BGP Extensions for Routing Policy Distribution (RPD)
draft-ietf-idr-rpd-14
Network Working Group Z. Li
Internet-Draft Huawei
Intended status: Standards Track L. Ou
Expires: 4 February 2022 Y. Luo
China Telcom Co., Ltd.
S. Lu
Tencent
G. Mishra
Verizon Inc.
H. Chen
Futurewei
S. Zhuang
H. Wang
Huawei
3 August 2021
BGP Extensions for Routing Policy Distribution (RPD)
draft-ietf-idr-rpd-14
Abstract
It is hard to adjust traffic and optimize traffic paths in a
traditional IP network from time to time through manual
configurations. It is desirable to have a mechanism for setting up
routing policies, which adjusts traffic and optimizes traffic paths
automatically. This document describes BGP Extensions for Routing
Policy Distribution (BGP RPD) to support this.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] [RFC8174]
when, and only when, they appear in all capitals, as shown here.
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/.
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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."
This Internet-Draft will expire on 4 February 2022.
Copyright Notice
Copyright (c) 2021 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Inbound Traffic Control . . . . . . . . . . . . . . . . . 4
3.2. Outbound Traffic Control . . . . . . . . . . . . . . . . 5
4. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 6
4.1. Using a New AFI and SAFI . . . . . . . . . . . . . . . . 6
4.2. BGP Wide Community and Atoms . . . . . . . . . . . . . . 8
4.2.1. RouteAttr Sub-TLV . . . . . . . . . . . . . . . . . . 8
4.2.2. Sub-TLVs of the Parameters TLV . . . . . . . . . . . 12
4.3. Capability Negotiation . . . . . . . . . . . . . . . . . 14
5. Operations . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Application Scenario . . . . . . . . . . . . . . . . . . 15
5.2. About Failure . . . . . . . . . . . . . . . . . . . . . . 16
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17
7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
9.1. Existing Assignments . . . . . . . . . . . . . . . . . . 17
9.2. RouteAttr Atom Type . . . . . . . . . . . . . . . . . . . 18
9.3. Route Attributes Sub-sub-TLV Registry . . . . . . . . . . 18
9.4. Attribute Change Sub-TLV Registry . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Normative References . . . . . . . . . . . . . . . . . . 19
10.2. Informative References . . . . . . . . . . . . . . . . . 20
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
It is difficult to optimize traffic paths in a traditional IP network
because of the following:
* Complex. Traffic can only be adjusted device by device. The
configurations on all the routers that the traffic traverses need
to be changed or added. There are already lots of policies
configured on the routers in an operational network. There are
different types of policies, which include security, management
and control policies. These policies are relatively stable.
However, the policies for adjusting traffic are dynamic. Whenever
the traffic through a route is not expected, the policies to
adjust the traffic for that route are configured on the related
routers. It is complex to dynamically add or change the policies
to the existing policies on the special routers to adjust the
traffic. Some people would like to separate the stable route
policies from the dynamic ones even though they have configuration
automation systems (including YANG models).
* Difficult maintenance. The routing policies used to adjust
network traffic are dynamic, posing difficulties to subsequent
maintenance. High maintenance skills are required.
* Slow. Adding or changing some route policies on some routers
through a configuration automation system for adjusting some
traffic to avoid congestions may be slow.
It is desirable to have an automatic mechanism for setting up routing
policies, which can simplify routing policy configuration and be
fast. This document describes extensions to BGP for Routing Policy
Distribution to resolve these issues.
2. Terminology
The following terminology is used in this document.
* ACL: Access Control List
* BGP: Border Gateway Protocol [RFC4271]
* FS: Flow Specification
* NLRI: Network Layer Reachability Information [RFC4271]
* PBR: Policy-Based Routing
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* RPD: Routing Policy Distribution
* VPN: Virtual Private Network
3. Problem Statement
Providers have the requirement to adjust their business traffic
routing policies from time to time because of the following:
* Business development or network failure introduces link congestion
and overload.
* Business changes or network additions produce unused resources
such as idle links.
* Network transmission quality is decreased as the result of delay,
loss and they need to adjust traffic to other paths.
* To control OPEX and CPEX, they may prefer the transit provider
with lower price.
3.1. Inbound Traffic Control
In Figure 1, for the reasons above, the provider P of AS100 may wish
the inbound traffic from AS200 to enter AS100 through link L3 instead
of the others. Since P doesn't have any administrative control over
AS200, there is no way for P to directly modify the route selection
criteria inside AS200.
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Traffic from PE1 to Prefix1
----------------------------------->
+-----------------+ +-------------------------+
| +---------+ | L1 | +----+ +----------+|
| |Speaker1 | +------------+ |IGW1| |policy ||
| +---------+ |** L2**| +----+ |controller||
| | ** ** | +----------+|
| +---+ | **** | |
| |PE1| | **** | |
| +---+ | ** ** | |
| +---------+ |** L3**| +----+ |
| |Speaker2 | +------------+ |IGW2| AS100 |
| +---------+ | L4 | +----+ |
| | | |
| AS200 | | |
| | | ... |
| | | |
| +---------+ | | +----+ +-------+ |
| |Speakern | | | |IGWn| |Prefix1| |
| +---------+ | | +----+ +-------+ |
+-----------------+ +-------------------------+
Prefix1 advertised from AS100 to AS200
<----------------------------------------
Figure 1: Inbound Traffic Control case
3.2. Outbound Traffic Control
In Figure 2, the provider P of AS100 prefers link L3 for the traffic
to the destination Prefix2 among multiple exits and links to AS200.
This preference can be dynamic and might change frequently because of
the reasons above. So, provider P expects an efficient and
convenient solution.
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Traffic from PE2 to Prefix2
----------------------------------->
+-------------------------+ +-----------------+
|+----------+ +----+ |L1 | +---------+ |
||policy | |IGW1| +------------+ |Speaker1 | |
||controller| +----+ |** **| +---------+ |
|+----------+ |L2** ** | +-------+|
| | **** | |Prefix2||
| | **** | +-------+|
| |L3** ** | |
| AS100 +----+ |** **| +---------+ |
| |IGW2| +------------+ |Speaker2 | |
| +----+ |L4 | +---------+ |
| | | |
|+---+ | | AS200 |
||PE2| ... | | |
|+---+ | | |
| +----+ | | +---------+ |
| |IGWn| | | |Speakern | |
| +----+ | | +---------+ |
+-------------------------+ +-----------------+
Prefix2 advertised from AS200 to AS100
<----------------------------------------
Figure 2: Outbound Traffic Control case
4. Protocol Extensions
This document specifies a solution using a new AFI and SAFI with the
BGP Wide Community for encoding a routing policy.
4.1. Using a New AFI and SAFI
A new AFI and SAFI are defined: the Routing Policy AFI whose
codepoint 16398 has been assigned by IANA, and SAFI whose codepoint
75 has been assigned by IANA.
The AFI and SAFI pair uses a new NLRI, which is defined as follows:
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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
+-+-+-+-+-+-+-+-+
| NLRI Length |
+-+-+-+-+-+-+-+-+
| Policy Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Distinguisher (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Peer IP (4/16 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
NLRI Length: 1 octet represents the length of NLRI. If the Length
is anything other than 9 or 21, the NLRI is corrupt and the
enclosing UPDATE message MUST be ignored.
Policy Type: 1 octet indicates the type of a policy. 1 is for
Export policy. 2 is for Import policy. If the Policy Type is any
other value, the NLRI is corrupt and the enclosing UPDATE message
MUST be ignored.
Distinguisher: 4 octet unsigned integer that uniquely identifies the
content/policy. It is used to sort/order the polices from the
lower to higher distinguisher. They are applied in order. The
policy with a lower/smaller distinguisher is applied before the
policies with higher/larger distinguishers.
Peer IP: 4/16 octet value indicates IPv4/IPv6 peers. Its default
value is 0, which indicates that when receiving a BGP UPDATE
message with the NLRI, a BGP speaker will apply the policy in the
message to all its IPv4/IPv6 peers.
Under RPD AFI/SAFI, the RPD routes are stored and ordered according
to their keys. Under IPv4/IPv6 Unicast AFI/SAFI, there are IPv4/IPv6
unicast routes learned and various static policies configured. In
addition, there are dynamic RPD policies from the RPD AFI/SAFI when
RPD is enabled.
Before advertising an IPv4/IPv6 Unicast AFI/SAFI route, the
configured policies are applied to it first, and then the RPD Export
policies are applied.
The NLRI containing the Routing Policy is carried in MP_REACH_NLRI
and MP_UNREACH_NLRI path attributes in a BGP UPDATE message, which
MUST also contain the BGP mandatory attributes and MAY contain some
BGP optional attributes.
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When receiving a BGP UPDATE message with routing policy, a BGP
speaker processes it as follows:
* If the peer IP in the NLRI is 0, then apply the routing policy to
all the remote peers of this BGP speaker.
* If the peer IP in the NLRI is non-zero, then the IP address
indicates a remote peer of this BGP speaker and the routing policy
will be applied to it.
The content of the Routing Policy is encoded in a BGP Wide Community.
4.2. BGP Wide Community and Atoms
The BGP wide community is defined in
[I-D.ietf-idr-wide-bgp-communities]. It can be used to facilitate
the delivery of new network services and be extended easily for
distributing different kinds of routing policies.
A wide community Atom is a TLV (or sub-TLV), which may be included in
a BGP wide community container (or BGP wide community for short)
containing some BGP Wide Community TLVs. Three BGP Wide Community
TLVs are defined in [I-D.ietf-idr-wide-bgp-communities], which are
BGP Wide Community Target(s) TLV, Exclude Target(s) TLV, and
Parameter(s) TLV. The value of each of these TLVs comprises a series
of Atoms, each of which is a TLV (or sub-TLV). A new wide community
Atom is defined for BGP Wide Community Target(s) TLV and a few new
Atoms are defined for BGP Wide Community Parameter(s) TLV. For your
reference, the format of the TLV is illustrated below:
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
+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value (variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Format of Wide Community Atom TLV
4.2.1. RouteAttr Sub-TLV
A RouteAttr Atom sub-TLV (or RouteAttr sub-TLV for short) is defined
and may be included in a Target TLV. It has the following format.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD1) | Length (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-sub-TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Format of RouteAttr Atom sub-TLV
The Type for RouteAttr is TBD1. In RouteAttr sub-TLV, four sub-sub-
TLVs are defined: IPv4 Prefix, IPv6 Prefix, AS-Path, and Community
sub-sub-TLV.
An IP prefix sub-sub-TLV gives matching criteria on IPv4 prefixes.
Its format is illustrated below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type 1 | Length (N x 8) |M-Type | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | GeMask | LeMask |M-Type | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | GeMask | LeMask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Format of IPv4 Prefix sub-sub-TLV
Type: 1 for IPv4 Prefix.
Length: N x 8, where N is the number of tuples <M-Type, Flags, IPv4
Address, Mask, GeMask, LeMask>. If Length is not a multiple of 8,
the Atom is corrupt and the enclosing UPDATE message MUST be
ignored.
M-Type: 4-bit field specifying match type. The following four
values are defined. IPaddress is the IP address in the sub-sub-
TLV while IProute is the IP route being matched.
M-Type = 0: Exact match with the Mask length IP address prefix.
GeMask and LeMask MUST be sent as zero and ignored on receipt.
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M-Type = 1: Matches if the Mask number of prefix bits exactly
match between IPaddress and IProute and the actual prefix
length of IProute is greater than or equal to GeMask. LeMask
MUST be sent as zero and ignored on receipt.
M-Type = 2: Matches if the Mask number of prefix bits exactly
match between IPaddress and IProute and the actual prefix
length of IProute is less than or equal to LeMask. GeMask MUST
be sent as zero and ignored on receipt.
M-Type = 3: Matches if the Mask number of prefix bits exactly
match between IPaddress and IProute and the actual prefix
length of IProute is less than or equal to LeMask and greater
than or equal to GeMask.
Flags: 4 bits. No flags are currently defined. They MUST be sent
as zero and ignored on receipt.
IPv4 Address: 4 octets for an IPv4 address.
Mask: 1 octet for the IP address prefix length that needs to exactly
match between the IP address in the sub-sub-TLV and the route.
GeMask: 1 octet for route prefix length match range's lower bound,
MUST not be less than Mask or be 0.
LeMask: 1 octet for route prefix length match range's upper bound,
MUST be greater than Mask or be 0.
For example, tuple <M-Type=0, Flags=0, IPv4 Address = 1.1.0.0, Mask =
22, GeMask = 0, LeMask = 0> represents an exact IP prefix match for
1.1.0.0/22.
<M-Type=1, Flags=0, IPv4 Address = 16.1.0.0, Mask = 24, GeMask = 24,
LeMask = 0> represents match IP prefix 16.1.0.0/24 greater-equal 24
(i.e., route matches if route's first Mask=24 bits match 16.1.0 and
24 =< route's prefix length =< 32).
<M-Type=2, Flags=0, IPv4 Address = 17.1.0.0, Mask = 24, GeMask = 0,
LeMask = 26> represents match IP prefix 17.1.0.0/24 less-equal 26
(i.e., route matches if route's first Mask=24 bits match 17.1.0 and
24 =< route's prefix length <= 26).
<M-Type=3, Flags=0, IPv4 Address = 18.1.0.0, Mask = 24, GeMask = 24,
LeMask = 30> represents match IP prefix 18.1.0.0/24 greater-equal 24
and less-equal 30 (i.e., route matches if route's first Mask=24 bits
match 18.1.0 and 24 =< route's prefix length <= 30).
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Similarly, an IPv6 Prefix sub-sub-TLV represents match criteria on
IPv6 prefixes. Its format is illustrated below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type 4 | Length (N x 20) |M-Type | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Address (16 octets) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | GeMask | LeMask |M-Type | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Address (16 octets ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | GeMask | LeMask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Format of IPv6 Prefix sub-sub-TLV
An AS-Path sub-sub-TLV represents a match criteria in a regular
expression string. Its format is illustrated below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type 2 | Length (Variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AS-Path Regex String |
: :
| ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Format of AS Path sub-sub-TLV
Type: 2 for AS-Path.
Length: Variable, maximum is 1024.
AS-Path Regex String: AS-Path regular expression string.
A community sub-sub-TLV represents a list of communities to be
matched all. Its format is illustrated below:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type 3 | Length (N x 4 + 1) | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Community 1 Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ . . . ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Community N Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Format of Community sub-sub-TLV
Type: 3 for Community.
Length: N x 4 + 1, where N is the number of communities. If Length
is not a multiple of 4 plus 1, the Atom is corrupt and the
enclosing UPDATE MUST be ignored.
Flags: 1 octet. No flags are currently defined. These bits MUST be
sent as zero and ignored on receipt.
4.2.2. Sub-TLVs of the Parameters TLV
This document introduces 2 community values:
MATCH AND SET ATTR: If the IPv4/IPv6 unicast routes to a remote peer
match the specific conditions defined in the routing policy
extracted from the RPD route, then the attributes of the IPv4/IPv6
unicast routes will be modified when sending to the remote peer
per the actions defined in the RPD route.
MATCH AND NOT ADVERTISE: If the IPv4/IPv6 unicast routes to a remote
peer match the specific conditions defined in the routing policy
extracted from the RPD route, then the IPv4/IPv6 unicast routes
will not be advertised to the remote peer.
For the Parameter(s) TLV, two action sub-TLVs are defined: MED change
sub-TLV and AS-Path change sub-TLV. When the community in the
container is MATCH AND SET ATTR, the Parameter(s) TLV can include
these sub-TLVs. When the community is MATCH AND NOT ADVERTISE, the
Parameter(s) TLV's value is empty.
A MED change sub-TLV indicates an action to change the MED. Its
format is illustrated below:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type 1 | Length (5) | OP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Format of MED Change sub-TLV
Type: 1 for MED Change.
Length: 5. If Length is any other value, the sub-TLV is corrupt and
the enclosing UPDATE MUST be ignored.
OP: 1 octet. Three are defined:
OP = 0: assign the Value to the existing MED.
OP = 1: add the Value to the existing MED. If the sum is greater
than the maximum value for MED, assign the maximum value to
MED.
OP = 2: subtract the Value from the existing MED. If the
existing MED minus the Value is less than 0, assign 0 to MED.
If OP is any other value, the sub-TLV is ignored.
Value: 4 octets.
An AS-Path change sub-TLV indicates an action to change the AS-Path.
Its format is illustrated below:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type 2 | Length (n x 5) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AS1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Count1 |
+-+-+-+-+-+-+-+-+
~ . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASn |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Countn |
+-+-+-+-+-+-+-+-+
Format of AS-Path Change sub-TLV
Type: 2 for AS-Path Change.
Length: n x 5. If Length is not a multiple of 5, the sub-TLV is
corrupt and the enclosing UPDATE MUST be ignored.
ASi: 4 octet. An AS number.
Counti: 1 octet. ASi repeats Counti times.
The sequence of AS numbers are added to the existing AS Path.
4.3. Capability Negotiation
It is necessary to negotiate the capability to support BGP Extensions
for Routing Policy Distribution (RPD). The BGP RPD Capability is a
new BGP capability [RFC5492]. The Capability Code for this
capability is 72 assigned by the IANA. The Capability Length field
of this capability is variable. The Capability Value field consists
of one or more of the following tuples:
+--------------------------------------------------+
| Address Family Identifier (2 octets) |
+--------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) |
+--------------------------------------------------+
| Send/Receive (1 octet) |
+--------------------------------------------------+
BGP RPD Capability
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The meaning and use of the fields are as follows:
Address Family Identifier (AFI): This field is the same as the one
used in [RFC4760].
Subsequent Address Family Identifier (SAFI): This field is the same
as the one used in [RFC4760].
Send/Receive: This field indicates whether the sender is (a) willing
to receive Routing Policies from its peer (value 1), (b) would like
to send Routing Policies to its peer (value 2), or (c) both (value 3)
for the <AFI, SAFI>. If Send/Receive is any other value, that tuple
is ignored but any other tuples present are still used.
5. Operations
This section presents a typical application scenario and some details
about handling a related failure.
5.1. Application Scenario
Figure 3 illustrates a typical scenario, where RPD is used by a
controller with a Route Reflector (RR) to adjust traffic dynamically.
+--------------+
| Controller |
+-------+------+
\
\ RPD
.--\._.+--+ ___...__
__( \ '.---... ( )
/ RR o -------- A o) ---------- (o X AS2 )
(o E |\ ) _____//(___ ___)
( | \_______ B o) ____/ / '''
(o F \ ) ____/
( \_____ C o) ______/ ___...__
' AS1 _) \_____ ( )
'---._.-. ) \_______ (o Y AS3 )
'---' (___ ___)
'''
Figure 3: Controller with RR Adjusts Traffic
The controller connects the RR through a BGP session. There is a BGP
session between the RR and each of routers A, B and C in AS1, which
is shown in the figure. Other sessions in AS1 are not shown in the
figure.
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There is router X in AS2. There is a BGP session between X and each
of routers A, B and C in AS1.
There is router Y in AS3. There is a BGP session between Y and
router C in AS1.
The controller sends a RPD route to the RR. After receiving the RPD
route from the controller, the RR reflects the RPD route to routers
A, B and C. After receiving the RPD route from the RR, routers A, B
and C extract the routing policy from the RPD route. If the peer IP
in the NLRI of the RPD route is 0, then apply the routing policy to
all the remote peers of routers A, B and C. If the peer IP in the
NLRI of the RPD route is non-zero, then the IP address indicates a
remote peer of routers A, B and C and such routing policy is applied
to the specific remote peer. The IPv4/IPv6 unicast routes towards
router X in AS2 and router Y in AS3 will be adjusted based on the
routing policy sent by the controller via a RPD route.
The controller uses the RT extend community to notify a router
whether to receive a RPD policy. For example, if there is not any
adjustment on router B, the controller sends RPD routes with the RTs
for A and C. B will not receive the routes.
The process of adjusting traffic in a network is a close loop. The
loop starts from the controller with some traffic expectations on a
set of routes. The controller obtains the information about traffic
flows for the related routes. It analyzes the traffic and checks
whether the current traffic flows meet the expectations. If the
expectations are not met, the controller adjusts the traffic. And
then the loop goes to the starter of the loop (The controller obtains
the information about traffic ...).
5.2. About Failure
This section describes some details about handling a failure related
to a RPD route being applied.
A RPD route is not a configuration. When it is sent to a router from
a controller, no ack is needed from the router. The existing BGP
mechanisms are re-used for delivering a RPD route. After the route
is delivered to a router, it will be successful. This is guaranteed
by the BGP protocols.
If there is a failure for the router to install the route locally,
this failure is a bug of the router. The bug needs to be fixed.
For the errors mentioned in [RFC7606], they are handled according to
[RFC7606]. These errors are bugs, which need to be resolved.
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When the controller fails while a RPD route is being applied such as
on the way to the router, some existing mechanisms such BGP Graceful
Restart (GR) [RFC4724] and BGP Long-lived Graceful Restart (LLGR) can
be used to let the router keep the routes from the controller for
some time.
With support of "Long-lived Graceful Restart Capability"
[I-D.ietf-idr-long-lived-gr], the routes can be retained for a longer
time after the controller fails.
After the controller recovers from its failure, the router will have
all the routes (including the RPD route being applied) from the
controller.
In the worst case, the controller fails and the RPD routes for
adjusting the traffic are withdrawn. The traffic adjusted/redirected
may take its old path. This should be acceptable.
6. Contributors
The following people have substantially contributed to the definition
of the BGP-FS RPD and to the editing of this document:
Peng Zhou
Huawei
Email: Jewpon.zhou@huawei.com
7. Security Considerations
Protocol extensions defined in this document do not affect BGP
security other than as discussed in the Security Considerations
section of [RFC8955].
8. Acknowledgements
The authors would like to thank Acee Lindem, Jeff Haas, Jie Dong,
Lucy Yong, Qiandeng Liang, Zhenqiang Li, Robert Raszuk, Donald
Eastlake, Ketan Talaulikar, and Jakob Heitz for their comments to
this work.
9. IANA Considerations
9.1. Existing Assignments
IANA has assigned an AFI of value 16398 from the registry "Address
Family Numbers" for Routing Policy.
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IANA has assigned a SAFI of value 75 from the registry "Subsequent
Address Family Identifiers (SAFI) Parameters" for Routing Policy.
IANA has assigned a Code Point of value 72 from the registry
"Capability Codes" for Routing Policy Distribution.
9.2. RouteAttr Atom Type
IANA is requested to assign a code-point from the registry "BGP
Community Container Atom Types" as follows:
+---------------------+------------------------------+-------------+
| Atom Code Point | Description | Reference |
+---------------------+------------------------------+-------------+
| TBD1 (48 suggested) | RouteAttr Atom |This document|
+---------------------+------------------------------+-------------+
9.3. Route Attributes Sub-sub-TLV Registry
IANA is requested to create a registry called "Route Attributes Sub-
sub-TLV" under RouteAttr Atom Sub-TLV. The allocation policy of this
registry is "First Come First Served (FCFS)".
The initial code points are as follows:
+-------------+-----------------------------------+-------------+
| Code Point | Description | Reference |
+-------------+-----------------------------------+-------------+
| 0 | Reserved | |
+-------------+-----------------------------------+-------------+
| 1 | IPv4 Prefix Sub-sub-TLV |This document|
+-------------+-----------------------------------+-------------+
| 2 | AS-Path Sub-sub-TLV |This document|
+-------------+-----------------------------------+-------------+
| 3 | Community Sub-sub-TLV |This document|
+-------------+-----------------------------------+-------------+
| 4 | IPv6 Prefix Sub-sub-TLV |This document|
+-------------+-----------------------------------+-------------+
| 5 - 255 | Available | |
+-------------+-----------------------------------+-------------+
9.4. Attribute Change Sub-TLV Registry
IANA is requested to create a registry called "Attribute Change Sub-
TLV" under Parameter(s) TLV. The allocation policy of this registry
is "First Come First Served (FCFS)".
Initial code points are as follows:
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+-------------+-----------------------------------+-------------+
| Code Point | Description | Reference |
+-------------+-----------------------------------+-------------+
| 0 | Reserved | |
+-------------+-----------------------------------+-------------+
| 1 | MED Change Sub-TLV |This document|
+-------------+-----------------------------------+-------------+
| 2 | AS-Path Change Sub-TLV |This document|
+-------------+-----------------------------------+-------------+
| 3 - 255 | Available | |
+-------------+-----------------------------------+-------------+
10. References
10.1. Normative References
[I-D.ietf-idr-wide-bgp-communities]
Raszuk, R., Haas, J., Lange, A., Decraene, B., Amante, S.,
and P. Jakma, "BGP Community Container Attribute", Work in
Progress, Internet-Draft, draft-ietf-idr-wide-bgp-
communities-05, 2 July 2018,
<https://www.ietf.org/archive/id/draft-ietf-idr-wide-bgp-
communities-05.txt>.
[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>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <https://www.rfc-editor.org/info/rfc5492>.
[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>.
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[RFC8955] Loibl, C., Hares, S., Raszuk, R., McPherson, D., and M.
Bacher, "Dissemination of Flow Specification Rules",
RFC 8955, DOI 10.17487/RFC8955, December 2020,
<https://www.rfc-editor.org/info/rfc8955>.
10.2. Informative References
[I-D.ietf-idr-long-lived-gr]
Uttaro, J., Chen, E., Decraene, B., and J. G. Scudder,
"Support for Long-lived BGP Graceful Restart", Work in
Progress, Internet-Draft, draft-ietf-idr-long-lived-gr-00,
5 September 2019, <https://www.ietf.org/archive/id/draft-
ietf-idr-long-lived-gr-00.txt>.
[I-D.ietf-idr-registered-wide-bgp-communities]
Raszuk, R. and J. Haas, "Registered Wide BGP Community
Values", Work in Progress, Internet-Draft, draft-ietf-idr-
registered-wide-bgp-communities-02, 31 May 2016,
<https://www.ietf.org/archive/id/draft-ietf-idr-
registered-wide-bgp-communities-02.txt>.
[RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y.
Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724,
DOI 10.17487/RFC4724, January 2007,
<https://www.rfc-editor.org/info/rfc4724>.
[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>.
Authors' Addresses
Zhenbin Li
Huawei
Huawei Bld., No.156 Beiqing Rd.
Beijing
100095
China
Email: lizhenbin@huawei.com
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Liang Ou
China Telcom Co., Ltd.
109 West Zhongshan Ave,Tianhe District
Guangzhou
510630
China
Email: ouliang@chinatelecom.cn
Yujia Luo
China Telcom Co., Ltd.
109 West Zhongshan Ave,Tianhe District
Guangzhou
510630
China
Email: luoyuj@sdu.edu.cn
Sujian Lu
Tencent
Tengyun Building,Tower A ,No. 397 Tianlin Road
Shanghai
Xuhui District, 200233
China
Email: jasonlu@tencent.com
Gyan S. Mishra
Verizon Inc.
13101 Columbia Pike
Silver Spring, MD 20904
United States of America
Phone: 301 502-1347
Email: gyan.s.mishra@verizon.com
Huaimo Chen
Futurewei
Boston, MA,
United States of America
Email: Huaimo.chen@futurewei.com
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Shunwan Zhuang
Huawei
Huawei Bld., No.156 Beiqing Rd.
Beijing
100095
China
Email: zhuangshunwan@huawei.com
Haibo Wang
Huawei
Huawei Bld., No.156 Beiqing Rd.
Beijing
100095
China
Email: rainsword.wang@huawei.com
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