MPLS Questions from the books I'm reading

warriorfan808warriorfan808 Member Posts: 27 ■□□□□□□□□□
Hey guys,

Spent some time reading on MPLS today and wanted to go over what I read with you guys, to make sure I'm understanding things correctly.

This is how I see the MPLS cloud looking, in terms of MPLS Frame traversing through an LSP.

First you have your Customer Edge Router, which will peer with a PE. This PE will be both an imposing LSR and an ingress LSR. A label will be placed onto the datagram and then sent to the next LSR utilizing the LSP. These routers are defined as Provider Routers or Intermediate LSRs. In the case of MPLS TE, these P routers could also be considered Ingress LSR's or Egress LSRs, if another label is stacked. If it is Traffic Engineered, then it comes to the Ingress LSR that is also considered a Provider Router, most likely not running BGP. This Ingress LSR will stack another label based on a separate LSP and this will be sent towards the Egress LSR which is also defined as a P Router at this point. The end of the second LSP used for Traffic Engineering is stripped off, or Popped. The original Label is still there and the frame is sent towards the Egress LSR defined in the original LSP. This Egress LSR will be considered a Diposing LSR and since it will remove the label completely before gettign to the Customer Edge Router. This Router is also a Provider Edge Router because it will peer up with the Customer Edge Router (EBGP).

I'm just racking my mind right now. Tryign to understand what I just got done reading.


  • networker050184networker050184 Mod Posts: 11,962 Mod
    Sounds like you've got the gist of it. It will make a lot more sense when you lab it up and look at the LFIB along the way.
    An expert is a man who has made all the mistakes which can be made.
  • warriorfan808warriorfan808 Member Posts: 27 ■□□□□□□□□□
    Thanks Networker. Sometimes it helps me to talk through something. I do it with the guys at work, but none of them are MPLS guys. One guy is, but I don't work with him very often. Have you worked with TDP? I've gotten to the portion that talks about Cisco developing TDP and then it later turning into LDP once the standards finally caught up. The book doesn't cover TDP since it's not used often. So far it just makes it sound like LDP is more of an advancement.
  • networker050184networker050184 Mod Posts: 11,962 Mod
    Just know that TDP was the original Cisco implementation before the LDP standard. You don't have to worry about learning any details I wouldn't think. Its all LDP or RSVP these days.
    An expert is a man who has made all the mistakes which can be made.
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