also includes a Protocol Type sub-TLV (Section 3.4.1) specifying MPLS
as the protocol to be encapsulated. That is, if a TLV specifies
MPLS-in-GRE or if it includes a Protocol Type sub-TLV specifying
MPLS, the GRE tunnel advertised in that TLV MUST NOT be used for
carrying IP packets.
While it is not really necessary to have both the GRE and MPLS-in-GRE
tunnel types, both are included for reasons of backwards
compatibility.
3.3. Outer Encapsulation Sub-TLVs
The Encapsulation sub-TLV for a particular tunnel type allows one to
specify the values that are to be placed in certain fields of the
encapsulation header for that tunnel type. However, some tunnel
types require an outer IP encapsulation, and some also require an
outer UDP encapsulation. The Encapsulation sub-TLV for a given
tunnel type does not usually provide a way to specify values for
fields of the outer IP and/or UDP encapsulations. If it is necessary
to specify values for fields of the outer encapsulation, additional
sub-TLVs must be used. This document defines two such sub-TLVs.
If an outer encapsulation sub-TLV occurs in a TLV for a tunnel type
that does not use the corresponding outer encapsulation, the sub-TLV
is treated as if it were an unknown type of sub-TLV.
3.3.1. IPv4 DS Field
Most of the tunnel types that can be specified in the Tunnel
Encapsulation attribute require an outer IP encapsulation. The IPv4
Differentiated Services (DS) Field sub-TLV can be carried in the TLV
of any such tunnel type. It specifies the setting of the one-octet
Differentiated Services field in the outer IP encapsulation (see
[RFC2474]). The value field is always a single octet.
3.3.2. UDP Destination Port
Some of the tunnel types that can be specified in the Tunnel
Encapsulation attribute require an outer UDP encapsulation.
Generally there is a standard UDP Destination Port value for a
particular tunnel type. However, sometimes it is useful to be able
to use a non-standard UDP destination port. If a particular tunnel
type requires an outer UDP encapsulation, and it is desired to use a
UDP destination port other than the standard one, the port to be used
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can be specified by including a UDP Destination Port sub-TLV. The
value field of this sub-TLV is always a two-octet field, containing
the port value.
3.4. Sub-TLVs for Aiding Tunnel Selection
3.4.1. Protocol Type Sub-TLV
The protocol type sub-TLV MAY be included in a given TLV to indicate
the type of the payload packets that may be encapsulated with the
tunnel parameters that are being signaled in the TLV. The value
field of the sub-TLV contains a 2-octet value from IANA's ethertype
registry [Ethertypes].
For example, if we want to use three L2TPv3 sessions, one carrying
IPv4 packets, one carrying IPv6 packets, and one carrying MPLS
packets, the egress router will include three TLVs of L2TPv3
encapsulation type, each specifying a different Session ID and a
different payload type. The protocol type sub-TLV for these will be
IPv4 (protocol type = 0x0800), IPv6 (protocol type = 0x86dd), and
MPLS (protocol type = 0x8847), respectively. This informs the
ingress routers of the appropriate encapsulation information to use
with each of the given protocol types. Insertion of the specified
Session ID at the ingress routers allows the egress to process the
incoming packets correctly, according to their protocol type.
3.4.2. Color Sub-TLV
The color sub-TLV MAY be encoded as a way to "color" the
corresponding tunnel TLV. The value field of the sub-TLV is eight
octets long, and consists of a Color Extended Community, as defined
in Section 4.3. For the use of this sub-TLV and Extended Community,
please see Section 7.
Note that the high-order octet of this sub-TLV's value field MUST be
set to 3, and the next octet MUST be set to 0x0b. (Otherwise the
value field is not identical to a Color Extended Community.)
If a Color sub-TLV is not of the proper length, or the first two
octets of its value field are not 0x030b, the sub-TLV should be
treated as if it were an unrecognized sub-TLV (see Section 11).
3.5. Embedded Label Handling Sub-TLV
Certain BGP address families (corresponding to particular AFI/SAFI
pairs, e.g., 1/4, 2/4, 1/128, 2/128) have MPLS labels embedded in
their NLRIs. We will use the term "embedded label" to refer to the
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MPLS label that is embedded in an NLRI, and the term "labeled address
family" to refer to any AFI/SAFI that has embedded labels.
Some of the tunnel types (e.g., VXLAN, VXLAN-GPE, and NVGRE) that can
be specified in the Tunnel Encapsulation attribute have an
encapsulation header containing "Virtual Network" identifier of some
sort. The Encapsulation sub-TLVs for these tunnel types may
optionally specify a value for the virtual network identifier.
Suppose a Tunnel Encapsulation attribute is attached to an UPDATE of
an embedded address family, and it is decided to use a particular
tunnel (specified in one of the attribute's TLVs) for transmitting a
packet that is being forwarded according to that UPDATE. When
forming the encapsulation header for that packet, different
deployment scenarios require different handling of the embedded label
and/or the virtual network identifier. The Embedded Label Handling
sub-TLV can be used to control the placement of the embedded label
and/or the virtual network identifier in the encapsulation.
The Embedded Label Handling sub-TLV may be included in any TLV of the
Tunnel Encapsulation attribute. If the Tunnel Encapsulation
attribute is attached to an UPDATE of a non-labeled address family,
the sub-TLV is treated as a no-op. If the sub-TLV is contained in a
TLV whose tunnel type does not have a virtual network identifier in
its encapsulation header, the sub-TLV is treated as a no-op. In
those cases where the sub-TLV is treated as a no-op, it SHOULD NOT be
stripped from the TLV before the UPDATE is forwarded.
The sub-TLV's Length field always contains the value 1, and its value
field consists of a single octet. The following values are defined:
1: The payload will be an MPLS packet with the embedded label at the
top of its label stack.
2: The embedded label is not carried in the payload, but is carried
either in the virtual network identifier field of the
encapsulation header, or else is ignored entirely.
Please see Section 8 for the details of how this sub-TLV is used when
it is carried by an UPDATE of a labeled address family.
3.6. MPLS Label Stack Sub-TLV
This sub-TLV allows an MPLS label stack ([RFC3032]) to be associated
with a particular tunnel.
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The value field of this sub-TLV is a sequence of MPLS label stack
entries. The first entry in the sequence is the "topmost" label, the
final entry in the sequence is the "bottommost" label. When this
label stack is pushed onto a packet, this ordering MUST be preserved.
Each label stack entry has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: MPLS Label Stack Sub-TLV
If a packet is to be sent through the tunnel identified in a
particular TLV, and if that TLV contains an MPLS Label Stack sub-TLV,
then the label stack appearing in the sub-TLV MUST be pushed onto the
packet. This label stack MUST be pushed onto the packet before any
other labels are pushed onto the packet.
In particular, if the Tunnel Encapsulation attribute is attached to a
BGP UPDATE of a labeled address family, the contents of the MPLS
Label Stack sub-TLV MUST be pushed onto the packet before the label
embedded in the NLRI is pushed onto the packet.
If the MPLS label stack sub-TLV is included in a TLV identifying a
tunnel type that uses virtual network identifiers (see Section 8),
the contents of the MPLS label stack sub-TLV MUST be pushed onto the
packet before the procdures of Section 8 are applied.
The number of label stack entries in the sub-TLV MUST be determined
from the sub-TLV length field. Thus it is not necessary to set the S
bit in any of the label stack entries of the sub-TLV, and the setting
of the S bit is ignored when parsing the sub-TLV. When the label
stack entries are pushed onto a packet that already has a label
stack, the S bits of all the entries MUST be cleared. When the label
stack entries are pushed onto a packet that does not already have a
label stack, the S bit of the bottommost label stack entry MUST be
set, and the S bit of all the other label stack entries MUST be
cleared..
By default, the TC (Traffic Class) field ([RFC3032], [RFC5462]) of
each label stack entry is set to 0. This may of course be changed by
policy at the originator of the sub-TLV. When pushing the label
stack onto a packet, the TC of the label stack entries is preserved
by default. However, local policy at the router that is pushing on
the stack MAY cause modification of the TC values.
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By default, the TTL (Time to Live) field of each label stack entry is
set to 255. This may be changed by policy at the originator of the
sub-TLV. When pushing the label stack onto a packet, the TTL of the
label stack entries is preserved by default. However, local policy
at the router that is pushing on the stack MAY cause modification of
the TTL values. If any label stack entry in the sub-TLV has a TTL
value of zero, the router that is pushing the stack on a packet MUST
change the value to a non-zero value.
Note that this sub-TLV can be appear within a TLV identifying any
type of tunnel, not just within a TLV identifying an MPLS tunnel.
However, if this sub-TLV appears within a TLV identifying an MPLS
tunnel (or an MPLS-in-X tunnel), this sub-TLV plays the same role
that would be played by an MPLS Encapsulation sub-TLV. Therefore, an
MPLS Encapsulation sub-TLV is not defined.
3.7. Prefix-SID Sub-TLV
[I-D.ietf-idr-bgp-prefix-sid] defines a BGP Path attribute known as
the "Prefix-SID Attribute". This attribute is defined to contain a
sequence of one or more TLVs, where each TLV is either a "Label-
Index" TLV, an "IPv6 SID (Segment Identifier)" TLV, or an "Originator
SRGB (Source Routing Global Block)" TLV.
In this document, we define a Prefix-SID sub-TLV. The value field of
the Prefix-SID sub-TLV can be set to any valid value of the value
field of a BGP Prefix-SID attribute, as defined in
[I-D.ietf-idr-bgp-prefix-sid].
The Prefix-SID sub-TLV can occur in a TLV identifying any type of
tunnel. If an Originator SRGB is specified in the sub-TLV, that SRGB
MUST be interpreted to be the SRGB used by the tunnel's Remote
Endpoint. The Label-Index, if present, is the Segment Routing SID
that the tunnel's Remote Endpoint uses to represent the prefix
appearing in the NLRI field of the BGP UPDATE to which the Tunnel
Encapsulation attribute is attached.
If a Label-Index is present in the prefix-SID sub-TLV, then when a
packet is sent through the tunnel identified by the TLV, the
corresponding MPLS label MUST be pushed on the packet's label stack.
The corresponding MPLS label is computed from the Label-Index value
and the SRGB of the route's originator.
If the Originator SRGB is not present,it is assumed that the
originator's SRGB is known by other means. Such "other means" are
outside the scope of this document.
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The corresponding MPLS label is pushed on after the processing of the
MPLS Label Stack sub-TLV, if present, as specified in Section 3.6.
It is pushed on before any other labels (e.g., a label embedded in
UPDATE's NLRI, or a label determined by the procedures of Section 8
are pushed on the stack.
The Prefix-SID sub-TLV has slightly different semantics than the
Prefix-SID attribute. When the Prefix-SID attribute is attached to a
given route, the BGP speaker that originally attached the attribute
is expected to be in the same Segment Routing domain as the BGP
speakers who receive the route with the attached attribute. The
Label-Index tells the receiving BGP speakers that the prefix-SID is
for the advertised prefix in that Segment Routing domain. When the
Prefix-SID sub-TLV is used, the BGP speaker at the head end of the
tunnel need even not be in the same Segment Routing Domain as the
tunnel's Remote Endpoint, and there is no implication that the
prefix-SID for the advertised prefix is the same in the Segment
Routing domains of the BGP speaker that originated the sub-TLV and
the BGP speaker that received it.
4. Extended Communities Related to the Tunnel Encapsulation Attribute
4.1. Encapsulation Extended Community
The Encapsulation Extended Community is a Transitive Opaque Extended
Community. This Extended Community may be attached to a route of any
AFI/SAFI to which the Tunnel Encapsulation attribute may be attached.
Each such Extended Community identifies a particular tunnel type. If
the Encapsulation Extended Community identifies a particular tunnel
type, its semantics are exactly equivalent to the semantics of a
Tunnel Encapsulation attribute Tunnel TLV for which the following
three conditions all hold:
1. it identifies the same tunnel type,
2. it has a Remote Endpoint sub-TLV for which one of the following
two conditions holds:
A. its "Address Family" subfield contains zero, or
B. its "Address" subfield contains the same IP address that
appears in the next hop field of the route to which the
Tunnel Encapsulation attribute is attached
3. it has no other sub-TLVs.
We will refer to such a Tunnel TLV as a "barebones" Tunnel TLV.
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The Encapsulation Extended Community was first defined in [RFC5512].
While it provides only a small subset of the functionality of the
Tunnel Encapsulation attribute, it is used in a number of deployed
applications, and is still needed for backwards compatibility. To
ensure backwards compatibility, this specification establishes the
following rules:
1. If the Tunnel Encapsulation attribute of a given route contains a
barebones Tunnel TLV identifying a particular tunnel type, an
Encapsulation Extended Community identifying the same tunnel type
SHOULD be attached to the route.
2. If the Encapsulation Extended Community identifying a particular
tunnel type is attached to a given route, the corresponding
barebones Tunnel TLV MAY be omitted from the Tunnel Encapsulation
attribute.
3. Suppose a particular route has both (a) an Encapsulation Extended
Community specifying a particular tunnel type, and (b) a Tunnel
Encapsulation attribute with a barebones Tunnel TLV specifying
that same tunnel type. Both (a) and (b) MUST be interpreted as
denoting the same tunnel.
In short, in situations where one could use either the Encapsulation
Extended Community or a barebones Tunnel TLV, one may use either or
both. However, to ensure backwards compatibility with applications
that do not support the Tunnel Encapsulation attribute, it is
preferable to use the Encapsulation Extended Community. If the
Extended Community (identifying a particular tunnel type) is present,
the corresponding Tunnel TLV is optional.
Note that for tunnel types of the form "X-in-Y", e.g., MPLS-in-GRE,
the Encapsulation Extended Community implies that only packets of the
specified payload type "X" are to be carried through the tunnel of
type "Y".
In the remainder of this specification, when we speak of a route as
containing a Tunnel Encapsulation attribute with a TLV identifying a
particular tunnel type, we are implicitly including the case where
the route contains a Tunnel Encapsulation Extended Community
identifying that tunnel type.
4.2. Router's MAC Extended Community
[I-D.ietf-bess-evpn-inter-subnet-forwarding] defines a Router's MAC
Extended Community. This Extended Community provides information
that may conflict with information in one or more of the
Encapsulation Sub-TLVs of a Tunnel Encapsulation attribute. In case
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of such a conflict, the information in the Encapsulation Sub-TLV
takes precedence.
4.3. Color Extended Community
The Color Extended Community is a Transitive Opaque Extended
Community with the following encoding:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x03 | 0x0b | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Color Extended Community
For the use of this Extended Community please see Section 7.
5. Semantics and Usage of the Tunnel Encapsulation attribute
[RFC5512] specifies the use of the Tunnel Encapsulation attribute in
BGP UPDATE messages of AFI/SAFI 1/7 and 2/7. That document restricts
the use of this attribute to UPDATE messsages of those SAFIs. This
document removes that restriction.
The BGP Tunnel Encapsulation attribute MAY be carried in any BGP
UPDATE message whose AFI/SAFI is 1/1 (IPv4 Unicast), 2/1 (IPv6
Unicast), 1/4 (IPv4 Labeled Unicast), 2/4 (IPv6 Labeled Unicast),
1/128 (VPN-IPv4 Labeled Unicast), 2/128 (VPN-IPv6 Labeled Unicast),
or 25/70 (Ethernet VPN, usually known as EVPN)). Use of the Tunnel
Encapsulation attribute in BGP UPDATE messages of other AFI/SAFIs is
outside the scope of this document.
It has been suggested that it may sometimes be useful to attach a
Tunnel Encapsulation attribute to a BGP UPDATE message that is also
carrying a PMSI (Provider Multicast Service Interface) Tunnel
attribute [RFC6514]. If the PMSI Tunnel attribute specifies an IP
tunnel, the Tunnel Encapsulation attribute could be used to provide
additional information about the IP tunnel. The usage of the Tunnel
Encapsulation attribute in combination with the PMSI Tunnel attribute
is outside the scope of this document.
The decision to attach a Tunnel Encapsulation attribute to a given
BGP UPDATE is determined by policy. The set of TLVs and sub-TLVs
contained in the attribute is also determined by policy.
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When the Tunnel Encapsulation attribute is carried in an UPDATE of
one of the AFI/SAFIs specified in the previous paragraph, each TLV
MUST have a Remote Endpoint sub-TLV. If a TLV that does not have a
Remote Endpoint sub-TLV, that TLV should be treated as if it had a
malformed Remote Endpoint sub-TLV (see Section 3.1).
Suppose that:
o a given packet P must be forwarded by router R;
o the path along which P is to be forwarded is determined by BGP
UPDATE U;
o UPDATE U has a Tunnel Encapsulation attribute, containing at least
one TLV that identifies a "feasible tunnel" for packet P. A
tunnel is considered feasible if it has the following three
properties:
* The tunnel type is supported (i.e., router R knows how to set
up tunnels of that type, how to create the encapsulation header
for tunnels of that type, etc.)
* The tunnel is of a type that can be used to carry packet P
(e.g., an MPLS-in-UDP tunnel would not be a feasible tunnel for
carrying an IP packet, UNLESS the IP packet can first be
converted to an MPLS packet).
* The tunnel is specified in a TLV whose Remote Endpoint sub-TLV
identifies an IP address that is reachable.
Then router R SHOULD send packet P through one of the feasible
tunnels identified in the Tunnel Encapsulation attribute of UPDATE U.
If the Tunnel Encapsulation attribute contains several TLVs (i.e., if
it specifies several tunnels), router R may choose any one of those
tunnels, based upon local policy. If any of tunnels' TLVs contain
the Color sub-TLV(Section 3.4.2) and/or the Protocol Type sub-TLV
(Section 3.4.1, the choice of tunnel may be influenced by these sub-
TLVs.
Note that if none of the TLVs specifies the MPLS tunnel type, a Label
Switched Path SHOULD NOT be used unless none of the TLVs specifies a
feasible tunnel.
If a particular tunnel is not feasible at some moment because its
Remote Endpoint cannot be reached at that moment, the tunnel may
become feasible at a later time (when its endpoint becomes
reachable). Router R SHOULD take note of this. If router R is
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already using a different tunnel, it MAY switch to the tunnel that
just became feasible, or it MAY decide to continue using the tunnel
that it is already using. How this decision is made is outside the
scope of this document.
A TLV specifying a non-feasible tunnel is not considered to be
malformed or erroneous in any way, and the TLV SHOULD NOT be stripped
from the Tunnel Encapsulation attribute before redistribution.
In addition to the sub-TLVs already defined, additional sub-TLVs may
be defined that affect the choice of tunnel to be used, or that
affect the contents of the tunnel encapsulation header. The
documents that define any such additional sub-TLVs must specify the
effect that including the sub-TLV is to have.
Once it is determined to send a packet through the tunnel specified
in a particular TLV of a particular Tunnel Encapsulation attribute,
then the tunnel's remote endpoint address is the IP address contained
in the sub-TLV. If the TLV contains a Remote Endpoint sub-TLV whose
value field is all zeroes, then the tunnel's remote endpoint is the
IP address specified as the Next Hop of the BGP Update containing the
Tunnel Encapsulation attribute. The address of the remote endpoint
generally appears in a "destination address" field of the
encapsulation.
The full set of procedures for sending a packet through a particular
tunnel type to a particular remote endpoint depends upon the tunnel
type, and is outside the scope of this document. Note that some
tunnel types may require the execution of an explicit tunnel setup
protocol before they can be used for carrying data. Other tunnel
types may not require any tunnel setup protocol.
Sending a packet through a tunnel always requires that the packet be
encapsulated, with an encapsulation header that is appropriate for
the tunnel type. The contents of the tunnel encapsulation header MAY
be influenced by the Encapsulation sub-TLV. If there is no
Encapsulation sub-TLV present, the router transmitting the packet
through the tunnel must have a priori knowledge (e.g., by
provisioning) of how to fill in the various fields in the
encapsulation header.
Whenever a new Tunnel Type TLV is defined, the specification of that
TLV should describe (or reference) the procedures for creating the
encapsulation header used to forward packets through that tunnel
type. If a tunnel type codepoint is assigned in the IANA "BGP Tunnel
Encapsulation Tunnel Types" registry, but there is no corresponding
specification that defines an Encapsulation sub-TLV for that tunnel
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type, the transmitting endpoint of such a tunnel is presumed to know
a priori how to form the encapsulation header for that tunnel type.
If a Tunnel Encapsulation attribute specifies several tunnels, the
way in which a router chooses which one to use is a matter of policy,
subject to the following constraint: if a router can determine that a
given tunnel is not functional, it MUST NOT use that tunnel. In
particular, if the tunnel is identified in a TLV that has a Remote
Endpoint sub-TLV, and if the IP address specified in the sub-TLV is
not reachable from router R, then the tunnel SHOULD be considered
non-functional. Other means of determining whether a given tunnel is
functional MAY be used; specification of such means is outside the
scope of this specification. Of course, if a non-functional tunnel
later becomes functional, router R SHOULD reevaluate its choice of
tunnels.
If router R determines that it cannot use any of the tunnels
specified in the Tunnel Encapsulation attribute, it MAY either drop
packet P, or it MAY transmit packet P as it would had the Tunnel
Encapsulation attribute not been present. This is a matter of local
policy. By default, the packet SHOULD be transmitted as if the
Tunnel Encapsulation attribute had not been present.
A Tunnel Encapsulation attribute may contain several TLVs that all
specify the same tunnel type. Each TLV should be considered as
specifying a different tunnel. Two tunnels of the same type may have
different Remote Endpoint sub-TLVs, different Encapsulation sub-TLVs,
etc. Choosing between two such tunnels is a matter of local policy.
Once router R has decided to send packet P through a particular
tunnel, it encapsulates packet P appropriately and then forwards it
according to the route that leads to the tunnel's remote endpoint.
This route may itself be a BGP route with a Tunnel Encapsulation
attribute. If so, the encapsulated packet is treated as the payload
and is encapsulated according to the Tunnel Encapsulation attribute
of that route. That is, tunnels may be "stacked".
Notwithstanding anything said in this document, a BGP speaker MAY
have local policy that influences the choice of tunnel, and the way
the encapsulation is formed. A BGP speaker MAY also have a local
policy that tells it to ignore the Tunnel Encapsulation attribute
entirely or in part. Of course, interoperability issues must be
considered when such policies are put into place.
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6. Routing Considerations
6.1. No Impact on BGP Decision Process
The presence of the Tunnel Encapsulation attribute does not affect
the BGP bestpath selection algorithm.
Under certain circumstances, this may lead to counter-intuitive
consequences. For example, suppose:
o router R1 receives a BGP UPDATE message from router R2, such that
* the NLRI of that UPDATE is prefix X,
* the UPDATE contains a Tunnel Encapsulation attribute specifying
two tunnels, T1 and T2,
* R1 cannot use tunnel T1 or tunnel T2, either because the tunnel
remote endpoint is not reachable or because R1 does not support
that kind of tunnel
o router R1 receives a BGP UPDATE message from router R3, such that
* the NLRI of that UPDATE is prefix X,
* the UPDATE contains a Tunnel Encapsulation attribute specifying
two tunnels, T3 and T4,
* R1 can use at least one of the two tunnels
Since the Tunnel Encapsulation attribute does not affect bestpath
selection, R1 may well install the route from R2 rather than the
route from R3, even though R2's route contains no usable tunnels.
This possibility must be kept in mind whenever a Remote Endpoint sub-
TLV carried by a given UPDATE specifies an IP address that is
different than the next hop of that UPDATE.
6.2. Looping, Infinite Stacking, Etc.
Consider a packet destined for address X. Suppose a BGP UPDATE for
address prefix X carries a Tunnel Encapsulation attribute that
specifies a remote tunnel endpoint of Y. And suppose that a BGP
UPDATE for address prefix Y carries a Tunnel Encapsulation attribute
that specifies a Remote Endpoint of X. It is easy to see that this
will cause an infinite number of encapsulation headers to be put on
the given packet.
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This could happen as a result of misconfiguration, either accidental
or intentional. It could also happen if the Tunnel Encapsulation
attribute were altered by a malicious agent. Implementations should
be aware of this. This document does not specify a maximum number of
recursions; that is an implementation-specific matter.
Improper setting (or malicious altering) of the Tunnel Encapsulation
attribute could also cause data packets to loop. Suppose a BGP
UPDATE for address prefix X carries a Tunnel Encapsulation attribute
that specifies a remote tunnel endpoint of Y. Suppose router R
receives and processes the update. When router R receives a packet
destined for X, it will apply the encapsulation and send the
encapsulated packet to Y. Y will decapsulate the packet and forward
it further. If Y is further away from X than is router R, it is
possible that the path from Y to X will traverse R. This would cause
a long-lasting routing loop. The control plane itself cannot detect
this situation, though a TTL field in the payload packets would
presumably prevent any given packet from looping infinitely.
These possibilities must also be kept in mind whenever the Remote
Endpoint for a given prefix differs from the BGP next hop for that
prefix.
7. Recursive Next Hop Resolution
Suppose that:
o a given packet P must be forwarded by router R1;
o the path along which P is to be forwarded is determined by BGP
UPDATE U1;
o UPDATE U1 does not have a Tunnel Encapsulation attribute;
o the next hop of UPDATE U1 is router R2;
o the best path to router R2 is a BGP route that was advertised in
UPDATE U2;
o UPDATE U2 has a Tunnel Encapsulation attribute.
Then packet P SHOULD be sent through one of the tunnels identified in
the Tunnel Encapsulation attribute of UPDATE U2. See Section 5 for
further details.
However, suppose that one of the TLVs in U2's Tunnel Encapsulation
attribute contains the Color Sub-TLV. In that case, packet P SHOULD
NOT be sent through the tunnel identified in that TLV, unless U1 is
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carrying the Color Extended Community that is identified in U2's
Color Sub-TLV.
Note that if UPDATE U1 and UPDATE U2 both have Tunnel Encapsulation
attributes, packet P will be carried through a pair of nested
tunnels. P will first be encapsulated based on the Tunnel
Encapsulation attribute of U1. This encapsulated packet then becomes
the payload, and is encapsulated based on the Tunnel Encapsulation
attribute of U2. This is another way of "stacking" tunnels (see also
Section 5.
The procedures in this section presuppose that U1's next hop resolves
to a BGP route, and that U2's next hop resolves (perhaps after
further recursion) to a non-BGP route.
8. Use of Virtual Network Identifiers and Embedded Labels when Imposing
a Tunnel Encapsulation
If the TLV specifying a tunnel contains an MPLS Label Stack sub-TLV,
then when sending a packet through that tunnel, the procedures of
Section 3.6 are applied before the procedures of this section.
If the TLV specifying a tunnel contains a Prefix-SID sub-TLV, the
procedures of Section 3.7 are applied before the procedures of this
section. If the TLV also contains an MPLS Label Stack sub-TLV, the
procedures of Section 3.6 are applied before the procedures of
Section 3.7.
8.1. Tunnel Types without a Virtual Network Identifier Field
If a Tunnel Encapsulation attribute is attached to an UPDATE of a
labeled address family, there will be one or more labels specified in
the UPDATE's NLRI. When a packet is sent through a tunnel specified
in one of the attribute's TLVs, and that tunnel type does not contain
a virtual network identifier field, the label or labels from the NLRI
are pushed on the packet's label stack. The resulting MPLS packet is
then further encapsulated, as specified by the TLV.
8.2. Tunnel Types with a Virtual Network Identifier Field
Three of the tunnel types that can be specified in a Tunnel
Encapsulation TLV have virtual network identifier fields in their
encapsulation headers. In the VXLAN and VXLAN-GPE encapsulations,
this field is called the VNI (Virtual Network Identifier) field; in
the NVGRE encapsulation, this field is called the VSID (Virtual
Subnet Identifier) field.
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When one of these tunnel encapsulations is imposed on a packet, the
setting of the virtual network identifier field in the encapsulation
header depends upon the contents of the Encapsulation sub-TLV (if one
is present). When the Tunnel Encapsulation attribute is being
carried on a BGP UPDATE of a labeled address family, the setting of
the virtual network identifier field also depends upon the contents
of the Embedded Label Handling sub-TLV (if present).
This section specifies the procedures for choosing the value to set
in the virtual network identifier field of the encapsulation header.
These procedures apply only when the tunnel type is VXLAN, VXLAN-GPE,
or NVGRE.
8.2.1. Unlabeled Address Families
This sub-section applies when:
o the Tunnel Encapsulation attribute is carried on a BGP UPDATE of
an unlabeled address family, and
o at least one of the attribute's TLVs identifies a tunnel type that
uses a virtual network identifier, and
o it has been determined to send a packet through one of those
tunnels.
If the TLV identifying the tunnel contains an Encapsulation sub-TLV
whose V bit is set, the virtual network identifier field of the
encapsulation header is set to the value of the virtual network
identifier field of the Encapsulation sub-TLV.
Otherwise, the virtual network identifier field of the encapsulation
header is set to a configured value; if there is no configured value,
the tunnel cannot be used.
8.2.2. Labeled Address Families
This sub-section applies when:
o the Tunnel Encapsulation attribute is carried on a BGP UPDATE of a
labeled address family, and
o at least one of the attribute's TLVs identifies a tunnel type that
uses a virtual network identifier, and
o it has been determined to send a packet through one of those
tunnels.
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8.2.2.1. When a Valid VNI has been Signaled
If the TLV identifying the tunnel contains an Encapsulation sub-TLV
whose V bit is set, the virtual network identifier field of the
encapsulation header is set as follows:
o If the TLV contains an Embedded Label Handling sub-TLV whose value
is 1, then the virtual network identifier field of the
encapsulation header is set to the value of the virtual network
identifier field of the Encapsulation sub-TLV.
The embedded label (from the NLRI of the route that is carrying
the Tunnel Encapsulation attribute) appears at the top of the MPLS
label stack in the encapsulation payload.
o If the TLV does not contain an Embedded Label Handling sub-TLV, or
if contains an Embedded Label Handling sub-TLV whose value is 2,
the embedded label is ignored entirely, and the virtual network
identifier field of the encapsulation header is set to the value
of the virtual network identifier field of the Encapsulation sub-
TLV.
8.2.2.2. When a Valid VNI has not been Signaled
If the TLV identifying the tunnel does not contain an Encapsulation
sub-TLV whose V bit is set, the virtual network identifier field of
the encapsulation header is set as follows:
o If the TLV contains an Embedded Label Handling sub-TLV whose value
is 1, then the virtual network identifier field of the
encapsulation header is set to a configured value.
If there is no configured value, the tunnel cannot be used.
The embedded label (from the NLRI of the route that is carrying
the Tunnel Encapsulation attribute) appears at the top of the MPLS
label stack in the encapsulation payload.
o If the TLV does not contain an Embedded Label Handling sub-TLV, or
if it contains an Embedded Label Handling sub-TLV whose value is
2, the embedded label is copied into the virtual network
identifier field of the encapsulation header.
In this case, the payload may or may not contain an MPLS label
stack, depending upon other factors. If the payload does contain
an MPLS lable stack, the embedded label does not appear in that
stack.
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9. Applicability Restrictions
In a given UPDATE of a labeled address family, the label embedded in
the NLRI is generally a label that is meaningful only to the router
whose address appears as the next hop. Certain of the procedures of
Section 8.2.2.1 or Section 8.2.2.2 cause the embedded label to be
carried by a data packet to the router whose address appears in the
Remote Endpoint sub-TLV. If the Remote Endpoint sub-TLV does not
identify the same router that is the next hop, sending the packet
through the tunnel may cause the label to be misinterpreted at the
tunnel's remote endpoint. This may cause misdelivery of the packet.
Therefore the embedded label MUST NOT be carried by a data packet
traveling through a tunnel unless it is known that the label will be
properly interpreted at the tunnel's remote endpoint. How this is
known is outside the scope of this document.
Note that if the Tunnel Encapsulation attribute is attached to a VPN-
IP route [RFC4364], and if Inter-AS "option b" (see section 10 of
[RFC4364] is being used, and if the Remote Endpoint sub-TLV contains
an IP address that is not in same AS as the router receiving the
route, it is very likely that the embedded label has been changed.
Therefore use of the Tunnel Encapsulation attribute in an "Inter-AS
option b" scenario is not supported.
10. Scoping
The Tunnel Encapsulation attribute is defined as a transitive
attribute, so that it may be passed along by BGP speakers that do not
recognize it. However, it is intended that the Tunnel Encapsulation
attribute be used only within a well-defined scope, e.g., within a
set of Autonomous Systems that belong to a single administrative
entity. If the attribute is distributed beyond its intended scope,
packets may be sent through tunnels in a manner that is not intended.
To prevent the Tunnel Encapsulation attribute from being distributed
beyond its intended scope, any BGP speaker that understands the
attribute MUST be able to filter the attribute from incoming BGP
UPDATE messages. When the attribute is filtered from an incoming
UPDATE, the attribute is neither processed nor redistributed. This
filtering SHOULD be possible on a per-BGP-session basis. For each
session, filtering of the attribute on incoming UPDATEs MUST be
enabled by default.
In addition, any BGP speaker that understands the attribute MUST be
able to filter the attribute from outgoing BGP UPDATE messages. This
filtering SHOULD be possible on a per-BGP-session basis. For each
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session, filtering of the attribute on outgoing UPDATEs MUST be
enabled by default.
11. Error Handling
The Tunnel Encapsulation attribute is a sequence of TLVs, each of
which is a sequence of sub-TLVs. The final octet of a TLV is
determined by its length field. Similarly, the final octet of a sub-
TLV is determined by its length field. The final octet of a TLV MUST
also be the final octet of its final sub-TLV. If this is not the
case, the TLV MUST be considered to be malformed. A TLV that is
found to be malformed for this reason MUST NOT be processed, and MUST
be stripped from the Tunnel Encapsulation attribute before the
attribute is propagated. Subsequent TLVs in the Tunnel Encapsulation
attribute may still be valid, in which case they MUST be processed
and redistributed normally.
If a Tunnel Encapsulation attribute does not have any valid TLVs, or
it does not have the transitive bit set, the "Attribute Discard"
procedure of [RFC7606] is applied.
If a Tunnel Encapsulation attribute can be parsed correctly, but
contains a TLV whose tunnel type is not recognized by a particular
BGP speaker, that BGP speaker MUST NOT consider the attribute to be
malformed. Rather, the TLV with the unrecognized tunnel type MUST be
ignored, and the BGP speaker MUST interpret the attribute as if that
TLV had not been present. If the route carrying the Tunnel
Encapsulation attribute is propagated with the attribute, the
unrecognized TLV SHOULD remain in the attribute.
If a TLV of a Tunnel Encapsulation attribute contains a sub-TLV that
is not recognized by a particular BGP speaker, the BGP speaker SHOULD
process that TLV as if the unrecognized sub-TLV had not been present.
If the route carrying the Tunnel Encapsulation attribute is
propagated with the attribute, the unrecognized TLV SHOULD remain in
the attribute.
If the type code of a sub-TLV appears as "reserved" in the IANA "BGP
Tunnel Encapsulation Attribute Sub-TLVs" registry, the sub-TLV MUST
be treated as an unrecognized sub-TLV.
In general, if a TLV contains a sub-TLV that is malformed (e.g.,
contains a length field whose value is not legal for that sub-TLV),
the sub-TLV should be treated as if it were an unrecognized sub-TLV.
This document specifies one exception to this rule -- within a tunnel
encapsulation attribute that is carried by a BGP UPDATE whose AFI/
SAFI is one of those explicitly listed in the second paragraph of
Section 5, if a TLV contains a malformed Remote Endpoint sub-TLV (as
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defined in Section 3.1, the entire TLV MUST be ignored, and SHOULD be
removed from the Tunnel Encapsulation attribute before the route
carrying that attribute is redistributed.
Within a tunnel encapsulation attribute that is carried by a BGP
UPDATE whose AFI/SAFI is one of those explicitly listed in the second
paragraph of Section 5, a TLV that does not contain exactly one
Remote Endpoint sub-TLV MUST be treated as if it contained a
malformed Remote Endpoint sub-TLV.
A TLV identifying a particular tunnel type may contain a sub-TLV that
is meaningless for that tunnel type. For example, perhaps the TLV
contains a "UDP Destination Port" sub-TLV, but the identified tunnel
type does not use UDP encapsulation at all. Sub-TLVs of this sort
SHOULD be treated as no-ops. That is, they SHOULD NOT affect the
creation of the encapsulation header. However, the sub-TLV MUST NOT
be considered to be malformed, and MUST NOT be removed from the TLV
before the route carrying the Tunnel Encapsulation attribute is
redistributed. (This allows for the possibility that such sub-TLVs
may be given a meaning, in the context of the specified tunnel type,
in the future.)
There is no significance to the order in which the TLVs occur within
the Tunnel Encapsulation attribute. Multiple TLVs may occur for a
given tunnel type; each such TLV is regarded as describing a
different tunnel.
The following sub-TLVs defined in this document SHOULD NOT occur more
than once in a given Tunnel TLV: Remote Endpoint (discussed above),
Encapsulation, IPv4 DS, UDP Destination Port, Embedded Label
Handling, MPLS Label Stack, Prefix-SID. If a Tunnel TLV has more
than one of any of these sub-TLVs, all but the first occurrence of
each such sub-TLV type MUST be treated as a no-op. However, the
Tunnel TLV containing them MUST NOT be considered to be malformed,
and all the sub-TLVs SHOULD be propagated if the route carrying the
Tunnel Encapsulation attribute is propagated.
The following sub-TLVs defined in this document may appear zero or
more times in a given Tunnel TLV: Protocol Type, Color. Each
occurrence of such sub-TLVs is meaningful. For example, the Color
sub-TLV may appear multiple times to assign multiple colors to a
tunnel.
12. IANA Considerations
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12.1. Subsequent Address Family Identifiers
IANA is requested to modify the "Subsequent Address Family
Identifiers" registry to indicate that the Encapsulation SAFI is
deprecated. This document should be the reference.
12.2. BGP Path Attributes
IANA has previously assigned value 23 from the "BGP Path Attributes"
Registry to "Tunnel Encapsulation Attribute". IANA is requested to
add this document as a reference.
12.3. Extended Communities
IANA has previously assigned values from the "Transitive Opaque
Extended Community" type Registry to the "Color Extended Community"
(sub-type 0x0b), and to the "Encapsulation Extended
Community"(0x030c). IANA is requested to add this document as a
reference for both assignments.
12.4. BGP Tunnel Encapsulation Attribute Sub-TLVs
IANA is requested to add the following note to the "BGP Tunnel
Encapsulation Attribute Sub-TLVs" registry:
If the Sub-TLV Type is in the range from 0 to 127 inclusive, the
Sub-TLV Length field contains one octet. If the Sub-TLV Type is
in the range from 128-255 inclusive, the Sub-TLV Length field
contains two octets.
IANA is requested to change the registration policy of the "BGP
Tunnel Encapsulation Attribute Sub-TLVs" registry to the following:
o The values 0 and 255 are reserved.
o The values in the range 1-63 and 128-191 are to be allocated using
the "Standards Action" registration procedure.
o The values in the range 64-125 and 192-252 are to be allocated
using the "First Come, First Served" registration procedure.
o The values in the range 126-127 and 253-254 are reserved for
experimental use; IANA shall not allocate values from this range.
IANA has assigned the following codepoints in the "BGP Tunnel
Encapsulation Attribute Sub-TLVs registry:
6: Remote Endpoint
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7: IPv4 DS Field
8: UDP Destination Port
9: Embedded Label Handling
10: MPLS Label Stack
11: Prefix SID
IANA has previously assigned codepoints from the "BGP Tunnel
Encapsulation Attribute Sub-TLVs" registry for "Encapsulation",
"Protocol Type", and "Color". IANA is requested to add this document
as a reference.
12.5. Tunnel Types
IANA is requested to add this document as a reference for tunnel
types 8 (VXLAN), 9 (NVGRE), 11 (MPLS-in-GRE), and 12 (VXLAN-GPE) in
the "BGP Tunnel Encapsulation Tunnel Types" registry.
IANA is requested to add this document as a reference for tunnel
types 1 (L2TPv3), 2 (GRE), and 7 (IP in IP) in the "BGP Tunnel
Encapsulation Tunnel Types" registry.
13. Security Considerations
The Tunnel Encapsulation attribute can cause traffic to be diverted
from its normal path, especially when the Remote Endpoint sub-TLV is
used. This can have serious consequences if the attribute is added
or modified illegitimately, as it enables traffic to be "hijacked".
The Remote Endpoint sub-TLV contains both an IP address and an AS
number. BGP Origin Validation [RFC6811] can be used to obtain
assurance that the given IP address belongs to the given AS. While
this provides some protection against misconfiguration, it does not
prevent a malicious agent from inserting a sub-TLV that will appear
valid.
Before sending a packet through the tunnel identified in a particular
TLV of a Tunnel Encapsulation attribute, it may be advisable to use
BGP Origin Validation to obtain the following additional assurances:
o the origin AS of the route carrying the Tunnel Encapsulation
attribute is correct;
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o the origin AS of the route to the IP address specified in the
Remote Endpoint sub-TLV is correct, and is the same AS that is
specified in the Remote Endpoint sub-TLV.
One then has some level of assurance that the tunneled traffic is
going to the same destination AS that it would have gone to had the
Tunnel Encapsulation attribute not been present. However, this may
not suit all use cases, and in any event is not very strong
protection against hijacking.
For these reasons, BGP Origin Validation should not be relied upon
exclusively, and the filtering procedures of Section 10 should always
be in place.
Increased protection can be obtained by using BGPSEC [RFC8205] to
ensure that the route carrying the Tunnel Encapsulation attribute,
and the routes to the Remote Endpoint of each specified tunnel, have
not been altered illegitimately.
If BGP Origin Validation is used as specified above, and the tunnel
specified in a particular TLV of a Tunnel Encapsulation attribute is
therefore regarded as "suspicious", that tunnel should not be used.
Other tunnels specified in (other TLVs of) the Tunnel Encapsulation
attribute may still be used.
14. Acknowledgments
This document contains text from RFC5512, co-authored by Pradosh
Mohapatra. The authors of the current document wish to thank Pradosh
for his contribution. RFC5512 itself built upon prior work by Gargi
Nalawade, Ruchi Kapoor, Dan Tappan, David Ward, Scott Wainner, Simon
Barber, and Chris Metz, whom we also thank for their contributions.
The authors wish to thank Lou Berger, Ron Bonica, Martin Djernaes,
John Drake, Satoru Matsushima, Dhananjaya Rao, John Scudder, Ravi
Singh, Thomas Morin, Xiaohu Xu, and Zhaohui Zhang for their review,
comments, and/or helpful discussions.
15. Contributor Addresses
Below is a list of other contributing authors in alphabetical order:
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Randy Bush
Internet Initiative Japan
5147 Crystal Springs
Bainbridge Island, Washington 98110
United States
Email: randy@psg.com
Robert Raszuk
Bloomberg LP
731 Lexington Ave
New York City, NY 10022
United States
Email: robert@raszuk.net
16. References
16.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation
Subsequent Address Family Identifier (SAFI) and the BGP
Tunnel Encapsulation Attribute", RFC 5512,
DOI 10.17487/RFC5512, April 2009,
<https://www.rfc-editor.org/info/rfc5512>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
16.2. Informative References
[Ethertypes]
"IANA Ethertype Registry",
<http://www.iana.org/assignments/ieee-802-numbers/
ieee-802-numbers.xhtml>.
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[I-D.ietf-bess-evpn-inter-subnet-forwarding]
Sajassi, A., Salam, S., Thoria, S., Drake, J., and J.
Rabadan, "Integrated Routing and Bridging in EVPN", draft-
ietf-bess-evpn-inter-subnet-forwarding-07 (work in
progress), February 2019.
[I-D.ietf-idr-bgp-prefix-sid]
Previdi, S., Filsfils, C., Lindem, A., Sreekantiah, A.,
and H. Gredler, "Segment Routing Prefix SID extensions for
BGP", draft-ietf-idr-bgp-prefix-sid-27 (work in progress),
June 2018.
[I-D.ietf-nvo3-vxlan-gpe]
Maino, F., Kreeger, L., and U. Elzur, "Generic Protocol
Extension for VXLAN", draft-ietf-nvo3-vxlan-gpe-06 (work
in progress), April 2018.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
DOI 10.17487/RFC2784, March 2000,
<https://www.rfc-editor.org/info/rfc2784>.
[RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE",
RFC 2890, DOI 10.17487/RFC2890, September 2000,
<https://www.rfc-editor.org/info/rfc2890>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC3931] Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed.,
"Layer Two Tunneling Protocol - Version 3 (L2TPv3)",
RFC 3931, DOI 10.17487/RFC3931, March 2005,
<https://www.rfc-editor.org/info/rfc3931>.
[RFC4023] Worster, T., Rekhter, Y., and E. Rosen, Ed.,
"Encapsulating MPLS in IP or Generic Routing Encapsulation
(GRE)", RFC 4023, DOI 10.17487/RFC4023, March 2005,
<https://www.rfc-editor.org/info/rfc4023>.
Rosen, et al. Expires August 26, 2019 [Page 39]
Internet-Draft Tunnel Encapsulation Attribute February 2019
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
[RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, DOI 10.17487/RFC5462, February
2009, <https://www.rfc-editor.org/info/rfc5462>.
[RFC5566] Berger, L., White, R., and E. Rosen, "BGP IPsec Tunnel
Encapsulation Attribute", RFC 5566, DOI 10.17487/RFC5566,
June 2009, <https://www.rfc-editor.org/info/rfc5566>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
[RFC6811] Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
Austein, "BGP Prefix Origin Validation", RFC 6811,
DOI 10.17487/RFC6811, January 2013,
<https://www.rfc-editor.org/info/rfc6811>.
[RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
eXtensible Local Area Network (VXLAN): A Framework for
Overlaying Virtualized Layer 2 Networks over Layer 3
Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
<https://www.rfc-editor.org/info/rfc7348>.
[RFC7510] Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
"Encapsulating MPLS in UDP", RFC 7510,
DOI 10.17487/RFC7510, April 2015,
<https://www.rfc-editor.org/info/rfc7510>.
[RFC7637] Garg, P., Ed. and Y. Wang, Ed., "NVGRE: Network
Virtualization Using Generic Routing Encapsulation",
RFC 7637, DOI 10.17487/RFC7637, September 2015,
<https://www.rfc-editor.org/info/rfc7637>.
[RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
Specification", RFC 8205, DOI 10.17487/RFC8205, September
2017, <https://www.rfc-editor.org/info/rfc8205>.
Rosen, et al. Expires August 26, 2019 [Page 40]
Internet-Draft Tunnel Encapsulation Attribute February 2019
Authors' Addresses
Eric C. Rosen (editor)
Juniper Networks, Inc.
10 Technology Park Drive
Westford, Massachusetts 01886
United States
Email: erosen@juniper.net
Keyur Patel
Arrcus, Inc
2077 Gateway Pl
San Jose, CA 95110
United States
Email: keyur@arrcus.com
Gunter Van de Velde
Nokia
Copernicuslaan 50
Antwerpen 2018
Belgium
Email: gunter.van_de_velde@nokia.com
Rosen, et al. Expires August 26, 2019 [Page 41]