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LSP and LDP

dangal.43
Level 1
Level 1

what is difference between both or both are the same?

How can we configure the Static SLP in cisco router network?

2 Accepted Solutions

Accepted Solutions

There are 2 labels in a MPLS VPN scenario. If its only MPLS there is only 1 label.

Now coming to this, the first required label is called MPLS IGP label, as this label is assigned using LDP based upon IGP path (OSPF,EIGRP,STATIC).

Now you have labels to switch across the MPLS core (MPLS IGP label), but the core doesnt know anything about the connected customer VPN's or their routes, so MPBGP comes into picture. MPBGP uses route targets to exchange routing information from different PE's and builds the VRF routing table and then assigns labels to those routes.(but since the BGP session was established between the PE's using the existing MPLS IGP labels, we need to use 2 labels when sending traffic to the other end of the VPN;s. (1) MPLS IGP Label (2) BGP VPN Label.

And yes using multiple RT you can have connecitivty with multiple VPN;s, this is called as Extranet.

As mentioned in the previous post, the books would be very helpful too.

HTH-Cheers,

Swaroop

# As I said Mohammed , it happens all the time, when we are active at the posts.

View solution in original post

Hi Dan,

I guess that you are talking about MPLS VPN case, where you have 2 labels, the Top label, which is the LDP label (and it is the label to reach the egress PE router), and the VPN label which is propagated via MP-BGP between the PEs and they are used to reach the VPN customer interfaces.

And yes you can overlap VPNs using multiple RTs.

I would suggest another book beside Swaroop's suggested one.

MPLS Fundamentals

Luc De Ghein, CCIE

No. 1897

[edit] Swaroop, i guess we were writing nearly the same answer at the same time :)

HTH,

Mohammed Mahmoud.

View solution in original post

8 Replies 8

mohammedmahmoud
Level 11
Level 11

Hi,

Simply, LSP is a sequence of LSRs used to forward labeled packets of a certain FEC (An LSP is simillar to FR or ATM VC), while LDP is the protocol used for label distribution in the MPLS domain (it can be Cisco proprietary TDP or the standard LDP).

The relation between LSP and LDP is that, LDP/TDP is used to exchange labels and build LSPs dynamically.

LSPs can be statically configured via MPLS TE.

HTH,

Mohammed Mahmoud.

As Mohammed has already explained the LSP, its nothing but the best routing path from you IGP between 2 ends, used for label switching, with help of labels assigned by LDP.

There are 2 ways you can think of buidling static LSP's.

1) You can configure static routing in the core, and then run LDP, so the LSP will be built as per your static routing path.

2) You can as Mohammed specified use MPLS TE, with explicit routing to define a static/manual path.

Also to benefit more, it would great if you can go through this link, for some books and recommended study, (if you like self study).

http://forums.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Service%20Providers&topic=MPLS&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.1ddf95d6

Enjoy the documents.

HTH-Cheers,

Swaroop

HTH-Cheers,

Swaroop

Swaroop and Mohmmad,

again as there were two labels for the MPLS one is the MPLS and IGP so what is IGP label again? what is the use of IGP label?

one more thing is can i have multiple route-target value to have multiple vpn connectivity with multiple customers?

then how does it work?

There are 2 labels in a MPLS VPN scenario. If its only MPLS there is only 1 label.

Now coming to this, the first required label is called MPLS IGP label, as this label is assigned using LDP based upon IGP path (OSPF,EIGRP,STATIC).

Now you have labels to switch across the MPLS core (MPLS IGP label), but the core doesnt know anything about the connected customer VPN's or their routes, so MPBGP comes into picture. MPBGP uses route targets to exchange routing information from different PE's and builds the VRF routing table and then assigns labels to those routes.(but since the BGP session was established between the PE's using the existing MPLS IGP labels, we need to use 2 labels when sending traffic to the other end of the VPN;s. (1) MPLS IGP Label (2) BGP VPN Label.

And yes using multiple RT you can have connecitivty with multiple VPN;s, this is called as Extranet.

As mentioned in the previous post, the books would be very helpful too.

HTH-Cheers,

Swaroop

# As I said Mohammed , it happens all the time, when we are active at the posts.

thanks Swaroop and Mohammed again for you reply, so here first label which is understood by the Provider routers including PE and P and the other label is for the PE router again to identify the perticular customer so thats why they have two lable right???

Hi Dan,

Totally right, and you are very welcomed and thank you for using the rating system.

HTH,

Mohammed Mahmoud.

Hi Dan,

I guess that you are talking about MPLS VPN case, where you have 2 labels, the Top label, which is the LDP label (and it is the label to reach the egress PE router), and the VPN label which is propagated via MP-BGP between the PEs and they are used to reach the VPN customer interfaces.

And yes you can overlap VPNs using multiple RTs.

I would suggest another book beside Swaroop's suggested one.

MPLS Fundamentals

Luc De Ghein, CCIE

No. 1897

[edit] Swaroop, i guess we were writing nearly the same answer at the same time :)

HTH,

Mohammed Mahmoud.

If you have an MPLS VPN environment (Layer 3 VPNs), you will have to labels on the packet. An outer label representing the Label Switch Path (LSP) to get from ingress PE to egress PE. This can be derived directly from the IGP and use LDP to assign the labels, or it can be an explicit path using MPLS Traffic Engineering, in which case the label would be learned by RSVP. Either way, it is represents the LSP to get from ingress PE to egress PE. The second label or inner label represents the VPN that packet is destined to (VPN label). The VPN the packet is destined to is determined by an extended community value called a route target (RT). This route target is sent in an MP-BGP update when the vrf is configured and the route-target values are assigned to the VRF. PEs forward packets from the MPLS network into a VRF based on the import RT value and forward packets from the VRF into the MPLS network with the export RT value.

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