One of the virtual devices of Dynamips– Virtual Bridge
Thursday, September 27th, 2007 | Dynamips-Links
One of the virtual devices of Dynamips– Virtual Bridge www.ciscosim.net
One of the virtual devices of Dynamips– Virtual Bridge
One of the virtual devices of Dynamips– Virtual Bridge
Dynamips can also provide us some virtual devices besides simulation of routers. By the network of these devices, we can save a lot of system resources.
The most common virtual device—Virtual Bridge?
Among the network devices, virtual bridge is on the second layer. It transmit frame selectively through MAC address learning. It can divide conflict domain but not broadcast domain. Layer 2 switch is the developing of bridges, which are sometimes referred to as multi-port bridge. Is the Virtual Bridge provided by Dynamips a real bridge? Let’s try it by the following experiment?
First build a simple network:
2007-9-26 01:56
Related documents:
R1.bat
dynamips -P 3600 -t 3620 -i 0 -G ghost_ram_3620 –idle-pc 0×60378158 -p 0:NM-4E -s 0:0:udp:20000:127.0.0.1:20001 -b vb.cfg C3620-I-.BIN
R2.bat
dynamips -P 3600 -t 3620 -i 1 -G ghost_ram_3620 –idle-pc 0×60378158 -p 0:NM-4E -s 0:0:udp:20002:127.0.0.1:20003 C3620-I-.BIN
R3.bat
dynamips -P 3600 -t 3620 -i 2 -G ghost_ram_3620 –idle-pc 0×60378158 -p 0:NM-4E -s 0:0:udp:20004:127.0.0.1:20005 C3620-I-.BIN
vb.cfg
I0:udp:20001:127.0.0.1:20000
I1:udp:20003:127.0.0.1:20002
I2:udp:20005:127.0.0.1:20004
Configuration explanation:
1?Use -s 0:0:udp:20000:127.0.0.1:20001 to define the local interface be 20000, and the opposite one be the interface 20001 of virtual bridge on R1
2?Use -s 0:0:udp:20002:127.0.0.1:20003 to define the local interface be 20002, and the opposite one be the interface 20003 of virtual bridge on R2
3?Use -s 0:0:udp:20004:127.0.0.1:20005 to define the local interface be 20004, and the opposite one be the interface 20005 of virtual bridge on R3
3?Define the local and opposite interface of virtual bridge in vb.cfg configuration file.
4?Configure IP address and start it in the corresponding interface of R1,R2 and R3.
Experiment steps:
1?Ping R1, R2 and R3 between each of them, when you succeed, you can connect many routers with virtual bridge. Thus you can save a NM-16ESW module or a VMWARE virtual NIC.
2?Ping broadcast address 10.0.0.255?R2?R3 from R1, and all are responded. This means that Virtual Bridge support broadcasting.
3?In the further studying, we want to know whether Virtual Bridge has MAC address study and selective transmit function. When guaranteed each arp-cashe of R1?R2 and R3 has each other’s MAC address, ping R1 from R3, if Virtual Bridge can transmit selectively, R2 will not receive any frame.
But, this is not the case. When we capture local package with CommView 4.1 and check UDP head with StripUDP, we find that every ICMP message from R3 to R1 would appear in UDP interfaced for three times, that is it appears in 20004->20005?20001->20000?20003->20002. 20004->20005 is a message from R3 to Virtual Bridge, 20001->20000 from Virtual Bridge to R1, and 20003->20002 from Virtual Bridge to R2. That is to say, Virtual Bridge transmits the received frame to all the interfaces, not selectively to R1. Thus it is not Bridge, but HUB.
Conclusion:
1?With Virtual Bridge we can connect more routers with fewer resources.
2?Virtual Bridge acts more like HUB than bridge, so call it Virtual HUB would be better.
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