Re: BGP and aggregation

[Scott Granados <scott () graphidelix net>]

Actually I ran this way for a while as a primary.  I had three sites 
attached via cogent entirely all announcing a /19 and the internally a 
/21 each and a couple /21's out of the primary location.  In the main 
location was a 7507 and in the two other pops 6509's.  We set ospf 
internally, set up bgp for the announcements at each site and used the 
no-export tag for the more specifics.  Then gre tunnels:) for the 
internal.  It worked and I pushed probably 45 to 50mb over the internal 
loops or gre tunnels.  Not ideal but it worked.

On Sun, 12 May 2002, 
Stephen J. Wilcox wrote:

> Interesting point there Scott.. we were discussing just that at a recent
> IXP meeting I was at. Theres a number of different ways (well hacks) in
> which you can keep connectivity between two halves of an AS network in the
> event of a split. 
>
> Is anyone out there actually doing something either this or similar to
> keep two halves connected in the event of a split.. and have you actually
> run successfully on your backup and maintained a reasonable throughput
> (say 30 or 40Mbs) ? I'd be interested if anyone has a proven technique as
> I want to implement something myself and dont really want to test it by
> pulling the plug on some backbone links and waiting to see what happens!
>
> Steve
>
> On Sun, 12 May 2002, Scott Granados wrote:
>
> > Don't forget that if both sites use the same as even if the connection 
> > link drops they will not be able to see each  other over the upstream 
> > provider as routers won't take the srutes from the same as.  If this 
> > isn't a problem don't worry about it.  If you wish to preserve 
> > connectivity between cities you should have a back-up link or use 
> > different as's or gre tunnels:).
> >
> > On Sat, 11 May 2002, Ralph Doncaster 
> > wrote:
> >
> > > I have transit in 2 cities.  I have a circuit connecting the 2 cities as
> > > well.  So far I've been using non-contiguous IPs, so there's been no
> > > opportunity for aggregation.  Having just received my /20 from ARIN, I'm
> > > trying to plan my network.  Lets say I split the /20 into 2 /21's, one for
> > > each city.  I'd like to announce the aggregate /20 instead of 2 /21's, as
> > > long as the circuit connecting the 2 cities is working.  If the circuit
> > > goes down I want each city to announce the local /21.  Is this
> > > possible? (using either a Cisco router or Zebra)
> > >
> > > Ralph Doncaster
> > > principal, IStop.com     
> > > div. of Doncaster Consulting Inc.