Incomplete Arp

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Dec 3rd, 2007
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I have a cisco here which is giving an incomplete arp on one of my fast ethernet connections. Cisco interface and protocols are in an up status. When I do a show arp, it shows the IP address, interface, but instead of the mac it shows incomplete arp and the connection is down.

What are the usual problems in these instances?


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ccbootcamp Mon, 12/03/2007 - 19:05
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An incomplete ARP entry is learned through an ARP request but has not yet been completed with the MAC address of the external host.

In this type of situation, I would take a close look at your cables/connectors. Try swapping out the rj45 cable (assuming it's an rj45 cable not fibre) and see if that fixes the problem. Let me know if that fixes it.


(please rate the post if this helps!)

shivlu jain Tue, 12/04/2007 - 03:54
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do one thing only for testing purpose try to add the static mac entry in the switch.



Kevin Dorrell Tue, 12/04/2007 - 05:57
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Also, check hat the device you are trying to access is in the same VLAN, i.e. that your switchports are configured correctly on both sides.

Is the router and the device you are trying to access on the same switch? If not, check thta the trunk between the switches is carrying that VLAN. Also, check the MAC forwarding table on each switch to see that the MAC addresses of both sides are present.

Perhaps you could also post the respective IP addresses and masks so we can check them.

Kevin Dorrell



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