KB.15.15

About configuring peer-keepalive links

Distributed trunking uses UDP-based peer-keepalive messages to determine if an ISC link failure is

at the link level or the peer has completely failed. The following operating rules must be followed

to use peer-keepalive links:

• An IP address must be configured for a peer-keepalive VLAN interface and the same IP address

must be configured as a peer-keepalive destination on the peer DT switch.

• There must be logical Layer 3 connectivity between the two IP addresses configured for the

peer-keepalive VLAN interface.

• Only peer-keepalive messages are sent over the peer-keepalive VLAN (Layer 3 link.) These

messages indicate that the DT switch from which the message originates is up and running.

No data or synchronization traffic is sent over the peer-keepalive VLAN.

• STP cannot run on peer-keepalive links.

• The peer-keepalive VLAN can have only one member port. If you attempt to assign a second

member port to this VLAN, or if you attempt to configure a VLAN that has more than one

member port as a peer-keepalive VLAN, this message displays:

A keepalive VLAN can only have one member port.

• A port cannot be a member of a regular VLAN and a peer-keepalive VLAN. An error message

displays:

A port cannot simultaneously be a member of a keepalive and a

non-keepalive VLAN.

• The DEFAULT VLAN cannot be a peer-keepalive VLAN. An error message displays:

The default VLAN cannot be configured as a keepalive VLAN.

NOTE: If you are upgrading your software from a version prior to K.15.05.xxxxx with a

configuration that violates any of the above operating rules, the following message displays:

DT: Keepalive mis-configuration detected. Reconfigure the keepalive

VLAN.

You must then manually correct the configuration.

DT switches have an operational role that depends on the system MAC address. The bridge with

the lowest system MAC address acts as the DT primary device; the other device is the DT secondary

device. These roles are used to determine which device forwards traffic when the ISC link is down.

162 Port Trunking