dynamips lab:Configuring Virtual Bridge
After the following configuration, the fa0/0 of R1 、 R2 、 R3 are then in a conflict domain, like joining to a switch. When the address of the three interfaces on the same segment, they can ping with each other.

Methods and steps:
bridge.conf1:udp:10000:127.0.0.1:100012:udp:10002:127.0.0.1:100033:udp:10004:127.0.0.1:10005
1 、 set up text file named bridge.conf1, with the following contents:
bridge.conf1:udp:10000:127.0.0.1:100012:udp:10002:127.0.0.1:100033:udp:10004:127.0.0.1:10005
2 、 Designate a dynamips example to execute the text in step 1.
R4—dynamips -i 0 -T 2004 -b bridge.conf 1/home/dynamips/image.bin
R1—dynamips -i 1 -T 2001 -X -s 0:0:udp:10001:127.0.0.1:10000 /home/dynamips/image.bin
R2—dynamips -i 2 -T 2002 -X -s 0:0:udp:10003:127.0.0.1:10002 /home/dynamips/image.bin
R3—dynamips -i 3 -T 2003 -X -s 0:0:udp:10005:127.0.0.1:10004 /home/dynamips/image.bin