can access internet, but not other users

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IB4GAINS

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I have a computer that can access the internet through a linksys router, but can't ping the gateway or other users. The computer is able to pickup a dhcp address and recognize the gateway via arp, won't see anyother mac address. It can ping itself. Any thoughts?
 

Law

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So you're saying that the computer can't ping it's own default gateway but can still access the internet? Makes no sense.

Can you do a ipconfig /all on the computer and on another computer and show me the result.
 

IB4GAINS

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I've done all that. it registers and resolves the gateway in arp, but still can't ping. I'm an engineer and can't figure out this issue. Maybe someone has come across this issue befor, but I've been through all troubleshooting steps.
 

Ethereal_Dragon

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Can you provide the Linksys router model info and firmware verison? Perhaps there is an option on the router to disable ICMP requests through the router. Can you give more details about the network topology, is it just some PC's and a Linksys router, or is there other hardware on it too, like a firewall perhaps?

Also, as Law requested above, can you provide us with the 'ipconfig / all' info from 2 of the PC's?



EDIT ALSO, when you said... "won't see anyother mac address"... what are you referring to? The router is only seeing the MAC address of one PC, or the PC is only getting packets from 1 MAC address?

If the you are saying the PC is getting packets from only 1 MAC address, this would be correct. that is because the MAC address is stripped off of the packet and replaced with each physical hop the packet takes... (except for hubs / repeators).

Example:

PC1 - packet leaves with MAC address of PC1, destined for IP address of PC 2.
Packet is recieved by switch or router, and the MAC address for PC1 is stipped from the packet. The packet is then sent towards PC2 with a SOURCE MAC address of the router / switch...
 

IB4GAINS

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The problem was occuring before I placed the router. The arp was toward the linksys router (gateway) and no other computer on the network. I'm A+, Net +, MCP and soon security + and have almost ten years experience, so I do understand process of elimination. What I need to know, has anyone experienced this problem. Could this be an os issue or a virus that caused these symtoms. I appreciate all input.
 

mikesgroovin

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No need to throw your credentials down :)
Since you did go through a series of steps, can you please post what you have done so far? No matter how insignificant it seems (Like disabling the XP firewall, pinging loopback with results, etc)? May as well not re-invent the wheel while trying to help you. :p :)
 

Law

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So you are saying you only see the arp request going to the default gateway (router interface)? Something like "who has 192.168.1.1 tell 192.168.1.100" "192.168.1.1 is at 00:43:etc MAC address"



Those computers are in the same broadcast domain am I correct?

Have you tried purging out the arp cache? My suggestion is to clear the arp cache on all the computers. You know how to, since you sound pretty experience.

Not sure if you have a virus problem but sometime people can spoof a MAC address of another device so that it confuses the other computer. A DoS attack can simply be spoofing the MAC address so that the client computer doesn't have the correct MAC address for it's default gateway or another computer.

Man in the Middle attack using ARP Poisoning exploit to capture information between two communicating party.

I highly doubt these are the case, but it does happen.
 
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