Subject: [rbridge] Proposed resolution of DRB election/MTU testing

From: "Jeff Pickering" <[email-masked]>
Date: Thu, 30 Apr 2009 13:18:19 -0700

Radia,

Just for clarification, when determining
"The campus-wide minimum MTU size chosen is the smallest size "S" reported in any LSP",
I am assuming you need to look all LSPs, not just "reachable via spf" ones. Correct?
What happens when S shrinks and there are already extant LSPs with size > old S?

Jeff

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From: Radia Perlman <[email-masked]>
Date: Thu, 30 Apr 2009 14:03:43 -0700

> What happens when S shrinks and there are already extant LSPs with 
Yes, you'd have to look at all LSPs, look at the "S" contained in each 
one, and choose the smallest S
as the campus-wide S. (though with the minimum value of S set to be an 
architectural constant,
say 1470).

As for whether it's just "reachable via spf", I'd say yes, it should 
only be ones reachable via spf.
Otherwise, one bad LSP from an about-to-die router can make the rest of 
the campus have
to stick with a low value of S until that LSP times out.

As for already extant LSP fragments that are now bigger than S -- good 
question!

Obviously, the source of those LSPs
needs to reformat its LSP and flood the newer, smaller-fragmented LSP.

However, as to what to do with LSPs in your database before they get 
reflooded from the source -- I'd
say time them out. In DECnet we had something where one router R could 
decide to time out
some other router, R2's, LSP, by setting the time to zero and 
reflooding. But then I remember
some sort of controversy about that (perhaps worrying about the security 
of allowing someone
to do that, since there couldn't be a way of cryptographically 
preventing a malicious router
from prematurely timing out someone else's LSP if it has to be possible 
for a nonmalicious router
to legitimately time out someone else's LSP). Is that timing-out 
mechanism still in IS-IS?

But anyway, I don't have any strong opinions on what to do with LSP 
fragments of size > S
that already exist. Seems like the possibilities are:
a) silently discard them
b) "noisily" time them out (i.e., flood them with age 0)
c) use them as if they're OK

Radia