jhg6308's profile

Regular Visitor

 • 

11 Messages

Sat, Jun 18, 2022 10:59 PM

Modem admin address while in bridge mode

Software engineer here with strong network admin skills.

I have always run XFinity in bridge mode, with a Linux-based router/firewall between my LAN and the modem, and this has worked well.

I recently noticed I can no longer access the modem's admin page at 10.0.0.1.  This used to work as recently as last month but now it appears the modem in bridge mode is no longer responding to SYN packets on port 80 or 443 and I get "Connection timed out".

I've also tried connecting to the modem's external address, with the same (non-)result. In the past I could ping 10.0.0.1, but no longer.

nmap -Pn 10.0.0.1

fails to find any open ports, and I even tried

route add -host 10.0.0.1 gw [modem external address] dev enp3s0

with similar (non-) result.

The online Xfi management page just says the modem is in bridge mode and can't be managed there, and the XFinity app doesn't list the modem at all after switching to bridge mode.

Has Comcast changed the way you get to the modem's setup page in bridge mode? What's the magic incantation?

DreamSayerZ

Contributor

 • 

189 Messages

16日前

After unplugging your cable modem and router for a few minutes, booting up the modem first, then plugging back in your router you still cannot login? As well as shutting down and rebooting all the devices you are using to connect? Also try connecting the modem directly to a pc or laptop.

I have an XB7 in bridge mode and can access the modem admin page no problem. And I'm on a WiFI network. You could always do a factory reset on the modem. Hopefully someone here on forums with more knowledge will have a solution.

(edited)

Regular Visitor

 • 

11 Messages

16日前

I didn't have to power-cycle the modem after turning on bridge mode, the Linux router detected the momentary interface down and immediately did a DHCP_DISCOVER and got a new (routable) IP address.

Are you saying that a power-cycle is required in order to be able to access the admin site?

As to factory reset, I had to do that yesterday after my Internet access dropped for some unknown reason.  The symptom then was no response from the modem to DHCP request packets, which forced the adapter on the Linux router to discard its address.  At that point, after some troubleshooting, I did a factory reset, got back in to the admin page and re-enabled Bridge mode.  I had to do that twice because the first time, after setting up bridge mode AND power-cycling, the router again lost contact with the DHCP server.

I guess right now my experience says that if I power-cycle the modem I'll lose the connection again.

I'll go ahead and try it, and post the results.

DreamSayerZ

Contributor

 • 

189 Messages

16日前

I'm not saying that a power cycle is required, however when something is not working properly, then yes. I always find when something goes wonky, I unplug my cable modem and router, and shut down all my connected devices.

Plug cable modem in first and wait for it to be back fully online.

Plug in the router and wait for it to be fully online.

Then turn back on devices.

Regular Visitor

 • 

11 Messages

16日前

OK, now this is getting weird.  I think I may have discovered a bug.

  • As you suggested, I power-cycled the modem.
  • Prior to power-cycling, the Linux router/firewall's WAN interface had a valid, routable, external address (73.96.x.x).
  • After power-cycling, the modem ignored all DHCP traffic, replicating the failure mode I had yesterday.

However, after the Network Manager failed to establish the connection, I ran dhclient in foreground mode to see the debug log.  Here's what I got

$ sudo dhclient -4 -d enp3s0
Internet Systems Consortium DHCP Client 4.3.6
Copyright 2004-2017 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/enp3s0/00:01:2e:70:3b:ff
Sending on   LPF/enp3s0/00:01:2e:70:3b:ff
Sending on   Socket/fallback
DHCPREQUEST on enp3s0 to 255.255.255.255 port 67 (xid=0x4d920d0c)
DHCPREQUEST on enp3s0 to 255.255.255.255 port 67 (xid=0x4d920d0c)
DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 3 (xid=0x788b750b)
DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 7 (xid=0x788b750b)
DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 8 (xid=0x788b750b)
DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 15 (xid=0x788b750b)
DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 20 (xid=0x788b750b)
DHCPDISCOVER on enp3s0 to 255.255.255.255 port 67 interval 8 (xid=0x788b750b)
No DHCPOFFERS received.
Trying recorded lease 10.0.0.101
PING 10.0.0.1 (10.0.0.1) from 10.0.0.101 enp3s0: 56(84) bytes of data.

--- 10.0.0.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 4.491/4.491/4.491/0.000 ms
bound: renewal in 68372 seconds.

dhclient "remembered" its previous lease from when the modem was NOT in bridge mode, pinged it, got a response, and bound the old lease to the interface.

I now have full connectivity again, but the modem is in a weird state.

  • The modem's admin status page says it's in bridge mode
  • The modem is actually behaving as if it's NOT in bridge mode.  With a bound address of 10.0.0.101 the modem is forwarding and NATting traffic to the Internet.
  • My external IP address is back to the one I had while not in bridge mode (24.22.x.x)
  • The modem is not responding to DHCP requests at all

So it appears that in order to get into bridge mode I have to

  1. Factory reset the modem
  2. Establish a DHCP-mediated connection to the modem (i.e. the Linux box gets a 10.0.0.x address)
  3. Login to the admin page
  4. Enable bridge mode; the Linux box automatically gets a new routable IP address
  5. DO NOT power-cycle the modem

The modem is an Arris TG3482G (provided by Comcast, black mini-tower with only 1 status light), which I believe is obsolete and being replaced with a newer model.

Is it possible/likely that it is no longer fully compatible with Comcast's network?  Time to replace?

EG

Expert

 • 

94.4K Messages

15日前

@jhg6308 

http://192.168.100.1 is the IP addy that is used to access the U.I. pages in the Comcast rented gateway devices when they are placed into bridge mode. The page will only have a limited function because it is now a plain vanilla cable modem. Some WAN and RF signal status items will be passively viewable.

(edited)

Regular Visitor

 • 

11 Messages

15日前

So you're telling me a DIFFERENT address, 192.168.100.1 is used now? This is definitely a change from before, as I've always been able to use 10.0.0.1 in bridge mode.

Unfortunately, this is contradicted by my current status.  From the state described in my previous email I did the following

  • Disabled "bridge mode" in the admin UI - "bridge mode" is in quotes because the modem was in a weird state
  • Verified connectivity
  • Re-enabled bridge mode (for real) - IP changed back to 73.96.x.x netblock
  • Verified connectivity

I then noticed the router admin page refreshed itself, at 10.0.0.1

So I'm now back to where I was last month:

  • Bridge mode is enabled and working correctly - DHCP requests are being passed on to Comcast's DHCP server
  • The admin page is reachable at 10.0.0.1
  • Attempting to connect to 192.168.100.1 times out

Clearly there are software issues in the modem. 

I will be trading in my modem for a newer model.  Is there a way to accomplish this without having to call in, navigate VR trees, and wait forever on hold?

(edited)

EG

Expert

 • 

94.4K Messages

@jhg6308​ wrote:

So you're telling me a DIFFERENT address, 192.168.100.1 is used now?

No. From my experience here over the years, it's always been the 192. addy to access the U.I. (WAN / RF signal status page when the device is in bridge mode. And the 10. addy to access both the WAN and the LAN stats (and router functions) when it is in router mode. Something in the firmware load must of been changed. 

FWIW. We've seen all kinds of quirks, glitches, and issues here with their customized firmware loads..... If you are not using that device for your routing/firewall/WiFi needs, why not send it back and use your own third-party/retail purchased straight cable modem and save the rental fee ? It will pay for itself in short order and perform as it should ! Good luck !


(edited)

I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
We ask that you post publicly so people with similar questions may benefit from the conversation.

Was your question answered? Please mark an Accepted Answer!tick
DreamSayerZ

Contributor

 • 

189 Messages

@jhg6308​ Send a private message in this forum to order a new modem. It's the chat icon on the upper right next to the bell. On the next screen click on the pencil and paper icon, next to Conversations. In the To: field, type in Xfinity Support. Type your message stating you would like to upgrade your modem and send.

They will ask you for your account info and address etc. They can ship it for free. You can send back your old one, return to an Xfinity store or UPS store.

EG's advice of purchasing your own modem is always an option. I will be doing that once my promo is up that includes the modem rental. Unless I can extend it! Also if you do purchase, get one that supports higher speeds in case you upgrade your service in the future.

(edited)

Regular Visitor

 • 

11 Messages

@jhg6308​ wrote:

So you're telling me a DIFFERENT address, 192.168.100.1 is used now?

No. From my experience here over the years, it's always been the 192. addy to access the U.I. (WAN / RF signal status page when the device is in bridge mode. And the 10. addy to access both the WAN and the LAN stats (and router functions) when it is in router mode. Something in the firmware load must of been changed.

@EG Well, according to all the documentation and my personal experience, the address is 10.0.0.1 (except when the modem gets into a funky state)

Official Employee

 • 

53 Messages

Great, I'm sure you'll experience a difference. Please don't hesitate to reach back out if you need any further assistance.

I am an Official Xfinity Employee.
Official Employees are from multiple teams within Xfinity: CARE, Product, Leadership.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Please, mark a reply as the Accepted Answer.tick

Regular Visitor

 • 

11 Messages

15日前

@EG, I'm considering that option.  Since I have phone as well I'd have to price in the cost of a voice-capable EMTA, or a non-EMTA modem plus VOIP (i.e. OOMA).  There's some savings but not enough to justify the added complexity.

Which specific device is Comcast shipping to replace the Arris TG3482?

DreamSayerZ

Contributor

 • 

189 Messages

@jhg6308​ You will receive the XB7. The XB8 is on backorder. Gigabit+ customers are the only ones able to get that modem right now anyway. 

Regular Visitor

 • 

11 Messages

14日前

I went ahead and ordered the XB7 upgrade.  I'll post an update on its bridge-mode behavior after I get it installed.

EG

Expert

 • 

94.4K Messages

13日前

Good luck.........

Regular Visitor

 • 

11 Messages

11日前

The replacement XB7 modem shipped immediately and arrived the next day.

It did not work on plugging in.  It came up (admin pages OK) but was not able to acquire an IP address (blinking white)

It was stuck in DNS-capture mode (where all DNS queries, regardless of site name, return "A 10.0.0.1"

Spent 3 hours troubleshooting with various Comcast people.  Finally someone looked up the replacement order and noted it hadn't been closed, so even though the modem showed as registered to my account, it hadn't been provisioned in DHCP. As soon as she closed the order it started working. Sigh...

So far it seems to be working fine in bridge mode, and I can get to the admin pages at 10.0.0.1.

DreamSayerZ

Contributor

 • 

189 Messages

@jhg6308​ Bummer about the 3 hour troubleshooting. Good news that it's working in bridge mode!

forum icon

New to the Community?

Start Here