North American Network Operators Group

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Re: IP over SONET considered harmful?

  • From: Paul E. Erkkila
  • Date: Fri Mar 20 17:00:17 1998

> copying Tag-TTL into IP TTL. However, doing this introduces another
> problem - it breaks traceroute. And there are enough folks in the MPLS
> WG who think that the ability to traceroute through all the LSRs is an
> "unalienated right".

	Without going to far into the traceroute source , would
  a solution to this problem be a modified traceroute that 
  "understood" and could report Tag/MPLS "hops" as well as
  the normal method? There would need to be some way of
  identifying which devices were forwarding using Tag/Mpls
  and which were not, as well as getting and reporting
  the information. I think it falls into the same category of
  tracing cell forwarding in ATM without having access to the
  equipment doing the work.

> In view of the above here are some of the possible avenues:
> 
> (a) try to get "rough consensus" with the MPLS WG to allow
>     decrement IP TTL by 1 on egress (rather than copy Tag TTL
>     into IP TTL), or
> 
> (b) talk to your favorite vendor(s), and ask the vendor(s) to put
>     a "knob" that would decrement IP TTL by 1 on egress (rather
>     than copying Tag TTL into IP TTL).

	Alan and I discussed the "knob" solution before, it seems
   to solve the problem, but under certain circumstances a packet 
   could end up being forwarded forever because of (mis)configuration.


   -pee