Configuring BGP

[karanbakshi201758092]

How to configure more than 2 autonomous systems that may have same internal network IP? I have configured 3 AS : 100, 200 and 300 respectively. AS 200 and AS 300 have the same internal network. Now when I send a packet from AS 300 to AS 100 , the packet reaches the right destination but the acknowledgment reaches the wrong AS that is AS 200. AS 200 and 300 have the same internal network that is 10.1.1.0/24. Each router in AS is also configured as DHCP . The interfaces connecting the three routers via switch are on networks 15.1.1.0/24. On AS 200 the excluded IP addresses are in range 10.1.1.2 to 10.1.1.100 .Please help!

[omz]

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@karanbakshi201758092 wrote:

How to configure more than 2 autonomous systems that may have same internal network IP? I have configured 3 AS : 100, 200 and 300 respectively. AS 200 and AS 300 have the same internal network. 

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You could configure NAT or MP-BGP with VRF if you are advertising the same internal subnet from 2 locations.

It would be easier to just NAT the internal network 

[omz · Accepted solution]

! AS200 or AS300 router
int GigabitEthernet0/0/0
 ip nat outside
int GigabitEthernet0/0/1
 ip nat inside
ip nat inside source list 1 interface GigabitEthernet0/0/0 overload
access-list 1 permit any

if you are excluding ip addresses from dhcp pool .. exclude the address assigned to the router interface as well .. 

see attached .. hope that helps

[paul driver]

Hello

@omz  Although this is just a PT simulation, I would just like to add that the use of "any any" in a ACL used for NAT statements isn't really supported and not a recommended.