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Can't ping on cisco 871

Posted on 2008-10-16
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Last Modified: 2010-04-12
Hi,

I set up a Cisco 871 router that connects a network A and network B.
Network A has one Linux laptop with one NIC.
Network B has one Windows PC with multiple NICs.
I configured 2 VLANs along with static routes.
I ping from A to B and use Wireshark (filter string = icmp) to monitor traffic on both A and B.
On A network, I can only see requests (ICMP packets) coming to B but no replies from B.
On the other hand, I can see Replies from B to A but no requests.

There's no connectivity between A and B.

Yet, if I diable other NICs on the Window PC, I see both request and replies on both sides and there's connectivity.

Can someone explain why ? How do I enable connectivity without bringing other NICs down ?

Thanks


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Question by:kevinnnguyen
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by:bkepford
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A PC can only have one default gateway. Is there a default gateway on the second NIC?
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by:kevinnnguyen
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Yes. The PC has multiple NICs with multiple gateways.
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by:bkepford
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This won't work properly basically the PC creates a routing table and that table can only have one entry for a default gateway.  
With two gateways it's like having two doors in a room with an exit sign on each of them. The PC has no way of telling which is the better path. The NIC that lets you get to the Internet is the one that needs the default gateway remove it from the other side and that should get you up and runing.
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rexxus earned 125 total points
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As mentioned you can't have two default gateways.  

What you can do is remove the default gateway on Network B pointing to the router and enter a static route in a Windows command prompt directing traffic for the Network A traffic to the 871.

At the command prompt type:

route ADD x.x.x.x M.ASK x.x.x.x  y.y.y.y  METRIC 3 IF 2
       destination^               ^mask    ^gateway metric^    ^
                                                                                Interface
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