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Community Member

ARP problem on 1750

Hi group

I have a problem between my 1750 router with Fasteth interface, and a 16 port Hub (3 Com) I set the speed to 10MB and half duplex.

The PC's connected to the switch can ping the router fasteth interface. When the entry in the arp table times out, the PC's cannot ping the router anymore. From the router you cannot ping the PC anymore either. When I clear the arp cache on the router, I can ping again. The default arp timer is set to 4 minutes.



Re: ARP problem on 1750

Try configuring the fastethernet port in the router with speed and duplex se tu auto:

int fa0/0

speed auto

duplex auto

I've seen some strange problems with some NIC's that have their speed and/or duplex manually set.


Community Member

Re: ARP problem on 1750


The settings was on Auto.

I replaced the hub with a switch, which sorted out the problem.

Thanks for the input


Community Member

Re: ARP problem on 1750


What I would suggest is isloating the problem one by one. First connect one PC directly to the fast-ethernet interface of the router using a cross cable and see whether the problem repeats. If its not working fine, ensure that the speed and duplex is made auto, no access-list is configured on the router's interface.

Apply the latest patch/service pack for the OS running in the PC.

If the problem still continues, try upgrading the IOS of the router.

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