Routing Extensions for Discovery of Multiprotocol (MPLS) Label Switch Router (LSR) Traffic Engineering (TE) Mesh Membership
Extracted elements (17)
A full mesh of TE LSPs between N LSRs requires O(N^2) configurations, and adding a new LSR requires 2*N additional TE LSP configurations. This combinatorial complexity motivates IGP-based automatic discovery of TE mesh-group membership rather than manual configuration.
The document explicitly limits scope to IGP-based discovery of mesh membership; the actual mechanism for dynamically creating TE LSPs once membership is discovered is implementation-specific and outside scope. This separation keeps the IGP extensions minimal and stable.
The TE-MESH-GROUP information is carried in the existing OSPF Router Information LSA and IS-IS Router Capability TLV (defined in RFC 4970 and RFC 4971) rather than new LSA types. This choice leverages established advertisement and flooding mechanisms without introducing new IGP machinery.
The TE-MESH-GROUP TLVs do not introduce interoperability issues. OSPF routers not supporting the TLV SHOULD silently ignore it per RFC 2370; IS-IS routers not supporting the sub-TLV SHOULD silently ignore it.
A router MUST originate a new LSA/LSP whenever the content of the TE-MESH-GROUP TLV/sub-TLV changes or whenever required by regular routing procedures (e.g., periodic updates).
If an LSR desires to join or leave a TE mesh-group in IS-IS, it MUST originate a new IS-IS LSP comprising the refreshed Router Capability TLV with the updated TE-MESH-GROUP sub-TLV.
If either the IPv4 or IPv6 TE-MESH-GROUP TLV/sub-TLV occurs more than once within the Router Information LSA or IS-IS Router Capability TLV, only the first instance is processed; subsequent instances SHOULD be silently ignored.
If the flooding scope of a TE-MESH-GROUP sub-TLV is limited to an IS-IS level/area, it MUST NOT be leaked across level/area boundaries and the S flag of the Router Capability TLV MUST be cleared. If the scope is the entire routing domain, the TLV MUST be leaked and the S flag MUST be set.
If the MPLS TE mesh-group is contained within a single OSPF area, the TE-MESH-GROUP TLV MUST be generated within an Area-local Router Information LSA. If it spans multiple areas, the TLV MUST be generated within a Routing-domain scope Router Information LSA.
The TE-MESH-GROUP TLV is OPTIONAL and MUST NOT include more than one IPv4 instance or more than one IPv6 instance within a given Router Information LSA or Router Capability TLV.
A TE mesh-group is defined as a group of LSRs connected by a full mesh of TE LSPs. Each mesh-group membership advertisement includes a mesh-group number, a tail-end address (used as TE LSP tail-end by peer members), and a tail-end name display string.
IANA assigned two new IS-IS sub-TLV code-points in the Router Capability TLV registry: value 3 for TE-MESH-GROUP sub-TLV (IPv4) and value 4 for TE-MESH-GROUP sub-TLV (IPv6), both referencing RFC 4972.
IANA assigned two new OSPF TLV code-points in the Router Information LSA registry: value 3 for TE-MESH-GROUP TLV (IPv4) and value 4 for TE-MESH-GROUP TLV (IPv6), both referencing RFC 4972.
Advertisement of fake TE Mesh Group memberships by a misconfigured or malicious LSR does not have major network impact because a TE LSP can only be established if the same mesh-group membership is configured on both the head-end and tail-end LSRs. Thus fake advertisements cannot amplify DoS attacks beyond overloading the IGP.
The IS-IS TE-MESH-GROUP sub-TLV for IPv6 (Type 4) encodes entries with a 32-bit mesh-group-number, 128-bit tail-end IPv6 address, 1-octet name-length, and variable-length tail-end name, carried within the IS-IS Router Capability TLV.
The OSPF TE-MESH-GROUP TLV for IPv4 (Type 3) encodes one or more entries each containing: a 32-bit mesh-group-number, a 32-bit tail-end IPv4 address, a 1-octet name-length field, and a variable-length tail-end name. The TLV is padded to 4-octet alignment; padding is not included in the length field.
The OSPF TE-MESH-GROUP TLV for IPv6 (Type 4) encodes one or more entries each containing: a 32-bit mesh-group-number, a 128-bit tail-end IPv6 address, a 1-octet name-length field, and a variable-length tail-end name. Format otherwise mirrors the IPv4 variant.