<br><font size=2 face="sans-serif">Hi Folks,</font>
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<br><font size=2 face="sans-serif">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.</font>
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<br><font size=2 face="sans-serif">Test WS ---- PE1 ----- P ----- PE2 ----|Sniffer|----- FireWall ----- External Network</font>
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<br><font size=2 face="sans-serif">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.</font>
<br><font size=2 face="sans-serif">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.</font>
<br><font size=2 face="sans-serif">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.</font>
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<br><font size=2 face="sans-serif">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.</font>
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<br><font size=2 face="sans-serif">Thanks, Yves</font>