IS-IS Extensions Supporting IEEE 802.1aq Shortest Path Bridging
Extracted elements (32)
802.1aq requires no IS-IS state machine or other substantive changes; it only requires a new NLPID (0xC1) and a set of TLVs. Where this document conflicts with IS-IS, IS-IS should be taken as authoritative.
Head-end replication eliminates multicast state in core bridges entirely by having the ingress SPBM node replicate and unicast to each receiver, making it suitable for sparse I-SID communities. Tandem replication is bandwidth-efficient but requires multicast FDB state on every transit node along the shortest path tree.
Two MCIDs are carried in the SPB-MCID sub-TLV (primary and auxiliary) to allow non-disruptive transitions between VID allocation configurations; the auxiliary MCID permits SPT Regions to migrate VLAN-to-FDB mappings without interrupting existing traffic.
IS-IS for SPB currently only supports peer-to-peer adjacencies; pseudonodes and links to/from pseudonodes are not used in IS-IS SPF computations for SPB and will be avoided if present in the physical topology. Other NLPIDs may use pseudonodes normally.
A stand-alone implementation supporting only NLPID=0xC1 Must use an IS-IS area address value of 0, and the SYSID Must be the well-known MAC address of the SPB device.
Failure of two SPB nodes to establish an SPB adjacency MUST NOT cause rejection of an adjacency for the purposes of other network layer protocols such as IPv4 and IPv6.
IEEE 802.1aq NLPID value 0xC1 MUST be included in the IS-IS IIH PDU Protocols Supported TLV (type 129) to indicate ability to run 802.1aq. 802.1aq frames MUST only flow on adjacencies that advertise this NLPID in both directions of IIH PDUs.
IS-IS for SPB Must use the IS-IS three-way handshake for IS-IS point-to-point adjacencies as described in RFC 5303.
IS-IS SPB implementations Must support level 1 and May support level 2 operations. SPB TLVs Should Not be leaked between level 1 and level 2, as hierarchical SPB is for further study.
SPB computations MUST consider any adjacency that has not advertised NLPID 0xC1 in both directions as non-existent (infinite link metric) and MUST ignore any IIH SPB TLVs received over such adjacencies.
SPB shortest path calculations Must use the maximum value of the two nodes' advertised SPB-LINK-METRICs when different ends of an adjacency advertise different values, to ensure symmetry and determinism.
The SPB-Inst sub-TLV MUST be carried within the MT-Capability TLV in the fragment ZERO LSP. If there is an additional SPB instance, it MUST be declared under a separate MT-Capability TLV also carried in fragment ZERO LSP.
The SPB-Inst sub-TLV Must contain at least one ECT-ALGORITHM entry, specifically the default 00-80-C2-01. The ECT-ALGORITHM and Base VID Must match what is generated in the IIHs of the same node.
The SPB-LINK-METRIC maximum value (2^24 - 1) signals that although the IS-IS adjacency has formed, incompatible SPB parameter values have been detected; the link Must Not be used for carrying SPB traffic.
VIDs Must Not overlap between SPB instances regardless of how the control planes are isolated, since data plane traffic for a given MT ID is intrinsically isolated by the VLANs assigned to the SPB instance.
When supported, the SPB-Digest sub-TLV MUST be carried on every IIH between SPB neighbors, not just when a Digest changes. When one peer supports this TLV and the other does not, loop prevention by Agreement Digest Must Not be done by either side.
When two equal-cost paths exist, the path with fewest hops between fork/join points Must win the tie; if hops are also equal, the path traversing the intermediate node with the lower BridgeID Must be selected by the default tie-breaking rule.
ECT-ALGORITHMs are 32-bit worldwide unique identifiers (IEEE OUI 00-80-C2 concatenated with an index) for SPF tie-breaking rules. Sixteen standard algorithms (00-80-C2-01 through 00-80-C2-10) each apply XOR byte-by-byte of a predefined ECT-MASK with BridgeID, producing up to 16 diverse equal-cost shortest path trees per node-pair.
The MT-Capability TLV (type 144, new in this document) is the LSP container for all SPB node information. It carries an O (overload) bit with SPB adjacency semantics and an MT ID; a new IANA sub-registry starting at sub-TLV value 1 is managed by Expert Review.
The SPB-B-VID sub-TLV (type 6, carried in IIH MT-Port-Cap TLV) advertises ECT-ALGORITHM to Base VID mappings as 6-byte tuples each containing a 32-bit ECT-ALGORITHM, 12-bit Base VID, Use-Flag (U), and mode bit (M: SPBM=1, SPBV=0).
The SPB-Digest sub-TLV (type 5, optional, carried in MT-Port-Cap TLV in IIH) carries an Agreement Digest computed over all SPB adjacencies in all MT instances. V bit (digest valid), A bits (2-bit Agreement Number), and D bits (2-bit Discarded Agreement Number) govern loop prevention during topology convergence.
The SPB-Inst sub-TLV (type 1, in MT-Capability TLV of LSP) carries the node's 64-bit CIST Root Identifier, 32-bit CIST External Root Path Cost, 16-bit Bridge Priority, V bit (auto-allocated SPSourceID), 20-bit SPSourceID, and per-tree VLAN-ID tuples containing ECT-ALGORITHM, Base VID, SPVID, and U/M/A flags.
The SPB-MCID sub-TLV (type 4, carried in MT-Port-Cap TLV in IIH) carries two 51-byte MCIDs: a primary MCID and an auxiliary MCID. Each MCID contains a 1-byte format selector, 32-byte configuration name, 2-byte revision level, and 16-byte HMAC-MD5 signature over VID-to-protocol assignments.
The SPB-Metric sub-TLV (type 29, in MT-ISN TLV type 222 or Extended IS Reachability TLV type 22) carries a 24-bit SPB-LINK-METRIC, Num of Ports count, and Port Identifier values. Absence of this sub-TLV for an adjacency means that adjacency Must not carry SPB traffic.
The SPBM-SI sub-TLV (type 3, in MT-Capability TLV of LSP) advertises a B-MAC unicast address, associated 12-bit Base VID, and a list of 24-bit I-SIDs each with Transmit (T) and Receive (R) bits indicating service group membership role. Multiple repetitions are allowed for additional B-MACs or overflow I-SIDs.
The SPBV-ADDR sub-TLV (type 4, in MT-Capability TLV of LSP) advertises group MAC addresses for SPBV mode, associated with a 12-bit SPVID and 2-bit SR (service requirement) bits from MMRP. Each 48-bit MAC entry includes T (Transmit) and R (Receive) bits controlling multicast FDB state installation on transit bridges.
This document assigns: MT-Capability TLV type 144 (new, with Expert Review sub-registry starting at 1); sub-TLVs SPB-MCID=4, SPB-Digest=5, SPB-B-VID=6 in MT-Port-Cap TLV (IIH); SPB-Inst=1, SPB-I-OALG=2, SPBM-SI=3, SPBV-ADDR=4 in MT-Capability TLV (LSP); SPB-Metric=29, SPB-A-OALG=30 in MT-ISN/Extended IS Reachability TLVs (LSP). NLPID 0xC1 was previously assigned by IANA via RFC 6328.
Advertising an I-SID with the Transmit (T) bit set can create significant amounts of multicast state across the network and should be carefully controlled to prevent denial-of-service attacks (per RFC 4732) in zero-configuration environments.
Zero-configuration environments that auto-detect and form NNI or UNI ports introduce intrinsic security risks; authentication procedures should be applied to mitigate unauthorized adjacency or service formation, though such procedures are beyond the scope of this document.
SPB-MCID sub-TLV: Type=4, Length=102; value consists of two concatenated 51-byte MCIDs (primary and aux), each comprising a 1-byte format selector, 32-byte config name, 2-byte revision level, and 16-byte HMAC-MD5 digest.
SPB-Metric sub-TLV: Type=29; value contains a 3-byte (24-bit) unsigned SPB-LINK-METRIC, a 1-byte Num of Ports field, and 2-byte Port Identifier per port. Only one metric is allowed per SPB instance per link.
SPBM multicast DA is a 6-byte Ethernet address: M=1 (multicast bit), L=1 (local bit), TYP=00 (2 bits), 20-bit SPSourceID, and 24-bit I-SID occupying the lower three bytes. SPSourceID=0 indicates dynamic allocation not yet completed.