A while back, a netizen I’m quite familiar with asked me how to configure bridging on a Cisco router. Due to work commitments at the time, I only gave him a brief overview. Today, I’ll share the complete configuration commands for setting up bridging on a Cisco router. Through this example, you can learn how to use a router to connect several networks together.
First, let’s talk about the concept of bridging. It refers to the process of forwarding network data packets based on the link-layer address of the OSI network model. It operates at Layer 2 of the OSI model. Typical switches and bridges have this bridging function. For a switch, it has an internal port-to-MAC mapping table, which isolates collision domains. Simply put, a bridge can connect two different physical LANs; it is a store-and-forward device that achieves LAN interconnection at the link layer. A bridge receives a MAC frame from one LAN, decapsulates, checks, and verifies it, then reassembles it according to the format of the other LAN and sends it to its physical layer.
Below is the configuration command for a router bridge:
router#sh ru
Building configuration…
Current configuration:
!
version 12.1
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname router
!
enable secret 5 $1$BE0q$hj.WBtIBYppMX3zyfaPbR1
!
!
!
!
!
memory-size iomem 25
ip subnet-zero
no ip routing
!
!
!
!
interface Serial0
description 128k DL546267 connect to SZ
ip address 198.127.18.4 255.255.255.0
no ip route-cache
no fair-queue
bridge-group 1
!
interface FastEthernet0
ip address 198.127.18.3 255.255.255.0
no ip route-cache
speed auto
bridge-group 1
!
ip classless
no ip http server
!
bridge 1 protocol ieee bridge 1 route ip
!
line con 0
transport input none
line aux 0
line vty 0 4
password csl
login
!
no scheduler allocate
end