On Tue, 18 Nov 2025 at 17:04, Dale W. Carder <[email protected]> wrote:
> It's hard to discern implicit from explicit behavior. In RFC1771,
> there is no global uniqueness requirement for the ID, it is just to
> be mapped to a host address. So, it must be that hosts were to be
> required to be globally unique, but I realized even RFC 1597 existed
> by then.
Apologies for failing to communicate that RFC1771 explicitly requires
a unique routerID.
---
1. The BGP Identifier of the local system is compared to the BGP
Identifier of the remote system (as specified in the OPEN
message).
2. If the value of the local BGP Identifier is less than the
remote one, the local system closes BGP connection that already
exists (the one that is already in the OpenConfirm state), and
accepts BGP connection initiated by the remote system.
3. Otherwise, the local system closes newly created BGP connection
(the one associated with the newly received OPEN message), and
continues to use the existing one (the one that is already in the
OpenConfirm state).
Comparing BGP Identifiers is done by treating them as (4-octet
long) unsigned integers.
---
Without unique routerID these two ASN may have identical routerID,
therefore the collision mechanism does not work.
--
++ytti
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