
120
link between backbone layer3 Switch10 and Switch11. The area edge layer3 switches exchange
summary information via the backbone layer3 switch, each area edge layer3 switch listens to the
summary information from the other edge layer3 switches.
Virtual link can not only maintain the connectivity of the backbone area, but also strengthen
the backbone area. For example, if the connection between backbone layer3 SwitchG and
Switch10 is cut down, the backbone area will become incontinuous. The backbone area can
become more robust by establishing a virtual link between backbone layer3 switches SwitchF
and Switch10. In addition, the virtual link between SwitchF and Switch10 provide a short path
from area 3 to layer3 SwitchF.
Take area 1 as an example. Assume the IP address of layer3 SwitchA is 10.1.1.1, IP
address of layer3 SwitchB interface VLAN2 is 10.1.1.2, IP address of layer3 SwitchC interface
VLAN2 is 10.1.1.3, IP address of layer3 SwitchD interface VLAN2 is 10.1.1.4. SwitchA is
connecting to network N1 through Ethernet interface VLAN1 (IP address 20.1.1.1); SwitchB is
connecting to network N2 through Ethernet interface VLAN1 (IP address 20.1.2.1); SwitchC is
connecting to network N4 through Ethernet interface VLAN3 (IP address 20.1.3.1). All the three
addresses belong to area 1. SwitchC is connecting to layer3 SwitchE through Ethernet interface
VLAN1 (IP address 10.1.5.1); SwitchD is connecting to layer3 SwitchD through Ethernet
interface VLAN1 (IP address 10.1.6.1); both two addresses belong to area 1. Simple
authentication is implemented among layer3 switches in area1, edge layer3 switches of area 1
authenticate with the area 0 backbone layer3 switches by MD5 authentication..
The followings are just configurations for all layer3 switches in area 1, configurations for
layer3 switches of the other areas are omitted. The following are the configurations of SwitchA
SwitchB.SwitchC and SwitchD:
1)SwitchA
:
Configure IP address for interface vlan2
SwitchA#config
SwitchA(config)# interface vlan 2
SwitchA(config-If-Vlan2)# ip address 10.1.1.1 255.255.255.0
SwitchA(config-If-Vlan2)#exit
Enable OSPF protocol, configure the area number for interface vlan2.
SwitchA(config)#router ospf
SwitchA(config-router)#network 10.1.1.0/24 area 1
SwitchA(config-router)#exit
Configure simple key authentication.
SwitchA(config)#interface vlan 2
SwitchA(config-If-Vlan2)#ip ospf authentication
SwitchA(config-If-Vlan2)#ip ospf authentication-key DCS
SwitchA(config-If-Vlan2)exit