Overlapping network issue

[kumar.krishna1]

Dear all,

My company has planned to move all the VM servers in our local data center to central DC. our local site is connecting to Central site with MPLS. As per the migration plan, only VM servers are moving. physical servers are remain in our local DC.

The problem is, each server VLAN consists of both VM and physical servers in various ratios. So they are migrating part of the subnet/vlan to Central. So, I have to provide a proposal on how to route the local user traffic towards central DC where these migrated VM servers are located without having much user impact and less network admin overload.

We can do IP re-addressing to either local servers(physical) or migrated servers. But its a tedious job from network point of view as it might involve a lot of analysis and firewall policy change. so IP re-addressing is not a recommended solution and it is finalized that all the servers which are migrating will be going to use its original IPs only so as with local servers.

For example, if 50 IPs of a class C subnet are moving to central and 50 IPs of the same subnet are in local DC, how can we route the user traffic for those 50 migrated server toward the MPLS link which is connecting to Central DC?

What are the different solutions that are in use in today's network world for this scenario? Kindly help me to propose a solution for this issue.

There are 100s of such a server VLANs are moving/migrating to Central DC. 

[Georg Pauwen]

Hello,

NAT is probably the way to go here, is that an option for you ? Also, there used to be a feature called 'IP Mobility' that might work in your situation...

Cisco Mobile Networks

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mob_ntwks/configuration/15-mt/mob_ntwks-15-mt-book/imo-mbl-ntwks.html

[kumar.krishna1]

Hi George,

Thanks for your reply. I think NAT is the only viable option for this scenario. we have many servers which are migrating, dont know the huge static nat statements would cause any issue in network administration and during troubleshooting.

[paul driver]

Hello

how large are these subnets - would these hosts be grouped together for example at the beginning or end of the ip range?

Nat would be a option and this recent post shows such an example of overlapping subnets using nat with-without vrf

But the viable way would be to shorten the current ip range of the vlan or re-address

[kumar.krishna1]

Hi Paul,

thanks for your reply and suggestions. I think we have to consider the NAT. But dont know its the best practice for a huge servers. around 160 servers are moving.

Currently central migration team is using OTV link for server migration and will going to terminate this link once completely migrated. then we have to switch over the user traffic via our MPLS link.

Is there any L2 tunnelling like OTV over our existing MPLS possible?

[Jon Marshall · Accepted solution]

In addition to the suggestions from Georg and Paul you may also want to look at LISP host mobility which would allow you to do what you want. 

That said you are ruling out the most sensible option already. 

NAT, in my opinion, would be a very bad choice simply because you would need to setup all the NAT translations and maintain them and personally if I was inheriting a network setup like that I would seriously question what the previous network admin was thinking. 

Readdressing is a one off thing ie. once you have done it you do not need to go back to it and yes it is tedious and it does take a lot of planning in terms of firewall rules etc. but once done you can just leave it and forget. 

Jon

[kumar.krishna1]

Hi Jon,

Thanks for your reply. I have gone through the LISP. I think this require additional hardware to implement this and dont know it would be best practice for servers.

[kumar.krishna1]

Hi Jon,

Thanks for your view. we are planning for readdressing.