From: Price, Jamie (jprice@xxxxxxxxxxx)
Date: Sat Apr 08 2000 - 01:59:31 GMT-3
Title: BGP Intelligence??
Hi,
I was working on a BGP lab this afternoon - no big deal - but once I'd
finished with that I moved on to playing (or at least intending to)
with dialer profiles, callback, etc. I have 5 x 2600's. In the BGP
lab I was working on, the 2 2600's (routers 3 and 4) that have BRI
interfaces both had EBGP peers. Obviously these were the ones I
needed to work on.
Anyway - without thinking anything of it I just did a "wr er" and
"reload" on the 2 routers with the BRI's in them. When they came back
up however they immediately started looking for network config files.
I hadn't touched the config registers and I was a bit stumped as to
why they would do this all of a sudden. Once they had both timed out
I looked over the config and found that everything but the IP address
on the serial interface that connected the routers to the EBGP peers
had been erased. Those interfaces were still active too. So I did a
"wr er" and "reload" again.....and again same deal.
Only when I had erased the configs of the EBGP peers (routers 2 and 5)
that were still active in the lab and reloaded everything at the same
time did routers 3 and 4 boot normally (when I say normally I mean the
way I have them - to go straight to setup). I'm assuming the same
would have happened if I powered off routers 2 and 5. So, to
investigate further I threw a bunch of configs on all the routers in
the lab that I saved from some OSPF stuff that I'd done previous.
Recreating the scene I erased and reloaded routers 3 and 4 but this
time they booted normally.
Am I right in thinking that the router/IOS is intelligent enough to
realize that it is an edge device in a BGP autonomous system even
after an erase and as a last ditch attempt to retain functionality,
considering that routers in this role would be pretty mission
critical, it does what I saw?? That, or the keepalives from the
active router make an effort to get the inactive peer on line. Has
anyone experienced this or actually knows of it? My theory, without
delving too deeply into it yet, is that on reboot the BGP keepalives
were saying to the peer (ex-peer actually) "this is who you should be"
and those keepalives somehow forced the interface to come up with the
intended address. The router then seeing it had no config did what it
should do and went to the network looking for one. But how does the
interface come up when default is for it to be in a shutdown state?
Or are all interfaces actually live on initial boot and then go into
shutdown??
If what I think was happening then I think that's a really cool
feature. I could see the admins of both AS's agreeing to store
configs for each other in case of emergencies such as a router
failure/config loss.
Or have I simply been studying too much and the hermit lifestyle I
have adopted of late is granting me hallucinations and causing my mind
to wander on spectacular tangents?? Maybe I'm simply fried and need
to go to bed.
Jamie
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