generate default route and export to kernel if remote peer is up

[Nikola Mitev]

Hi,

I have a setup of ISP1 -- R1 -- LAN -- R2 -- ISP2
with BGP peerings from R1 to ISP1 and R2 to ISP2

Some hosts on the LAN have R1 as primary gateway, others R2 to
distribute the load between the ISPs.

I want to add a default route to the kernel on each router but only if
the remote peer is up. The remote peer does not respond to BFD so
that's not an option.

Once both routers have a conditionally defined default route for their
ISP, it should be easy to propagate that to each other with increased
metric as a backup route. I am assuming here that if R1 has a default
through R2 and ISP1 is down, R1 will respond with an ICMP redirect to
any requests from hosts that need to be routed out of LAN.

I searched for a recipe that would fit the above but found nothing yet,
hoping someone here can help :)

Nik