сделал как написано у вас
interface FastEthernet0/0
ip address 10.200.200.1 255.255.255.0
duplex auto
speed auto
bridge-group 1

interface Serial1/0
no ip address
no fair-queue
bridge-group 1

bridge 1 protocol ieee

получаем: sh int se 1/0
Serial1/0 is up, line protocol is down
Hardware is CD2430 in sync mode
MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input 00:05:01, output 00:00:06, output hang 17:32:44
Last clearing of "show interface" counters 17:07:37
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue :0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
117 packets input, 15636 bytes, 0 no buffer
Received 114 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
6166 packets output, 147977 bytes, 0 underruns
0 output errors, 0 collisions, 2055 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up


какие идеи?