E

Backup Links

This chapter describes how to use Backup Links on the hub. Topics described include:

■how backup links work■examples of backup links■configuring a backup link■identifying a backup link■indications of backup link activation■reactivating the primary link

How Backup Links Work

In some network configurations a critical link exists, for example between two workgroups that regularly share or exchange data over the network. To maintain the integrity of such a critical link, the HP Hub-16M offer a backup link feature. A backup link is a separate cable run between two hubs that is automatically enabled if the connection designated as the primary link fails.

The hub on which the redundant link is configured (hub A in the illustration— the “Monitoring Hub”), is responsible for monitoring the link. It sends IEEE

802.2Test packets to the hub at the other end of the link (hub B in the illustration—the “Remote Hub”) and looks for response packets from that hub. If the response packets fail to come back, the primary link is considered as having failed and the backup link, which had not been carrying any traffic, is enabled automatically. If the primary link does fail, it is automatically disabled until it can be repaired and re-enabled.

When the primary link is repaired, you must re-enable the primary port. It is not re-enabled automatically. When the primary port is enabled, the backup port is automatically disabled and returned to backup mode. See “Reactivating the Primary Link” later in this appendix.