MPLS questions

wera711wera711 Member Posts: 23 ■□□□□□□□□□
Hi,

I need something cleared up. We have two networks at work, using 2 different providers. One is Sprint with MPLS. The other is Qwest with MPLS.

If I tracert some of our networks through Sprint's MPLS network, I can see the PE and P routers all along the way.

If I do this in Qwest's MPLS network, I never see any P routers. Its usually just 3 hops.

Are there different kinds of MPLS? I assumed Qwest's MPLS was MPLS-VPN since I do not see the provider routers. If yes, then what is Sprint's?

thanks

Comments

  • networker050184networker050184 Mod Posts: 11,962 Mod
    They are most likely using the "no mpls ip propagate-ttl" feature which causes the router not to copy the TTL to the label. That way only the non labeled hops send back the hops for the traceroute.
    An expert is a man who has made all the mistakes which can be made.
  • SettSett Member Posts: 187
    Ops, didn't see that networker050184 already replayed.


    Probably Qwest's routers have TTL Propagation disabled - this means that the TTL of the original IP packed is not copied to the MPLS Label's TTL field. The Labels TTL is set to 255. In result the traceroute doesn't receive TTL expired message until it reaches the edge of the MPLS Network where the label is stripped and IP Packet's TTL is used again. This "no mpls ip propagate-ttl " command causes the whole MPLS network to be seen as a single hop by the end user. Pretty cool.
    Non-native English speaker
  • wera711wera711 Member Posts: 23 ■□□□□□□□□□
    Great, thanks!
    Do you guys know if a 2621xm maxed out on memory can run MPLS ok?
  • networker050184networker050184 Mod Posts: 11,962 Mod
    Check the feature navigator for your IOS.
    An expert is a man who has made all the mistakes which can be made.
  • wera711wera711 Member Posts: 23 ■□□□□□□□□□
    Last question......Are the PE routers generally also the LERs? I'm assuming that is where the labeling occurs?
  • networker050184networker050184 Mod Posts: 11,962 Mod
    Yes the LER is basically the same thing as a PE router. They both serve as the entry/exit to the MPLS cloud.
    An expert is a man who has made all the mistakes which can be made.
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