Actually, if the switch is routing, it will decrement the hop or ttl
value. And the ttl on a RIP update is in the UDP header. If you are
not convinced I will send you the traces. And finally, as Travis
stated, a RIP update should only have max ttl of 2.
Lance
Cormac Long wrote:
> 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
> >
> >
> >
> > ___________________________________
> > UPDATED Posting Guidelines:
> > http://www.groupstudy.com/list/guide.html
> > FAQ, list archives, and subscription info:
> > http://www.groupstudy.com
> > Report misconduct and Nondisclosure violations to
> [EMAIL PROTECTED]
>
> =====
> http://www.cormaclong.com
>
> __________________________________________________
> Do You Yahoo!?
> Yahoo! Photos -- now, 100 FREE prints!
> http://photos.yahoo.com
___________________________________
UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html
FAQ, list archives, and subscription info: http://www.groupstudy.com
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
