Dynamic Hostname Exchange Mechanism for IS-IS
obsoletes
- rfc-2763 — Dynamic Hostname Exchange Mechanism for IS-IS
updated by
- rfc-6232 — Purge Originator Identification TLV for IS-IS
Extracted elements (9)
Static configuration of hostname-to-systemID mappings does not scale: every router must maintain entries for all other routers, and any addition, deletion, or change requires updating all routers. DNS was considered but rejected due to potential unavailability during network problems, added complexity, and lack of CLNS/NSAP support in some implementations. Flooding names in IS-IS LSPs was chosen as simpler and more manageable.
The value field hostname can be an FQDN, a subset of an FQDN, or any operator-chosen string; use of FQDN or a subset is strongly recommended. The content is treated as a domain name per RFC 2181.
User interfaces that permit Unicode characters for the hostname field are responsible for applying the ToASCII and/or ToUnicode algorithm (RFC 3490 / IDNA) to convert to and from the 7-bit ASCII on-wire encoding.
If a system receives a mapping for a name or system ID that differs from the local cache, an implementation SHOULD replace the existing mapping with the latest information.
If the Dynamic Hostname TLV is present in a pseudonode LSP, it SHOULD NOT be interpreted as the DNS hostname of the router.
The Dynamic Hostname TLV is defined as TLV type 137, carrying a variable-length value field of 1 to 255 bytes representing the symbolic hostname of the router originating the LSP. The system ID of the router can be derived from the LSP identifier.
TLV type 137 ('Dynamic Name') is used by this document. The codepoint was already allocated and reserved by RFC 2763; no new IANA action is required.
Because name-to-systemID mappings rely on information provided by the routers themselves, a misconfigured or compromised router can inject false mapping information. This information should be treated with suspicion, especially when diagnosing suspected security incidents.
The Dynamic Hostname TLV value field is a string of 1 to 255 bytes encoded in 7-bit ASCII, representing the router's symbolic name. The string is not null-terminated.