6500 Arp issue

skiran · ‎11-21-2003

Hi all

I have 2 6500 series switches @ the distribution layer doin the intervlan routing for 1500 users..The access layer consists of 12 of 4500 series switches all dual homed to the 6500 switches..

The issue is that when i give a show cam dynamic on any of the access switches i can see it learning all the arp entries of all the users (1500users )...I think it should only show me the local pc's arp which is connected to the switch..and it should forward any traffic to the 6500 VIP ...Please correct me if i wrong..

We have a seperate Management VLAN interface ( VLAN 10 ) and its being routed on the 6500 (i.e interface vlan 10 ).

And all the arp entries are learnt through both the gigabit interface through which its dual homed to the 6500's

Appreciate ur quick response in this issue

Regards

Shashi

mark-obrien · ‎11-21-2003

Shashi,

When a station sends an ARP request, it is broadcast throughout the broadcast domain (VLAN). The ARP request goes out over all trunks that carry the VLAN. So, all switches will enter the MAC address of the requestor into the CAM table, associated with the port it saw that MAC address on. This includes trunk ports.

If your switches are learning of the MAC addressed via both trunk ports you probably have spanning tree disabled or a spanning tree failure. You don't mention whether or not there is a trunk between the two 6500 switches. If there is, you definitely can not disable spanning tree because this trunk, combined with the two trunks to a 4500, form a physical loop.

HTH

Mark

skiran · ‎11-21-2003

Hi Mark

Yes there is a trunk between the two 6500 switches. the two switches act as a root switches for odd & even vlans respectively. For this reason i think i can see Mac addresses on both the trunk. Spanning tree is enabled...But is this a normal behavior ?

regards

Shashi

mark-obrien · ‎11-22-2003

No, I don't think it is normal, unless you have several MAC addresses that appear in more than one VLAN. A switch should only see a MAC address on one port per VLAN that the MAC address appears in.

Mark