[15749] in North American Network Operators' Group
Re: IP over SONET considered harmful?
daemon@ATHENA.MIT.EDU (Yakov Rekhter)
Fri Mar 20 13:59:04 1998
To: Alan Hannan <alan@globalcenter.net>
cc: nanog@merit.edu
In-reply-to: Your message of "Thu, 19 Mar 98 23:26:25 PST."
<19980319232625.15308@isi.net>
Date: Fri, 20 Mar 98 09:33:17 PST
From: Yakov Rekhter <yakov@cisco.com>
Alan,
> Subject: IP over SONET considered harmful?
[clipped...]
> I'd hoped that MPLS would solve this problem, but from reviewing
> the drafts I believe that the LSRs _WILL_ decrement the TTL.
To be more precise, the issue is that an ingress LSR is required to
copy IP TTL into Tag-TTL, *and* the egress LSR is *required* to copy
Tag-TTL into IP TTL. The problem you mentioned in your message would be
solved if the egress LSR would just decrement IP TTL by 1, rather than
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".
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).
Yakov.
