Can't connect through cable modem

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Robnw
DD-WRT Novice


Joined: 22 Mar 2017
Posts: 39

PostPosted: Wed Dec 27, 2017 22:06    Post subject: Can't connect through cable modem Reply with quote
I had this working for about 18 months or so, then last week we had some internet access issues and my cable provider recommended replacing the my Hitron 2250 cable modem. Now I can't get my tplink archer c7 DD-WRT router to connect through this new cable modem to acquire the 2nd IP that's on my cable account. I've tried for several days now and at best the DD-WRT router acquires an IP for about 30 seconds then looses internet access. Most of the time it won't acquire an IP.



I have the DD-WRT router set up for WAN auto DHCP. I have the Hitron cable modem configured for IP Passthrough via MAC addressing. I have a 2nd IP on my cable account.



Things I've tried:

1. restarting the cable modem and the router

2. confirming that the router cable is from the WAN port to the cable modem LAN port (not that there's any other choice on the cable modem)

3. resetting the cable modem and starting from scratch

4. using IP Passthrough on the cable modem with port and MAC filters. I've confirmed that I can get the 2nd IP from my cable provider if I use my laptop MAC and hook it up directly.

5. using static IP from the DD-WRT router



I'd rather not reset my DD-WRT router and start that config all over again but other than that or return this new cable modem, I'm out of ideas.



Thanks in advance for any suggestions.



For now, I'm connecting in through my cable modem, which works well enough but it doesn't provide enough coverage for the house, hence my interest to get the 2nd router working.



Robnw
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ian5142
DD-WRT Guru


Joined: 23 Oct 2013
Posts: 2180
Location: Canada

PostPosted: Thu Dec 28, 2017 5:19    Post subject: Upgrade Reply with quote
Just out of curiosity, what dd-wrt build are you using? I would suggest 34080 in most cases. See the link in my signature on where to download it.

As for the problem. The purpose of Auto DHCP connection type is that the modem just hands the router an IP address. If you have something set up on the modem side to hand it a specific address it would probably be better to use Static IP.

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Atheros:
Netgear R7800 - gateway, DHCP, QoS, VPN
TP-Link Archer C7 v2 x2 - WDS AP, WDS Station
TP-Link TL-WDR3600 v1 - WDS Station
TP-Link 841nd v8 - WDS Station
D-Link 615 C1 x 4 - not used
D-Link 615 E3 x 2 - not used
D-Link 825 B1 - WDS Station
D-Link 862L A1 x2 - WDS Station
Netgear WNDR3700v2 - WDS Station
UBNT loco M2 x2 - airOS

Broadcom
Asus N66U - backup Gateway
Netgear r6300 v1 - AP
Linksys E2500 - not used
Linksys EA2700 - not used
Linksys 160N v3 x2 - not used
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MediaTek
UBNT EdgeRouter X - not used
Alozaros
DD-WRT Guru


Joined: 16 Nov 2015
Posts: 4167
Location: UK, London, just across the river..

PostPosted: Thu Dec 28, 2017 7:12    Post subject: Reply with quote
did you change DD-WRT GUI IP different from modem GUI IP??
most modems are providing PPPoE interface do you know
your credentials if so??
some modems are MAC limited so only specific MAC clients can connect chick this if you have to clone MAC...
Is your modem in bridge mode ??

_________________
Atheros
TP-Link WR740Nv1 -----DD-WRT 45711 BS AP,NAT
TP-Link WR740Nv4 -----DD-WRT 44251 BS WAP/Switch
TP-Link WR1043NDv2 ---DD-WRT 45849 BS AP,NAT,AP Isolation,Firewall,Local DNS,Forced DNS,DoT,VPN,VLAN
TP-Link WR1043NDv2 ---DD-WRT 45711 BS AP,NAT,AD/Block,Firewall,Local DNS,Forced DNS,DoT,VPN,VLAN
TP-Link WR1043NDv2 ---Gargoyle OS 1.12.0 AP,NAT,QoS,Quotas
Qualcomm/IPQ8065
Netgear R7800 -----DD-WRT 45735 BS AP,NAT,AD-Block,AP&Net Isolation,VLAN's,Firewall,Local DNS,DoT
Broadcom
Netgear R7000 -----DD-WRT 45735 BS AP,Wi-Fi OFF,NAT,AD-Block,Firewall,Local DNS,Forced DNS,VLAN's,DoT,VPN
-----------------------------------------------------------------------------------------------
Stubby for DNS over TLS I DNSCrypt v2 by mac913
Robnw
DD-WRT Novice


Joined: 22 Mar 2017
Posts: 39

PostPosted: Thu Dec 28, 2017 17:20    Post subject: Reply with quote
Thank you both for your replies.

Ian - I was on a 31xxx build but I don't know which one as I bit the bullet and did both a factory reset (only through the webgui) and an upgrade to 34080, which I'll explain in a moment.

Alozaros - I had (and still have) both the modem and the router on different subnets. I did not know that most modems use PPPoE - I'll check into that (I'm not familiar with the differences). The modem was not in full bridge mode but does provide a "semi-bridge" mode called IP Passthrough which I was using.

To bring you up to date, I did a router (DD-WRT) factory reset (through the webgui only initially) and was then able to get a WAN IP from the modem and get internet access through the router. However, as soon as I changed any of the DD-WRT parameters (other than the gui log-in parameters, e.g., enabling wifi security then applying update), I lost internet access through the router (however, I could get it if I connected directly through the cable modem). What was interesting and I don't yet understand about this scenario was that the router would get a valid WAN IP but my (Windows) laptop connected through it couldn't access the internet (but could access my home LAN).

I then gave up on the older FW and upgraded to the 34080 FW but I'm seeing the same behaviour when I apply an update. I have tried the 30/30/30 reset with this upgraded FW in place but no better ability to change anything.

Today I'm going to play with this a little more including a proper factory reset (30/30/30 before and after) and reapply the 34080 FW.

Thanks all.

Robnw
Alozaros
DD-WRT Guru


Joined: 16 Nov 2015
Posts: 4167
Location: UK, London, just across the river..

PostPosted: Thu Dec 28, 2017 17:53    Post subject: Reply with quote
do not use 30/30/30 as its only for an old linksys WRT routers and on some routers it can cause a mess

use either command: erase nvram && reboot
logged in via telnet or SSh
or reset to factory defaults on GUI

just for the test try to turn off SPI firewall and see if you still have internet than if firewall is a problem
you have to add rule via iptables

check your ISP for instructions how to use your DD-WRT router to connect to your new modem what WAN interface they provide and if they need you to add your router mac address
if your ISP can provide you with static IP passtrough or if they need to bound it with MAC address or so

_________________
Atheros
TP-Link WR740Nv1 -----DD-WRT 45711 BS AP,NAT
TP-Link WR740Nv4 -----DD-WRT 44251 BS WAP/Switch
TP-Link WR1043NDv2 ---DD-WRT 45849 BS AP,NAT,AP Isolation,Firewall,Local DNS,Forced DNS,DoT,VPN,VLAN
TP-Link WR1043NDv2 ---DD-WRT 45711 BS AP,NAT,AD/Block,Firewall,Local DNS,Forced DNS,DoT,VPN,VLAN
TP-Link WR1043NDv2 ---Gargoyle OS 1.12.0 AP,NAT,QoS,Quotas
Qualcomm/IPQ8065
Netgear R7800 -----DD-WRT 45735 BS AP,NAT,AD-Block,AP&Net Isolation,VLAN's,Firewall,Local DNS,DoT
Broadcom
Netgear R7000 -----DD-WRT 45735 BS AP,Wi-Fi OFF,NAT,AD-Block,Firewall,Local DNS,Forced DNS,VLAN's,DoT,VPN
-----------------------------------------------------------------------------------------------
Stubby for DNS over TLS I DNSCrypt v2 by mac913
Robnw
DD-WRT Novice


Joined: 22 Mar 2017
Posts: 39

PostPosted: Thu Dec 28, 2017 18:00    Post subject: Reply with quote
Alozaros wrote:
do not use 30/30/30 as its only for an old linksys WRT routers and on some routers it can cause a mess

use either command: erase nvram && reboot
logged in via telnet or SSh
or reset to factory defaults on GUI

just for the test try to turn off SPI firewall and see if you still have internet than if firewall is a problem
you have to add rule via iptables

check your ISP for instructions how to use your DD-WRT router to connect to your new modem what WAN interface they provide and if they need you to add your router mac address
if your ISP can provide you with static IP passtrough or if they need to bound it with MAC address or so


OK, thank you. I haven't done the 30/30/30 yet.
Robnw
DD-WRT Novice


Joined: 22 Mar 2017
Posts: 39

PostPosted: Thu Dec 28, 2017 19:51    Post subject: Reply with quote
Turning off SPI didn't help.

And I now believe that applying an update to DD-WRT isn't the problem.

If I reset DD-WRT (through the webgui), it appears that I have internet access (in that Windows believes it has internet access) but I can't seem to access any external websites. And after a few minutes, I then formally loose internet access (according to Windows) even though the DD-WRT router still holds a valid WAN IP and my windows laptop still holds a valid LAN IP.

So now I'm back to thinking that my problem is again with the cable modem.

Robnw
Robnw
DD-WRT Novice


Joined: 22 Mar 2017
Posts: 39

PostPosted: Thu Dec 28, 2017 21:07    Post subject: Reply with quote
@eibgrad:

1. yes, same make & model
2. yes, trying for the DD-WRT router to pick up the 2nd IP from my ISP. This is now working.
3. I might eventually put the 2250 into bridge mode if I can't get this to work and that does work, but this config was working successfully on the former 2250 using the "IP Passthrough" mode instead of bridge mode. I prefer this config for three reasons: 1) I can get better house coverage (though admittedly with two subnets but that's rarely an issue), 2) I have an easy internet access backup in case of problems like this, and 3) I can easily access the hitron gui when required.
Robnw
DD-WRT Novice


Joined: 22 Mar 2017
Posts: 39

PostPosted: Fri Dec 29, 2017 1:09    Post subject: Reply with quote
@eibgrad

All good points. And maybe it's the better way to go.

I don't tend to have anything connected to the cable modem, most everything connects to the more central router. And it might not be clear that the "IP Passthrough" I referred to is a form of bridge on cable modem but limited to the DD-WRT router connection.

Perhaps I'm just flogging a dead horse but because it used to work I keep pursuing it. I was a bit surprised that the cable modem replacement wasn't plug-n-play. For me now it's about trying to solve this puzzle even if bridge mode is the better route.
Robnw
DD-WRT Novice


Joined: 22 Mar 2017
Posts: 39

PostPosted: Fri Dec 29, 2017 4:31    Post subject: Reply with quote
An odd update - I got it working but I can't explain why it worked.

I had been trying all of this through the DD-WRT router wifi because it was easier. On a whim, I decided to try it wired. And it worked! No other changes. I tested a few URLs and connected to each of them.

I then disconnected and could get internet via wifi. For about 30 seconds. Then it lost connectivity. So I wired in again, it worked, I unplugged, and it has continued to work so for, for about 15 minutes. Even after some updates and reboots.

Another odd piece of this puzzle - for the above testing I used a cable that connected the DD-WRT router to a device that was on and presumably had an IP from the router. Then I tried another cable connecting the DD-WRT router to a device that was off and I couldn't get any connection.

Anyone have an idea what happened?
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