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Sihanu N

Blocking selected ARP broadcasts from particular Trunk port via DAI

Hi Experts,

We  had a core switch (Cisco 4503), distribution switches(Cisco 3750) and access switches in our  network and consists of many vlans. Almost all vlans uses DHCP Pools.  But for few vlans DHCP is not yet configured due to initial design poblems. Recently one of the rogue  user in vlan 1 connected to one of the access switch send rogue arp packets to the network (suspecting arp packet with interface vlan 1 ip of core switch with wrong mac-address (gateway ip of vlan 1)) and resulted in a prolonged network outage for the vlan 1.  Any way we are going to seggregate vlan 1 into different vlans, but  before that we need a temporary plan to block such kinds of attack like enabling DAI in the switch. I have checked the DAI implemenation feasibility with my knowledge and found that it is not possible to configure to the access switches(Cisco 2960) in which the user directly connected. But found that Distribution switch connected to that particular access switch seems to be able to configure since DAI commands are available to configure in switch.

Is it possible to block ARP packets with the interface vlan 1 IP Address with rogue mac-address by configuring DAI in the above mentioned Distribution switch and the port connected to the mentioned access switch?

Any suggetions and advices are highly appreciable.

Thanks & Regards

Sihanu N


Looks like u are fighting symptoms where it would be better to address the cause.

There is no good reason to block arp requests, never!



Hi Leo,

Many Many Thanks for Reply,

Actually the interface vlan 1 ip of core switch is and all machines in the vlan 1 configured the gateway as vlan 1 interface ip. From one of the access switch an interface fastE 0/24 is connected to outside (Family Quarters location) for restricted Corporate Access. Recently we experienced a serious outage of devices in Vlan 1 and resolved only after shutting down of the interface 0/24 of that access switch. We found which was due to the ARP cache poisoning of machines because during that timethe mac-address table of vlan 1 machines(found that wrong mac-address binded in the vlan 1 machines arp table instead of HSRP gateway mac-address).

Is there any possibility to implement DAI to block such kinds of broadcasts to Corporate network only in Vlan 1?

Thanks and Regards,

Sihanu N