Hitachi GR2000 - Manual (Page 280)

When you use the bridge function of GR2000, pay attention to the following.
4.11.1 Protocol and Topology Restrictions
4.11.1.1 Spanning-Tree Protocol
When you use the spanning-tree protocol, ensure that all the bridge-connected
routers and bridges are set to use the same level of the spanning-tree protocol
(IEEE802.1).
The following timers used for the spanning tree in this router are set so that they
operate earlier than the normal bridge router. If operation is carried out in a network
in which a bridge router other than this router is combined, adjust the timer values
by using the spanning tree configuration definition if any inconvenience occurs
because of the relationship with the other router.
Timer type Default value of this router Normal default value
Max age time 18 20
Forward delay time 10 15