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
