Re: Dual Homed BGP

[Blake Hudson <blake () ispn net>]

On 1/23/2020 6:01 PM, Brian wrote:
> Hello all. I am having a hard time trying to articulate why a Dual 
> Home ISP should have full tables. My understanding has always been 
> that full tables when dual homed allow much more control. Especially 
> in helping to prevent Async routes.

Brian, you're correct that having more routing information will give you 
more control over routing decisions. However, for me, it's not about 
control/traffic engineering but about basic redundancy/availability. 
Taking full tables gives you visibility into whether an actual path 
exists (or does not exist) via each of your upstream providers. If you 
just take a default route originated by your peer you'll only have 
visibility that there's a connection between your router and your peer - 
not to the rest of the internet or to a specific destination past your 
peer. As Job said, maintenance, router reboots, and other upstream 
connectivity issues can cause an upstream peer to be missing routes that 
the other peer might have.

In my experience, most folks multi-home for improved 
redundancy/availability. So for those that are multi-homed, I recommend 
taking full tables so that you can get the most benefit. This may come 
at an additional expense so I understand why some would choose to take a 
default route only.

--Blake