User-configurable MAC address per IP interface
Manual configuration of one IP MAC address for each Layer 3 physical or virtual ethernet (VE) interface on a device is permitted. The configured MAC address is used as the source MAC address by routing protocols or hardware communication related to the IPv4 or IPv6 addresses on the interface, for example in ARP or neighbor discovery (ND) packets to the interface. The IPv4 and IPv6 addresses use the same IP MAC address for any software and hardware communication.
If an IP MAC address is not configured, the IP interface uses the MAC address from the router or stack.
The user-configurable IP MAC address feature supports the following unicast protocols:
- IPv4 support—ARP, BGP, OSPF, RIP
- IPv6 support—BGP4+, Neighbor Discovery (ND),OSPFv3, RD, RIPng
In addition to the unicast protocol support, the configured MAC address is used by IPv4 and IPv6 unicast software-generated packets (for example, ping) and IPv4 and IPv6 hardware-forwarded packets. For IPv4 addresses that are configured on the IP interface, gratuitous ARP is generated when the IP MAC address is configured. For IPv6 addresses, DAD is started and link-local addresses are regenerated when the IP MAC address is configured.
If Virtual Router Redundancy Protocol (VRRP) IPv4 or IPv6 sessions are configured on an interface where an IP MAC is configured, the VRRP sessions continue to use the virtual MAC address assigned to the virtual router ID (VRID) for any ARP or ND queries.
Some restrictions apply to the user-configurable MAC address per IP interface feature:
- The manually configured IP MAC address is not supported for multicast communications.
- The IP MAC address must be unique on the device including any interfaces. If the device is configured as part of a stack, the IP MAC address must not be the same as the MAC address of other stack units. If a stack MAC address is configured it must not be the same as the IP MAC on any interface.
- The IP MAC address configured manually for a VE interface must be unique within the same VLAN.
- There is a maximum number of IP interfaces (248) on which an IP MAC address can be configured and the number of VRRP virtual interfaces that can be supported simultaneously is affected by any increase over the default number of 120 interfaces. If the system-max max-ip-mac command is set above 120, a reduction in the number of IPv4 VRRP entries supported is calculated as <configured-value> - 120. For example, if the system-max max-ip-mac value is set to 130, the number of IPv4 VRRP entries is reduced by 10 entries (130-120).