Clear arp-cache to ping

perrymichael · ‎05-24-2006

I have an SMS server on my network that is unreachable from vlans other that its own. This happened after we pushed out tumbleweed via SMS. Now, in order to ping the server I must issue a clear arp-cache in the core switch, this only last for about 1 min and then the SMS server is unreachable again. Any help would be great.

gpulos · ‎05-24-2006

almost sounds like you could have another host on the network with the same IP addy!?!

you clear the arp cache and the server pings for a minute, then begins to fail again...is this correct?

does the arp cache have two macs for the same ip addy? i've seen this in some IOS imagaes & situations where the arp cache got corrupted.

perrymichael · ‎05-25-2006

No that is not the case. The arp cache only shows one entry for the ip and the mac address.

kdamisch · ‎06-22-2006

I am having the same problem, only it is with access points. Did you resolve the issue? If so, what was the resolution? I cannot ping an access point until I do a "clear arp" on the access point. After about 15 minutes, I cannot ping it again. Then, I do another "clear arp" and it fixes it. Doing a "show arp" shows the same entries in the arp table when I can and can't ping.

Any thoughts?

Thanks,

Kevin

perrymichael · ‎06-30-2006

I moved the server to a different vlan. The vlan that the server was on is the native vlan, but it has been like this for about 5 years. Now the server still becomes unreachable at times, but not as frequent. I have a TAC case open but cisco is as confused as I am. We recently had to other servers experience the same issue. No resolution as of yet.

roadhouse1387 · ‎06-30-2006

Hi Perry,

There isnt another layer 3 device on there somewhere doing proxy-arp by any chance ?

Cheers

Shaun

dabels · ‎06-30-2006

this is a great thought we have seen this in the past where proxy arp gets turned on. so if you look in the sms server at the arp entries for the router is it the correct mac for the right default gateway?

how about if you look in the default gatway and show arp for the sms server is it correct? if you are issuing the clear arp * on the router this causes the router to send out a gratuitus arp to all of the device in the arp table, so if the arp entry in the sms server was corrupted some how this clear on the router would fix it for some time but then what ever device is corrupting it sends back an arp reply for the default gateway it would get corrupted again.

roadhouse1387 · ‎06-30-2006

Thanks Dabels,

I have had this problem as well, it turned out to be a pix.

Proxy-arp is enabled by default on all interfaces and its not apparent in the config when its on or off. Its configured as a sysopt and therefore, it often gets overlooked.

Agree with everything you say, check the mac in the arp table of the server when your pings are failing, then trace the MAC you find there which corresponds to the ip address of the router.

Or check the arp entry in the router (again when its failing) and verify the MAC is the SMS server, it may just turn out to be a router or a pix or even....another server which is routing between a pair of NIC's, such as a unix box or a windows server.

Let us know how you get on.

Cheers

Shaun