Layer 2 And Layer 3 Redundancy; Master Election And Failover - HP ProCurve 9304M Installation And Configuration Manual

In this example, two HP devices are configured as redundant paths for VRID 1. On each of the devices, a Virtual
Router ID (VRID) is configured on a port-based VLAN. Since VSRP is primarily a Layer 2 redundancy protocol,
the VRID applies to the entire VLAN. However, you can selectively remove individual ports from the VRID if
needed.
Following Master election (described below), one of the HP devices becomes the Master for the VRID and sets
the state of all the VLAN's ports to Forwarding. The other device is a Backup and sets all the ports in its VRID
VLAN to Blocking.
If a failover occurs, the Backup becomes the new Master and changes all its VRID ports to the Forwarding state.
Other HP devices can use the redundant paths provided by the VSRP devices. In this example, three HP devices
use the redundant paths. An HP device that is not itself configured for VSRP but is connected to an HP device
that is configured for VSRP, is VSRP aware . In this example, the three HP devices connected to the VSRP
devices are VSRP aware. An HP device that is VSRP aware can failover its link to the new Master in sub-second
time, by changing the MAC address associated with the redundant path.
When you configure VSRP, make sure each of the non-VSRP HP devices connected to the VSRP devices has a
separate link to each of the VSRP devices.
NOTE: An HP device must be running software release 07.6.01b or later to be a VSRP device or a VSRP-aware
device.

Layer 2 and Layer 3 Redundancy

You can configure VSRP to provide redundancy for Layer 2 only or also for Layer 3.
• Layer 2 only – The Layer 2 links are backup up but specific IP addresses are not backed up.
• Layer 2 and Layer 3 – The Layer 2 links are backup up and a specific IP address is also backed up. Layer 3
VSRP is the same as VRRPE. However, using VSRP provides redundancy at both layers at the same time.
Routing Switches support Layer 2 and Layer 3 redundancy. You can configure a Routing Switch for either Layer 2
only or Layer 2 and Layer 3. To configure for Layer 3, specify the IP address you are backing up.
NOTE: If you want to provide Layer 3 redundancy only, disable VSRP and use VRRPE.

Master Election and Failover

• Each VSRP device advertises its VSRP priority in Hello messages. During Master election, the VSRP device
with the highest priority for a given VRID becomes the Master for that VRID. After Master election, the Master
sends Hello messages at regular intervals to inform the Backups that the Master is healthy. If there is a tie for
highest VSRP priority, the Routing Switch whose virtual routing interface has a higher IP address becomes
the master.
VSRP Failover
Each Backup listens for Hello messages from the Master. The Hello messages indicate that the Master is still
available. If the Backups stop receiving Hello messages from the Master, the election process occurs again and
the Backup with the highest priority becomes the new Master.
Each Backup waits for a specific period of time, the Dead Interval, to receive a new Hello message from the
Master. If the Backup does not receive a Hello message from the Master by the time the Dead Interval expires,
the Backup sends a Hello message of its own, which includes the Backup's VSRP priority, to advertise the
Backup's intent to become the Master. If there are multiple Backups for the VRID, each Backup sends a Hello
message.
When a Backup sends a Hello message announcing its intent to become the Master, the Backup also starts a
hold-down timer. During the hold-down time, the Backup listens for a Hello message with a higher priority than its
own.
• If the Backup receives a Hello message with a higher priority than its own, the Backup resets its Dead Interval
Configuring Metro Features
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