HP switches provide for maintaining Layer 3 VLAN configurations when migrating distribution routers in networks not centrally managed, by configuring the MAC address of the previous router on the VLAN interfaces of the HP routing switch.
HP switches use one unique MAC address for all VLAN interfaces. If you assign an IP address to a VLAN interface, ARP resolves the IP address to the MAC address of the routing switch for all incoming packets.
The Layer 3 VLAN MAC Configuration feature lets you reconfigure the MAC address used for VLAN interfaces, using the CLI. Packets addressed to the reconfigured Layer 3 MAC address, such as ARP and IP data packets, are received and processed by the HP routing switch.
Packets transmitted from the routing switch (packets originating from the router and forwarded packets) use the original HP Switch MAC address as the source MAC address in Ethernet headers.
ARP reply packets use the reconfigured MAC address in both the:
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ARP Sender MAC address field
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Source MAC address field in the Ethernet frame header
When reconfiguring the MAC address, you may specify a keepalive timeout to transmit heartbeat packets that advertise the new MAC address
By configuring the MAC address of the previously installed router as the MAC address of each VLAN interface on an HP Switch, you can swap the physical port of a router to the HP Switch after the switch has been properly configured in the network.
These are received and processed on the routing switch according to the MAC address of the previously installed router configured for each VLAN interface.
This uses the MAC address of the HP Sswitch 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:
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ARP Sender MAC address field
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Source MAC address field in the Ethernet frame header
When proxy ARP is enabled on a VLAN interface, the "gracious" 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:
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ARP Sender MAC address field
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Source MAC address field in the Ethernet frame header
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NOTE: The Virtual Router Redundancy Protocol (VRRP) is not supported on VLAN interfaces on which the MAC address for incoming traffic has been reconfigured. |
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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 HP 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.)
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 stream 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 HP 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 HP Switch unicast MAC address in the destination field. This MAC address is assigned to the HP Switch and is not used by other non-HP 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 HP 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.
When installing HP routing switches in place of existing routers in a network configuration, you can achieve Layer 3 VLAN migration by using the ip-recv-mac-address command at the VLAN configuration level to:
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Configure the MAC address of the previously installer router on each VLAN interface of an HP routing switch.
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Optionally configure the time interval to use for sending heartbeat packets with the configured MAC address.
Syntax:
[no] ip-recv-mac-address <mac-address> [interval <seconds>]Configures a VLAN interface with the specified MAC address. Enter the
noversion of the command to remove the configured MAC address and return to the original MAC address of the HP switch.(Optional) Configures the time interval, in seconds (1 to 255, default: 60), used between transmissions of heartbeat packets to all network devices configured on the VLAN.
Operating notes
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The
ip-recv-mac-addresscommand lets you configure only one MAC address for a specified VLAN. If you re-enter the command to configure another MAC address, the previously configured MAC address is overwritten. -
Enter the
noform of the command to remove a configured MAC address and restore the default MAC address of the HP switch. -
When you configure a VLAN MAC address, you may also specify a heartbeat interval. The
intervalparameter is optional.<seconds> -
Immediately after you configure a VLAN MAC address or remove a configured MAC address, a gratuitous ARP message is broadcast on the connected segment to announce the change of the IP-to-MAC address binding to all connected IP-based equipment.
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A configured VLAN MAC address supports proxy ARP and gracious ARP.
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A new MIB variable,
ifRcvAddressTable, is introduced to support VLAN MAC configuration. -
You cannot configure a VLAN MAC address using the WebAgent or menu interface. You must use the CLI.
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VRRP is not supported on a VLAN interface with a user-configured MAC address.
Configuring a MAC address
The following example shows how to configure a MAC address on VLAN 101.
HP Switch#: configure terminal HP Switch(config)#: vlan 101 HP Switch(vlan-101)#: ip-recv-mac-address 0060b0-e9a200 interval 100
Verifying a VLAN MAC address configuration
To verify the configuration of Layer 3 MAC addresses on the VLAN interfaces of a switch, use the show ip-recv-mac-address command.