MX in HA with Comcast Business (CBR-T modem)

[jrsilvius]

Comcast recently upgraded our cable modem to the CBR-T and since then we seem to have issue with failover.

When we fail over from our primary to a back up nothing works and when we fail back any traffic bound for the WAN 2 (our cable modem) seems to time out.

I don't know how the previous device was configured, but we have a /28 network for this with our MX handling all the traffic. I'm wondering if the new cable modem isn't responding correctly to failover. 

Can you put these modems in bridge mode so we don't need anything from Comcast but the handoff. I love our Comcast Metro Ethernet, but the modem is giving me headaches.

[PhilipDAth]

I don't know anything about Comcast (I think they are a US only ISP).

You have a /28 of public IP address space, and both of your MXs are configured with a public IP address on them?  Should work.

Does the Comcast router have any kind of firewall on it?

[AIOtech]

We have used Comcast.  I've always put the Comcast modem in bridge mode with a static IP purchased from them.  From the MX side login locally to the firewall via IP (not the dashboard) so you can set the static ip address info for your "wan 2".  You'll need to enter the IP, Gateway, Subnet etc.  First thing:  You will need to call Comcast support to have them put modem into bridge mode.  Second: login to your MX locally so you can enter the network details for WAN2.  Then you can test it out some more by unplugging your WAN1.  Also check the appliance status via the meraki dashboard.  Your primary connection should show as "active" and the secondary should show as "ready".  If it doesn't show as ready something is wrong with the config.

[jrsilvius · Accepted solution]

Thanks all, We called Comcast and they put the modem in "passthrough mode". That seemed to fix the issue.