Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Labels

How implicit NULL and Explicit NULL label are useful in MPLS netowrk? what is main function of both the labels?

4 REPLIES
Cisco Employee

Re: Labels

Dan,

implicit (label value of 3) and explicit (label value of 0) null labels are used by the router terminating an LSP to tell the penultimate hop how to behave when sending traffic along the LSP. An implicit null means that the penultimate hop router has to pop the label before forwarding to the egress router and explicit null means swap the incoming label with a label value of 0 (explicit null). The explicit null is sometimes used to convey the MPLS QOS value down to the egress router (sometimes refer to the pipe mode).

Refer to the following document for more information on the pipe mode.

http://www/en/US/tech/tk828/technologies_q_and_a_item09186a00800a43f5.shtml#wp27375

Regards,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Cisco Employee

Re: Labels

Hi,

A good portion of it is explained in my post

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40.1de01831/1#selected_message

The usage of implicit-null is for Penultimate Hop Popping (PHP), whereas the explicit-null label is mainly used to transport QoS markings, i.e. experimental bits in some specific scenarios.

Regards, Martin

New Member

Re: Labels

but who will propagate both type of LABEL and for what kind of prefix it will use this label?

Cisco Employee

Re: Labels

Hi,

imp-null label is for signalling purposes only, and will be assigned to directly connected networks on a LSR.

Explicit null label will be assigned to directly connected networks in a LSR, but is actually really sent in labeled packets.

Both are signalled f.e. to the LDP neighbors, who will use the information to forward traffic to the LSR with the connected network.

Hope this helps! Please use the rating system.

Regards, Martin

132
Views
5
Helpful
4
Replies
CreatePlease to create content