We're wanting to apply antispoofing on an interface which has a default route pointing out of it.
Does this mean, for traffic ingress to this port, no matter what the source IP address is, the default route will satisfy the condition that there is a route for the source address out of the interface this pkt is currently ingressing on? Hence uRPF is useless in this scenario?
I don't see how loose uRPF would help.
Thanks for any help.
Put simply yes having a default-route will pretty much negate the use of uRPF as the router will always have a path back to the source. Using loose or strict makes no real difference here. In fact you would use strict unless you had multiple paths in and out.
Ordinarily uRPF will not use the default-route unless you use the keyword "allow-default".
In your case you may be better off using traditional acl's to block RFC1918 addressing etc.