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Sprint 3G-CDMA module in 28xx series router

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  • Sprint 3G-CDMA module in 28xx series router

    Has anyone out there set up a router with a wireless broadband (cellular) wic as a backup interface?

    We have a remote office whose T1 circuit was extremely unreliable due to a series of central office issues. We purchased a 2811 (with advanced security license), a DSU-T1 V2 wic and a HWIC-3G-CDMA wic with the intentions of using Sprint's broadband network (with VPN) whenever the T1 circuit went down.

    FYI: The router needs to have IOS 12.4 (15)T before it will recognize the 3G-CDMA wic.

    I followed the documentation online and successfully activated the wireless card with our Sprint service. I then followed the instructions to configure the interface (Cellular0/1/0).

    The part I am having trouble understanding is how to set up the automatic failover from the T1 interface to the cellular. The documentation has a dial backup example config, but it does not show how to fit a VPN tunnel into the dial backup scheme. Automatically connecting to the Sprint network does us no good if a VPN tunnel with corporate HQ is not automatically established as well.

    This IOS treats VPN differently than I am used to. It has a Virtual Tunnel Interface. From what I've read about configuring a VTI, it appears to be easy to use. So here is how I think it will work: (Somebody check my logic)
    1. The VPN Virtual Tunnel Interface is configured to use the Cellular interface as its source.
    2. The VPN VTI is then set up as a standby backup to the T1 interface.
    3. When the T1 goes down, the VPN interface is activated. Once it tries to pass data over the Cell interface to establish the VPN connection, the Cell interface "dials" the Sprint network and establishes the wireless connection.

    If the above is correct then, my only other question is whether or not the VTI on the 2811 can establish a VPN tunnel with an ASA 5510 at our corp HQ. The ASA does not appear to support VTI's(do I need to upgrade the ASA version?)

    Thanks in advance,
    JasonL

  • #2
    Re: Sprint 3G-CDMA module in 28xx series router

    Lookup using ip sla's. Basically what you can do is setup a ip sla object to ping the upstream on your T1, and then with object tracking you can set your default routes based on the tracked SLAs. If the router can't ping the upstream on the T1 it will fail over to the cell link.
    Thanks,
    Brian Desmond
    Microsoft MVP - Directory Services
    www.briandesmond.com

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    • #3
      Re: Sprint 3G-CDMA module in 28xx series router

      Thanks for the suggestion. I had been wondering how I was going to get around the fact that our MPLS WAN is statically routed. I think I'll need to set up the sla both on this router and on the "hub" router at corp hq so traffic can be routed over the vpn tunnel when the t1 is down.

      I created a Cisco TAC request, and am working with Cisco support right now. I'll post the final solution when we've got it running and tested.

      Originally posted by bdesmond-mvp View Post
      Lookup using ip sla's. Basically what you can do is setup a ip sla object to ping the upstream on your T1, and then with object tracking you can set your default routes based on the tracked SLAs. If the router can't ping the upstream on the T1 it will fail over to the cell link.

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      • #4
        Re: Sprint 3G-CDMA module in 28xx series router

        You have a couple of options depending on your needs. You could create a GRE tunnel with the source of address of the 3G card and use the backup interface command on the serial interface. The down side is if for some reason your circuit or routing in the cloud was gone but the interface did not drop you would not failover. You could track a route by using the ip sla functionality which would give you failover even if the WAN interface was still up/up. Of course for the GRE to work you need to configure the other end of the tunnel. If you are using multiple locations then you may consider using a mGRE tunnel on the host or hub router. Also depending on the service you purchased with Sprint you may want to make sure you do not have keepalives configured on the tunnels as it will keep your RF active as would running a dynamic protocol. No need for surprises from the wireless provider. If you device (router) is in an area where there is interferance or the signal is not as good as you would like I would consider using the Airlink Raven. The benefit is that it is connected with an Ethernet cable and the cable to extend the antennae for the cisco card is quite expensive when compared to the the cost of an Ethernet cable. Sprint offers very good managed network services which would support this type of activity and your entire MPLS network solution.

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