Multi site BGP Routing design

["Justin Krejci" <jkrejci () usinternet com>]

We have two geographically distinct locations that currently both fall under
the same ASN.

At site 1 we have a particular set of ip networks (/20 and bigger) in use
only locally to this site

At site 2 we have a separate set of ip networks (/20 and bigger) in use only
locally to this site

 

Each site has at least one upstream internet connection advertising with
BGP.

There is also a (reliable) private link between to the two sites where our
routers at each site are all talking iBGP (as well as ospf). There is a
router subnet (/27) that spans the two sites.

We currently advertise all subnets out all upstream connections as if both
sites were only one and traffic routes between sites without issue via the
private link.

 

If the private link between the two sites fails, will BGP allow for us to
access the IP subnets at site 2 from site 1 via the internet given that both
sites are advertising under the same ASN?

Is this a case where having multiple ASNs makes sense to treat each site as
remote peers to each other?

 

Thanks,

Justin