BGP config.

[Stefano Previdi - BIM Engineering Europe <[e-mail]>]

Hello,

sorry to disturb you, I don't know if this list is the correct place
for such mails, if not please point me to the right place.

Currently we are implementing a connection between our AS and the one
belonging to a service provider. I've seen the configuration of the
two BGP-3 neighbors and I have a little question on that.

The topology is as follows:


     LAN belonging to AS 111 (ip address: 1.2.3.4)
____________________________________________________
              |                          |
	+----------+              +----------+
        | Router-1 |              | Router-2 |
	+----------+              +----------+
              |                          |
         /--------\               /-----------\
       /            \            /             \
      |    AS 111    |          |    AS 222     |
       \            /            \             /
        ------------              -------------

Router-1 is the BGP speaker for AS 111 and establish a BGP connection
with Router-2 which is the BGP speaker of AS 222.

When configuring Cisco routers with BGP you can use the "network"
command to define network adresses that will be advertised
as originating from the router AS.

Router-1 have the following configuration:

	Router bgp 111
	network 1.2.3.4
	...
	...

It seems that router-2 have the following:

	Router bgp 222
	network 1.2.3.4
	...
	...

In this case I presume that we have a conflict. Network 1.2.3.4 cannot
be originated by 2 ASes. Am I on the right way ?  In addition Router-2
expect from Router-1 (using the different distribute and filter lists)
the advertisement of network 1.2.3.4.

Following a few set of tests, people have seen correct routing updates
going from Router-1 to Router-2 but all the updates received by
Router-1 from Router-2 were received with the UNREACHABLE attribute.
Unfortunately Router-2 is the service provider router and I do not have
any access on it.

If I'm on the right way the routing table of the two routers is
probably affected. But it concerns only the network 1.2.3.4 route or
all the routing table is corrupted ?

Anyway, what are the risks and consequences of such configuration ?

By the way we have already BGP connections with 2 other ASes without any
problem but also probalby without this double network definition.

Help will be highly appreciated.



		        Stefano.


+-----------------------------------------------------------------+
| Stefano Previdi                                                 |
| BIM Engineering Europe on contract to the European Space Agency |
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| email: [e-mail]                        |
|        [e-mail]                                                |
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