Outgoing VLAN traffic
This uses the MAC address of the switch as the source MAC address in packet headers. The MAC address
configured on VLAN interfaces is not used on outbound VLAN traffic.
When the routing switch receives an ARP request for the IP address configured on a VLAN interface, the ARP
reply uses the reconfigured MAC address in both the:
• ARP Sender MAC address field
• Source MAC address field in the Ethernet frame header
When proxy ARP is enabled on a VLAN interface, the ARP reply sent for an ARP request received from VLAN
devices located outside the directly connected IP subnets also contains the reconfigured MAC address in
both the:
• ARP Sender MAC address field
• Source MAC address field in the Ethernet frame header
To hosts in the network, VLAN traffic continues to be routed (using the reconfigured MAC address as
destination address), but outbound VLAN traffic appears to be sent from another router attached to the
same subnet (using the Switch MAC address as source address) attached to the same subnet. Although it
appears as an asymmetric path to network hosts, the MAC address configuration feature enables Layer 3
VLAN migration. (A successful VLAN migration is achieved because the hosts do not verify that the source
MAC address and the destination MAC address are the same when communicating with the routing switch.)
Sending heartbeat packets with a configured MAC Address
On the VLAN interfaces of a routing switch, the user-defined MAC address only applies to inbound traffic. As
a result, any connected switches need to learn the new address that is included in the Ethernet frames of
outbound VLAN traffic transmitted from the routing switch.
If a connected switch does not have the newly configured MAC address of the routing switch as a
destination in its MAC address table, it floods packets to all of its ports until a return packet allows the switch
to learn the correct destination address. As a result, the performance of the switch is degraded as it tries to
send Ethernet packets to an unknown destination address.
To allow connected switches to learn the user-configured MAC address of a VLAN interface, the routing
switch can send periodic heartbeat-like Ethernet packets. The Ethernet packets contain the configured MAC
address as the source address in the packet header. IP multicast packets or Ethernet service frames are
preferred because they do not interrupt the normal operation of client devices connected on the segment.
Because the aging time of destination addresses in MAC address tables varies on network devices, you must
also configure a time interval to use for sending heartbeat packets.
Heartbeat packets are sent at periodic intervals with a specific Switch unicast MAC address in the
destination field. This MAC address is assigned to the Switch and is not used by other non- routers. Because
the heartbeat packet contains a unicast MAC address, it does not interrupt host operation. Even if you have
multiple 1-65 Static Virtual LANs (VLANs) Introducing tagged VLAN technology into networks running
untagged VLANs switches connected to the network, there is no impact on network performance because
each switch sends heartbeat packets with its configured MAC address as the destination address.
The format of a heartbeat packet is an extended Ethernet OUI frame with an extended OUI Ethertype (88B7)
and a new protocol identifier in the 5-octet protocol identifier field.
Displaying a VLAN MAC address configuration (CLI)
Syntax:
show ip-recv-mac-address
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Aruba 2530 Advanced Traffic Management Guide for
ArubaOS-Switch 16.09
