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RE: iBGP next hop and multi-access media

  • From: alex
  • Date: Mon Oct 07 10:22:10 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?

Can someone please explain to me *why* are you trying to come up with
*complicated* configurations as opposite to 

(a) defining your connected routes on all the routers that would be using
it.

or

(b) letting IP to what it is supposed to do?


Oh, and finally, should you be using such super-intersting methods of
finding where to go, I certainly hope that the network is secure from little
arp games that someone can play.

Alex


> 
> > -----Original Message-----
> > From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On 
> > Behalf Of Ralph Doncaster
> > Sent: Monday, October 07, 2002 12:56 AM
> > To: Jason Lixfeld
> > Cc: 'Alex Rubenstein'; nanog@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@merit.edu [mailto:owner-nanog@merit.edu] On 
> > > > Behalf Of Ralph Doncaster
> > > > Sent: Monday, October 07, 2002 12:43 AM
> > > > To: Alex Rubenstein
> > > > Cc: nanog@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@nac.net, latency, 
> > Al Reuben --
> > > > > --    Net Access Corporation, 800-NET-ME-36, 
> http://www.nac.net   --
> > > > 
> > > > 
> > > > 
> > > 
> > 
> > 
> 
> 

-- 





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