1.组网需求
Switch A、Switch B、Switch C和Switch D都运行IS-IS路由协议以实现互连，它们属于同一区域10，网络类型为广播网（以太网）。
Switch A和Switch B是Level-1-2交换机，Switch C为Level-1交换机，Switch D为Level-2交换机。要求通过改变接口的DIS优先级，将Switch A配置为Level-1-2的DIS。
2.配置步骤
1）配置ISIS
SW A [SwitchA] isis 1 [SwitchA-isis-1] network-entity 10.0000.0000.0001.00 [SwitchA-isis-1] quit [SwitchA] interface vlan-interface 100 [SwitchA-Vlan-interface100] isis enable 1 SW B [SwitchB] isis 1 [SwitchB-isis-1] network-entity 10.0000.0000.0002.00 [SwitchB-isis-1] quit [SwitchB] interface vlan-interface 100 [SwitchB-Vlan-interface100] isis enable 1 SW C [SwitchC] isis 1 [SwitchC-isis-1] network-entity 10.0000.0000.0003.00 [SwitchC-isis-1] is-level level-1 [SwitchC-isis-1] quit [SwitchC] interface vlan-interface 100 [SwitchC-Vlan-interface100] isis enable 1 SW D [SwitchD] isis 1 [SwitchD-isis-1] network-entity 10.0000.0000.0004.00 [SwitchD-isis-1] is-level level-2 [SwitchD-isis-1] quit [SwitchD] interface vlan-interface 100 [SwitchD-Vlan-interface100] isis enable 1
2）查看当前配置
# 查看Switch A的IS-IS邻居信息。 [SwitchA] display isis peer Peer information for IS-IS(1) ---------------------------- System ID: 0000.0000.0002 Interface: Vlan-interface100 Circuit Id: 0000.0000.0003.01 State: Up HoldTime: 21s Type: L1(L1L2) PRI: 64 System ID: 0000.0000.0003 Interface: Vlan-interface100 Circuit Id: 0000.0000.0003.01 State: Up HoldTime: 27s Type: L1 PRI: 64 System ID: 0000.0000.0002 Interface: Vlan-interface100 Circuit Id: 0000.0000.0004.01 State: Up HoldTime: 28s Type: L2(L1L2) PRI: 64 System ID: 0000.0000.0004 Interface: Vlan-interface100 Circuit Id: 0000.0000.0004.01 State: Up HoldTime: 30s Type: L2 PRI: 64
# 显示Switch A的IS-IS接口信息。 [SwitchA] display isis interface Interface information for IS-IS(1) ---------------------------------- Interface: Vlan-interface100 Index IPv4 state IPv6 state Circuit ID MTU Type DIS 00001 Up Down 1 1497 L1/L2 No/No # 显示Switch C的IS-IS接口信息。 [SwitchC] display isis interface Interface information for IS-IS(1) ---------------------------------- Interface: Vlan-interface100 Index IPv4 state IPv6 state Circuit ID MTU Type DIS 00001 Up Down 1 1497 L1/L2 Yes/No # 显示Switch D的IS-IS接口信息。 [SwitchD] display isis interface Interface information for IS-IS(1) ---------------------------------- Interface: Vlan-interface100 Index IPv4 state IPv6 state Circuit ID MTU Type DIS 00001 Up Down 1 1497 L1/L2 No/Yes
从接口信息中可以看到，在使用缺省DIS优先级的情况下，Switch C为Level-1的DIS，Switch D为Level-2的DIS。Level-1和Level-2的伪节点分别是0000.0000.0003.01和0000.0000.0004.01。
3）修改DIS
# 配置Switch A的DIS优先级。 [SwitchA] interface vlan-interface 100 [SwitchA-Vlan-interface100] isis dis-priority 100 # 查看Switch A的IS-IS邻居信息。 [SwitchA] display isis peer Peer information for IS-IS(1) ---------------------------- System ID: 0000.0000.0002 Interface: Vlan-interface100 Circuit Id: 0000.0000.0001.01 State: Up HoldTime: 21s Type: L1(L1L2) PRI: 64 System ID: 0000.0000.0003
Interface: Vlan-interface100 Circuit Id: 0000.0000.0001.01 State: Up HoldTime: 27s Type: L1 PRI: 64 System ID: 0000.0000.0002 Interface: Vlan-interface100 Circuit Id: 0000.0000.0001.01 State: Up HoldTime: 28s Type: L2(L1L2) PRI: 64 System ID: 0000.0000.0004 Interface: Vlan-interface100 Circuit Id: 0000.0000.0001.01 State: Up HoldTime: 30s Type: L2 PRI: 64 # 查看Switch A的IS-IS接口信息。 [SwitchA] display isis interface Interface information for IS-IS(1) ---------------------------------- Interface: Vlan-interface100 Index IPv4 state IPv6 state Circuit ID MTU Type DIS 00001 Up Down 1 1497 L1/L2 Yes/Yes
从上述信息中可以看到，在改变IS-IS接口的DIS优先级后，Switch A立即成为Level-1-2的DR（DIS），且伪节点是0000.0000.0001.01。