Subject: [Isis-wg] too many segments

From: "Christian E. Hopps" <[email-masked]>
Date: Sun, 11 Jun 2000 11:51:03 -0400

I'm curious what the standard way to deal with overflowing 255 LSP
segments for an IS is.  At first I was tempted to use the overload
state, but this doesn't strike me as fitting well in its definition.
(e.g., how do you report which LSP caused the overload when there
is no LSP).  Also overflowing 255 segments is a gross misconfiguration
error which the overload state doesn't appear to be directly intended
for (given that it waits some time and then switches back to normal).

Its pretty easy to overflow the LSP by redistributing e.g., BGP
into ISIS.  Even if it doesn't overflow the IS LSPs itself you can
then get into trouble at the level 1/level 2 boundary when summarization
occurs.

I'm curious what other implementations do in this situation.

Thanks for any help,
Chris.

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From: Tony Li <[email-masked]>
Date: Sun, 11 Jun 2000 10:24:12 -0700 (PDT)

| I'm curious what the standard way to deal with overflowing 255 LSP
 | segments for an IS is.  At first I was tempted to use the overload
 | state, but this doesn't strike me as fitting well in its definition.
 | (e.g., how do you report which LSP caused the overload when there
 | is no LSP).  Also overflowing 255 segments is a gross misconfiguration
 | error which the overload state doesn't appear to be directly intended
 | for (given that it waits some time and then switches back to normal).
 | 
 | Its pretty easy to overflow the LSP by redistributing e.g., BGP
 | into ISIS.  Even if it doesn't overflow the IS LSPs itself you can
 | then get into trouble at the level 1/level 2 boundary when summarization
 | occurs.
 | 
 | I'm curious what other implementations do in this situation.

Chris,

There is no "standard" way of dealing with this problem.  The most commonly
suggested local hack for dealing with this, if one intentionally wants to
generate more segments, is to have the administrator manually allocate
another system ID.  You then establish a zero cost adjacency between your
primary system ID and your secondary.  We discussed this at length back
when we were discussing more than 255 adjacencies, tho the driver there was
the ability to have more pseudo-node numbers.  The same mechanism gives you
more space to play in as well...  

As to the accidental overflow, the simplest mechanism is: don't.  ;-)

Tony