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3750 Multicast MAC address Limitation

When I issue the following command:

mac-address-table static 01:00:5e:03:ca:f7 vlan 2 interface f1/0/20

I get the following message:

Supports only l3-ipmulticast addresses

Is there a way to add this multicast address of my firewall or extend this limit?


Community Member

Re: 3750 Multicast MAC address Limitation

Create a global static ARP entry

arp x.x.x.x w.w.w arpa

where x.x.x.x is the ip address of the FW and w.w.w is the MAC address. This is the only way to do this since RFC for IPv4 routers does not allow a router to accept a multicast ARP entry.

Here is an excerpt from the RFC:

RFC 1812 - Requirements for IP version 4 Routers (Section 3.3.2)

Here is the relevant part of the RFC:

3.3.2 Address Resolution Protocol - ARP

Routers that implement ARP MUST be compliant and SHOULD be unconditionally compliant with the

requirements in [INTRO:2].

The link layer MUST NOT report a Destination Unreachable error to IP solely because there is no ARP

cache entry for a destination; it SHOULD queue up to a small number of datagrams briefly while

performing the ARP request/reply sequence, and reply that the destination is unreachable to one of

the queued datagrams only when this proves fruitless.

"A router MUST not believe any ARP reply that claims that the Link Layer address of another host or

router is a broadcast or multicast address."

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