Passive Interface
In ISP and large enterprise networks, many of the distribution routers have more than 200 interfaces. Before the Default Passive-Interface feature, there were two possibilities for obtaining routing information from tall of these interfaces:
• Configure a routing protocol on the backbone interfaces and redistribute connected interfaces.
• Configure the routing protocol on all interfaces and manually set most of them as passive, which was time consuming.
The solution to this problem was to configure the routing protocol on all interfaces and manually set the passive interface command on the interfaces where adjacency was not desired. In certain networks, this meant coding 200 or more passive-interface statements. With the Default Passive Interface feature, this problem is solved by allowing all interfaces to be set as passive by default using a single passive-interface default command, then configuring individual interfaces in which adjacencies are desired using the no passive-interface command.
Usage
1. When a specific interface is configured as passive using the passive-interface command:
• The interface loses its adjacency on that interface, for example, eth1.
• The interface (eth1) is still advertised by other IS-IS speaking interfaces to their neighbors.
2. When a specific interface is configured as passive using passive-interface command followed by removing the configuration using no passive-interface command:
• The interface is IS-IS disabled and must be enabled using the ipv6 router isis command (for example, ipv6 router isis 1).
• The interface (for example, eth1) is not advertised by other IS-IS speaking interfaces to their neighbors.
3. When an interface is configured with the passive interface command:
• All interfaces lose their adjacency, except the interface with the higher index number. (For example: If eth1, eth2, eth3, and eth4 are the router interfaces, eth4 has the highest index number.)
• All interfaces are advertised by the active IS-IS speaking interface to its neighbors.
4. When an interface is configured with the no passive interface command:
• All interfaces are IS-IS disabled, except the interface that was active, and all interfaces must enable IS-IS on these interfaces using the ipv6 router isis command (for example, ipv6 router isis 1).
• All interfaces are not advertised by the active IS-IS speaking interface to its neighbors.
Topology
Figure 7-59: IS-ISv6 Passive Interface
Configuration
R1
#configure terminal | Enter configure mode. |
(config)#interface eth1 | Enter interface mode. |
(config-if)#ipv6 router isis ABC | Enable IS-ISv6 routing on an interface for area 49(ABC). |
(config-if)#ipv6 address 1000::1/64 | Configure IPv6 address on interface. |
(config-if)#exit | Exit interface mode. |
(config)#router isis ABC | Create an IS-IS routing instance for area 49 (ABC). |
(config-router)#is-type level-2-only | Configure instance as level-2-only routing. |
(config-router)#net 49.0005.0000.0000.0001.00 | Set a Network Entity Title for this instance, specifying the area address and the system ID. |
(config-router)#end | Exit the current mode and enter privilege mode. |
R2
#configure terminal | Enter configure mode. |
(config)#interface eth1 | Enter interface mode. |
(config-if)#ipv6 router isis ABC | Enable IS-ISv6 routing on an interface for area 49(ABC). |
(config-if)#ipv6 address 1000::2/64 | Configure IPv6 address on interface. |
(config-if)#exit | Exit interface mode. |
(config)#interface eth2 | Enter interface mode. |
(config-if)#ipv6 router isis ABC | Enable OSPFv3 routing on an interface and assign the Area ID 0. |
(config-if)#ipv6 address 2000::1/64 | Configure IPv6 address on interface. |
(config-if)#exit | Exit interface mode. |
(config)#router isis ABC | Create an IS-IS routing instance for area 49 (ABC). |
(config-router)#is-type level-2-only | Configure instance as level-2-only routing. |
(config-router)#net 49.0005.0000.0000.0002.00 | Set a Network Entity Title for this instance, specifying the area address and the system ID. |
(config-router)#passive-interface eth1 | Configure interface eth1 as a passive-interface. |
(config-router)#end | Exit the current mode and enter privilege mode. |
R3
#configure terminal | Enter configure mode. |
(config)#interface eth2 | Enter interface mode. |
(config-if)#ipv6 router isis ABC | Enable IS-ISv6 routing on an interface for area 49(ABC). |
(config-if)#ipv6 address 2000::2/64 | Configure IPv6 address on interface. |
(config-if)#exit | Exit interface mode. |
(config)#router isis ABC | Create an IS-IS routing instance for area 49 (ABC). |
(config-router)#is-type level-2-only | Configure instance as level-2-only routing. |
(config-router)#net 49.0005.0000.0000.0003.00 | Set a Network Entity Title for this instance, specifying the area address and the system ID. |
(config-router)#end | Exit the current mode and enter privilege mode. |
Validation
R1#show clns neighbors
Total number of L1 adjacencies: 0
Total number of L2 adjacencies: 0
Total number of adjacencies: 0
Tag ABC: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
R1#
R2#show clns neighbors
Total number of L1 adjacencies: 0
Total number of L2 adjacencies: 1
Total number of adjacencies: 1
Tag ABC: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0003 eth2 b86a.97c7.32c5 Up 7 L2 IS-IS
R2#
R3#show clns neighbors
Total number of L1 adjacencies: 0
Total number of L2 adjacencies: 1
Total number of adjacencies: 1
Tag ABC: VRF : default
System Id Interface SNPA State Holdtime Type Protocol
0000.0000.0002 eth2 b86a.97c4.31c5 Up 24 L2 IS-IS
R3#
R1#show ipv6 isis route
Codes: C - connected, E - external, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, D - discard, e - external metric
Tag ABC: VRF : default
C 1000::/64 [10]
via ::, eth1
R1#
R2#show ipv6 isis route
Codes: C - connected, E - external, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, D - discard, e - external metric
Tag ABC: VRF : default
C 1000::/64 [0]
via ::, eth1
C 2000::/64 [10]
via ::, eth2
R2#
R3#show ipv6 isis route
Codes: C - connected, E - external, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, D - discard, e - external metric
Tag ABC: VRF : default
L2 1000::/64 [10]
via fe80::ba6a:97ff:fec4:31c5, eth2
C 2000::/64 [10]
via ::, eth2
R3#
R1#show isis database verbose
Tag ABC: VRF : default
IS-IS Level-2 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0000.0001.00-00* 0x0000000E 0x0E19 931 0/0/0
Area Address: 49.0005
NLPID: 0x8E
IPv6 Address: 1000::1
Metric: 10 IPv6 1000::/64
0000.0000.0001.01-00* 0x00000009 0xE110 0 (931) 0/0/0
0000.0000.0002.00-00 0x00000011 0xABC7 440 0/0/0
Area Address: 49.0005
NLPID: 0x8E
IPv6 Address: 1000::2
Metric: 10 IS 0000.0000.0001.01
Metric: 10 IS 0000.0000.0003.01
Metric: 10 IPv6 1000::/64
Metric: 10 IPv6 2000::/64
0000.0000.0003.00-00 0x00000002 0x9ED3 439 0/0/0
Area Address: 49.0005
NLPID: 0x8E
IPv6 Address: 2000::2
Metric: 10 IS 0000.0000.0003.01
Metric: 10 IPv6 2000::/64
0000.0000.0003.01-00 0x00000001 0x2DA9 436 0/0/0
Metric: 0 IS 0000.0000.0003.00
Metric: 0 IS 0000.0000.0002.00
R1#
R1#
R2#show isis database verbose
Tag ABC: VRF : default
IS-IS Level-2 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0000.0001.00-00 0x0000000D 0x2666 879 0/0/0
Area Address: 49.0005
NLPID: 0x8E
IPv6 Address: 1000::1
Metric: 10 IS 0000.0000.0001.01
Metric: 10 IPv6 1000::/64
0000.0000.0001.01-00 0x00000009 0x11C1 821 0/0/0
Metric: 0 IS 0000.0000.0001.00
Metric: 0 IS 0000.0000.0002.00
0000.0000.0002.00-00* 0x00000012 0x669F 906 0/0/0
Area Address: 49.0005
NLPID: 0x8E
IPv6 Address: 2000::1
Metric: 10 IS 0000.0000.0003.01
Metric: 0 IPv6 1000::/64
Metric: 10 IPv6 2000::/64
0000.0000.0003.00-00 0x00000002 0x9ED3 439 0/0/0
Area Address: 49.0005
NLPID: 0x8E
IPv6 Address: 2000::2
Metric: 10 IS 0000.0000.0003.01
Metric: 10 IPv6 2000::/64
0000.0000.0003.01-00 0x00000001 0x2DA9 436 0/0/0
Metric: 0 IS 0000.0000.0003.00
Metric: 0 IS 0000.0000.0002.00
R2#
R3#show isis database verbose
Tag ABC: VRF : default
IS-IS Level-2 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
0000.0000.0001.00-00 0x0000000D 0x2666 879 0/0/0
Area Address: 49.0005
NLPID: 0x8E
IPv6 Address: 1000::1
Metric: 10 IS 0000.0000.0001.01
Metric: 10 IPv6 1000::/64
0000.0000.0001.01-00 0x00000009 0x11C1 821 0/0/0
Metric: 0 IS 0000.0000.0001.00
Metric: 0 IS 0000.0000.0002.00
0000.0000.0002.00-00 0x00000012 0x669F 905 0/0/0
Area Address: 49.0005
NLPID: 0x8E
IPv6 Address: 2000::1
Metric: 10 IS 0000.0000.0003.01
Metric: 0 IPv6 1000::/64
Metric: 10 IPv6 2000::/64
0000.0000.0003.00-00* 0x00000002 0x9ED3 440 0/0/0
Area Address: 49.0005
NLPID: 0x8E
IPv6 Address: 2000::2
Metric: 10 IS 0000.0000.0003.01
Metric: 10 IPv6 2000::/64
0000.0000.0003.01-00* 0x00000001 0x2DA9 437 0/0/0
Metric: 0 IS 0000.0000.0003.00
Metric: 0 IS 0000.0000.0002.00
R3#
Last modified date: 07-13-2023