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New Member

Cat6509/MSFC2 produces tons of ARPs

We have two Cat6509 with a MSFC2-Module each. They are configured to use HSRP.

In the main VLAN there are 5 IP-networks configured.

It seems that the active router (MSFC2) sends ARPs for all IP adresses that are included in these 5 networks. It looks like it is happening all the time but I can see peaks in 4 hour offsets.

Does anybody have an idea what triggers this behaviour?

6 REPLIES
Bronze

Re: Cat6509/MSFC2 produces tons of ARPs

Hi Arno,

are they arp requests? Are they sent to the vlan itself? How many do you see? Are they always different addresses or do some (all) addresses repeat?

It would be normal for a router to send arp requests in order to learn mac addresses, so it's only strange if you see the same arp requests again and again in a short timeframe. In that case, do you have a "arp timeout" command configured with a small timeout value?

hth

Herbert

Herbert

New Member

Re: Cat6509/MSFC2 produces tons of ARPs

ARP-timeout ist default (4 hours)

I can see ARP-requests sent every 10 Minutes by the MSFC2 to the same IP-Adresses

Proxy-ARP and Local-Proxy-ARP are turned off at the MSFC2

Arno

New Member

Re: Cat6509/MSFC2 produces tons of ARPs

Hi Herbert,

I just had another look at the trace. I found even ARP for some IP-Adresses that happened 4 times a minute for the tracing period of 1/2 hour

Arno

Bronze

Re: Cat6509/MSFC2 produces tons of ARPs

Do you see arp replies for those addresses?

And do they show up in the list if you do a "show arp"?

New Member

Re: Cat6509/MSFC2 produces tons of ARPs

Hi,

The MSFC will re-ARP all local cache entries 60 seconds before aging out. Four hours is the default ARP aging time. This will assure that we are not keeping stale entries for inactive hosts. If you by chance did a "clear arp" on the MSFC, then the timer for all entries built at that time are in sync and will re-ARP or refresh at the same time.

-Robert

New Member

Re: Cat6509/MSFC2 produces tons of ARPs

I don't mean to step on this conversation, but noticed it to be rlevant to an ARP issue on a 3725 at one of our locations. WWondering if some one can explain why some entrys age to the 4 hour time out value, while others are agging to 1 or 2 minutes the resetting. All these on the same Bcast domain.

Clearing arp resets all, but issue recurrs.

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