MPLS TE - Explicit Path Configuration

Unanswered Question

Hi all


Few questions about explicit path configuration.


1) next-hop IP address , point to next-hop interface ip or router-id(loopback) , which is prefer with? and why.


2) Attached the diagram, 3 example of explicit-path configuration. Like to know it isi possible and valid.

 

Explicit path <1> & <2> the purpose is the TE path must via either one of the "pink" WAN links. Are both configuration valid ?

<3> have same purpose, but mixed with interface & router-ID as next hop. Does this kind config work ?


<1>TE Tunnel Site-A PE1 to Site-B PE1

ip explicite-path name APE1-BPE1_1 enable

next-address 10.1.1.1

exclude-address 10.1.3.2

next-address 10.1.4.2


<2>TE Tunnel Site-A PE1 to Site-B PE1

ip explicite-path name APE1-BPE1_2 enable

next-address 10.1.1.1

exclude-address 10.1.3.2

<3>TE Tunnel Site-A PE1 to Site-B PE1

ip explicite-path name APE1-BPE1_3 enable

next-address 10.1.1.1

next-address

1.1.1.2

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shivlu jain Fri, 07/02/2010 - 00:15
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Hi


In RSVP-TE, if you want to use the next hop address of the adjacent router then you need to use strict in the explicit path option. If you want to use the next hop address as loopback which is not adjacent to the node then you can use the loose path option.


Regards

Shivlu Jain

http://www.mplsvpn.info

Mohamed Sobair Fri, 07/02/2010 - 04:21
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Hi,


Your loopback is not part of MPLS and is not enabled with RSVP protocol, hence , Traffic Engineering tunnels should be explicitly set with an MPLS RSVP enabled interface.


However, if your loopback is enabled for mpls with RSVP , then there would be no problems adding a loopback as nexthop.


for TE tunnels , RSVP examines tunnel resources by sending messages from the source of the Label switch path to the destination of the LSP, these messages identifies RSVP resources, and these messages are:


1- path tear

2- path error

3- Reservation

4- Reservation confirmation.




HTH

Mohamed

Hi Mohamed,


Can you explain meaning of "router loopback IP is not part of MPLS/RSVP enable"

As I knew loopback interface not require ip rsvp command to be configure. Only physical interface connect between MPLS routers.


I have network running without the need to enable rsvp on loopback interface.


Or you have sample command of enable rsvp on loopback ip interface.


Regards

Reza Sharifi Fri, 07/02/2010 - 19:39
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As Shivlu explained if you use the next hop physical address then that is an strict hop but if you specify a loopback address as your next hop then that is considered as loose hop.  Usually a loose hop is more flexible if you have multiple paths to the same destination.  On the other hand when you specify the next hop as strict if that next hop goes down then your LSP goes down with it too.  Although not very common but you can use a combination of loose and strict hop together.


Have a look at this doc for more info:


http://www.cisco.com/en/US/docs/ios/mpls/configuration/guide/mp_te_inter_as_te.html


HTH

Reza

Mohamed Sobair Fri, 07/02/2010 - 23:07
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Hi,


What I pointed here is that your loopback should be MPLS enabled , and you might or might not reserve bandwidth on the loopback depends if you are setting it on the physical interface using the RSVP reservation towards the headend of the tunnel.



HTH

Mohamed

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