Hi all,
I'm trying to implement RFC 9666 Area Proxy in FRRouting's isisd. A few places
in the spec are open enough that I'd appreciate the working group's read. I
also have written my current leaning under each one, please confirm it.
1. Reachability in the election. RFC 9667 §6.3 says "not reachable" nodes
aren't eligible, but doesn't say reachable how. For Area Proxy the candidates
are Inside Routers advertising the Area Leader Sub-TLV
in their L2 LSPs. Should reachable mean L1 SPF, L2 SPF, or just a non-zero-age
LSP in the L1 LSDB? My leaning is L1 SPF, since the leader represents the L1
area.
2. Proxy System ID derivation. §4.2 says candidates SHOULD be configured with
the same Proxy System ID, but gives no default when it isn't configured. I
currently derive it deterministically (first 6 bytes of SHA-256 over the area
tag, forcing a zero first octet to 0x01) with an explicit override taking
precedence. Is that acceptable as a fallback, or should it always be explicitly
configured?
3. Area SID flags. §4.3.2 defines F/V/L but not who sets them. I'm treating
them as the Area Leader's local config, defaulting to F=0/V=0/L=0 (IPv4, index,
global), with no requirement that Inside Nodes agree. Does that match the
intent?
4. Who advertises the Proxy System Identifier. §4.3.1 says other candidates MAY
also advertise it, but also calls multiple identifiers a misconfiguration. I've
gone with only the elected leader advertising it, and candidates staying silent
until they win — that avoids churn and the multiple-identifier case. Is that
the intended reading?
5. Boundary LANs. §2 says multi-access boundary circuits with multiple Inside
Edge Routers are "not supported." Should I reject that config, warn and
continue, or leave it undefined? And is using the originally configured sysid
for the DIS pseudonode on a boundary LAN a hard requirement?
6. Algorithm 0. My reading is that Area Proxy should always advertise algorithm
0 with no flooding topology (dynamic flooding disabled), since the leader
produces a Proxy LSP rather than a flooding topology. Can you confirm?
7. Proxy LSP fragmentation. The spec doesn't say whether the Proxy LSP can be
fragmented. My assumption is yes. Reuse normal IS-IS fragmentation, since
§3.1's fragment-0 rule applies to the Area Proxy
TLV in a node's own L2 LSP, not to the Proxy LSP itself. Is that right?
Thanks,
Shenshen Luan
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