On Wed, Jan 07, 2004 at 07:18:26PM +0000, Antony Stone wrote: > The whole point of the TTL field in IP headers in the first place was to avoid > routing loops (small or large). Absolutely. > > TTL gets decremented by every router a packet passes through, so that > eventually after passing through some (larger than is reasonable for a normal > journey) number of routers, the packet gets discarded. In normal > circumstances this does not happen, however when it does happen it is > important that it happens correctly. > > If you ever increase the value of TTL on a packet's journey through a router, > then a routing loop involving that router will not be detected unless the > number of other routers involved in the loop is at least as many as the > amount you have increased the TTL by. Good point. I like the formulation :-) > Therefore I would suggest that leaving TTL as it is (ie: not decrementing it, > but not incrementing it either) on its way through a router is just about > acceptable (and this will prevent the machien from showing up in traceroutes, > which I understand is the requirement here?) All that said, I believe there is no harm in incrementing the TTL for the inbound packets __iff__ one's network is not that deep and most definitely not a transit network. Ramin > but incrementing it so that its > value on leaving a machine is any higher than it was on arriving at the > machine is a Very Bad Idea(TM). > > IMHO & YMMV, etc... > > Antony. > > -- > This is not a rehearsal. > This is Real Life. > > Please reply to the list; > please don't CC me. >
