Internet Engineering Task Force A. Przygienda
Internet-Draft Ericsson
Intended status: Standards Track September 27, 2014
Expires: March 31, 2015
BIER support via ISIS
draft-przygienda-bier-isis-ranges-00
Abstract
Specification of an ISIS extension to support BIER domains.
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 RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 31, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
4. Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.1. BIER as Capability . . . . . . . . . . . . . . . . . . . 4
4.2. BIER Domain Identifier . . . . . . . . . . . . . . . . . 4
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Enabling a BIER Domain . . . . . . . . . . . . . . . . . 4
5.2. Length of Bitmasks . . . . . . . . . . . . . . . . . . . 4
5.2.1. Special Consideration . . . . . . . . . . . . . . . . 5
5.3. Encapsulation . . . . . . . . . . . . . . . . . . . . . . 5
5.4. Label Advertisements . . . . . . . . . . . . . . . . . . 5
5.4.1. Special Consideration . . . . . . . . . . . . . . . . 5
5.5. BFR-id Advertisements . . . . . . . . . . . . . . . . . . 5
6. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. BIER BFR sub-TLV . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. Normative References . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Bit Index Explicit Replication (BIER)
[I-D.draft-wijnands-bier-architecture-00] defines an architecture
where all intended multicast receivers are encoded as bitmask in the
Multicast packet header within different encapsulations such as
[I-D.draft-wijnands-mpls-bier-encapsulation-00]. A router that
receives such a packet will forward the packet based on the Bit
Position in the packet header towards the receiver(s), following a
precomputed tree for each of the bits in the packet. Each receiver
is represented by a unique bit in the bitmask.
This document presents necessary extensions to the currently deployed
ISIS for IP [RFC7142] protocol to support distribution of information
necessary for operation of BIER domains. This document defines a new
TLV to be distributed by every router participating in such BIER
domains.
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2. Terminology
Some of the terminology specified in
[I-D.draft-wijnands-bier-architecture-00] is replicated here and
extended by necessary definitions:
BIER: Bit Index Explicit Replication (The overall architecture of
forwarding multicast using a Bit Position).
BIER-OL: BIER Overlay Signaling. (The method for the BFIR to learn
about BFER's).
BM: Bit Mask (A bit stream of a certain fixed length. Each Bit
represents a receiver).
P-BM: Packet Bit Mask (A Bit Mask included in the Multicast Packet).
BP: Bit Position (A single Bit from the Bit Mask that represents a
receiver).
BFR: Bit Forwarding Router (A router that participates in Bit Index
Multipoint Forwarding).
BFIR: Bit Forwarding Ingress Router (The ingress border router that
inserts the BM into the packet).
BFER: Bit Forwarding Egress Router. A router that participates in
Bit Index Forwarding as leaf. Each BFER must be a BFR.
BFT: Bit Forwarding Tree used to reach all BFERs in a domain.
BIFT: Bit Index Forwarding Table (A Bit index forwarding table).
BMS: Bit Mask Set. Set containing bit positions of all BFER
participating in a set.
BMP: Bit Mask Position, a given bit in a BMS.
3. IANA Considerations
This document requests IANA to assign sub-TLV type values from the
ISIS router capability TLV [RFC4971] registry.
4. Concepts
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4.1. BIER as Capability
This draft introduces a sub-TLV in the router capabilites TLV
[RFC4971] to distribute the information. Any of the router's
loopback addresses that it originates are considered BFR prefixes as
required by [I-D.draft-wijnands-bier-architecture-00]. The question
whether a particular loopback address is routable in a specific
topology [RFC5120] can be resolved by
[I-D.draft-xu-isis-routable-ip-address-01].
4.2. BIER Domain Identifier
ISIS can carry BIER information not only for a single BIER domain but
for multiple, distinct domains. This allows to run many disjoint
BIER layers within the same Multi-Topology [RFC5120] easily instead
of always forcing different multicast overlays to share the exactly
same set of BFRs and resources. Moreover, multi topology [RFC5120]
can be used for the purpose of restricting links that certain set of
BIER domains can use or change metrics of such links. A BIER set is
therefore always uniquely identified by the tuple of topology T,
domain D it belongs to and its number S, denoted as <T,D,S>. The
domain itself has as its unique attributes the encapsulation, bitmask
length and the type of tree it is using to forward BIER frames
(currently always SPF).
5. Procedures
5.1. Enabling a BIER Domain
A given domain D in a multi-topology T [RFC5120] (denoted as <T,D>
from now on) is normally not advertised to preserve the scaling of
the protocol (i.e. ISIS carries no TLVs containing any of the
elements related to <T,D>) and is enabled by a first BIER sub-TLV
(Section 6.1) containing <T,D> being advertised into the area. The
trigger itself is outside the scope of this draft but can be .e.g. a
VPN desiring to initiate a domain as MP2MP or P2MP tree or a BMP
being administratively assigned to a BFER and advertised via BIER TLV
into the area or any other means within Multicast BIER Overlay(s)
using BIER domains.
5.2. Length of Bitmasks
All routers in the flooding scope of the BIER TLVs SHOULD advertise
the same bit mask length for a given <T,D>. A router discovering
bitmask lengths advertised that are shorter than its own MUST report
a misconfiguration of a specific <T,D>. Each router MUST compute
BFTs for <T,D> using only routers having the same mask length as its
own advertised Bit Mask Length in BIER sub-TLV for <T,D>.
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5.2.1. Special Consideration
The same router MAY advertise for different <T,D> combinations two
different mask lengths. This allows to cleanly delineate domains
crossing the same router but using different mask lengths in the
encoding, even within the same topology.
5.3. Encapsulation
Since encapsulation is an attribute of a domain <T,D> just like
bitmask length, all rules that apply to Bitmask Length per
Section 5.2 apply to it well.
5.4. Label Advertisements
Each router MAY advertise within the sub-TLV of an according <T,D>
(denoted further as TLV<T,D>) a valid starting label value and a non-
zero range length. It MUST advertise a valid label value and a non-
zero range length IF it has computed itself as being on the BFT
rooted at any of the BFRs with valid BFR-ids (except itself)
participating in <T,D>.
A router CAN withdraw its TLV<T,D> if it does not want to participate
in the domain due to resource constraints, label space optimization,
administrative configuration or any other reasons. In case a router
advertises a label range size of 0 for <T,D> it MUST be excluded from
the BIER BFTs for <T,D>.
5.4.1. Special Consideration
A router MUST advertise a for <T,D> label range size that guarantees
to cover the maximum BFR-id injected into <T,D> (which implies a
certain set id as described in
[I-D.draft-wijnands-bier-architecture-00]). Any router that violates
this condition MUST be excluded from BIER BFTs for <T,D>.
5.5. BFR-id Advertisements
Each BFER MAY advertise with its TLV<T,D> the according BFR-id that
it has administratively chosen.
If two BFRs advertise in their TLV<T,D> the same value for BFR-id,
all routers MUST report it as misconfiguration and disregard those
routers for all BIER calculations and procedures to align with
[I-D.draft-wijnands-bier-architecture-00]. Such routers with
colliding assignments MAY still act as BFIRs but will be never able
to receive traffic.
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6. Packet Formats
All ISIS BIER information is carried within the router capability TLV
[RFC4971] with S bit clear.
6.1. BIER BFR sub-TLV
This sub-TLV carries the information for the BIER domains that the
router participates in as BFR. It can repeat multiple times. If the
same <T,D> is advertised more than once, the first one in the first
sub-TLV in the fragment with the lowest ID MUST be used.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID | Bier Domain ID | Bit Msk Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lbl Range Size| Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFR-id |A|R|T| Reserv | Encaps |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: TBD1.
Length: 2 octets.
MT-ID: Multi-Topology [RFC5120], 1 octet.
BIER Domain ID: Unique identifier for a BIER domain, 2 octets.
Label Range Size: Number of labest in the range used on
encapsulation for this BIER domain, 1 octet.
Label: First label of the range used on encapsulation for this BIER
domain, 20 bits. The label is used by e.g.
[I-D.draft-wijnands-mpls-bier-encapsulation-00] to forward traffic
to sets of BFERs.
Local BitMask Length: Bitmask length for this BFR per
[I-D.draft-wijnands-bier-architecture-00].
Encapsulation Type: The BIER encapsulation type, 1 octet. Allowed
values are:
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0 MPLS per [I-D.draft-wijnands-mpls-bier-encapsulation-00].
A Indicates administratively set value if set, otherwise the BFR-id
value MUST be considered as not assigned in this TLV.
R Reserved for future use. MUST be 0.
T Reserved for future use. MUST be 0.
Reserved MUST be 0 on send, ignored on receive.
7. Security Considerations
The extension does not introduce any known new protocol
vulnerabilities.
8. Acknowledgements
The draft is aligned with the
[I-D.draft-kumar-ospf-bier-extension-00] draft as far as the protocol
mechanisms overlap.
9. Normative References
[I-D.draft-kumar-ospf-bier-extension-00]
Psenak, P. and IJ. Wijnands, "OSPF Extension for Bit Index
Explicit Replication", internet-draft draft-ietf-ospf-
prefix-link-attr-00.txt, September 2014.
[I-D.draft-wijnands-bier-architecture-00]
Wijnands, IJ., "Stateless Multicast using Bit Index
Explicit Replication Architecture", internet-draft draft-
wijnands-bier-architecture-00.txt, February 2014.
[I-D.draft-wijnands-mpls-bier-encapsulation-00]
Wijnands et al., IJ., "Bit Index Explicit Replication
using MPLS encapsulation", internet-draft draft-wijnands-
mpls-bier-encapsulation-00.txt, February 2014.
[I-D.draft-xu-isis-routable-ip-address-01]
Chunduri et al., U., "Carrying Routable IP Addresses in
IS-IS Router Capability TLV", internet-draft draft-xu-
isis-routable-ip-address-01.txt, September 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC4971] Vasseur, JP., Shen, N., and R. Aggarwal, "Intermediate
System to Intermediate System (IS-IS) Extensions for
Advertising Router Information", RFC 4971, July 2007.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120, February 2008.
[RFC7142] Shand, M. and L. Ginsberg, "Reclassification of RFC 1142
to Historic", RFC 7142, February 2014.
Author's Address
Tony Przygienda
Ericsson
300 Holger Way
San Jose, CA 95134
USA
Email: antoni.przygienda@ericsson.com
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