Hi All,
I was just making my way through a couple ISDN/DDR Snapshot =
routing scenarios and made a unlikely observation.
For reference purposes I was making use of my CZone =
privileges(disclaimer) in mocking up David wolsefer ISDN lab exercise =
and got the following results. Before attempting this lab I worked =
through another BGP related lab. In saying so I moved right into this =
scenario without performing a write erase on the routers. To my benefit =
one of the routers I used in this ISDN mock up was clean and not used in =
the previous lab. =20
OK, so I get everything all configured baseline snapshot (just the ISDN =
circuit and 1 loopback) and it works great. I progressed to follow the =
requirements of David's scenario which makes use of the Ethernet circuit =
and commands to support ISDN backup of the Ethernet line. Here is where =
things get interesting.... The ISDN line keep flapping up..down..up.. =
down. =20
The "debug ip packet", "debug dialer packet" , and debug dialer events" =
revealed that the client-side of the snapshot circuit was trying to make =
a connection to 11.1.1.2 (eth0). As mentioned before I was doing a BGP =
lab and the Snapshot server router was one of the routers used in that =
scenario. Although there was no ip configurations for the address =
11.1.1.2, the bgp process on the snapshot server keep trying to make a =
tcp connection on the segment(11.1.1.2). This caused the ISDN line to =
try and route packets to that address as defined in the running bgp =
process (neighbor 11.1.1.2 remote-as 1).=20
Once I removed the bgp process everything worked as it should. My =
questions now go to the fact that I have an ospf process running that =
hasn't caused any problems at all. I'm trying to understand what I =
experienced. =20
In knowing BGP uses protocol TCP port 179, OSPF IP port 89, and RIP UDP =
port 520. Now I recognize that the "dialer-list" used in the exercise =
is baseline(dialer-list 1 protocol ip permit), but does this make any =
sense at all. Why would this non-active bgp connection cause the ISDN =
line to flap... There was no redistribution being performed so isn't =
this a good example of "ships in the night" routing? =20
Thoughts anyone.
TIA
Nigel
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