On Fri, Aug 31, 2007 at 03:58:54AM +0200, Stig Venaas wrote:
> I'm not arguing for keeping source routing here, but one quite useful
> thing it can be used for is traceroute. You can for instance trace from
> a remote point in the network towards yourself. This can be very helpful
> when debugging routing problems.

engineers also can use it when setting up, debugging, or for periodic
testing of peering sessions to make sure that the other side isn't doing
anything against the contractual terms of the peer (e.g. overriding the
normal policies that result from standard RIB->FIB route selection).

examples:
http://ptd.mbo.ma.rcn.net/peerinfo/

All peers are requested to enable LSRR on router interfaces facing RCN
peering sessions to facilitate network diagnostics at least during session
activation.

http://www.via.net/support/support_peer.html 
We require that our peers permit LSR, loose source routing, at least at the 
border.

http://www.noc.wiscnet.net/peering/
We require that our peers permit LSR, loose source routing, at least at
the border for diagnostic purposes.

i don't have an ACM account, but:
http://portal.acm.org/citation.cfm?coll=GUIDE&dl=GUIDE&id=1016718

without comparable functionality in IPv6, we lose a feature actively in
use (through IPv4) by some networks for verification of proper peering.

if i'm out of touch with current policies on peering & LSRR, please let
me know. sure, diehards of the end-to-end principle certainly believe
that removing source routing is an assult on said principle[1]. there
are other uses for source routing in some form, beyond e2e, that is
helpful.

-- bill

1. http://www.postel.org/pipermail/end2end-interest/2007-May/006711.html

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