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EES4710BD 10 Slots L2/L3/L4 Chassis Switch
Switch11 are edge layer 3 switches of the area, Switch5 and Switch7 are edge layer 3 switches of
the autonomous system.
To area1, layer 3 switches Switch1 and Switch2 are both in-area switches, area edge switches
Switch3 and Switch4 are responsible for reporting distance cost to all destination outside the area,
while they are also responsible for reporting the position of the AS edge layer 3 switches Switch5
and Switch7, AS exterior link-state advertisement from Switch5 and Switch7 are flooded throughout
the whole autonomous system. When ASE LSA floods in area 1, those LSA are included in the area
1 database to get the routes to network N11 and N15.
In addition, layer 3 switches, Switch3 and Switch4, must summary the topology of area 1 to the
backbone area (area 0, all non-0 areas must be connected via area 0, direct connections are not
allowed), and advertise the networks in area 1 (N1-N4) and the costs from Switch3 and Switch4 to
those networks. As the backbone area is required to maintain connection, there must be a virtual link
between backbone layer 3 switch Switch10 and Switch11. The area edge layer 3 switches exchange
summary information via the backbone layer 3 switch, each area edge layer 3 switch listens to the
summary information from the other edge layer 3 switches.
Virtual links can not only maintain the connectivity of the backbone area, but also strengthen the
backbone area. For example, if the connection between backbone layer 3 switch Switch8 and
Switch10 is cut down, the backbone area will become discontinued. The backbone area can become
more robust by establishing a virtual link between backbone layer 3 switches Switch7 and Switch10.
In addition, the virtual link between Switch7 and Switch10 provides a short path from area 3 to
layer 3 switch Switch7.
Take area 1 as an example. Assume the IP address of layer 3 switch Switch1 is 10.1.1.1, IP address
of layer 3 switch Switch2 interface VLAN2 is 10.1.1.2, IP address of layer 3 switch Switch3
interface VLAN2 is 10.1.1.3, IP address of layer 3 switch Switch4 interface VLAN2 is 10.1.1.4.
Switch1 is connecting to network N1 through Ethernet interface VLAN1 (IP address 20.1.1.1);
Switch2 is connecting to network N2 through Ethernet interface VLAN1 (IP address 20.1.2.1);
Switch3 is connecting to network N4 through Ethernet interface VLAN3 (IP address 20.1.3.1). All
the three addresses belong to area 1. Switch3 is connecting to layer 3 switch Switch6 through
Ethernet interface VLAN1 (IP address 10.1.5.1); Switch4 is connecting to layer 3 switch Switch5
through Ethernet interface VLAN1 (IP address 10.1.6.1); both two addresses belong to area 1.
Simple authentication is implemented among layer 3 switches in area1, edge layer 3 switches of
area 1 authenticate with the area 0 backbone layer 3 switches by MD5 authentication.
The followings are just configurations for layer 3 switches in area 1, configurations for layer 3
switches of the other areas are omitted. The following are the configurations of Switch1
Switch2.Switch3 and Switch4:
1)Switch1：
!Configuration of the IP address for interface vlan2
Switch1#config
Switch1(Config)# interface vlan 2
Switch1(Config-If-Vlan2)# ip address 10.1.1.1 255.255.255.0