From: Gianpietro Lavado (gianpietro1@gmail.com)
Date: Tue May 30 2006 - 18:59:10 ART
Hi Dave,
It should be clear that, in order to achieve connectivity to a directly
connected hop on a FR NBMA interface, the router should 'know' not only
through which physical interface to send the packet, but also through which
DLCI. If there's not mapping between the directly connected IP hops and a
DLCI, all packets sent to them will fail encapsulation.
The eigrp routing will make the routers learn other networks through the
directly connected hops already learned through mapping. The split-horizon
deactivation is necessary in the hub on this kind of topology
(hub&spoke) just to override the looping-avoidance eigrp mechanism in which
a router can't sent updates through a physical interface from which it
receives them (spoke to spoke updates going through the hub).
Note that an eigrp neighborship will only form between directly connected
networks, that means just hub-to-spokes in a point-to-multipoint topology.
In conclusion, you need to map the hub and the other spokes on each spoke
through the DLCI that connects to the hub, statically or via inverse arp*.
HTH
Gianpietro
*There's an exception in which you don't need mapping between spokes: when
using OSPF point-to-multipoint, you get on each spoke a /32 route of the
other spokes, learned from and through the already mapped hub IP address.
On 5/30/06, Schulz, Dave <DSchulz@dpsciences.com> wrote:
>
> Question on split horizon....
>
> I set up a hub router on a frame with the following configuration.....
>
> interface Serial0/0
> ip address 192.168.1.1 255.255.255.0
> encapsulation frame-relay
> no ip split-horizon eigrp 100
> frame-relay map ip 192.168.1.1 102
> frame-relay map ip 192.168.1.2 102 broadcast
> frame-relay map ip 192.168.1.3 103 broadcast
> no frame-relay inverse-arp
> !
> router eigrp 100
> network 192.168.1.0
> no auto-summary
>
> There are two remote sites, with the following configuration.....
>
> interface Serial0/0
> ip address 192.168.1.2 255.255.255.0
> encapsulation frame-relay
> no frame-relay inverse-arp IP 203
> no frame-relay inverse-arp IP 204
>
>
> and......
>
> interface Serial0
> ip address 192.168.1.3 255.255.255.0
> encapsulation frame-relay
> no frame-relay inverse-arp IP 302
> no frame-relay inverse-arp IP 304
> !
> Both set up with eigrp 100. They both form the neighbor relationship
> with the hub router. However, there is still not connectivity from
> spoke to spoke (even though split horizon is disabled). I know that
> everything works if I statically map everything, just trying to
> understand a little further on the eigrp between multiple routers. I
> was thinking that this may be a recursive issue, but I see that we have
> the route recursing to the hub router, but not continuing from the hub
> to the second spoke.....
>
> R2#sh ip rou 192.168.1.3
> Routing entry for 192.168.1.0/24
> Known via "connected", distance 0, metric 0 (connected, via interface)
> Redistributing via eigrp 100
> Routing Descriptor Blocks:
> * directly connected, via Serial0/0
> Route metric is 0, traffic share count is 1
>
> I may be missing something. Sorry for hitting on some of the more basic
> things.
>
>
>
>
>
>
> Dave Schulz,
>
> Email: dschulz@dpsciences.com <mailto:dschulz@dpsciences.com >
>
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