topic Re: Overlapping Subnets in Routing and SD-WAN

Overlapping Subnets

wjj13 — Wed, 05 Aug 2020 07:00:59 GMT

Hi,

Requesting assistance regarding issue with overlapping subnets

I have two existing sites (Site A & B) and acquired an additional site (Site C)

The issue is that Site C is overlapping with my existing Site B, both have the same subnet 192.168.2.0/24

Renumbering the subnet of Site B and C is not option for some reasons

Using BGP as the routing protocol for all the sites and one router for each site. I have attached a sample diagram for reference

Any idea will be greatly appreciated

Thank you

Re: Overlapping Subnets

Deepak Kumar — Wed, 05 Aug 2020 07:23:44 GMT

Hi,

I think you are missing some information on site to site connectivity types. Are you using any type of VPN/MPLS?

Re: Overlapping Subnets

wjj13 — Wed, 05 Aug 2020 07:44:07 GMT

Thank you for your reply

Using MPLS for WAN Connectivity

Re: Overlapping Subnets

Seb Rupik — Wed, 05 Aug 2020 07:49:14 GMT

Hi there,

At either Site B or Site C you should configure SNAT for the 192.168.2.0/24 subnet. Dynamic SNAT should be configured for the subnet which has devices which do not provide resources that other devices need to reach. If both subnets have resources which need to be reachable, then select one subnet and configured static 1:1 SNAT to an 'outside translated' pool of IP addresses. Advertise this outside pool of IPs via BGP to the other sites.

cheers,

Seb.

Re: Overlapping Subnets

wjj13 — Wed, 05 Aug 2020 08:10:34 GMT

Thank you for your reply

Yes, Both Site B & C have resources that needs to be reachable.

Do you mean to use 1:1 Static NAT to translate Site C subnet 192.168.2.0/24 to another subnet (ex: 192.168.3.0/24). Then advertise the 192.168.3.0/24 to BGP

Therefore the other sites will use 192.168.3.0/24 in order to reach Site C?

Re: Overlapping Subnets

Seb Rupik — Wed, 05 Aug 2020 10:44:50 GMT

Yep, your summary captures the solution 🙂

cheers,

Seb.