[c-nsp] IOS XR and IS-IS default origination

[John Neiberger]

I've noticed that in IOS XR, if you have default-information originate
configured in ISIS, it will behave similar to "default-information
originate always" in OSPF. It will advertise a default whether or not it
has learned one from an external source. I thought this was a bug, but now
I'm starting to wonder if this is expected behavior.

I also see that a route policy could be added to conditionally advertise a
default. If ISIS in XR always originates a default when that command is
configured, what would a route policy look like that would only allow a
default to be advertised if it was learned via eBGP? I'd swear I've done
something similar in IOS before, but it's been a while.

Any thoughts?

Thanks,
John