So, are you suggesting that the RIP update be passed through 16 router hops? I am
not the routing protocol expert of this group, but I know that you will only
update your neighboring router routers.
This may not be a big deal, since rip updates are sent via a broadcast (v1) or
multicast address (v2). But, every vendor puts in a ttl of _. I just want to
know how a ttl of 1 works, when most routers decrement before looking at the
packet.
Lance
Nimesh Vakharia wrote:
> If I remember this right, RIP scales upto 16 hops... after that you can
> ICMP host unreachables.. so max TTL would be 16..
>
> Nimesh.
>
> On Mon, 5 Jun 2000, Lance Simon wrote:
>
> > Yes, I was wrong about it not being in the IP header. The ttl is in the ip
> > header. RIP updates are transported over UDP port 520. Now, what do you
> > think the ttl for a RIP update should be, Nimesh? And why?
> >
> > Nimesh Vakharia wrote:
> >
> > > It would be very interesting to see these traces. The switch must be doing
> > > something very wierd. A UDP header consists of Source Port, Dest Port,
> > > Length and the checksum... TTL's are usually L3 and a max TTL 2 indicates
> > > somethings really screwed up.
> > >
> > > Nimesh.
> > >
> > > On Sun, 4 Jun 2000, Lance Simon wrote:
> > >
> > > > 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
> > > > > >
> > > > > >
> > > > > >
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