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Starting a week and half ago my router stopped working with my cable modem. I went to sleep with it working and woke up with it not. I swapped in another router and am still having issues; I was gone for 10 days so now I'm back to trying to figure it out. While I was gone I left everything (cable modem, router, and computer) powered off.

My setup:

  • Comcast Ambit cable modem (from Comcast)
  • Netgear WGR614 v4 router --> replaced with Linksys WRT54GS v1.1
  • Windows XP SP3
  • other computers, all currently unplugged
  • The modem is using the firmware (ver 2.105.2001) provided by Comcast; hardware version 1.3
  • The Linksys router is using FW ver 4.71.4 (latest for this release of HW), factory defaults
  • I am only using the wired connections; no wireless.
  • I have swapped out all of the cat5 cable.
  • The router is cloning the MAC address of my PC (according to Comcast, this is not needed)

If I plug my computer directly into the cable modem, I can ping by name or number. Everything works perfectly.

If I plug my computer into the router and the router into the modem, I cannot access anything outside of my local network. This is the exact setup I've used for the past 5 years; there were no changes in the past year.

Now here's the interesting part: I can log into the Linksys router and get status information from it; everything appears good. Using the Diagnostics, I can run ping and traceroute to any site on the internet. These work perfectly. From my computer, I can ping the router and the modem. However, I cannot ping anything on the internet by with name or number. If I plug in another computer, I can ping it successfully.

I've included two transcripts below that show these two attempts. Addresses, DNS, gateways, etc. look good. I cannot access the internet through either router.

I am at a loss here. Suggestions? Help!


Computer to Router to Cable Modem

C:\>ipconfig /renew

Windows IP Configuration

Ethernet adapter Local Area Connection:

        Connection-specific DNS Suffix  . : hsd1.ca.comcast.net.
        IP Address. . . . . . . . . . . . : 192.168.1.100
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 192.168.1.1


C:\>ipconfig /all

Windows IP Configuration

        Host Name . . . . . . . . . . . . : wynton
        Primary Dns Suffix  . . . . . . . :
        Node Type . . . . . . . . . . . . : Unknown
        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 . . . . . . . . . . . : Intel(R) 82562V-2 10/100 Network Connection
        Physical Address. . . . . . . . . : 00-1D-09-9B-45-EB
        Dhcp Enabled. . . . . . . . . . . : Yes
        Autoconfiguration Enabled . . . . : Yes
        IP Address. . . . . . . . . . . . : 192.168.1.100
        Subnet Mask . . . . . . . . . . . : 255.255.255.0
        Default Gateway . . . . . . . . . : 192.168.1.1
        DHCP Server . . . . . . . . . . . : 192.168.1.1
        DNS Servers . . . . . . . . . . . : 68.87.76.178
                                            68.87.78.130
        Lease Obtained. . . . . . . . . . : Monday, March 22, 2010 10:21:55 PM
        Lease Expires . . . . . . . . . . : Tuesday, March 23, 2010 10:21:55 PM

C:\>ping google.com

    Ping request could not find host google.com. Please check the name and try again
.

C:\>ping 74.125.19.104

Pinging 74.125.19.104 with 32 bytes of data:

    Request timed out.
    [...snip 3 more failures...]

Ping statistics for 74.125.19.104:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),


C:\>route print
===========================================================================
Interface List
0x1 ........................... MS TCP Loopback interface
0x2 ...00 1d 09 9b 45 eb ...... Intel(R) 82562V-2 10/100 Network Connection - Pa
cket Scheduler Miniport
0x10004 ...00 0a 3a 6f 68 41 ...... Bluetooth LAN Access Server Driver - Packet
Scheduler Miniport
===========================================================================
===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0      192.168.1.1   192.168.1.100       20
        127.0.0.0        255.0.0.0        127.0.0.1       127.0.0.1       1
      169.254.0.0      255.255.0.0    192.168.1.100   192.168.1.100       20
      192.168.1.0    255.255.255.0    192.168.1.100   192.168.1.100       20
    192.168.1.100  255.255.255.255        127.0.0.1       127.0.0.1       20
    192.168.1.255  255.255.255.255    192.168.1.100   192.168.1.100       20
        224.0.0.0        240.0.0.0    192.168.1.100   192.168.1.100       20
  255.255.255.255  255.255.255.255    192.168.1.100   192.168.1.100       1
  255.255.255.255  255.255.255.255    192.168.1.100           10004       1
Default Gateway:       192.168.1.1
===========================================================================
Persistent Routes:
  None

C:\>


Computer to Cable Modem Directly

C:\>ipconfig /renew

Windows IP Configuration

Ethernet adapter Local Area Connection:

        Connection-specific DNS Suffix  . : hsd1.ca.comcast.net.
        IP Address. . . . . . . . . . . . : 71.204.149.195
        Subnet Mask . . . . . . . . . . . : 255.255.252.0
        Default Gateway . . . . . . . . . : 71.204.148.1

C:\>ipconfig /all

Windows IP Configuration

        Host Name . . . . . . . . . . . . : wynton
        Primary Dns Suffix  . . . . . . . :
        Node Type . . . . . . . . . . . . : Unknown
        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 . . . . . . . . . . . : Intel(R) 82562V-2 10/100 Network Connection
        Physical Address. . . . . . . . . : 00-1D-09-9B-45-EB
        Dhcp Enabled. . . . . . . . . . . : Yes
        Autoconfiguration Enabled . . . . : Yes
        IP Address. . . . . . . . . . . . : 71.204.149.195
        Subnet Mask . . . . . . . . . . . : 255.255.252.0
        Default Gateway . . . . . . . . . : 71.204.148.1
        DHCP Server . . . . . . . . . . . : 68.87.76.10
        DNS Servers . . . . . . . . . . . : 68.87.76.178
                                            68.87.78.130
        Lease Obtained. . . . . . . . . . : Monday, March 22, 2010 10:18:50 PM
        Lease Expires . . . . . . . . . . : Monday, March 22, 2010 11:12:31 PM

C:\>ping google.com

Pinging google.com [74.125.19.99] with 32 bytes of data:

    Reply from 74.125.19.99: bytes=32 time=20ms TTL=55
    [...snip 3 more success...]

Ping statistics for 74.125.19.99:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:
    Minimum = 17ms, Maximum = 28ms, Average = 20ms

C:\>ping 74.125.19.104

Pinging 74.125.19.104 with 32 bytes of data:

    Reply from 74.125.19.104: bytes=32 time=18ms TTL=55
    [...snip 3 more success...]

Ping statistics for 74.125.19.104:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:
    Minimum = 16ms, Maximum = 18ms, Average = 17ms

C:\>route print
===========================================================================
Interface List
0x1 ........................... MS TCP Loopback interface
0x2 ...00 1d 09 9b 45 eb ...... Intel(R) 82562V-2 10/100 Network Connection - Packet Scheduler Miniport
0x10004 ...00 0a 3a 6f 68 41 ...... Bluetooth LAN Access Server Driver - Packet
Scheduler Miniport
===========================================================================
===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0     71.204.148.1  71.204.149.195       20
     71.204.148.0    255.255.252.0   71.204.149.195  71.204.149.195       20
   71.204.149.195  255.255.255.255        127.0.0.1       127.0.0.1       20
   71.255.255.255  255.255.255.255   71.204.149.195  71.204.149.195       20
        127.0.0.0        255.0.0.0        127.0.0.1       127.0.0.1       1
      169.254.0.0      255.255.0.0   71.204.149.195  71.204.149.195       20
        224.0.0.0        240.0.0.0   71.204.149.195  71.204.149.195       20
  255.255.255.255  255.255.255.255   71.204.149.195  71.204.149.195       1
  255.255.255.255  255.255.255.255   71.204.149.195           10004       1
Default Gateway:      71.204.148.1
===========================================================================
Persistent Routes:
  None

share|improve this question
    
@dwj: including lots of detail is good, but also makes your question hard to read. i've reformatted it so it should be easier to follow; next time, consider posting small snippets (~10 lines each or so) here, and link to the full output posted to a site like pastebin.ca –  quack quixote Mar 23 '10 at 6:59
    
Can you include the output of route print ? –  einstiien Mar 23 '10 at 7:03
    
@einstiien: I added the output of route print to both outputs. –  dwj Mar 23 '10 at 14:32
    
@~quack: Thanks for the reformatting. –  dwj Mar 23 '10 at 14:33

6 Answers 6

I'm thinking that things were good until your ISP changed your IP address, gateway, or DNS servers recently. Check your computer's host file. Could you have some ancient settings in there that are blocking things? Also, could you have some obsolete firewall settings?

Also, make sure that your ISP is giving you valid DNS server addresses, and that you are using them. The ones in your listing don't work for me, but I think it's just because I'm not on comcast.

iMacCoreDuo:~ jamiecox$ nslookup www.apple.com 68.87.76.178
Server: 68.87.76.178 Address: 68.87.76.178#53

** server can't find www.apple.com.cfl.rr.com: REFUSED

But, if they don't work from Comcast, maybe they are obsolete.

So, do
nslookup www.google.com

and see what your get. Then try
nslookup www.google.com 192.168.1.1

this will be asking your router instead of the external DNS servers.


Added this:

It seems obvious, but check that things are cabled up right. Is the cable modem connected to the WAN port of the router? It should be. Is the computer connected to a normal LAN port -- not designated as a monitor port or something?

I suggest that if you don't need to be doing MAC Address cloning, that you turn that off. It could be causing a weird problem.

If I was your ISP, and I wanted to create this situation, (say I didn't want you to use a router, or I wanted to force you to buy my router), I would make sure that all inbound IP traffic coming out of your cable modem had TTL (time to live) of 1. Any such traffic would be (correctly) dropped by the first router it hit. Your outbound traffic would still work, but you just couldn't get anything back. This would be an underhanded trick, and I've never heard of anyone doing it, but it would exactly explain your symptoms.

Check to see if the PC and the router can ping their default gateways. This should be the easiest thing to get working. Then see if the PC can ping the external gateway (the one the router sees).

share|improve this answer

I had a similar problem that occurred when I upgraded to Comcast 50Mbps and had to change to a new DOCSIS 3.0 cable modem. Having my router (a Cisco RVS4000) Clone the MAC address of my primary PC that I used to perform the self-installation fixed the problem.

Here is apparently why this worked...

Comcast technical support says that they use a MAC address authorization solution in their routers to prevent unauthorized access to the cable (as if spoofing a MAC address wasn't easy, but that's another story). There are two MAC addresses that they store in their central office system, the MAC address of your cable modem and the MAC address of the PC that you connect to it. Since their self-installation system requires that you connect your PC directly to the cable modem (rather than putting in a router first), this is typically the MAC address that they store. If you had your cable modem installed by a Comcast technician they may have done the same thing to make it quick and easy, even though they may have later set up a router/wireless AP for your house (in which case they will likely "clone" the MAC address on their standard Linksys wireless router setup that they install rather than have the CO-stored address changed).

They can easily change the MAC address stored in their system if you call their customer service line, but either way this is the only way to get it working because it is being limited access by their upline system.

share|improve this answer
    
I'm on Time Warner RoadRunner. What they appear to do is record the MAC address of the system which most recently successfully used the connection. If you plug another device with a different MAC then it won't work ... for a bit. If I power off the cable modem, wait a minute or two, then power up the modem and connect my router DHCP accepts the "new" MAC and will configure it. I'm not sure what the purpose of this is, but I think it must confuse the heck out of naive users who expect DHCP to work instantly after they move the cables around. –  irrational John Jul 3 '10 at 22:14

Is the router successfully pulling an IP from the modem? Is the modem running its own DHCP server? Modems like to reset themselves to factory defaults when things go wrong and you may need to get into its config pages to put them back where you want them.

share|improve this answer
    
@NSD: Yes, the router is pulling a valid IP from the modem; I can use the on-board diagnostics to run ping and traceroute. The modem does not appear to be running DHCP since it gives my router an external IP address. I've never changed any settings on the modem itself. –  dwj Mar 23 '10 at 14:35

Try doing a DNS flush on your PC: http://technet.microsoft.com/en-us/library/cc781949(WS.10).aspx

share|improve this answer

Check your router's clock. Did this happen when daylight saving time started? If the time is off by an hour, your router could always think its DHCP lease has expired. It looks like your ISP issues DHCP leases valid for exactly one hour. Check the computer clock too.

share|improve this answer
    
Interesting idea; it occurred a few days before DST kicked in -- Mar 10th. –  dwj Mar 26 '10 at 5:14
up vote 0 down vote accepted

I ended up buying a new Netgear WGRWGR614v9 router just to give it a shot; I did this before a few other, excellent suggestions were posted here. I plugged it in: nothing! I cloned the MAC address (contrary to what Comcast told me was necessary): it works! After several days of aggravation, $40 is worth it.

I am tempted to try a few of the suggestions posted here with my older Netgear; maybe this weekend; maybe not. If I do, I'll post here.

share|improve this answer

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