Could TTL=2 be to allow transit to the loop back interface and avoid the drop after hitting an interface?
Mike On Aug 1, 2012, at 7:24 PM, <[email protected]> wrote: > Thanks for the replies, interesting reading... especially the RFC :) > > I'm still not clear on exactly why the TTL is two, this may be something > I just let go for now. Usually when I don't understand why something is > the way it is, it means I am missing something fundamental... > > Doug > > -------- Original Message -------- > Subject: Re: [OSL | CCIE_RS] TTL on EIGRP multicast packets set to 2? > From: Bal Birdy <[email protected]> > Date: Wed, August 01, 2012 1:27 am > To: Joe Sanchez <[email protected]> > Cc: [email protected], IPexpert Online Study List > <[email protected]> > > Doug, > > The multicast IP for EIGRP is 224.0.0.10. This is within the Multicast > Permanent address range which states that 224.0.0.0 - 224.0.0.255 are > non routable (so local subnet only). The Multicast Permanent address > range also includes 224.0.1.0- 224.0.1.255, which are routable, but this > is out of scope of your question. > > The TTL set to 1, is a method of multicast TTL scoping to limit packets > being routed out of your administrative domain, but I dont think this is > the purpose here. > > B > > On Wed, Aug 1, 2012 at 2:31 PM, Joe Sanchez <[email protected]> wrote: > Doug,, > > There have been lots of statements about EIGRP that have been > misleading at > best. Take a look at the link below and see another discussion about > this > topic: > > http://www.groupstudy.com/archives/ccielab/200506/msg00687.html > http://www.mail-archive.com/[email protected]/msg72839.html > https://supportforums.cisco.com/thread/211406 > https://learningnetwork.cisco.com/thread/40817 > > In times like these, I like to refer back to this RFC which sum's it > all up. > > http://tools.ietf.org/rfc/rfc1925.txt > > > Joe Sanchez > > > > On Tue, Jul 31, 2012 at 9:02 PM, <[email protected]> wrote: > >> My understanding of EIGRP multicast packets was that the TTL is set > to >> one, and that this is the mechanism that prevents the packet from > being >> routed off the local subnet. >> >> However, doing a packet capture reveals that the TTL on EIGRP > multicast >> packets is actually 2. Some research hints that the same may be true > for >> RIP and OSPF, although I haven't verified. The Wireshark expert note >> refers to RFC 3171, but that RFC doesn't mention TTL. Here is the > actual >> text of the note: >> >> "Time To Live" != 1 for a packet sent to the Local Network Control > Block >> (see RFC 3171) >> >> So what is the purpose of setting these TTL's to 2? Obviously, they > are >> not getting routed off the subnet, so some other mechanism is being > used >> to prevent this. >> >> Thanks, >> >> Doug >> _______________________________________________ >> For more information regarding industry leading CCIE Lab training, > please >> visit www.ipexpert.com >> >> Are you a CCNP or CCIE and looking for a job? Check out >> www.PlatinumPlacement.com >> >> http://onlinestudylist.com/mailman/listinfo/ccie_rs >> > _______________________________________________ > For more information regarding industry leading CCIE Lab training, > please visit www.ipexpert.com > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com > > http://onlinestudylist.com/mailman/listinfo/ccie_rs > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com > > http://onlinestudylist.com/mailman/listinfo/ccie_rs _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs
