Automatic Network Verification - HP 10:10 LAN Bridge MB Installation And Reference Manual

Backup Bridge. Backup bridges are held in reserve and do not forward traffic. If an
active bridge fails, the bridges will use STP to automatically reconfigure themselves.
As a result, a backup bridge may become a forwarding bridge. In figure 6-2, if either
Bridge 1 or Bridge 2 fails, Bridge 3 will reconfigure to forward traffic between subnets
B and C.
If the HP 10:10 LAN Bridge MB is functioning as a root or forwarding bridge, it will discard or
forward packets based on its operating state, address table entries, and wildcard filters. If the
bridge is functioning as a backup bridge, all received packets (except those explicitly addressed
to the bridge) are discarded.
For more information on how the spanning tree algorithm works, see the specification from the
IEEE, 802.1d MAC Bridges.

Automatic Network Verification

(why the bridge's ports must be terminated for self-test to pass)
One of the features of the HP 10:10 LAN Bridge MB is that during self-test and initialization, it
automatically tests its network ports to verify that the networks are properly attached to the
bridge and are properly terminated (for example, 50-ohm terminators are installed at both ends
of a thin coax LAN segment).
One result of this feature though, is that the bridge will not pass self-test unless the attached
networks are good, or the bridge's network ports are terminated with HP loopback connectors.
See appendix A, "Cables and Connectors" for information on the loopback connectors.
6-8 How the Bridge Works