[huawei-nsp] A Multi-VPN-Instance CE and DN bit

[Victor Sudakov]

Dear Colleagues,

I've spent a futile day trying to understand why in the topology shown
here: http://noc.sibptus.ru/~sudakov/MCE.PNG
the CE has a certain prefix in its lsdb but not in the routing table.
It was not being installed into the routing table because of the DN
bit set by the PE announcing the prefix.

Now I know that the "vpn-instance-capability simple" on the CE makes
it ignore the DN bit and install the route.

My question is, why is "vpn-instance-capability simple" not the
default behavior? What is the worst case scenario in the topology
above if it were the default?

Anyway, the left PE or the right PE would break the routing loop on
seeing the DN bit (in each VRF), why does the CE have to look at it at all?

Thanks in advance for any input.

-- 
Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
AS43859