[j-nsp] 'family mpls' for vpn interfaces

[Hannes Gredler]

Bala Venkata wrote:
>  From JunOS docs (looking at "Configuring Interfaces for 
> Carrier-of-Carriers VPNs" in the VPN guide) it seems that you don't need 
> to set 'family mpls' on a vpn interface if it is not a coc vpn. What is 
> the need for 'family mpls' in coc and what happens if the same is set 
> for a non-coc vpn ?

bala,

a little bit of history first:

the original requirement to have family mpls on the egress vpn router
is b/c historically all mpls next-hop types

1. ipv4->mpls
2. mpls->mpls
3. mpls->ipv4

required a mandatory family mpls statement - therwise the kernel could not
install the required forwarding satte; case #3 has been fixed b/c configuring
family mpls w/o a mpls packet ever touching the wire is arguably a bit odd;

for a coc asbr the possible label stack operations are SWAP (egress) and
SWAP/PUSH, SWAP/PUSHPUSH (ingress) in other words true mpls next-hops [#2]

conclusion:

1. if you don't configure family mpls in a coc setup  the kernel will refuse
    to install the required next-hop;

2. it does not harm to configure family mpls (except confusing the uneducated)
    in a non-coc vpn case. (read: configuration downwards compatability)

HTH,

/hannes