same ip subnet at different data centers - tracking

[carl_townshend]

Hi All

We are looking at some cold standby options for our servers, and are looking to have the same IP subnet at our other datacentre for a manual failover, there will be no layer 2 between the sites.

My question is, obviously we can shut down a vlan at the main site and bring it up at the other and route accordingly, is there any automatic way of doing this by tracking etc?

also what if we wanted to route individual servers on the same subnet only, is this possible ?

cheers

[Julio E. Moisa]

Hi,

In order to have the same IP on different location, I think you could use a NAT of one location or use VRF.

[Richard Burts]

The original post asks about routing certain servers differently and this is certainly possible. You can configure a host specific route (ip route 1.2.3.4 255.255.255.255 5.6.7.8) that would send traffic for that specific host in a different direction. If that server were multiple hops away you would need the host specific route on each of the routers (or layer 3 switches) along the path. In that case you might consider configuring a GRE tunnel between the router where the host specific route is configured and the router at the destination where the server is and sending traffic for that server over the tunnel (eliminating the need for a specific route at each hop).

HTH

Rick

[David Lee]

If you are using some kind of private networking ( I think it would even work with public/IPSec but I havent tested it) you can use route AS-Prepending and route mapping.  Basiclly, you can have both networks running and if your primary datacenter goes down, then the secondary comes up automatically. 

I am using a MPLS network using BGP as my protocol and I have the same network being advertised at 2 different locations.   10.11.0.0 has a really long trip as a result of the pre-pending.  You could also change the AD for the network at the backup datacenter so that it is less preferred.

GGR-C2901-18#sh ip bgp
BGP table version is 2458, local router ID is 10.10.18.250
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
              x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>  0.0.0.0          152.181.78.61                          0 65000 65000

 *>  10.0.0.128/25    152.181.78.61                          0 65000 65000 ?
 *>  10.0.5.0/24      152.181.78.61                          0 65000 65000 ?
 *>  10.2.2.0/24      152.181.78.61                          0 65000 65000 i
 *>  10.2.3.0/24      152.181.78.61                          0 65000 65000 i
 *>  10.2.4.0/24      152.181.78.61                          0 65000 65000 i
 *>  10.11.0.0/16     152.181.78.61                          0 65000 6167 6167 6167 6167 6167 6167 6167 6167 6167 6167 ?

[Georg Pauwen]

On a side note, you might want to look into feature called IP Mobility. It essentially does what Richard mentions, which is inserting host routes.

Configuring Mobile IP

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mob_ip/configuration/15-mt/mob-ip-15-mt-book/imo-cfg-mobip.html

[David Lee]

True it might do that, but its more for if the physical device ( Laptop, computer, tablet) is phyiscally moving between locations.  He has separate devices at separate locations and wants to use the same IP subnet at both.