利用Bridge的方式穿透Router連通兩端Switch 802.1q Trunk

最近在vlab討論區上有人提出一個很有趣的問題，想要透過Router來建立Trunking(SW1 - R1 - R2 - R3 - SW2)，我原本的想法是很簡單，Router兩邊的介面直接設定trunk，然後在子介面上設定IP即可。後來利用Dynamips實作，才突然發現如果在Router兩邊的介面上設定相同的子介面(對應vlan)，將會發生同一段network在同一個Router上不同的介面，這在Router IOS上是不允許的…所以我後來想到一個方式，那就是利用bridge-group的方式，將兩邊同個vlan對應的子介面設定為同一個bridge-group即可，然後最重要的是要再建立bvi interface。

以下是個人設定的組態，供各位參考：

hostname R1
bridge irb
interface FastEthernet0/0
description Connect to R2
no ip address
duplex auto
speed auto
!
interface FastEthernet0/0.10
encapsulation dot1Q 10
bridge-group 10
!
interface FastEthernet0/0.20
encapsulation dot1Q 20
bridge-group 20
!
interface FastEthernet0/0.99
encapsulation dot1Q 99 native
bridge-group 99
!
interface FastEthernet1/0
description Connect to SW1
no ip address
duplex auto
speed auto
!
interface FastEthernet1/0.10
encapsulation dot1Q 10
bridge-group 10
!
interface FastEthernet1/0.20
encapsulation dot1Q 20
bridge-group 20
!
interface FastEthernet1/0.99
encapsulation dot1Q 99 native
bridge-group 99
!
interface BVI10
ip address 10.10.10.1 255.255.255.0
!
interface BVI20
ip address 20.20.20.1 255.255.255.0
!
interface BVI99
ip address 99.99.99.1 255.255.255.0
!
router ospf 1
log-adjacency-changes
network 99.99.99.0 0.0.0.255 area 0
!
bridge 10 protocol vlan-bridge
bridge 10 route ip
bridge 20 protocol vlan-bridge
bridge 20 route ip
bridge 99 protocol vlan-bridge
bridge 99 route ip

====================================================================

hostname R2
bridge irb
!
interface FastEthernet0/0
description Connect to R1
no ip address
duplex auto
speed auto
!
interface FastEthernet0/0.10
encapsulation dot1Q 10
bridge-group 10
!
interface FastEthernet0/0.20
encapsulation dot1Q 20
bridge-group 20
!
interface FastEthernet0/0.99
encapsulation dot1Q 99 native
bridge-group 99
!
interface FastEthernet1/0
description Connect to R3
no ip address
duplex auto
speed auto
!
interface FastEthernet1/0.10
encapsulation dot1Q 10
bridge-group 10
!
interface FastEthernet1/0.20
encapsulation dot1Q 20
bridge-group 20
!
interface FastEthernet1/0.99
encapsulation dot1Q 99 native
bridge-group 99
!
interface BVI10
ip address 10.10.10.2 255.255.255.0
!
interface BVI20
ip address 20.20.20.2 255.255.255.0
!
interface BVI99
ip address 99.99.99.2 255.255.255.0
!
router ospf 1
log-adjacency-changes
network 99.99.99.0 0.0.0.255 area 0
!
bridge 10 protocol vlan-bridge
bridge 10 route ip
bridge 20 protocol vlan-bridge
bridge 20 route ip
bridge 99 protocol vlan-bridge
bridge 99 route ip

====================================================================

hostname R3
bridge irb
!
interface FastEthernet0/0
no ip address
duplex auto
speed auto
!
interface FastEthernet0/0.10
encapsulation dot1Q 10
bridge-group 10
!
interface FastEthernet0/0.20
encapsulation dot1Q 20
bridge-group 20
!
interface FastEthernet0/0.99
description Connect to R2
encapsulation dot1Q 99 native
bridge-group 99
!
interface FastEthernet1/0
description Connect to SW2
no ip address
duplex auto
speed auto
!
interface FastEthernet1/0.10
encapsulation dot1Q 10
bridge-group 10
!
interface FastEthernet1/0.20
encapsulation dot1Q 20
bridge-group 20
!
interface FastEthernet1/0.99
encapsulation dot1Q 99
bridge-group 99
!
interface BVI10
ip address 10.10.10.3 255.255.255.0
!
interface BVI20
ip address 20.20.20.3 255.255.255.0
!
interface BVI99
ip address 99.99.99.3 255.255.255.0
!
ip classless
!
ip http server
no ip http secure-server
!
router ospf 1
log-adjacency-changes
network 99.99.99.0 0.0.0.255 area 0
!
bridge 10 protocol vlan-bridge
bridge 10 route ip
bridge 20 protocol vlan-bridge
bridge 20 route ip
bridge 99 protocol vlan-bridge
bridge 99 route ip