I think it just "clicked" for me...we'll see. I think "ip nhrp map multicast <NBMA IP>" is saying "hey man, if you want to multicast, eventually your tunnel destination is going to be NBMA". What made this click for me is that we don't have a tunnel destination on the mGRE tunnel. Therefore, at some point there HAS to be a mapping because it is an NBMA network, just like frame-relay. I knew that CCIE R&S would be useful for something ;)
On Fri, Mar 16, 2012 at 10:47 AM, Joe Astorino <[email protected]> wrote: > Thanks man, that actually helps me keep the logic straight. Obviously > , the multicast ultimately is still going to be encapsulated in the > tunnel so you would have a protocol stack looking something like this > say with OSPF between tunnel peers (Let's assume ESP transport mode!) > > [Outside IP] [ESP] [GRE] [Inside IP] [OSPF] [ESP Trailer] > > That is why specifying the public IP is confusing to me there because > the destination address of the OSPF after the multicast gets changed > to a unicast I think is going to be the tunnel address of the hub, say > 172.16.1.1 to use your example. Perhaps when you specify the public > IP, it maps it to the private IP based on the already existing ip nhrp > map command > > > On Fri, Mar 16, 2012 at 3:24 AM, Piotr Matusiak <[email protected]> wrote: >> I think this is to keep those commands straight :) >> >> I think this way. All NHRP map command are like 'ip nhrp map <priv> >> <public>' so that on spokes you have: >> >> ip nhrp map 172.16.1.1 100.1.1.1 >> >> to map between priv-public IP address on the hub. And you also have (in case >> of mGRE on the spoke) command: >> >> ip nhrp multicast 100.1.1.1 >> >> <multicast> is just a keyword specifying priv part. >> >> Similarly on Hub you have: >> >> ip nhrp map multicast dynamic which means send all multicast traffic to >> dynamically learnt Public (NBMA) IP addresses of your spokes (from NHRP DB). >> >> I know, this is not enough technical answer :) Also, note that sending mcast >> traffic over multipoint interface must have some replication features >> enabled. In this case you instruct the router to send mcast traffic to Hub's >> Public IP and this must be tunnel destination IP I suppose. >> >> Regards, >> Piotr >> >> >> >> >> 2012/3/16 Joe Astorino <[email protected]> >>> >>> Can anybody shed some light on understanding why the "ip nhrp map >>> multicast" command on a spoke maps to the public NMBA IP and not the >>> tunnel IP of the hub? >>> >>> I understand that it is used so that any broadcasts/multicasts sent >>> out the interface get sent to the hub only just trying to understand >>> why the NBMA address is used. >>> >>> Any tips on how do you keep straight which NHRP commands use the >>> tunnel IP vs the NBMA IP? >>> >>> -- >>> Sent from my mobile device >>> >>> Regards, >>> >>> Joe Astorino >>> CCIE #24347 >>> http://astorinonetworks.com >>> >>> "He not busy being born is busy dying" - Dylan >>> _______________________________________________ >>> 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 >> >> > > > > -- > Regards, > > Joe Astorino > CCIE #24347 > http://astorinonetworks.com > > "He not busy being born is busy dying" - Dylan -- Regards, Joe Astorino CCIE #24347 http://astorinonetworks.com "He not busy being born is busy dying" - Dylan _______________________________________________ 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
