[rbridge] Pseudonode minimization thoughts...

[Les Ginsberg (ginsberg)]

Radia -

It seems you missed my point entirely. When I objected to your
characterization of the proposal as:

"I don't think it is complex. It costs 2 bits in Hellos."

I was not trying to demonstrate that the problem is insolvable - just
that the solution is not trivial - and requires care in both
specification and implementation. This raises the bar - at least to me -
in that the benefits have to be worth the cost. Obviously we differ on
that value judgment.

As to your questions:

> a) without configuration, would an IS-IS router today create a
> pseudonode if it is the only router on an Ethernet link?
> For instance, suppose R1 and R2
> are neighbors on an Ethernet, and R2 goes down. Will R1 will issue two
> LSPs, one saying the pseudonode is R1.25 with neighbor R1,
> and another saying R1 has neighbor R1.25? Or when R2 goes down, does
R1
> get rid of the pseudonode?

In order for a router to elect itself DIS on a circuit it MUST have at
least one ES or IS adjacency on that circuit in the UP state. (ISO
10589:2002 Section 8.4.5)

> 
> b) suppose R1 and R2 are both on the same Ethernet, and one is
> configured that that port is pt-to-pt and the other is not configured
> that way. What happens?

No adjacency will be formed as the router which is configured to be
Pt-Pt discards LAN IIHs it receives on that circuit.

> 
> c) suppose R1, R2, and R3 are all on the same Ethernet, and all are
> configured that that port is pt-to-pt. What happens?

No more than one adjacency will be formed on each router. Received
hellos whose system ID does not match an existing adjacency are
discarded.

See Section 4.5 of 

http://www.ietf.org/internet-drafts/draft-ietf-isis-igp-p2p-over-lan-06.
txt

for further details.

   Les