Redundent link config

[persiantools]

I have a Cisco AS5350 already connected to the internet through a leased line link. I am thinking of adding a secondary link from a different ISP to increase redundency. Putting aside the issue of load-balancing or policy-based routing, the problem is that with the new setuup I would be connected to two different AS networks and need new routing strategies. Do I need to get a pair of new IP addresses from the new AS network to make things work? How can I prevent my network from acting as a bridge between the two ASes and therefore blocking the transit inter-AS traffic? The reason why is to use the links for local traffic only.

[Richard Burts]

Adding another link on the AS5350 to a different service provider introduces a number of complexities which you will need to consider (especially if you have not connected to another AS before).

Some of the answers are fairly simple, yes you probably do need to get a new IP address from the new provider to make the new link work. There are several alternatives which address your concern about not being a transit network for inter-AS traffic. If you decide to run BGP with the providers there are AS path filters that you can use for this. If you do not run BGP then you might want to consider an access list inbound on the link which would deny any traffic whose destination address is not in your address space. (That access list should also deny any traffic whose source address IS in your address space, deny any traffic with bogon source address, etc)

Some of the questions you will need to consider as you plan how to achieve redundancy is how you control traffic outbound to the providers, and how routers in the Internet will get traffic to you (how will your addresses show up in their route table) will one provider be primary and the other purely a backup or will traffic balance between them (a particularly complicated question if your IP address space comes from your original service provider).

HTH

Rick