Extended Administrative Groups in MPLS Traffic Engineering (MPLS-TE)
Extracted elements (14)
EAG is intended for use within a single domain only. No signaling analog (e.g., SESSION_ATTRIBUTE C-Type 1 or PCEP LSPA object) is defined, so EAG-based path constraints can only be applied at the ingress node.
The existing 32-bit Administrative Group (AG) sub-TLV is insufficient for large networks. Operators using AGs to flag geographic regions (e.g., metro areas) quickly exhaust 32 bits; color reuse across geographies is impractical because it prevents building LSPs that include one region while excluding another with the same bit value.
Nodes that do not support EAG can still obtain link color information from the AG sub-TLV when both are advertised, allowing incremental deployment and eventual migration away from the 32-bit AG.
A receiving node that detects a mismatch between the AG value and the first 32 bits of the EAG SHOULD report the mismatch to the operator.
A receiving node that receives both AG and EAG MUST use the AG as bits 0–31 of administrative color and the EAG for bits 32 and higher.
An implementation SHOULD treat desired but unadvertised EAG bits as if they were set to 0, so that a node requiring a specific EAG bit will not use a link that does not advertise that bit.
An implementation that uses a strategy other than treating unadvertised EAG bits as 0 SHOULD be configurable to fall back to the recommended behavior in order to maximize interoperability.
If a node advertises both AG and EAG, the first 32 bits of the EAG MUST be identical to the advertised AG value.
The EAG value MUST be a multiple of 4 bytes in length; no other fixed upper bound is imposed beyond protocol/media-specific constraints such as maximum packet length.
EAG bits 0–31 are a superset of the existing AG bits: they carry the same semantics and numbering. Additional bytes beyond the first 4 extend the numbering contiguously; for example, the least significant bit of the fifth byte is bit 32.
The Extended Administrative Group (EAG) sub-TLV is defined for both OSPF and IS-IS to advertise more than 32 administrative group colors per link. The EAG is optional and may be of any non-zero length that is a multiple of 4 bytes, constrained only by protocol/media MTU limits.
IANA assigned sub-TLV type 26 in the OSPF 'Types for sub-TLVs of TE Link TLV (Value 2)' registry and type 14 in the IS-IS 'Sub-TLVs for TLV 22, 141, and 222' registry, both named 'Extended Administrative Group'. The IS-IS entry is marked 'y' for sub-TLVs 22, 141, and 222.
This extension adds no new security considerations beyond those already applicable to MPLS-TE IGP extensions.
The EAG sub-TLV carries one or more 32-bit Extended Admin Group words in sequence. The Type is 26 for OSPF and 14 for IS-IS. The Length field is the size of the EAG value in bytes and MUST be a multiple of 4.