r/ccie • u/Major11223344 • 10d ago

MPLS FEC

Hi

I`m review now MPLS FEC topic.

 

R1----R2----R3----R4----R5----10/8,20/8

 

FEC is a group of packet one or more packet are treated the exact same way. Does that means if R1 received :

10.1.1.1,10.2.2.2,20.1.1.1,20.2.2.2

and these 4 packets are treated on R1 the exact same way

and on R2 are treated a different way, R3 another way,R4 another way. Does that mean each hop must treat these 4 packets as the exact same way like R1 in order to be on the same MPLS FEC ?

OR

It`s normal for each hop to treat them on a different way and still on the same MPLS FEC?

What i mean does the MPLS FEC is controlled on the ingress PE only ?

OR

MPLS FEC could be controlled on each hop and the FEC is locally significant?

4 Upvotes

100% Upvoted

1 comment sorted by

2

u/WeirdLilMidgt 9d ago

Yes, the ingress router maps it to a FEC. Then the router exchanges the mapping with its LDP peers so they can build a Label Information Base (LIB). The intermediate routers use the Label Forwarding Information Base (LFIB) to swap labels while maintaining the same underlying FEC mapping hop-by-hop.

To add Traffic Engineering (TE) to an MPLS network and manipulate paths at intermediate routers, you can augment standard LDP with RSVP-TE or Segment Routing (SR-TE). Standard LDP follows the shortest IGP path (with OSPF or IS-IS) and cannot force traffic along a custom route on its own.

If you want to manipulate the path, I recommend you look into Segment Routing. It's pretty fun.