Re: iBGP next hop and multi-access media

["Stephen J. Wilcox" <steve () telecomplete co uk>]

No its not possible to say you can reach the subnet on the same media...

IP maps to the [Ethernet] with ARP, but before a packet is passed down to MAC
via ARP it is routed and if there is no route to the connected ethernet then it
will necessarily need to use the other router.

You must have the route before you can look at passing it to the media..

Steve

On Sun, 6 Oct 2002, Ralph Doncaster wrote:

> A and B are connected via the same multi-access media.  It is technically
> possible for B to tell A "you can reach 172.16.16.0/24 on the same media
> that you receive this update on".  However what people seem to be saying
> is that there is no dynamic routing protocol that implements this.
>
> Ralph Doncaster
> principal, IStop.com 
>
> On Sun, 6 Oct 2002, Stephen J. Wilcox wrote:
>
> > I dont understand this..
> >
> > A wants to get to a network which it [thinks it] is not connected to, the only
> > route is via B. therefore you must advertise the route from B with next hop B
> >
> > the only possible way (at least in ethernet IP) that A can send direct onto the
> > ethernet segment is if it is connected to the other (172.16) network and if
> > youre not willing to do that then your solution is not possible
> >
> > Steve
> >
> > On Sun, 6 Oct 2002, Ralph Doncaster wrote:
> >
> > > Background: 
> > > Router A and B are connected via a common ethernet segment 1. Router A
> > > uses 10.10.10.1/30, and Router B uses 10.10.10.2/30. Router B also has
> > > another subnet configured for ethernet segment 1; 172.16.16.0/24.
> > >
> > > When I setup a situation like the above, with Router B advertising the
> > > 172.16.16.0/24 to router A, router A sees a next hop of 10.10.10.2.  This
> > > is not good since packets from A going to the 172.16.16 subnet get sent to
> > > Router B, which then ARPs the desitnation, instead of just being ARPed by
> > > router A.
> > >
> > > I don't want to turn on ICMP redirects on B since they're insecure and
> > > ugly.  I've also made sure I'm not using next-hop self.  Is there a way to
> > > make this work?
> > >
> > > Ralph Doncaster
> > > principal, IStop.com