North American Network Operators Group

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Re: IP over SONET considered harmful?

  • From: Sean M. Doran
  • Date: Sun Mar 22 13:48:18 1998

Scott Brim wrote:

| For example, in order for TTL to be effective, not every node needs to
| decrement it -- we just need to be sure that no loops can form where it
| doesn't get decremented.

Yes, but you also want to make sure that the price-per-packet
is really really really close to zero in the "gap" between
ttl decrementing routers, otherwise, even though a loop may
never form in the non-ttl-decrementing fabric, it may form
across it, for example, between the two routers on either
side of the gap, or through the two routers on either side of
the gap.

If the "gap" is a sub-IP fabric a continent and an ocean wide, such
a loop tends to be somewhat expensive.  TTL decrementing as a loop
mitigation feature ought to be fairly popular in such circumstances.