Selecte IP Addresse Blacklisted....HELP!

Unanswered Question
Jun 19th, 2007

We use static ip addressing at our school. All has been working well until recently. Within the past month "selected" ip addresses no longer can access other vlans and outside our network, but they do work within their vlan. For instance VLAN 32 is a 10.1.32.0/24 network. About 1 month ago 10.1.32.91 (a client on the network) could no longer access VLAN 24, a 10.1.24.0/24 network, nor could the client ping the router 172.16.1.2 which it could do before. Other clients on VLAN 32 were not affected, and other clients could ping 10.1.32.91 and it could ping other clients on the VLAN 32. There was no other client with the same IP address (when we disconnect it you couldn't ping the address). By simply changing the ip of the client to 10.1.32.90 it was fine and was working again. Last week another client on the same VLAN lost its ability in a similar manner. Today 10.1.32.25 lost its ability (and each was working fine until the time it happened.) We have a Cisco 6506 Router as an internal router routing between all internal networks and a Cisco 7609 rouer connecting us to the rest of the world. Any help would be appreciated

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smothuku Tue, 06/19/2007 - 21:50

Hi ,

config of router and switch may be helpful to solve the problem...

any chance of seeing the config of both the devices..

Thanks,

Satish

Richard Burts Wed, 06/20/2007 - 07:43

Bart

These symptoms sound like there might be an issue with the ARP table on the 6506. If the client can communicate with other devices within its subnet/VLAN but can not communicate with devices in other subnets then I believe that the CAM table on the switch is ok but that there may be some issue in the ARP table which is used in forwarding between subnets. When this happens again can you examine the content of the ARP table for problems. The problem might be that there is no ARP entry or might be that the MAC indicated in the ARP entry is not the MAC of this client. Can you check this and let us know?

HTH

Rick

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