OK. So my network has spontaneously started routing externally :(

[Scouse]

Bear with me gents. This one should have a simple answer but for the life of me my brain's stopped working. Help a wanker out with his home setup pretty please!

Two PC's: Laptop A and PC B.

Laptop A's (wireless) addy: 192.168.1.10
PC B's (wired) addy: 192.168.1.11

Router's addy: Internal 192.168.1.1, External: 81.100.100.100

Until recently pinging B from A would happily return a reply from 192.168.1.11

Now pinging A from B or vice versa returns a reply from 81.100.100.100

Also, the reply is from <device A or B>.cable.virginmedia.net.

Now, I'm not in the habit of joining virgin media's domain. I've got a nice little setup behind a router so why would this all of a sudden start happening?

Both machines are Win7 btw. In case it makes a difference. Configured as part of the same workgroup.

 

[TdC]

sounds like something manky in the router re routes and things. you have local admin?

 

[Bob007]

Hm thats a bit strange. Guess you have an ISR (intergrated services router), most folks do and refer to them as a router(incorrectly). You realy have 3 devices. a switch, a wireless access point and the router its self.

When you ping a class A, B or C private IP address, if its on the same network that the switch can handle it, it should forward it out the correct port (if it knows it, all ports if it don't).

If its on another subnet the switch part will push it to the router. Now this is the bit i find strange. Most IRS's are setup to deny forwarding of private IP addresses and should just drop the packet. Which is prob whats happening at you ISP so you getting a returned public address as that the last 1 it sent to.

Is the ping timing out or you getting a responce ?

If its timing out, it should like a routing and permissions issue. Its routing private ip to the public network and its allowing it.

If you getting a responce it should then be a network address translation issue and a permissions issue. As then it would be translating the private to a public which it should do. But its seeing your local addresses as addresses for outside your local network and that brings us back to a routing issue.

I'd double check your network IP settings against the routers DHCP settings, make sure you pinging right subnet, and also try the Homegroup and see if thats working. Then I'd prob reset the router and set everything up again and see if its still doing it. If it does. I'd then be looking at flashing it or replacing*.

It's a strange one. As this should not happen at any time. Chances are it something stupid and would prob clear up with a reset.

*You could prob look around the inet and find a away to telnet into your device, some of them are capable of this, from here to could check the permisions, the nat settings, ACL's and router tables.

 

[Zenith.UK]

Check that your router has NAT enabled and is not using a DMZ.

If you carry on having problems, you might also want to hard set your network addresses and use the HOSTS file.

Manually set the IP address for each PC.
1) IP:192.168.1.10 Subnet: 255.255.255.0 Gateway: 192.168.1.1
2) IP:192.168.1.11 Subnet: 255.255.255.0 Gateway: 192.168.1.1

Set the hostname for each PC and make a note of each one.

On each PC, go to...
C drive > Windows folder > system32 > drivers > etc
Open the HOSTS file in notepad.

Add the lines:

192.168.1.10 hostname1
192.168.1.11 hostname2

Save and close the HOSTS file.

You should now be able to ping each hostname without going outside your home network.

 

[Scouse]

Don't want to do it through static hosts, tho ta anyway

I guess it's the router. It's still got all the MAC addresses I use to tie things down correctly, shows the DHCP table fine, seems configured peachy.

Not made any changes to it in months.

 

[MYstIC G]

Have you tried turning everything off and turning it all back on again?

 

[Scouse]

Have you tried turning everything off and turning it all back on again?

 

[Bob007]

do a pathping from command promt and paste the results.

Pathping {IP} -q 20

Pathping {Hostname} -4 -q 20


-4 forces IP version 4.
-q the number of queries.