BIER support via
ISISCisco Systems510 McCarthy Blvd.MilpitasCA95035USAginsberg@cisco.comJuniper Networksprz@juniper.netGoogle1600 Amphitheatre ParkwayMountain ViewCAUSAaldrin.ietf@gmail.comJuniper Networks, Inc.10 Technology Park DriveWestfordMA01886USAzzhang@juniper.netInternet Engineering Task ForceSpecification of an ISIS extension to support BIER domains and
sub-domains.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 .Bit Index Explicit Replication (BIER) defines an architecture where all
intended multicast receivers are encoded as bitmask in the Multicast
packet header within different encapsulations such as . 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
protocol to support distribution of information necessary for operation
of BIER domains and sub-domains. This document defines a new TLV to be
advertised by every router participating in BIER signaling.Some of the terminology specified in is replicated here and extended by
necessary definitions:Bit Index Explicit Replication (The overall
architecture of forwarding multicast using a Bit Position).BIER Overlay Signaling. (The method for the
BFIR to learn about BFER's).Bit Forwarding Router (A router that participates
in Bit Index Multipoint Forwarding). A BFR is identified by a unique
BFR-prefix in a BIER domain.Bit Forwarding Ingress Router (The ingress
border router that inserts the BM into the packet). Each BFIR must
have a valid BFR-id assigned.Bit Forwarding Egress Router. A router that
participates in Bit Index Forwarding as leaf. Each BFER must be a
BFR. Each BFER must have a valid BFR-id assigned.Bit Forwarding Tree used to reach all BFERs in a
domain.A further distinction within a BIER
domain identified by its unique sub-domain identifier. A BIER
sub-domain can support multiple BitString Lengths.An optional, unique identifier for a BFR
within a BIER sub-domain.Unassigned BFR-id. The special value 0
is reserved for this purpose.BIER Algorithm. Algorithm used to calculate
nexthops.This document adds the following new sub-TLV to the registry of sub-
TLVs for TLVs 235, 237 and TLVs 135,236 ,.Value: 32 (suggested - to be assigned by IANA)Name: BIER InfoThis document also introduces a new registry for sub-sub-TLVs for the
BIER Info sub-TLV added above. The registration policy is Expert Review
as defined in [RFC8126]. This registry is part of the "IS-IS TLV
Codepoints" registry. The name of the registry is "sub-sub-TLVs for BIER
Info sub-TLV". The defined values are:An ISIS signalled BIER domain is aligned with the scope of
distribution of BFR-prefixes that identify the BFRs within ISIS. ISIS
acts in such a case as the supporting BIER underlay.Within such a domain, the extensions defined in this document
advertise BIER information for one or more BIER sub-domains. Each
sub-domain is uniquely identified by a subdomain-id. Each subdomain is
associated with a single ISIS topology , which may be any of the topologies
supported by ISIS. Local configuration controls which <MT,SD>
pairs are supported by a router. The mapping of sub-domains to
topologies MUST be consistent within the IS-IS flooding domain used to
advertise BIER information.Each BIER sub-domain has as its unique attributes the encapsulation
used and the type of tree it is using to forward BIER frames
(currently always SPF). Additionally, per supported bitstring length
in the sub-domain, each router will advertise the necessary label
ranges to support it.BIER information advertisements are associated with a new sub-TLV
in the extended reachability TLVs. BIER information is always
associated with a host prefix which MUST be a node address for the
advertising node. The following restrictions apply:Prefix length MUST be 32 for an IPv4 prefix or 128 for an IPv6
prefixWhen the Prefix Attributes Flags sub-TLV is present N flag MUST be
set.BIER sub-TLVs MUST be included when a prefix reachability
advertisement is leaked between levels.A given sub-domain is supported within one and only one topology.
All routers in the flooding scope of the BIER sub-TLVs MUST advertise
the same sub-domain within the same multi-topology. A router receiving
an <MT,SD> advertisement which does not match the locally
configured pair MUST report a misconfiguration of the received
<MT,SD> pair. All received BIER advertisements associated with
the conflicting <MT,SD> pair MUST be ignored.Example:The following combination of advertisements are valid: <0,0>
<0,1> <2,2>.The following combination of advertisements are invalid:
<0,0> <0,1> <2,0>. Advertisements associated with
<0,0> and <2,0> MUST be ignored.Multiple encapsulations MAY be advertised/supported for a given
<MT,SD>. Clearly, however, there MUST be at least one
encapsulation type in common in order for a BIER encapsulated packet
to be successfully forwarded between two BFRs.All routers in the flooding scope of the BIER TLVs MUST advertise a
supported algorithm for a given <MT,SD>. The specified
algorithm is used when calculating the optimal path. The supported
algorithm MUST be consistent for all routers supporting a given
<MT,SD>. A router receiving an <MT,SD> advertisement with
a BAR which does not match the locally configured value MUST report a
misconfiguration of the received <MT, SD> pair. All received
BIER advertisements associated with the conflicting <MT, SD>
pair MUST be ignored.Currently only the default algorithm "SPF" is defined - which has a
reserved value of 0 and represents Shortest Path First (SPF) based on
IGP link metric. This is the standard shortest path algorithm as
computed by the IS-IS protocol.A router that desires to participate in <MT,SD> MUST
advertise for each bitstring length it supports in <MT,SD>
a Maximum Set ID that guarantees to cover the maximum BFR-id injected
into <MT,SD> (which implies a certain maximum set id
per bitstring length as described in ). Any router that violates this
condition MUST be excluded from BIER BFTs for <MT,SD>.Each BFER/BFIR MAY advertise with its TLV<MT,SD> the
BFR-id that it has administratively chosen. A valid BFR-id MUST be
unique within the flooding scope of the BIER advertisements. All
BFERs/BFIRs MUST detect advertisement of duplicate valid BFR-IDs for a
given <MT, SD>. When such duplication is detected all of the
routers advertising duplicates MUST be treated as if they did not
advertise a valid BFR-id. This implies they cannot act as BFER or BFIR
in that <MT,SD>.Whenever an advertisement is received which violates any of the
constraints defined in this document the receiving router MUST report
the misconfiguration. Such reports SHOULD be dampened to avoid
excessive logging output.BIER domain information SHOULD change infrequently. Frequent
changes will increase the number of Link State PDU (LSP) updates and
negatively impact performance in the network.All ISIS BIER information is carried within the TLVs 235, 237 or TLVs 135 , or TLV 236.This sub-TLV carries the information for the BIER sub-domains that
the router participates in as BFR. This sub-TLV MAY appear multiple
times in a given prefix-reachability TLV - once for each sub-domain
supported in the associated topology.The sub-TLV advertises a single <MT,SD> combination followed
by optional sub-sub-TLVs as described in the following sections.as indicated in IANA section.variableBIER Algorithm. 0 is the only supported value
defined in this document. Other values may be defined in the
future. 8 bitsUnique value identifying the BIER
sub-domain. 1 octetA 2 octet field encoding the BFR-id, as
documented in . If no BFR-id has been assigned this field is
set to the invalid BFR-id.This sub-sub-TLV carries the information for the BIER MPLS
encapsulation including the label range for a specific bitstring
length for a certain <MT,SD>. It is advertised within
the BIER Info sub-TLV () . This sub-sub-TLV
MAY appear multiple times within a single BIER info sub-TLV.On violation of any of the following conditions, the receiving
router MUST ignore the encapsulating BIER Info sub-TLV.Label ranges in multiple sub-sub-TLV MUST NOT overlap.Bitstring lengths in multiple sub-sub-TLVs MUST NOT be
identical.The sub-sub-TLV MUST include the required bitstring lengths
encoded in precisely the same way as in .All labels in the range MUST represent valid label valuesvalue of 1 indicating MPLS encapsulation.4Encoded bitstring
length as per . 4 bits.Maximum Set Identifier (section 1 of
[RFC8279]) used in the encapsulation for this BIER sub-domain for
this bitstring length, 1 octet. Each SI maps to a single label in
the label range. The first label is for SI=0, the second label is
for SI=1, etc.First label of the range, 20 bits. The labels
are as defined in .Implementations must assure that malformed TLV and Sub-TLV
permutations do not result in errors which cause hard protocol
failures.The RFC is aligned with the draft as far as
the protocol mechanisms overlap.Many thanks for comments from (in no particular order) Hannes
Gredler, Ijsbrand Wijnands, Peter Psenak and Chris Bowers.OSPF Extension for Bit Index Explicit Replication