Same gateway address in two datacenters.

[frederic.hilpert1]

Hi guys, 

I am looking for some technical ways to have duplicated network gateways on same network. I mean two routers with the same IP address on the same L2 network.  Let me try to explain : 

• I have a network infrastructure composed of two datacenters. Each datacenter is active. 
• I have a Layer 2 network connection between these two datacenters.
• I need every virtual machine on both side to be able to connect directly to any other virtual machine, no matter if the other virtual machine is located remotely. 
• I have one big virtual cluster which allows me to migrate virtual machines from one datacenter to the other. 
• When virtual machines needs to go outside of my network, I need them to use local gateway. 
• I don't want the virtual machine which was originally located on datacenter A to continue to use datacenter A gateway. What I want is that when virtual machine is migrated from datacenter A to datacenter B it stops using datacenter A gateway and start using datacenter B gateway. 

Therefore I'm looking to have the same gateways address in datacenter A and in datacenter B. In other terms, in the same L2 network, I want to have a router in datacenter A with per example 10.0.0.1 IP address, and in datacenter B an other router with 10.0.0.1 address. 

In order to make it work, I think I would need to filter ARP requests messages towards 10.0.0.1 on the Layer 2 network connection between my two datacenters. In this way, virtual machines which are located on datacenter A will resolve 10.0.0.1 as the datacenter A gateway, and virtual machines located in datacenter B will resolve 10.0.0.1 as the datacenter B router. 

The drawback is that I think that I will need to find a way to refresh virtual machine's ARP tables when moving them from one datacenter to another.

Are there some better ways to achieve this ? 

Thank you ! 

Fred

[chrihussey]

HSRP, VRRP and GLBP are all available options.

However, I don't think any of them can ensure that one shared gateway between data centers will service only the local hosts.

HSRP has the option of having a common subnet with multiple HSRP groups, but this would require having different default gateways, on the same subnet, at each data center. But this then requires having to define the default gateway depending on location.

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp_fhrp/configuration/xe-3s/fhp-xe-3s-book/fhp-hsrp-mgo.html

GLBP can do a form of host dependent balancing, but will not fulfill your need to have the gateway used be data center dependent.

http://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/ip-services/product_data_sheet0900aecd803a546c.html

Hope this is of some help.

[Kirk J]

Greetings.

What you are describing sounds like a typical candidate for OTV (for Layer 2 extensions between DCs), HSRP, and the HSRP filtering that needs to be in place to avoid suboptimal paths.

http://www.cisco.com/c/dam/en/us/products/collateral/switches/nexus-7000-series-switches/guide_c07-728315.pdf

I'm not sure what of equipment you have.

Thanks,

Kirk...