[c-nsp] BGP default vs BGP full

[Justin M. Streiner]

On Fri, 20 May 2016, Satish Patel wrote:

> Just wonder what would be the advantage and disadvantage of running
> BGP full vs default route.
>
> We have single ISP connection and ISP decided to just run default
> route over BGP instead full.

If you have just a single connection, BGP doesn't gain you anything.  If 
you have multiple connections to the same provider, BGP can be useful.

Taking just a default route from your upstreams is fine if you want to use 
them in an active/passive setup - use provider B only if the connection to 
provider A is down.

To get finer control over outbound upstream traffic distribution, you need 
to accept a larger portion of the global routing table, in addition to a 
default route.  Taking default plus originated and customer-originated 
routes from your upstream providers is one approach that some networks use 
to get some control of their outbound upstream traffic distribution 
without taking full routes.

The global IPv4 routing table is roughly 610,000 routes, and the global 
IPv6 routing table is about 30,000 routes.  If you wanted to take full 
routes from your provider(s), you would need to ensure that your routers 
can handle that, allow for growth, taking feeds from multiple providers, 
etc.

jms