"mpls ip" global vs interface level command

[Kashish_Patel]

What is the purpose of "mpls ip" global command? I think just enabling mpls on an interface by using "mpls ip" should be sufficient, but then what is the purpose of the global level command?

[Reza Sharifi]

Usage Guidelines

Globally enabling MPLS forwarding does not enable it on the interfaces. You must enable MPLS forwarding on the interfaces separately.

MPLS forwarding of packets along normally routed paths (also called dynamic label switching) is enabled by this command. For a given interface to perform dynamic label switching, this switching function must be enabled.

The no form of this command stops dynamic label switching for all the interfaces regardless of the interface configuration; it also stops distribution of labels for dynamic label switching. However, the no form of this command does not affect the sending of labeled packets through the LSP tunnels.

link:

http://www.cisco.com/c/en/us/td/docs/optical/cpt/r9_3/command/reference/cpt93_cr/cpt93_cr_chapter_010.html#wp1254011620

HTH

[Kashish_Patel]

That's what my question was about, why do we need "mpls ip" global command at all (when we anyways have to enable mpls on interface level separately)...What is the point of global command?

[JohnTylerPearce]

Kashish,

Let's see you have a (P) router or Provider Router within an MPLS Core Network, with all links that should have MPLS enabled, it would be easier to configure a global command than 5 interface level commands.

A use for the interface-level command would be, on a PE router connecting to a CE device, you do't want to run MPLS, you just want to enable the VRF.

Hopefully that will explain the differences.

Reza's article post explained it pretty well.

[Kashish_Patel]

That makes sense, but I am still confused. I was reading article

http://blog.ipexpert.com/2009/09/16/mpls-l3-vpn/  where the author has used both global as well as interface level commands. Interface level would not have been needed at all if global command is used, right?

[Jon Marshall · Accepted solution]

Kashish

The interface commands are always needed. Just enabling it globally does not enable it on the interfaces.

The recommendation was always to enable it globally and on each interface you wanted to run MPLS on. I have seen more recent docs only showing it being enabled on the interfaces.

However whenever i have setup labs for this i have always used both. It is, after all, just one extra command.

According to the docs when you enable it globally you then still need to enable it per interface. However if you disable it globally this overrides the interface configuration so in effect it stops dynamic switching and the distribution of labels for dynamic switching on all interfaces.

Jon

[Kashish_Patel]

That makes more sense. Thanks Jon!

[Tushar Patil]

Hi Kashish

mpls ip global command it is necessary and think so its on by default in newer IOS version, so only interface command are needed to enable it on interface try disabling it by no mpls ip global MPLS will fail

Also try to configure  with mpls ldp autoconfig command under isis or ospf it will enable mpls on the interface running isis or ospf because mpls ip is on globally by default