problem with vlan + arp

Sep 07, 2008 2 Replies
M

Hi,



I have this situation, cisco 2811 + some catalyst 3560, connect in "trunk mode" and other unmanaged switch connect to catalyst 3560 with port configure in "access mode". Cisco 2811 term every vlan using sub-inf in "encapsulation dot1q vlan- id" and doing routing between every vlan. Sometimes some host connect to unmanaged l2 switch not reply to ping, this host usually are Access Point Mikrotik or Motorola, but traffic flow regular, infact if I connect in our l2 domain I can ping they...... so I type on cisco 2811 on console "clear arp-cache" and every return to work fine. I check arp table and it is correct, I disable ip proxy-arp on sub-inf but nothing. Every catalyst in trunk mode is connect to other by wireless link by Alavarion in bridge mode.



I haven't ideaa.... have you somethings that I can try ??



Thank you so much in advance,



Matteo


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T

The problem could be that the default arp-cache timeout on the router and the default mac-address timeout on the switches are different. I have run into this problem before and I consider this to be a bug (but Cisco doesn't.) Cisco recommends setting the arp-cache timeout on each VLAN to

300 seconds (which is the default mac-address timeout on the switches) using "arp timeout 300" on each VLAN interface. After not hearing from that IP address, the router interface will broadcast an ARP request, and the switches will relearn which port the MAC address belongs to.
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M

Thank you, I add "arp timeout 300" and now I check if it work fine, tomorrow I reply somethings to you.

Bye

Matteo

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