Question

Can't connect to internet through Linksys router and Comcast modem

Asked by: rdoving

I recently signed up for Comcast cable internet and digital phone service and the installer came out and hooked up a modem that runs both the internet and phone services. I plugged my computer directly into the modem and was able to access the internet. I then switched my computer to plug into my Linksys WRT54GL (running stock firmware) and plugged the Linksys into the Comcast modem.

At first the modem wouldn't get a WAN IP from the modem, but then I cloned my PC's MAC to the Linksys and was able to get a WAN IP. Did an ipconfig /release and /renew on the PC to make sure everything was current, but I'm not able to access the internet or ping google.com from the PC.

I can ping google.com through the Linksys's web-based config page, but I can't from my PC. What would cause this? Here is my ipconfig info:

Linksys IP: 192.168.1.1

PC IP: 192.168.1.100
Gateway: 192.168.1.1
DHCP server: 192.168.1.1
DNS servers: 68.87.76.**2, 68.87.76.**4

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Asked On: 2009-08-12 at 07:14:26ID24646525
Tags: internet comcast linksys wrt54gl
Topics: DSL Lines / Cable Internet
,; Network Routers
,; New Internet Users
Participating Experts: 3
Points: 250
Comments: 19

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Answers

by: mdpsolutionsPosted on 2009-08-12 at 07:20:57ID: 25078984

Change the default IP from 192.168.1 to a 10.0.0. subnet. You may have conflicting subnets between the Comcast modem and the lynksys.

Make sure you restart both the modem and router in that order.

Good luck,
MDP

by: btpringlePosted on 2009-08-12 at 07:42:09ID: 25079208

If you cloned your MAC address on the router, then any packets addressed to that MAC address will get routed to the router port instead of the computer. Change it back to the default settings on the router.

They lock down the modem to the first MAC address that appears on the modem so that you can't use a router. They claim that it is to make it more secure, but it is to get extra money out of you.

You need to call Comcast and have them release your MAC address from the modem. Don't tell them that you have a router or they will charge you extra. Tell them that you are switching out computers and need them to release the MAC address assigned to the modem.

When you call them, make sure that the router is plugged into the modem and have the configuration page open. When they ask you to do things on the computer, do them on the router. For example, they will tell you to do IPCONFIG on the workstation. Look at the STATUS page (or WAN, depending on the router) of the router and renew your IP address there.

by: mdpsolutionsPosted on 2009-08-12 at 07:49:38ID: 25079300

I also have comcast and didn't need to contact them to install my router.
I agree that comcast will attempt to sell you a bogus addition, but it is not necessary.

I have found that when changes are made on cable modem setups, you almost always are forced to restart the modem first and then the routers.
Good luck!
MDP

by: thegofPosted on 2009-08-12 at 17:18:57ID: 25084571

Comcast in the midwest doesn't lock down the router. The cable modem yes, but not the router. I'd suggest the following.

1. Configure this Cable Modem -> Router -> PC. Make sure the Router is reset to defaults (for now) and that the PC isn't somehow configured for a static IP (it doesn't look like it, but just to be complete for later readers).

2. Power all three off. Wait a few minutes (say 5 although Comcast will sometimes say 15)

3. Power these on as follows. Cable Modem first and ensure that the phone interface is all the way up and you can dial out (call your cell). Second, fire up the router, give it a minute to come up. Finally, your PC. Try to ping and report back the ipconfig results as well as what happens with the ping.

The reason for the full power cycle is to ensure the all the cached data on both the router and the cable modem are flushed. You can leave the router on the default 192.168.1.* address and don't clone the MAC. If the above doesn't work, then I'd call comcast and ask them why it's not letting you use a router. Of course, we're all assuming your router is configured appropriately, but from the tone of your question it sounds like it should be. Doesnt' hurt to double check though. We've all had Homer moments (D'oh!)

by: rdovingPosted on 2009-08-12 at 19:46:06ID: 25085152

I tried changing the router's LAN IP to 10.16.0.1. I have it setup from Cable Modem -> Linksys -> PC, and the PC has an IP of 10.16.0.100 (set to obtain automatically). I powered everything down, then turned on the cable modem. I waited until that was up and I had a dial tone, then I powered up the Linksys router. Lastly I powered on the PC and did an ipconfig /release and /renew. Same results, I could ping google.com from the router but not from the PC ("Ping request could not find host google.com").

Next I tried connecting my laptop to the router via Ethernet and disabled my wireless adapter. Did an ipconfig /release and /renew. Laptop's IP address was 10.16.0.103. I can't ping google.com from the laptop either. Here's the results from ipconfig /all on the laptop:

Windows IP Configuration

Host Name . . . . . . . . . . . . : DrPipperLaptop
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Broadcast
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
DNS Suffix Search List. . . . . . : hsd1.ca.comcast.net.

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . : hsd1.ca.comcast.net.
Description . . . . . . . . . . . : Realtek RTL8139/810x Family Fast Ethernet NIC
Physical Address. . . . . . . . . : 00-A0-**-**-**-**
Dhcp Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IP Address. . . . . . . . . . . . : 10.16.0.103
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 10.16.0.1
DHCP Server . . . . . . . . . . . : 10.16.0.1
DNS Servers . . . . . . . . . . . : 68.87.76.**2
68.87.78.**4
Lease Obtained. . . . . . . . . . : Wednesday, August 12, 2009 7:37:45 PM
Lease Expires . . . . . . . . . . : Thursday, August 13, 2009 7:37:45 PM

by: thegofPosted on 2009-08-12 at 21:03:02ID: 25085362

Odd. What happens when you use ping? Does it get the lookup for the IP number? Can you ping www.google.com or www.yahoo.com via IP number (74.125.95.147 and 209.191.93.52 respectively)? If you can ping via IP number then you might have a DNS issue, perhaps do a configuration error on the router. For example, my router replaces the DNS server with itself and acts as the middleman.

Try the ping via IP and see if it works. If it does, double check your settings for DNS. You might also check a route print to see that all the non-local network routes point to the network interface. For example:

===========================================================================
Interface List
  9 ...00 01 29 d8 c0 83 ...... Realtek RTL8168/8111 Family PCI-E Gigabit Ethernet NIC (NDIS 6.0)
  1 ........................... Software Loopback Interface 1
 17 ...00 00 00 00 00 00 00 e0  isatap.{DBB60219-AAF6-44A1-8DE2-321E030606C7}
 10 ...02 00 54 55 4e 01 ...... Teredo Tunneling Pseudo-Interface
===========================================================================
 
IPv4 Route Table
===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0      192.168.0.1     192.168.0.32    266
        127.0.0.0        255.0.0.0         On-link         127.0.0.1    306
        127.0.0.1  255.255.255.255         On-link         127.0.0.1    306
  127.255.255.255  255.255.255.255         On-link         127.0.0.1    306
      169.254.0.0      255.255.0.0         On-link      192.168.0.32     30
  169.254.255.255  255.255.255.255         On-link      192.168.0.32    266
      192.168.0.0    255.255.255.0         On-link      192.168.0.32    266
     192.168.0.32  255.255.255.255         On-link      192.168.0.32    266
    192.168.0.255  255.255.255.255         On-link      192.168.0.32    266
        224.0.0.0        240.0.0.0         On-link         127.0.0.1    306
        224.0.0.0        240.0.0.0         On-link      192.168.0.32    266
  255.255.255.255  255.255.255.255         On-link         127.0.0.1    306
  255.255.255.255  255.255.255.255         On-link      192.168.0.32    266
===========================================================================
Persistent Routes:
  Network Address          Netmask  Gateway Address  Metric
          0.0.0.0          0.0.0.0      192.168.0.1  Default
===========================================================================

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by: thegofPosted on 2009-08-12 at 21:25:48ID: 25085431

Also, to clarify, my ipconfig lists

Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.0.1
DHCP Server . . . . . . . . . . . : 192.168.0.1
DNS Servers . . . . . . . . . . . : 192.168.0.1

by: rdovingPosted on 2009-08-12 at 23:39:55ID: 25085837

The ping via IP (ping 74.125.95.147) doesn't work. Here is my route print:

>route print
===========================================================================
Interface List
0x1 ........................... MS TCP Loopback interface
0x3 ...00 a0 d1 30 10 20 ...... Realtek RTL8139/810x Family Fast Ethernet NIC - Packet Scheduler Min
iport
===========================================================================
===========================================================================
Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 10.16.0.1 10.16.0.103 20
10.16.0.0 255.255.255.0 10.16.0.103 10.16.0.103 20
10.16.0.103 255.255.255.255 127.0.0.1 127.0.0.1 20
10.255.255.255 255.255.255.255 10.16.0.103 10.16.0.103 20
127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
224.0.0.0 240.0.0.0 10.16.0.103 10.16.0.103 20
255.255.255.255 255.255.255.255 10.16.0.103 10.16.0.103 1
Default Gateway: 10.16.0.1
===========================================================================
Persistent Routes:
None

by: thegofPosted on 2009-08-13 at 05:24:44ID: 25087354

I'm at a loss at this point. Everything looks ok. What exactly does ping return? Request timed out? If so, I'm about out of options from this end.

The more drastic steps would be to either swap in another router just to test, reflash your current router to the latest firmware and ensure it's in the default config. Do a complete reset to make sure of that (which should happen on flash unless it has a separate protected memory). Finally, if you've reflashed and/or tested with another router, I'd call comcast and double check that they are not blocking NAT devices. The fact that you can ping via the router, but not from a PC behind is odd.

One oddball thought. Are you running the Comcast supplied McAfee security pack? Part of that includes a firewall software where you need to tell it you "trust" your network interface as well as give permission to programs that want to access the network. Perhaps you told it to NOT trust the ethernet port in your rush to reconfigure the first time? I ask because if you put your firewall into lockdown mode, it will show this kind of behaviour. IPCONFIG and ROUTE will show the right info, but nothing gets through. If so, check by going into the McAfee Security panel (double click on the M icon), select "Protection Status", then select "Internet & Network" in the middle, and finally click on the Configure arrow. You can temporarily turn Firewall Protection off to test. If that works, then look through all your firewall settings to find out what's the issue (or use the "Restore Firewall Defaults" and then reconfigure as well.

Good Luck!

by: mdpsolutionsPosted on 2009-08-13 at 05:36:14ID: 25087458

Ping the public address (wan address) of the router. If you can't reach that, then ping the private ip of the router which I'm sure you can reach. If the above is true, your router is the issue. It is probably not passing traffic in itself.
You should be able to get the wan ip from the status page in the router.

If this is the case, I would begin by restoring the router to default, and then doing the above steps you followed and listed earlier. You did correctly configure based on your entry.

I believe the router is the issue currently.
Even better if you have a seperate one that hasn't been configured.
Each time go back to the default ping to lan ip router, then to wan ip of router then to outside address if these are successful.

MDP

by: rdovingPosted on 2009-08-13 at 16:38:25ID: 25094157

I can ping the private IP (LAN side) of the router from my PC. I can also ping the WAN IP of the router from my PC. I can't ping the gateway IP from my PC, but I can ping it from the router.

If I plug the PC directly into the modem I can access the internet. If I plug my laptop directly into the modem I can't acquire an IP or ping anything.

If I clone the PC's MAC on the router I can ping google.com from the router. If I disable MAC cloning from the router I can't ping anything or acquire an IP.

It sounds like the initial problem suggested by btpringle is correct (modem locks down to first MAC that connects to it). I'm going to call Comcast and try to have them reset the modem.

by: mdpsolutionsPosted on 2009-08-13 at 17:39:18ID: 25094458

The gateway IP is supposed to be the same as the LAN IP.
If it is not, you will not get past the local network.
Verify this and give us your IPconfig/all settings from the PC when connected to the router.

MDP

by: mdpsolutionsPosted on 2009-08-13 at 17:45:14ID: 25094482

It sounds like your modem is not set to pass the public ip through to the associated device. If this is so, it will be as though you have two routers between the pc and the net.
Is the wan ip of the router a public ip or private ip?
MDP

by: rdovingPosted on 2009-08-13 at 20:04:49ID: 25094979

I called Comcast and had them reset the modem while I had PC->router->modem with MAC clone disabled on the router. The router was able to get an IP from the modem and I was able to ping outside addresses from the router, but I still couldn't ping outside sites from the PC.

I was able to ping the LAN IP (10.16.0.1) and the WAN IP (24.5.93.50) of the router from the PC. I was not able to ping the router's gateway IP (24.5.92.1). The PC's gateway is the same as router's LAN IP (10.16.0.1).

Here is the info from my router's status page:

Firmware Version:       4.30.12 build 3, Dec. 20, 2007
                    Current Time:      Thu, 13 Aug 2009 19:48:35
                    MAC Address:      *************
                    Router Name:      WRT54GL
                    Host Name:
                    Domain Name:      hsd1.ca.comcast.net.

Configuration Type
                    Login Type:      Automatic Configuration - DHCP
                    IP Address:      24.5.93.50
                    Subnet Mask:      255.255.252.0
                    Default Gateway:      24.5.92.1
                    DNS 1:      68.87.76.182
                    DNS 2:      68.87.78.134
                    DNS 3:
                    MTU:      1500

The PC's ipconfig info:
>ipconfig /all

Windows IP Configuration

Host Name . . . . . . . . . . . . : DrPipperDesktop
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Unknown
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Marvell Yukon Gigabit Ethernet 10/100/1000Base-T Adapter, Copper RJ-45
Physical Address. . . . . . . . . : ***************
Dhcp Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IP Address. . . . . . . . . . . . : 10.16.0.100
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 10.16.0.1
DHCP Server . . . . . . . . . . . : 10.16.0.1
DNS Servers . . . . . . . . . . . : 68.87.76.182, 68.87.78.134

Lease Obtained. . . . . . . . . . : Thursday, August 13, 2009 7:04:38 PM

Lease Expires . . . . . . . . . . : Saturday, August 15, 2009 7:04:38 PM

by: btpringlePosted on 2009-08-14 at 04:17:34ID: 25096813

The other possibility is that you may have a bad router.

by: mdpsolutionsPosted on 2009-08-14 at 04:52:11ID: 25096976

Are you manually inputting the DNS entries on your PC?
If so, allow it to pick them up via DHCP.
Typically your DNS is the same IP as the Router in your type of setup.
I'm trying to eliminate variables.
MDP

by: rdovingPosted on 2009-08-14 at 06:41:32ID: 25097838

I did not manually enter DNS IPs on the PC, I let it pick them up automatically.

I don't have another router to try and was hesitant to buy a new one, so in a last attempt to fix this I flashed the router with the Tomato firmware. Reset modem and router, ipconfig /release and /renew, and lo and behold everything worked! The only noticeable difference is that now when I do an ipconfig /all the DNS server is the same IP as my router as you just said.

I don't know why the default router firmware was causing problems. I tried flashing the latest firmware from Linksys to the router, reset everything to defaults, and still it wouldn't work. I tried calling Comcast, who said there shouldn't be any special settings needed on the router, that it should work out of the box.

by: rdovingPosted on 2009-08-14 at 06:43:21ID: 31614807

Thanks to all for your help. btpringle got me over the initial hump of the modem locking in to a single MAC, and mdpsolutions you helped guide me along the way. Much appreciated!

by: mdpsolutionsPosted on 2009-08-14 at 07:47:36ID: 25098605

Weird. Oh well. Glad it finally works!
Thanks for the points!
MDP

20120131-EE-VQP-002

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Can't connect to internet through Linksys router and Comcast modem

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