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Adding Static ARP Entries with Multicast MAC Addresses (CR00011204) 67
Version 276-05
C613-10474-00 REV D
Adding Static ARP Entries with Multicast MAC Addresses (CR00011204)
This Software Version allows you to add ARP entries with multicast MAC addresses and allows the router or switch to accept packets with conflicting IP and
MAC addresses. It introduces the enable ip macdisparity and disable ip macdisparity commands to support this.
Adding Static ARP Entries
Valid ARP entries are normally restricted to unicast IP with unicast MAC addresses. However, ARP entries can be configured with multicast MAC addresses
when macdisparity is enabled. Static ARP entries with multicast MAC addresses are necessary for some third party networking solutions, such as server
clustering.
Before you can add an ARP entry with a multicast MAC address, you must enable macdisparity using the command:
enable ip macdisparity
Once this feature is enabled, you can add an ARP entry with a multicast MAC address using the add ip arp command.
Accepting Packets with Conflicting Addresses
Enabling macdisparity also allows the router or switch to accept packets with conflicting IP and MAC addresses. Normally the router or switch discards these
packets as being invalid.
Conflicting IP and MAC addresses include:
■ A multicast IP address with a unicast MAC address
■ A unicast IP address with a multicast MAC address
Macdisparity is disabled by default. When disabled, only ARP entries with unicast IP and MAC addresses can be added, and packets with conflicting
addresses are discarded. Other routers or switches in the network may not accept packets with conflicting addresses unless configured to. To disable this
functionality, use the command:
disable ip macdisparity
ARP entries with multicast MAC addresses must be removed before the disable ip macdisparity command will work. To see details on the current ARP entries,
use the command:
show ip arp