Not sure what the nature of the problem is here, but
here are a couple of points to note:
1. The TTL field is in the IP header and not the UDP
header.
2. The TTL is only decremented after the packet
crosses a router hop ( a switch hop does NOT count).
3. The inital TTL=15, and it gets decremented after
that as it crosses routers. This makes it surprising
that you're seeing TTL=1 or 2. It implies alot of
router hops.
Cormac
Cormac Long, CCSI#21600
http://www.cormaclong.com
--- Lance Simon <[EMAIL PROTECTED]> wrote:
> Hi group!
>
> I am a lurker at best here, but today I saw
> something that really
> puzzled me. While I was looking at a trace file I
> noticed something
> unusual about the ttl values for RIP updates on a
> PacketEngines switch.
> This switch is connected to a Cat5000 and I had a
> sniffer in between the
>
> two.
> My understanding of RIP is that the ttl value = 2
> and that it is
> decremented as it enters a switch/router and then it
> is looked at.
> Therefore, a ttl=2 would become ttl=1 before the
> packet is even looked
> at. If the ttl=1 it would become ttl=0 and then,
> instead of being
> looked at, it would be discarded. Is this correct?
> First, let me say that the Packet Engines 2200
> switch is a very good box
>
> and it is communicating well with the Cat5k. The
> RIP updates are being
> handled well by both sides, but; when looking at
> the sniff, the ttl
> value from the packet Engines box is set to =1. How
> can this be?
> Do I totally misunderstand the UDP ttl value in
> relationship to RIP?
> Any insights would be helpful. BTW, I have got a
> call into a
> PacketEngines s/w engineer and am waiting for a
> response.
>
> Thanks,
>
> Lance
>
>
>
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