Routing

Why does Junos require including an interface in both "protocols mpls interface <interface name>" and "interfaces <interface name> family mpls" in order to enable MPLS on an interface?

This is something that I have been wondering about for a while, just out of curiousity as it seems redundant.

Is there some scenario where you would use one command, but not the other?

From what meager knowledge of Junos I have, the first command will configure the router to accept MPLS/labeled packets. By default, the interface can only accept IP packets so this command is needed to activate MPLS on the forwarding plane.

set interface <IF.UNIT> family mpls

From the perspective or the Routing/Forwarding Engine, MPLS is also a protocol, needing its own LIB/LFIB ("show route table mpls.0") where all the labels including the default labels such as Router Alert and explicit nulls will be stored.

To activate MPLS on the control plane then, you need the following

set protocols mpls interface <IF.UNIT>

 Thus, as far as I understand, the redundant configuration is needed to keep the configuration in line with the Junos philosophy of separate forwarding and control planes. First command for the forwarding plane, second to activate the control plane.

HTH,

Nic

I see your point, but it just seems like this approach is treating MPLS more like a "routing" protocol from a configuration perspective than a "transport" protocol.

Especially when enabling IPv4, IPv6, or ISO on an interface does not require a separate "protocols inet interface <IF.UNIT>", "protocols inet6 interface <IF.UNIT>", or "protocols iso interface <IF.UNIT>".

I had the same questions but only for IPv4 (didn't think far enough).

My reasoning (completely subjective) was that IPv4 is on by default on Junos so it does not need to be explicitly turned on. I would extend that reasoning (again completely subjective and I cannot back this up via independent sources) for IPv6.

Regarding ISO, Junos to my knowledge does not support CLNS as data traffic but only the IS-IS implementation. For that, the configuration would be congruent to the MPLS configuration in that IS-IS has to be turned on by "set protocols is-is" to enable the only ISO protocol supported.

It would be nice to have someone more knowledgeable comment.

Nic

Hello,

If you don't add interface under [protocols mpls], then only LDP would work.

Interface under [protocols mpls] is needed for:

1/ RSVP

2/ CCC and TCC

3/ MPLS ping and traceroute

HTH

Rgds

Alex

[quote]

Interface under [protocols mpls] is needed for:

1/ RSVP

2/ CCC and TCC

3/ MPLS ping and traceroute

[/quote]

Give me a proof link, please