Subject: [lisp] Please review section 9: traceroute behavior

From: Sam Hartman <[email-masked]>
Date: Tue, 01 Sep 2009 11:58:38 -0400

I skipped over section 9 on traceroute behavior when I first reviewed
the LISP draft.  I thought it simply described how LISP interacted
with traceroute, rather than providing normative behavior changes.

I have a few concerns:

1) It's not obvious to me how you tell a traceroute packet from a
non-traceroute packet.  We should provide normative guidance for this.

2) As far as I can tell, MPLS treats its tunnels as a single hop and provides another distinct facility for tracing through the MPLS hops.  Why is it desirable to expose the LISP tunnel?

3) Is the TTL text in 9.3 safe?  Does the fact that we are cross-AF
protect us from loops?

---

From: Dino Farinacci <[email-masked]>
Date: Tue, 1 Sep 2009 09:05:29 -0700

> non-traceroute packet.  We should provide normative guidance for this.

We preferred to leave this out because there are so many forms from  
the various OSes. Is it okay to leave this out because it will cause a  
big time sink. Let's leave it to the implementations to decide what  
signatures relate to traceroute.

> 2) As far as I can tell, MPLS treats its tunnels as a single hop and  
> provides another distinct facility for tracing through the MPLS  
> hops.  Why is it desirable to expose the LISP tunnel?

LISP doesn't really have traditional tunnels. They are dynamic  
encapsulating paths. It is really important to debug the path because  
users may not have physical access to the ITR to initiate a traceroute  
from there. This has proved useful when we debug on the LISP test  
network. We use it daily.

> 3) Is the TTL text in 9.3 safe?  Does the fact that we are cross-AF

There can be no loops because we use an increasing TTL for traceroute.  
And that is what is used across segment 2. In the cross-AF case, we  
make the ITR-to-ETR path look like one-hop. That is all there is to it.

Dino

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