From: Herbert Maosa (asawilunda@googlemail.com)
Date: Thu Jul 26 2007 - 12:37:23 ART
Technically, for any address family configured in BGP you have to activate
the neighbor. However. the Cisco IOS default is to automatically activate
neighbors for the IPV4 unicast address-family, so we usually never have to
consciously put this in the config, and it never shows up in the
configuration.
However, the moment you explicitly activate a bgp neighbor for any of the
address families ( eg IPV4 multicast ), you will then see the IPV4 Unicast
address family automatically showing up in the config, to make it apparent
to you, even though you may not have explicitly put those lines of config.
next-hop-self is usually configured on route-reflectors to the rr-clients,
or on any BGP speaker if you think the peer does not have an IGP path to the
BGP next hop that may be in the updates that you may be sending that
neighbor. Remember that BGP has to consider a route valid before considering
it in its decission making process, and part of the validation criteria is
next hop reachability.
regards,
Herbert.
On 7/26/07, Sangeetha Nadarajah <ccie1101@gmail.com> wrote:
>
> Hi,
> [1] I have read the cisco doc and it is not very clear when to use
> the
> 'address-family ipv4' and 'address-family ipv4 multicast' command ....
> Can someone explain when to use this and its purpose .....
>
> [2] Also, I was doing the technology lab from IE for multicast on
> 'Multicast BGP' and came to this part of the solution on R4 whereby it is
> connected to R2 by an ethernet segment ....... My question is why is
> there
> a next-hop-self to 150.1.24.2 which is the ethernet portion of R2 since it
> is a *directly connected neighbor ? Pls explain as I don't understand why
> the next-hop-self command is needed here ? Most of the time it is used on
> frame-relay back to back connections only right ?*
>
> address-family ipv4 multicast
> neighbor 150.1.24.2 activate
> *neighbor 150.1.24.2 next-hop-self
> *neighbor 150.1.45.5 activate
> exit address-family
> !
> address-family ipv4
> neighbor 150.1.24.2 activate
> neighbor 150.1.45.5 activate
> exit address-family
>
> Thank you,
>
> Cheers,
>
> - sn -
>
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-- Kindest regards, hm
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