RE: Traceroute issue - MPLS CE router replys 2 hops on ingress

From: Abbas Elzein (Abbas.Elzein@telus.com)
Date: Wed Aug 31 2005 - 15:26:45 GMT-3

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Are you seeing the same IP address on both the CE1 ingress and egress
interfaces?? if not.. the "CE1 egress_int" that address could be the IP
address of the PE receiving the your IP packets before they get labelled and
sent through the MPLS cloud..... Just guessing...

AE
________________________________

From: Jerry Wang [mailto:jerry-wang@rogers.com]
Sent: Wednesday, August 31, 2005 1:53 PM
To: Abbas Elzein; ccielab@groupstudy.com
Subject: RE: Traceroute issue - MPLS CE router replys 2 hops on ingress &
egress interfaces

Thanks Abbas,

Yes I agree the TTL propagation must be disabled on the PEs, this explains why
the traceroute output does not reflect PEs. But I still do not understand why
CE1 counts 2 hops for traceroute? See the 1st and 2nd hops, can you please
explain how this happens?

1. CE1_ingress_int
2. CE1_egress_int
3. CE2_ingress_int
4. R2_ingress_int

Thanks and best regards

Jerry

Abbas Elzein <Abbas.Elzein@telus.com> wrote:

        Most likely the TTL propagation is disabled on the PEs.. Disabling TTL
propagation allows the structure of the MPLS network to be hidden from
customers, but not the provider.

        -----Original Message-----
        From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Jerry
Wang
        Sent: Wednesday, August 31, 2005 12:16 PM
        To: ccielab@groupstudy.com
        Subject: Traceroute issue - MPLS CE router replys 2 hops on ingress & egress
interfaces

        Hi Guys,

        Please help to explain the following traceroute issue I found in my lab:

        I have 2 Routers R1 & R2 on two sites, both are connecting to MPLS/VPN cloud.
When I do traceroute from R1 to R2, I found the first 2 hops reflect the
ingress and egress interfaces on the same CE1 router, which is connecting to
R1. Please see following details:

        Traceroute path (on R1, do traceroute to R2's loopback address):

        R1 -- CE1 -- PE1 -- PE2 -- CE2 -- R2

        Tracing output:

        1. CE1_ingress_int
        2. CE1_egress_int
        3. CE2_ingress_int
        4. R2_ingress_int

        FYI: the /30 link route between CE1 & PE1 is not advertised to R1. not sure
if this affects or not.

        I have no access to to the MPLS CEs & PEs , I assume it might be related to
CE1's MPLS traceroute configuration. Or it might be related to the ttl
propagation between the IP & MPLS domain?

        Your help is highly appreciated!

        Thanks and best regards

        Juntao
        Network Engineer

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• Next message: Graham Hopkins: "IPv6 over Frame Relay"
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• Maybe in reply to: Abbas Elzein: "RE: Traceroute issue - MPLS CE router replys 2 hops on ingress"
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