IS-IS: Basic Configuration
IS-IS:
· IS-IS is an Interior Gateway Protocol (IGP) developed in the 1980s as the Routing Protocol for Open System Interconnection; RFC 1142.
· When IS-IS is used to support IP, it is called Integrated IS-IS (RFC 1195)
· IS-IS is also a link-state protocol like OSPF and runs SPF Algorithm to find the best routes.
· There is no Area-0 in IS-IS, But Backbone area (level-2) is a set of L1/L2 and L2 routers and has to be contiguous
· In OSPF, each link belongs to an Area, but in IS-IS each Router belongs to an Area.
· Integrated IS-IS still requires OSI address, called a “Connection-Less Network Services”, CLNS address.
· NSAP Address:
o NSAP Address varies from 8 to 20 octets and it has three parts.
· Area Address: Area is like an IP Subnet, describing a group or location
· System ID: ID identifies a particular member in that location, like the host portion of IP address
· NSEL: Similar to a TCP port, identifies the process on the host.
o Ex: 49.0001.1111.1111.1111.00
· All Cisco routers have NSEL 00
· System-ID is always 6 bytes length
· In the OSI, 49 represent Private address.
· The NET address is a NSAP address of the Host, with the NSEL set to 00
· In IS-IS terminology, a router is called Intermediate System (IS)
· Intermediate Systems can be in 3 Levels of Routing Hierarchy.
o L1, Level1: Which is responsible for intra-area routing
o L1/L2, Level-1-2: Responsible for intra-area and inter-area routing
o L2, Level-2: Inter-area only
Let me take a small topology to configure IS-IS:
· R1 & R2: Area1
· R3 & R4: Area2
· R5: Area3
Net Address:
· R1: 49.0001.1111.1111.1111.00
· R2: 49.0001.2222.2222.2222.00
· R3: 49.0002.3333.3333.3333.00
· R4: 49.0002.4444.4444.4444.00
· R5: 49.0003.5555.5555.5555.00
Configuration:
R1(config-if)#router isis
R1(config-router)#net 49.0001.1111.1111.1111.00
R1(config-router)#is-type level-1
R1(config-router)#int ser1/0
R1(config-if)#ip router isis
R1#
R1#show clns neighbors
System Id Interface SNPA State Holdtime Type Protocol
R2 Se1/0 *HDLC* Up 27 L1 IS-IS
R1#
R2(config-if)#router isis
R2(config-router)#net 49.0001.2222.2222.2222.00
R2(config-router)#is-type level-1-2
R2(config-router)#int ser1/0
R2(config-if)#ip router isis
R2(config-if)#isis circuit-type level-1
R2(config-if)#int ser1/1
R2(config-if)#ip router isis
R2(config-if)#isis circuit-type level-2-only
R2(config-if)#
R2#show clns neighbors
System Id Interface SNPA State Holdtime Type Protocol
R1 Se1/0 *HDLC* Up 26 L1 IS-IS
R3 Se1/1 *HDLC* Up 26 L2 IS-IS
R2#
R3(config-if)#router isis
R3(config-router)#net 49.0002.3333.3333.3333.00
R3(config-router)#is-type level-2-only
R3(config-router)#int ser1/1
R3(config-if)#ip router isis
R3(config-if)#int ser1/0
R3(config-if)#ip router isis
R3(config-if)#end
R3#
R3#show clns neighbors
System Id Interface SNPA State Holdtime Type Protocol
R2 Se1/1 *HDLC* Up 25 L2 IS-IS
R4 Se1/0 *HDLC* Up 27 L2 IS-IS
R3#
R4(config-if)#router isis
R4(config-router)#net 49.0002.4444.4444.4444.00
R4(config-router)#is-type level-2-only
R4(config-router)#int ser1/0
R4(config-if)#ip router isis
R4(config-if)#int ser1/1
R4(config-if)#ip router isis
R4(config-if)#end
R4#show clns neighbors
System Id Interface SNPA State Holdtime Type Protocol
R3 Se1/0 *HDLC* Up 27 L2 IS-IS
R5 Se1/1 *HDLC* Up 23 L2 IS-IS
R4#
R5(config-if)#router isis
R5(config-router)#net 49.0003.5555.5555.5555.00
R5(config-router)#is-type level-2-only
R5(config-router)#int ser1/1
R5(config-if)#ip router isis
R5(config-if)#end
R5#show clns neighbors
System Id Interface SNPA State Holdtime Type Protocol
R4 Se1/1 *HDLC* Up 20 L2 IS-IS
R5#
R1#show clns
Global CLNS Information:
1 Interfaces Enabled for CLNS
NET: 49.0001.1111.1111.1111.00
Configuration Timer: 60, Default Holding Timer: 300, Packet Lifetime 64
ERPDU's requested on locally generated packets
Running IS-IS in IP-only mode (CLNS forwarding not allowed)
R1#
R2#show clns
Global CLNS Information:
2 Interfaces Enabled for CLNS
NET: 49.0001.2222.2222.2222.00
Configuration Timer: 60, Default Holding Timer: 300, Packet Lifetime 64
ERPDU's requested on locally generated packets
Running IS-IS in IP-only mode (CLNS forwarding not allowed)
R2#
R3#show clns
Global CLNS Information:
2 Interfaces Enabled for CLNS
NET: 49.0002.3333.3333.3333.00
Configuration Timer: 60, Default Holding Timer: 300, Packet Lifetime 64
ERPDU's requested on locally generated packets
Running IS-IS in IP-only mode (CLNS forwarding not allowed)
R3#
R4#show clns
Global CLNS Information:
2 Interfaces Enabled for CLNS
NET: 49.0002.4444.4444.4444.00
Configuration Timer: 60, Default Holding Timer: 300, Packet Lifetime 64
ERPDU's requested on locally generated packets
Running IS-IS in IP-only mode (CLNS forwarding not allowed)
R4#
R5#show clns
Global CLNS Information:
1 Interfaces Enabled for CLNS
NET: 49.0003.5555.5555.5555.00
Configuration Timer: 60, Default Holding Timer: 300, Packet Lifetime 64
ERPDU's requested on locally generated packets
Running IS-IS in IP-only mode (CLNS forwarding not allowed)
R5#
R1#show clns interface ser1/0
Serial1/0 is up, line protocol is up
Checksums enabled, MTU 1500, Encapsulation HDLC
ERPDUs enabled, min. interval 10 msec.
CLNS fast switching enabled
CLNS SSE switching disabled
DEC compatibility mode OFF for this interface
Next ESH/ISH in 28 seconds
Routing Protocol: IS-IS
Circuit Type: level-1-2
Interface number 0x0, local circuit ID 0x100
Neighbor System-ID: R2
Level-1 Metric: 10, Priority: 64, Circuit ID: R2.00
Level-1 IPv6 Metric: 10
Number of active level-1 adjacencies: 1
Next IS-IS Hello in 4 seconds
if state UP
R1#
R2#show clns interface ser1/0
Serial1/0 is up, line protocol is up
Checksums enabled, MTU 1500, Encapsulation HDLC
ERPDUs enabled, min. interval 10 msec.
CLNS fast switching enabled
CLNS SSE switching disabled
DEC compatibility mode OFF for this interface
Next ESH/ISH in 12 seconds
Routing Protocol: IS-IS
Circuit Type: level-1
Interface number 0x0, local circuit ID 0x100
Neighbor System-ID: R1
Level-1 Metric: 10, Priority: 64, Circuit ID: R2.00
Level-1 IPv6 Metric: 10
Number of active level-1 adjacencies: 1
Next IS-IS Hello in 6 seconds
if state UP
R2#
R2#show clns interface ser1/1
Serial1/1 is up, line protocol is up
Checksums enabled, MTU 1500, Encapsulation HDLC
ERPDUs enabled, min. interval 10 msec.
CLNS fast switching enabled
CLNS SSE switching disabled
DEC compatibility mode OFF for this interface
Next ESH/ISH in 3 seconds
Routing Protocol: IS-IS
Circuit Type: level-2
Interface number 0x1, local circuit ID 0x101
Neighbor System-ID: R3
Level-2 Metric: 10, Priority: 64, Circuit ID: R2.01
Level-2 IPv6 Metric: 10
Number of active level-2 adjacencies: 1
Next IS-IS Hello in 2 seconds
if state UP
R2#
R3#show clns interface ser1/1
Serial1/1 is up, line protocol is up
Checksums enabled, MTU 1500, Encapsulation HDLC
ERPDUs enabled, min. interval 10 msec.
CLNS fast switching enabled
CLNS SSE switching disabled
DEC compatibility mode OFF for this interface
Next ESH/ISH in 32 seconds
Routing Protocol: IS-IS
Circuit Type: level-1-2
Interface number 0x0, local circuit ID 0x100
Neighbor System-ID: R2
Level-2 Metric: 10, Priority: 64, Circuit ID: R3.00
Level-2 IPv6 Metric: 10
Number of active level-2 adjacencies: 1
Next IS-IS Hello in 8 seconds
if state UP
R3#
R3#show clns interface ser1/0
Serial1/0 is up, line protocol is up
Checksums enabled, MTU 1500, Encapsulation HDLC
ERPDUs enabled, min. interval 10 msec.
CLNS fast switching enabled
CLNS SSE switching disabled
DEC compatibility mode OFF for this interface
Next ESH/ISH in 18 seconds
Routing Protocol: IS-IS
Circuit Type: level-1-2
Interface number 0x1, local circuit ID 0x101
Neighbor System-ID: R4
Level-2 Metric: 10, Priority: 64, Circuit ID: R3.01
Level-2 IPv6 Metric: 10
Number of active level-2 adjacencies: 1
Next IS-IS Hello in 428 milliseconds
if state UP
R3#
R4#show clns interface ser1/1
Serial1/1 is up, line protocol is up
Checksums enabled, MTU 1500, Encapsulation HDLC
ERPDUs enabled, min. interval 10 msec.
CLNS fast switching enabled
CLNS SSE switching disabled
DEC compatibility mode OFF for this interface
Next ESH/ISH in 37 seconds
Routing Protocol: IS-IS
Circuit Type: level-1-2
Interface number 0x1, local circuit ID 0x101
Neighbor System-ID: R5
Level-2 Metric: 10, Priority: 64, Circuit ID: R4.01
Level-2 IPv6 Metric: 10
Number of active level-2 adjacencies: 1
Next IS-IS Hello in 5 seconds
if state UP
R4#
R4#show clns interface ser1/0
Serial1/0 is up, line protocol is up
Checksums enabled, MTU 1500, Encapsulation HDLC
ERPDUs enabled, min. interval 10 msec.
CLNS fast switching enabled
CLNS SSE switching disabled
DEC compatibility mode OFF for this interface
Next ESH/ISH in 22 seconds
Routing Protocol: IS-IS
Circuit Type: level-1-2
Interface number 0x0, local circuit ID 0x100
Neighbor System-ID: R3
Level-2 Metric: 10, Priority: 64, Circuit ID: R4.00
Level-2 IPv6 Metric: 10
Number of active level-2 adjacencies: 1
Next IS-IS Hello in 3 seconds
if state UP
R4#
R5#show clns interface ser1/1
Serial1/1 is up, line protocol is up
Checksums enabled, MTU 1500, Encapsulation HDLC
ERPDUs enabled, min. interval 10 msec.
CLNS fast switching enabled
CLNS SSE switching disabled
DEC compatibility mode OFF for this interface
Next ESH/ISH in 33 seconds
Routing Protocol: IS-IS
Circuit Type: level-1-2
Interface number 0x0, local circuit ID 0x100
Neighbor System-ID: R4
Level-2 Metric: 10, Priority: 64, Circuit ID: R5.00
Level-2 IPv6 Metric: 10
Number of active level-2 adjacencies: 1
Next IS-IS Hello in 5 seconds
if state UP
R5#
R1#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is 100.1.12.2 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
C 1.1.1.1 is directly connected, Loopback0
100.0.0.0/24 is subnetted, 1 subnets
C 100.1.12.0 is directly connected, Serial1/0
i*L1 0.0.0.0/0 [115/10] via 100.1.12.2, Serial1/0
R1#ping 100.1.45.5
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 100.1.45.5, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 124/138/156 ms
R1#
R2#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
100.0.0.0/24 is subnetted, 4 subnets
i L2 100.1.34.0 [115/20] via 100.1.23.3, Serial1/1
i L2 100.1.45.0 [115/30] via 100.1.23.3, Serial1/1
C 100.1.12.0 is directly connected, Serial1/0
C 100.1.23.0 is directly connected, Serial1/1
R2#
R3#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
100.0.0.0/24 is subnetted, 4 subnets
C 100.1.34.0 is directly connected, Serial1/0
i L2 100.1.45.0 [115/20] via 100.1.34.4, Serial1/0
i L2 100.1.12.0 [115/20] via 100.1.23.2, Serial1/1
C 100.1.23.0 is directly connected, Serial1/1
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Loopback0
R3#
R4#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
100.0.0.0/24 is subnetted, 4 subnets
C 100.1.34.0 is directly connected, Serial1/0
C 100.1.45.0 is directly connected, Serial1/1
i L2 100.1.12.0 [115/30] via 100.1.34.3, Serial1/0
i L2 100.1.23.0 [115/20] via 100.1.34.3, Serial1/0
4.0.0.0/32 is subnetted, 1 subnets
C 4.4.4.4 is directly connected, Loopback0
R4#
R5#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
100.0.0.0/24 is subnetted, 4 subnets
i L2 100.1.34.0 [115/20] via 100.1.45.4, Serial1/1
C 100.1.45.0 is directly connected, Serial1/1
i L2 100.1.12.0 [115/40] via 100.1.45.4, Serial1/1
i L2 100.1.23.0 [115/30] via 100.1.45.4, Serial1/1
5.0.0.0/32 is subnetted, 1 subnets
C 5.5.5.5 is directly connected, Loopback0
R5#ping 100.1.12.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 100.1.12.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 88/120/152 ms
R5#
