[nsp] Re: [MPLS-OPS]: traceroute question

[M. ELK]

Yves

1- Quote
The external network is learned via static (E2) from PE2. Since the prefix 
is learned via static, there is no PHP on the P device
Unquote

Is it an observation specific to the setup U are using or it is
according to well know rule .
If the later , pls let me know the reference .

2- quote
this, since PE2 is sending the "TTL exceeded" message up the LSP to the
FireWall, which sends it back, as described in RFCs and in various books.
Unquote

the LSP end at PE2 . The PE2 is the edge of the MPLS domain and not the
Firewall .

3- Assume the prefix of the external netw is 10.0.0/8 ,
    PE2 advertise label L1 to P for such prefix .
    On PE2 , What is the action associated with incoming label L1 ?
    In other word ,what is the output of "sh tag f tags L1 details" .

Brgds





>From: Yves at Fauser.de
>To: mpls-ops at mplsrc.com
>CC: cisco-nsp at puck.nether.net
>Subject: [MPLS-OPS]: traceroute question
>Date: Mon, 17 Feb 2003 21:50:21 +0100
>
>Hi Folks,
>
>I have a question which might be an implementation specific issue, or an
>misunderstanding of some concepts from my part. here's the setup : - We
>have a small MPLS Network with 25 PEs and 5 Ps. All of them are Cisco7600
>(Catalyst6500) with 4-GE-WAN OSMs. We are still in the migration phase, so
>our Global-Routing-Table is still used for a bunch of prefixes. We use
>OSPF in a single area as IGP and TDP.
>
>Test WS  ---- PE1  -----  P  ----- PE2 ----|Sniffer|----- FireWall -----
>External Network
>
>The external network is learned via static (E2) from PE2. Since the prefix
>is learned via static, there is no PHP on the P device.
>Now if we do a traceroute from the Test WS (Global RT) to a host in the
>external network, we get an answer from every hop. What I don't understand
>is what we see in the Sniffer trace.
>In the trace the first thing we see is an "ICMP time exceeded" sourced by
>PE2 and send to the FireWall with the destination "Test WS". I understand
>this, since PE2 is sending the "TTL exceeded" message up the LSP to the
>FireWall, which sends it back, as described in RFCs and in various books.
>What I don't get is why we don't see the "ICMP Time Exceeded" send from
>the P device. If I understood the concepts right, we should see this in
>the trace, but we don't. Unfortunatly I didn't get the chance to do a
>Sniffer trace between the P and PE2 (lack of a Gigabit-Sniffer). Since we
>get a response from the P device in the traceroute output, either PE2 or P
>sends the "ICMP TTL Exceed" from the P device back to the workstation.
>
>So my main question is : - Should we see a "TTL Exceeded" with a source
>address of the P device and the workstation as destination in the Sniffer
>trace, or did I miss something in the concept.
>
>Thanks, Yves


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