Frame-relay redundancy

[rajesh444]

Hi,

I am trying to build a redundant hub-and-spoke frame topology to remote-site C from 2 hubs at A & B using point-to-point sub-interfaces as shown below.

A ----------

C

B ----------

I am using static routes and want to configure a floating static route for backup. However, if the local link at A were to go down, would the floating route to hub B be used at C since the line protocol for the primary link would still be up although the PVC might be inactive?

Thanks,

Rajesh

[omohamed]

Hi Rajesh,

You are right! The floating static route will not kick in if the line protocol is up. In this scenario I would recommend you to use a routing protocol instead of static routes which will help you to overcome this limitation.

[rajesh444]

Omar,

Thanks. The floating static route would only have the remote site's subinterface IP specified and not that of the physical interface.

In that case, although the line protocol will be up won't the subinterface status be down since the PVC status would be changing to inactive?

Thanks,

Rajesh

[tbaranski]

The floating static route will kick in if the subinterface changes state to "down", but that doesn't always happen when a PVC goes inactive (unless this has changed in recent code). The easiest solution is to configure Frame Relay End-to-End Keepalives on all the FR routers: http://www.cisco.com/en/US/products/sw/iosswrel/ps1830/products_feature_guide09186a0080087a58.html

[rajesh444]

Thanks for the response. Do you know of any scenarios where the subinterface stays up despite PVC changing state to inactive?

I thought the frame switches were performing the keepalive functions through LMI. Besides, the end-to-end keepalives are Cisco propreitary while some FR routers I use are Nortel.

Rajesh

[kuanderson]

LMI will include the status of all PVCs terminated at your DTE. But you are assuming the only possible cause of an outage is that a link or piece of hardware has gone down. Unfortunately, it is not unheard of in FR networks, that during network grooming at night, your PVC can become misconfigured. The only true way to have 100% guarantee of having you routing insync with your true end to end connectivity is to use a dynamic routing protocol.