Source Based Routes Dynamic Fallback

[sasaadamovic]

Hi All,

I have a network design challenge and would appreciate any suggestions.

Diagram of the setup is attached. We have two global DCs with multiple (main and backup) links to managed MPLS WAN cloud. Multiple offices are connected to managed MPLS network and access services at both DCs over MPLS. Additionally, there is a link between DCs that is dedicated for data replication. Currently we use source based routing so that traffic between ESX Farm Data VLANs at DCs is routed over dedicated line, while all other traffic to and from DCs is routed over MPLS. This works fine. However, in case there is failure on the DC to DC link traffic needs to be manually rerouted over MPLS network and rerouted back once link is back up. There is requirement to automate this process, i.e. to dynamically reroute traffic between data VLANs over MPLS when DC to DC link is down.

Looking forward to hearing tyour ideas.

Thanks,

Sasa

[Giuseppe Larosa]

Hello Sasa,

what you need is to add reliability to the PBR rules.

Depending on the IOS image running on the core switches of DC1 and DC2 you may use:

in route-map mode

you may be able to add

set ip next-hop verify-availability

this should work well if the core switch interfaces are configured as routed ports. The use of SVIs is not recommended as the autostate feature may keep the SVI up/up when the direct link fails if the corresponding L2 Vlan is allowed in any other L2 trunk.

On some newer releases you may be able to use IP SLA to track the state of the IP next-hop of the DC1-DC2 direct link.

see

http://www.cisco.com/en/US/docs/ios/12_3t/12_3t4/feature/guide/gtpbrtrk.html#wp1057544

The key point is that when  the next-hop invoked in PBR is considered down the device reverts to dynamic routing that is what you want to achieve.

In any case the use of routed port is to be preferred over the DC1-DC2 link.

Edit:

the support of IP SLAs for PBR tracking is not only a question of freshness of the IOS, but also of the feature set / type of license running on the core switches.

Hope to help

Giuseppe

[sasaadamovic]

Hi

Thanks a lot for your help on this and quick reply. However, I forgot to mention that our core switches are Nexus 5K, running 5.2(1)N1(1b), and SAA is not yet supported on those switches.

Regards,

Sasa