I believe Linux does not support recursive static routes, is this correct? If so, do we not see the use-case or is it just lacking quality implementation which would be accepted if such is presented?
Just to elaborate on one use case. Consider your Linux host has two BGP upstreams, you advertise your loopback/32 prefix and you receive something. Let's say you at least receive 192.0.2.0/24 from both BGP sessions. Now you probably would like to do something like 'ip route add 0.0.0.0/0 via 192.0.2.0 src lo' But this won't work, as we do not recurse 192.0.2.0 to where ever it may point at any given time. Why would you do this, instead of receive 0.0.0.0/0 from upstream? For one, you can set the 'src' parameter. And another, typical upstream generates 0.0.0.0/0 locally, so even if upstream device is isolated from network, it will continue to advertise 0.0.0.0/0 and blackhole your traffic. If you choose your prefix towards which you default-route, you can choose something which is more representative of functioning Internet from your POV. This is typical feature supported by IOS, IOS-XE, IOS-XR, JunOS, SROS, VRP and so forth. Some of them support it by standard without any additional toggle, another, like JunOS requires that you define specifically which static routes are recursed, in JunOS the keyword used is 'resolve'. But commonly the functionality is known as 'recurse', so if iproute2 were to need verb for this, 'recurse' would be preferred over 'resolve'. -- ++ytti
