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Missing MAC and ARP entry

I am using a 3750 switch. We just added some Avaya equipment but they do not show up on the switch's ARP table or Mac-address table. I have tried adding a static ARP entry, and it shows up on the table, but I am still unable to ping the device. I am also unable to perform a successful mac traceroute on it either. I am at a loss, I was told this is because a lot of the newer VoIP devices do not give out their MAC Address to prevent Man in the Middle attacks. Any ideas on how I can get it's MAC address into the switch and have it work? The cables are good, and the port is showing in the up status.


Re: Missing MAC and ARP entry

There must be something strange about its MAC address. I wonder what MAC address it is sourcing from, that it doesn't get into the switch forwarding table? Is it a multicast or something?

Could you tell us the MAC address, and what MAC addresses you see on the port where that equipment is supposed to be?

I wonder if there is something going on with port security.

Kevin Dorrell


New Member

Re: Missing MAC and ARP entry

The MAC is 00040d2a0dd5. The port shows no MAC address attached. So far, I have looked at the adjacency table, mac-address table, and the ARP tables but have not found it in there. We have the same Avaya equipment at another office and it does the same thing.

Cisco Employee

Re: Missing MAC and ARP entry


If the switch is not learning the MAC address of the phone dynamically, it appears there is no traffic from VoIP phone. Generally the switch will learn the MAC address from source MAC address field of the incoming frame.

Try the following,

1. Configure interface vlan in 3750 switch and assign an IP address from same range of VoIP phone and try pinging from switch with and without static ARP entry.

2. Change the cable and check if it solves the issue?

3. Change the port to which the phone connected.



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