[comp.protocols.tcp-ip] Loopy routes

stine@SPARTA.COM (Robert Havens Stine) (12/09/89)

An ftp connection between heisenberg.sparta.com &
devvax.tn.cornell.edu hung, so I ran traceroute from a nearby host
(narnia.saic.com) to see what was going on.  Answer: duelling
gateways!

traceroute output follows, from narnia.saic.com toward
devvax.tn.cornell.edu, on 8 Dec, about 20:50 EST:

 1  MCLEAN-MB.DDN.MIL (10.3.0.111)  80 ms  220 ms  120 ms
 2  MCLEAN-MB.DDN.MIL (10.3.0.111)  100 ms  120 ms  120 ms
 3  CAMBRIDGE-MB.DDN.MIL (10.3.0.5)  1060 ms  1020 ms  800 ms
 4  MCLEAN-MB.DDN.MIL (26.20.0.17)  1000 ms  660 ms  640 ms
 5  CAMBRIDGE-MB.DDN.MIL (10.3.0.5)  2120 ms  1200 ms *
 6  MCLEAN-MB.DDN.MIL (26.20.0.17)  1600 ms  1620 ms  1900 ms
 7  CAMBRIDGE-MB.DDN.MIL (10.3.0.5)  1580 ms  1620 ms  1740 ms
 8  * * *

What a ride!

In fairness, I ought to add that coherent routes were reestablished in
20-30 minutes.

Note: the McLean mailbridge entry is repeated at hops 1 & 2 because
vienna.saic.com, narnia's entry gateway, does not check the TTL field.

- Bob Stine