>28 193.251.133.117 (193.251.133.117) 586.776 ms 584.171 ms 586.944 ms
>29 193.251.133.117 (193.251.133.117) 608.677 ms 610.789 ms 618.232 ms
>30 193.251.133.117 (193.251.133.117) 641.141 ms 643.149 ms 639.050 ms
This sometimes happens when there is a filter on that router. All packets going through get an ICMP administratively denied sent back, and the traceroute host interprets that as an ICMP TTL expired or perhaps does not even notice what type of ICMP it is, just looks at the source IP address.
>27 208.63.128.3 (208.63.128.3) 111.475 ms 69.670 ms 69.267 ms
>28 208.63.128.1 (208.63.128.1) 68.883 ms 67.147 ms 72.106 ms
>29 208.63.128.3 (208.63.128.3) 69.842 ms 67.889 ms 66.944 ms
>30 208.63.128.1 (208.63.128.1) 70.986 ms 73.124 ms 68.452 ms
This looks exactly like a routing loop to me. Why do you think it is not a routing loop?
>27 208.63.128.3 (208.63.128.3) 111.475 ms 69.670 ms 69.267 ms
>28 208.63.128.1 (208.63.128.1) 68.883 ms 67.147 ms 72.106 ms
>29 208.63.128.3 (208.63.128.3) 69.842 ms 67.889 ms 66.944 ms
>30 208.63.128.1 (208.63.128.1) 70.986 ms 73.124 ms 68.452 ms
This looks exactly like a routing loop to me. Why do you think it is not a
routing loop?
I was assuming that any routing loop in the system would be transient, but
this one is not (the traceroute is still showing the same behavior). The
extent to which I see this also makes me think that there is something
else going on.
Do you think that it can be a real persistent routing loop (data packets
would actually shuttle between the two interfaces) as against some
wierdness because of traceroute?
I'd tell you a story, but it would make all of nanog cringe. Put
simply, I know of at least one medium size regional network who
when they couldn't make "bgp work" decided to implement a series
of scripts that logged into all routers and installed statics to
make things work.
Let me just tell you, after a few short weeks of adding and removing
(and missing) such routes there were loops all over the place, many
of which are probably still there.
There are a number of ways long lived loops can occur. I believe
others have pointed out some other methods.
Do you think that it can be a real persistent routing loop (data packets
would actually shuttle between the two interfaces) as against some
wierdness because of traceroute?
Seems like a persistent routing loop. One possibility I've
heard about is the persistent routing loops that can occur if an internal
router is not situated topologically close to its BGP route reflector:
Does anyone have any idea of if/how often these types of persistent loops
occur in practice? I guess there would be no way to really tell if this
was the cause without having some knowledge about the internal topology...
