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Using an Arris DG2470A Cable Modem / Router in Bridge Mode

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Summary / Key Points

When a combination modem / router is switched to bridge mode:

Note: some of this may be specific to the Arris DG2470A.

• it will no longer work as a router, only a modem

• only one of the eth<n> ports will work -- which one may vary, possibly depending on which one you have a device (e.g., a router) plugged into

• you will no longer be able to log in to the modem / router to view (or change) the configuration

• to get out of bridge mode, you may have to do a factory reset (some modem / routers may have alternate means available)

I should add:

• I didn't try to test or check every point that I might have -- my objective was to get the Arris working with the Edge Router for my LAN -- once I got it working, I adopted the "if it ain't broke don't fix it" philosophy and didn't do (much) further research or experimentation.

Discussion

Background: I recently switched from a DSL based ISP to a cable based ISP. The cable based ISP (Astound) provided an Arris DG2470A which is a combination modem and router.

(Aside: I run a small LAN at home, with sometimes as many as 8 devices on the LAN (in 3 locations, each with an Ethernet switch).)

In exploring the router, I realized it did not have all the features available in my old router (a Ubiquiti Edge Router X), so I decided that I wanted to use the Edge Router instead of the router portion of the Arris. To do so, I thought the way to do that was to put the Arris modem part into bridge mode. <An alternate way, that I didn't try, might be to put the Edge Router into the "DMZ" which can be established by the Arris (iiuc) -- I've neither tried that or thought through the ramifications -- I did find this suggestion somewhere on the Internet.>

I had some trouble getting the Arris into bridge mode and using it with the Edge Router, and the purpose of this page is to explain how I eventually accomplished that.

Aside: Catch 22: I tried to get technical support from Astound on putting the Arris into bridge mode, but the people I talked to (or chatted with) could not help and said it was out of their scope, and I would have to get help from the manufacturer (Arris). I talked to Arris and they said that the DG2470A is sold only to ISPs (or such) and not to end users, and thus I would have to get technical support from the ISP.

I wasn't thinking very clearly when I went to switch the Arris to bridge mode and made a rather fundamental mistake.

(Perhaps I should note that I had been using the Edge Router with a modem in bridge mode, and thus the Edge Router being responsible for establishing the connection to the ISP. (And, for the DSL based ISP, it used PPPoE as the "protocol" to make the connection.))

The mistake I made: The Arris modem / router, because it is a router, has multiple (4) Ethernet (RJ-45) sockets. I plugged a computer into one of those and the Edge Router into another, and then used that computer (set to a 192.168.0.n address) to log into the Arris in order to configure it (I wanted to disable WiFi and then set it to bridge mode).

The problem is that once the Arris modem is set to bridge mode, the router function no longer works, so only one of those RJ-45 sockets is usable to connect to the Edge Router.

Aside: I'm not sure whether that would always be the eth1 socket or maybe any one (but only one) of the RJ-45 sockets would work -- I didn't want to bother to test it, but in some of my googling (perhaps not specifically for the Arris DG2470A) I got the idea that in some combination modem / routers, any one of those sockets would work.

Anyway, when I finally realized my mistake, I followed a procedure something like the following:

• plug a computer (with a 192.168.0.n address) into the Arris, log into the Arris, disable WiFi (2.4 and 5.0 GHz) (see note below), and then switch to bridge mode. (The option to switch to bridge mode is a little hard to find, it is on the page to configure the LAN, under the heading "NAT".)

Note on WiFi: it is not necessary to disable WiFi in order to switch to bridge mode -- it is my personal preference to (maybe) provide some additional security. I do have another router with WiFi capabilities which I keep turned off but turn on if I need WiFi.

• I allowed time (a few minutes) for communication from that computer to occur and for the Arris to complete the switch to bridge mode (once you do that, that computer can no longer communicate to the Arris, so you don't know what is going on in the Arris). At least once I think I de-powered the Arris too soon, before it completed the switch to bridge mode. (Note that I simply de-powered the Arris, I did not do a factory reset -- a factory reset would have switched the Arris back out of bridge mode.)

• I then de-powered the Arris, unplugged that computer, plugged in the Edge Router, and re-powered the Arris.

• I then used a "Wizard" in the Edge Router to connect (to Astound) via DHCP rather than PPPoE.

• I did then have to go to all the computers on my LAN and switch them to use Astound's nameservers. (There are ways to have the computers on the LAN pick up the nameserver addresses "automatically" from the router -- my systems are not set up that way at present -- maybe someday.)

Contributors

• () RandyKramer - 2023-05-03
• If you edit this page: add your name here; move this to the next line; and if you've used a comment marker (your initials in parenthesis), include it before your WikiName.

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