Two somewhat intertwined questions. I'll ask the second
part first.
I buy transit from Global Crossing and another carrier on
HDLC
encapsulated DS3's.
Recently my BGP session has started flapping on the GX
circuit... It
looks something like this:
Jul 21 21:17:43.731 UTC: %BGP-3-NOTIFICATION: received from
neighbor
67.17.168.73 6/6 (cease) 0 bytes
Jul 21 21:17:43.731 UTC: %BGP-5-ADJCHANGE: neighbor
67.17.168.73 Down
BGP Notification received
Jul 21 21:18:25.439 UTC: %BGP-5-ADJCHANGE: neighbor
67.17.168.73 Up
Jul 21 21:29:52.315 UTC: %BGP-3-NOTIFICATION: received from
neighbor
67.17.168.73 6/6 (cease) 0 bytes
Jul 21 21:29:52.315 UTC: %BGP-5-ADJCHANGE: neighbor
67.17.168.73 Down
BGP Notification received
Jul 21 21:30:38.511 UTC: %BGP-5-ADJCHANGE: neighbor
67.17.168.73 Up
Jul 21 21:31:34.411 UTC: %BGP-3-NOTIFICATION: received from
neighbor
67.17.168.73 6/6 (cease) 0 bytes
Jul 21 21:31:34.411 UTC: %BGP-5-ADJCHANGE: neighbor
67.17.168.73 Down
BGP Notification received
Jul 21 21:32:20.535 UTC: %BGP-5-ADJCHANGE: neighbor
67.17.168.73 Up
Jul 21 21:32:52.547 UTC: %BGP-5-ADJCHANGE: neighbor
67.17.168.73 Down
Peer closed the session
Jul 21 21:33:32.703 UTC: %BGP-5-ADJCHANGE: neighbor
67.17.168.73 Up
There are no other log entries during the periods when this
occur.
Unfortunately this causes enough prefix flaps that any
prefixes which
are preferred through GX are damped for like a half hour by
certain
providers as my BGP routes get added/withdrawn through the
GX link.
GX claims (although I'm not sure they really know) that
these are caused
by SONET ring switches. I can believe this, since I
haven't seen any
real circuit flaps, and my understanding is that a SONET
switch should
generally be fast enough that you normally won't see the
transition
other than perhaps an error counter or two cranking up.
However, it
seems strange that I'm getting a 6/6 (cease) notification
which I read
as "configuration change" from their router.
GX also seems to be at a
loss to explain why my BGP is flapping - other than to point
at the
SONET switches.
I guess I'm trying to find out if someone on the list
recognizes what
this might be so I can perhaps help GX find and fix this.
I'm also
kinda curious as to whether or not typically a SONET ring
switch event
would actually propagate into a router in such a way that
BGP would try
to shut down the BGP sessions. I'm just having a hard
time visualizing
how a supposedly below-layer-two switch would cause bgp to
reset in this
manner. Not being a SONET expert even by any long stretch
of the
imagination leaves me with some holes here, but I thought
the whole goal
of SONET when used to provide DS3 circuits was to hide the
ring switches
as much as possible from the DS3 circuits - realizing that
framing may
be hard to preserve on a ring switch which would cause
momentary loss of
sync or similar - which usually shows up as an error instead
of a
interface flap.
And finally, does anyone have a contact within GX with a
clue? So far
I'm not sure I've talked to anyone who knows anything but
how to spell
BGP. I'd really like to talk to someone about the real
cause of these
flaps and try to resolve them so they don't reoccur.
-forrest
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