[c-nsp] Help with unique BGP setup

[Pete Templin]

Lobo wrote:

> This customer's requirements for bandwidth can be met if they use the 
> local connection only but should the connection go down, they would most 
> likely saturate the intercity connection and impact everyone else.  What 
> has been proposed is that they will use the local connection to get 
> internet access and should this access go down, they want the bgp 
> session to be dropped or something equivalent that will make sure they 
> don't go over the intercity.

We have the ability to do this in our network through the use of 
communities.  We'd tag the customer's incoming routes with 
our-ASN:2XX02, and the trailing '2' would tell the local city to 
advertise it (by matching the XX POP code) and the remote cities to not 
advertise it (by not-matching the XX POP code).  We'd selectively filter 
what routes we sent to the customer by limiting them to our-ASN:2.... 
(any customer in any POP), our-ASN:3.... (our routes in any POP), and 
our-ASN:4XX.. (upstream routes in this POP).  In this case, the session 
wouldn't go down, but the customer's routes wouldn't go to other markets 
(and therefore out the main upstream connection), and the customer would 
only receive external routes from the local connection(s).

We do this by sticking a coded community on EVERY route that goes into 
BGP at the point that the route enters our BGP mesh.  We redistribute 
connected and static routes into BGP through a route-map, and apply an 
inbound route-map to all BGP neighbors, then "send-community" to the 
rest of our iBGP mesh.  The coded community is our-ASN:ABCDE, where A 
represents the type of route (customer, ours, upstream), BC represents 
the POP number (I sorted them alphabetically; any new POPs just go on 
the end of the list), D represents how strong/weak we want the traffic 
to come in (useful by customers who want to use us a little less or as 
pure backup), and E signals our georouting (MED) logic (0 means bring it 
in through any POP, 1 means steer it towards the nearest POPs, 2 means 
this POP only).  It's worked exceptionally well in a huge variety of 
scenarios, and I'm painfully having to extend it to our parent network 
now that we've been acquired.

pt