iBGP next hop and multi-access media

Mon Oct 7 12:29:53 UTC 2002

Ok, so correct me if I'm wrong here (I'm just trying to paint a picture
of what this thread is trying to conceive), RA-FA1: 10.10.10.1/30,
RB-FA0: 10.10.10.2/30, 172.16.16.1/24 secondary?

iBGP setup between RA & RB, RB announces to RA with a next-hop of the
primary address on FA0, RA announces to RB with a next-hop of the
primary address on FA1.  When iBGP announces 172.16.16 to RA, you want
it announce with a next-hop of 172.16.16.1 as opposed to the primary
address 10.10.10.2.  Is that right?

> -----Original Message-----
> From: owner-nanog at merit.edu [mailto:owner-nanog at merit.edu] On 
> Behalf Of Ralph Doncaster
> Sent: Monday, October 07, 2002 12:56 AM
> To: Jason Lixfeld
> Cc: 'Alex Rubenstein'; nanog at merit.edu
> Subject: RE: iBGP next hop and multi-access media
> 
> 
> 
> It's a theoretical question. So far I've had one person email 
> me saying
> OSPF can advertise a subnet as local on a shared multi-access 
> media.  If
> in fact BGP can't do this, then it's no big deal to me as 
> nothing in my
> network relies on this functionality.
> 
> Ralph Doncaster
> principal, IStop.com 
> 
> On Mon, 7 Oct 2002, Jason Lixfeld wrote:
> 
> > Are you just asking a question to get a better understanding of how
> > things work, Ralph or have you already put this into 
> production and are
> > wondering why it doesn't work a certain way?
> > 
> > > -----Original Message-----
> > > From: owner-nanog at merit.edu [mailto:owner-nanog at merit.edu] On 
> > > Behalf Of Ralph Doncaster
> > > Sent: Monday, October 07, 2002 12:43 AM
> > > To: Alex Rubenstein
> > > Cc: nanog at merit.edu
> > > Subject: Re: iBGP next hop and multi-access media
> > > 
> > > 
> > > 
> > > My understanding is the route is valid as long as the interface is
> > > up; just like adding a secondary IP on the interface.
> > > 
> > > Ralph Doncaster
> > > principal, IStop.com 
> > > 
> > > On Mon, 7 Oct 2002, Alex Rubenstein wrote:
> > > 
> > > > 
> > > > Aha.
> > > > 
> > > > So, if you route to a ethernet interface, it will try to 
> > > arp for that
> > > > address on that subnet, even without having a local address 
> > > on the same
> > > > subnet?
> > > > 
> > > > This seems to me to be something you don't want to do.
> > > > 
> > > > Is the entire route valid as long as the router can ARP for 
> > > one of the
> > > > addresses in the routed subnet?
> > > > 
> > > > 
> > > > 
> > > > On Mon, 7 Oct 2002, Ralph Doncaster wrote:
> > > > 
> > > > > On Mon, 7 Oct 2002, Alex Rubenstein wrote:
> > > > >
> > > > > > I've been doing ip route statements going on 8 years 
> > > now, and I can't
> > > > > > imagine why ever -- and how it would even work -- you'd 
> > > want to ip route a
> > > > > > netblock with a next hop of a multi-access brandcast 
> > > media. As in, the
> > > > > > next hop is still truly undetermined.
> > > > > >
> > > > > > I guess I don't know this because I've never tried it. 
> > > But, how does the
> > > > > > router determine where to send the packets for a route 
> > > statement as
> > > > > > specified above (ip route a.b.c.d e.f.g.h f0/0) ?
> > > > >
> > > > > When you setup a secondary ip on an interface
> > > > >  int fa0/0
> > > > >    ip address a.b.c.d e.f.g.h secondary
> > > > >
> > > > > How does it determine where to send the packets?  ARP.
> > > > > Which is the same as adding the route described above.
> > > > >
> > > > > -Ralph
> > > > >
> > > > 
> > > > -- Alex Rubenstein, AR97, K2AHR, alex at nac.net, latency, 
> Al Reuben --
> > > > --    Net Access Corporation, 800-NET-ME-36, 
http://www.nac.net   --
> > > 
> > > 
> > > 
> > 
> 
> 