ISIS Simple Example
From IPFlow Netflow Collector
Basic Integrated IS-IS Example
This is a simple example of IS-IS basic configuration on Cisco routers (using Dynamips and GNS3).
Author: Christophe Fillot - 18-Nov-2007
| Table of contents |
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Topology
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IOS configurations
- R0 (http://www.ipflow.utc.fr/configs/ISIS/R0.cfg)
- R1 (http://www.ipflow.utc.fr/configs/ISIS/R1.cfg)
- R2 (http://www.ipflow.utc.fr/configs/ISIS/R2.cfg)
- R3 (http://www.ipflow.utc.fr/configs/ISIS/R3.cfg)
- R4 (http://www.ipflow.utc.fr/configs/ISIS/R4.cfg)
- R5 (http://www.ipflow.utc.fr/configs/ISIS/R5.cfg)
- R6 (http://www.ipflow.utc.fr/configs/ISIS/R6.cfg)
- R7 (http://www.ipflow.utc.fr/configs/ISIS/R7.cfg)
- R8 (http://www.ipflow.utc.fr/configs/ISIS/R8.cfg)
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Dynamips/Dynagen/GNS3 configuration
You can use this configuration file (http://www.ipflow.utc.fr/configs/ISIS/isis.net) directly with Dynagen or GNS3. Change the working directory and Cisco IOS image path to match your needs.
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IS-IS areas
- - R0, R1, R2, R3 and R8 are in area 1
- - R4 and R5 are in area 2
- - R6 and R7 are in area 3
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IS-IS L1/L2
- L1 routers have only information for intra-area routing. They use the closest L2 router to reach the outside of the area.
- L2 routers have information for inter-area routing (they don't have any information about intra-area).
- L1/L2 routers have intra and inter-area routing info. So they run 2 SPF.
In this example:
- - R0, R1, R4 and R6 are L1/L2 routers
- - R2, R3, R5 and R7 are L1 routers
- - R8 is an L2 router
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IS-IS configuration
The IS-IS router process is configured as follows:
router isis <process_name> net <NET> is-type [level-1|level-1-2|level-2-only] ! (the default being "level-1-2") !
There are 3 forms of NSAP addresses (http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a00800a3e6f.shtml#wp38674), here we use the area ID/system ID format. The <NET> (Network Entity Title) is an NSAP address with a NSEL (NSAP selector) value of 0.
The NET of R0 is "01.1111.2222.0001.00" with:
- 01 = Area ID
- 1111.2222.0001 = System ID. You can use different methods to define it (MAC address, simple counter, ...).
- 00 = NSEL (always 0)
The system ID has to be unique area-wide for L1 routers, domain-wide for L2 routers.
Here is the config of IS-IS process on R0:
router isis 100 net 01.1111.2222.0001.00 !
Then, IS-IS has to be configured on each interface:
interface FastEthernet1/0 description To R2 ip address 10.0.2.1 255.255.255.252 ip router isis 100 duplex half !
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IS-IS topology
Example on a L1-only router (R3). We can see that this router has only info about its own area:
R3#sh isis 100 topology
IS-IS paths to level-1 routers
System Id Metric Next-Hop Interface SNPA
R0 20 R1 Fa1/0 ca0a.0419.001c
R2 Fa0/0 ca0b.0419.0000
R1 10 R1 Fa1/0 ca0a.0419.001c
R2 10 R2 Fa0/0 ca0b.0419.0000
R3 --
Example on a L2-only router (R8). We can see that this router has no intra-area topology information:
R8#sh isis 100 topology IS-IS paths to level-2 routers System Id Metric Next-Hop Interface SNPA R0 10 R0 Fa0/0 ca09.0419.0054 R1 10 R1 Fa1/0 ca0a.0419.0054 R8 -- R4 20 R0 Fa0/0 ca09.0419.0054 R6 20 R1 Fa1/0 ca0a.0419.0054 R7 30 R1 Fa1/0 ca0a.0419.0054
Example on a L1/L2 router (R0). This router has information about intra-area and inter-area topologies:
R0#sh isis 100 topology
IS-IS paths to level-1 routers
System Id Metric Next-Hop Interface SNPA
R0 --
R1 10 R1 Fa0/0 ca0a.0419.0000
R2 10 R2 Fa1/0 ca0b.0419.001c
R3 20 R1 Fa0/0 ca0a.0419.0000
R2 Fa1/0 ca0b.0419.001c
IS-IS paths to level-2 routers
System Id Metric Next-Hop Interface SNPA
R0 --
R1 10 R1 Fa0/0 ca0a.0419.0000
R8 10 R8 Fa3/0 ca11.04f2.0000
R4 10 R4 Se2/0 *HDLC*
R6 20 R1 Fa0/0 ca0a.0419.0000
R7 30 R1 Fa0/0 ca0a.0419.0000
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Useful commands
Neighbors:
R1#sh isis 100 neighbors System Id Type Interface IP Address State Holdtime Circuit Id R8 L2 Fa3/0 10.0.6.2 UP 9 R8.03 R0 L1 Fa0/0 10.0.1.1 UP 23 R1.02 R0 L2 Fa0/0 10.0.1.1 UP 23 R1.02 R6 L2 Se2/0 30.0.1.2 UP 23 00 R3 L1 Fa1/0 10.0.3.2 UP 9 R3.03
Link-state database (to see the prefixes announced by the routers):
R1#sh isis 100 database detail IS-IS Level-1 Link State Database: LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL R0.00-00 0x0000000B 0x8E34 689 1/0/0 Area Address: 01 NLPID: 0xCC Hostname: R0 IP Address: 10.10.0.0 Metric: 10 IP 10.0.1.0 255.255.255.252 Metric: 10 IP 10.0.2.0 255.255.255.252 Metric: 10 IP 20.0.1.0 255.255.255.252 Metric: 10 IP 10.0.5.0 255.255.255.252 Metric: 10 IP 10.10.0.0 255.255.255.255 Metric: 10 IS R1.02 Metric: 10 IS R2.03 R1.00-00 * 0x0000000A 0xAD05 1134 1/0/0 Area Address: 01 NLPID: 0xCC Hostname: R1 IP Address: 10.10.0.1 Metric: 10 IP 10.0.1.0 255.255.255.252 Metric: 10 IP 10.0.3.0 255.255.255.252 Metric: 10 IP 30.0.1.0 255.255.255.252 Metric: 10 IP 10.0.6.0 255.255.255.252 Metric: 10 IP 10.10.0.1 255.255.255.255 Metric: 10 IS R1.02 Metric: 10 IS R3.03 R1.02-00 * 0x00000007 0x0512 800 0/0/0 Metric: 0 IS R1.00 Metric: 0 IS R0.00 R2.00-00 0x00000009 0xA16D 618 0/0/0 Area Address: 01 NLPID: 0xCC Hostname: R2 IP Address: 10.10.0.2 Metric: 10 IP 10.0.4.0 255.255.255.252 Metric: 10 IP 10.0.2.0 255.255.255.252 Metric: 10 IP 10.10.0.2 255.255.255.255 Metric: 10 IS R2.03 Metric: 10 IS R3.02 R2.03-00 0x00000007 0x0214 779 0/0/0 Metric: 0 IS R2.00 Metric: 0 IS R0.00 R3.00-00 0x00000009 0x58B0 669 0/0/0 Area Address: 01 NLPID: 0xCC Hostname: R3 IP Address: 10.10.0.3 Metric: 10 IP 10.0.4.0 255.255.255.252 Metric: 10 IP 10.0.3.0 255.255.255.252 Metric: 10 IP 10.10.0.3 255.255.255.255 Metric: 10 IS R3.03 Metric: 10 IS R3.02 R3.02-00 0x00000007 0x41D1 795 0/0/0 Metric: 0 IS R3.00 Metric: 0 IS R2.00 R3.03-00 0x00000007 0x21F1 481 0/0/0 Metric: 0 IS R3.00 Metric: 0 IS R1.00 IS-IS Level-2 Link State Database: LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL R0.00-00 0x0000000E 0x8FF8 715 0/0/0 Area Address: 01 NLPID: 0xCC Hostname: R0 IP Address: 10.10.0.0 Metric: 10 IS R8.02 Metric: 10 IS R1.02 Metric: 10 IS R4.00 Metric: 10 IP 10.0.1.0 255.255.255.252 Metric: 10 IP 10.0.2.0 255.255.255.252 Metric: 20 IP 10.0.3.0 255.255.255.252 Metric: 20 IP 10.0.4.0 255.255.255.252 Metric: 10 IP 10.0.5.0 255.255.255.252 Metric: 20 IP 10.0.6.0 255.255.255.252 Metric: 10 IP 10.10.0.0 255.255.255.255 Metric: 20 IP 10.10.0.1 255.255.255.255 Metric: 20 IP 10.10.0.2 255.255.255.255 Metric: 30 IP 10.10.0.3 255.255.255.255 Metric: 10 IP 20.0.1.0 255.255.255.252 Metric: 20 IP 30.0.1.0 255.255.255.252 R1.00-00 * 0x0000000D 0xBEF7 966 0/0/0 Area Address: 01 NLPID: 0xCC Hostname: R1 IP Address: 10.10.0.1 Metric: 10 IS R1.02 Metric: 10 IS R8.03 Metric: 10 IS R6.00 Metric: 10 IP 10.0.1.0 255.255.255.252 Metric: 20 IP 10.0.2.0 255.255.255.252 Metric: 10 IP 10.0.3.0 255.255.255.252 Metric: 20 IP 10.0.4.0 255.255.255.252 Metric: 20 IP 10.0.5.0 255.255.255.252 Metric: 10 IP 10.0.6.0 255.255.255.252 Metric: 20 IP 10.10.0.0 255.255.255.255 Metric: 10 IP 10.10.0.1 255.255.255.255 Metric: 30 IP 10.10.0.2 255.255.255.255 Metric: 20 IP 10.10.0.3 255.255.255.255 Metric: 20 IP 20.0.1.0 255.255.255.252 Metric: 10 IP 30.0.1.0 255.255.255.252 R1.02-00 * 0x00000007 0x940B 660 0/0/0 Metric: 0 IS R1.00 Metric: 0 IS R0.00 R8.00-00 0x0000000C 0x30B4 948 0/0/0 Area Address: 01 NLPID: 0xCC Hostname: R8 IP Address: 10.10.0.8 Metric: 10 IS R8.03 Metric: 10 IS R8.02 Metric: 10 IP 10.0.5.0 255.255.255.252 Metric: 10 IP 10.0.6.0 255.255.255.252 Metric: 10 IP 10.10.0.8 255.255.255.255 R8.02-00 0x00000007 0xB8DA 664 0/0/0 Metric: 0 IS R8.00 Metric: 0 IS R0.00 R8.03-00 0x00000007 0xCAC6 903 0/0/0 Metric: 0 IS R8.00 Metric: 0 IS R1.00 R4.00-00 0x00000009 0xE0DF 777 0/0/0 Area Address: 02 NLPID: 0xCC Hostname: R4 IP Address: 20.20.0.4 Metric: 10 IS R0.00 Metric: 10 IP 20.0.1.0 255.255.255.252 Metric: 10 IP 20.0.2.0 255.255.255.252 Metric: 10 IP 20.20.0.4 255.255.255.255 Metric: 20 IP 20.20.0.5 255.255.255.255 R6.00-00 0x0000000B 0xE895 1086 0/0/0 Area Address: 03 NLPID: 0xCC Hostname: R6 IP Address: 30.30.0.6 Metric: 10 IS R1.00 Metric: 10 IS R7.02 Metric: 10 IP 30.0.1.0 255.255.255.252 Metric: 10 IP 30.0.2.0 255.255.255.252 Metric: 10 IP 30.30.0.6 255.255.255.255 Metric: 20 IP 30.30.0.7 255.255.255.255 R7.00-00 0x00000009 0xF27F 651 0/0/0 Area Address: 03 NLPID: 0xCC Hostname: R7 IP Address: 30.30.0.7 Metric: 10 IS R7.02 Metric: 20 IP 30.0.1.0 255.255.255.252 Metric: 10 IP 30.0.2.0 255.255.255.252 Metric: 20 IP 30.30.0.6 255.255.255.255 Metric: 10 IP 30.30.0.7 255.255.255.255 R7.02-00 0x00000007 0x0E4F 401 0/0/0 Metric: 0 IS R7.00 Metric: 0 IS R6.00
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Routing tables
R0:
R0#sh 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
20.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
i L2 20.20.0.4/32 [115/20] via 20.0.1.2, Serial2/0
i L2 20.20.0.5/32 [115/30] via 20.0.1.2, Serial2/0
C 20.0.1.0/30 is directly connected, Serial2/0
i L2 20.0.2.0/30 [115/20] via 20.0.1.2, Serial2/0
10.0.0.0/8 is variably subnetted, 11 subnets, 2 masks
C 10.10.0.0/32 is directly connected, Loopback0
i L1 10.10.0.1/32 [115/20] via 10.0.1.2, FastEthernet0/0
i L1 10.10.0.2/32 [115/20] via 10.0.2.2, FastEthernet1/0
i L1 10.10.0.3/32 [115/30] via 10.0.2.2, FastEthernet1/0
[115/30] via 10.0.1.2, FastEthernet0/0
i L2 10.10.0.8/32 [115/20] via 10.0.5.2, FastEthernet3/0
C 10.0.2.0/30 is directly connected, FastEthernet1/0
i L1 10.0.3.0/30 [115/20] via 10.0.1.2, FastEthernet0/0
C 10.0.1.0/30 is directly connected, FastEthernet0/0
i L1 10.0.6.0/30 [115/20] via 10.0.1.2, FastEthernet0/0
i L1 10.0.4.0/30 [115/20] via 10.0.2.2, FastEthernet1/0
C 10.0.5.0/30 is directly connected, FastEthernet3/0
30.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
i L2 30.30.0.6/32 [115/30] via 10.0.1.2, FastEthernet0/0
i L2 30.30.0.7/32 [115/40] via 10.0.1.2, FastEthernet0/0
i L2 30.0.2.0/30 [115/30] via 10.0.1.2, FastEthernet0/0
i L1 30.0.1.0/30 [115/20] via 10.0.1.2, FastEthernet0/0
R3:
R3#sh 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 10.0.3.1 to network 0.0.0.0
20.0.0.0/30 is subnetted, 1 subnets
i L1 20.0.1.0 [115/30] via 10.0.4.1, FastEthernet0/0
[115/30] via 10.0.3.1, FastEthernet1/0
10.0.0.0/8 is variably subnetted, 10 subnets, 2 masks
i L1 10.10.0.0/32 [115/30] via 10.0.4.1, FastEthernet0/0
[115/30] via 10.0.3.1, FastEthernet1/0
i L1 10.10.0.1/32 [115/20] via 10.0.3.1, FastEthernet1/0
i L1 10.10.0.2/32 [115/20] via 10.0.4.1, FastEthernet0/0
C 10.10.0.3/32 is directly connected, Loopback0
i L1 10.0.2.0/30 [115/20] via 10.0.4.1, FastEthernet0/0
C 10.0.3.0/30 is directly connected, FastEthernet1/0
i L1 10.0.1.0/30 [115/20] via 10.0.3.1, FastEthernet1/0
i L1 10.0.6.0/30 [115/20] via 10.0.3.1, FastEthernet1/0
C 10.0.4.0/30 is directly connected, FastEthernet0/0
i L1 10.0.5.0/30 [115/30] via 10.0.4.1, FastEthernet0/0
[115/30] via 10.0.3.1, FastEthernet1/0
30.0.0.0/30 is subnetted, 1 subnets
i L1 30.0.1.0 [115/20] via 10.0.3.1, FastEthernet1/0
i*L1 0.0.0.0/0 [115/10] via 10.0.3.1, FastEthernet1/0
R5:
R5#sh 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 20.0.2.1 to network 0.0.0.0
20.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
i L1 20.20.0.4/32 [115/20] via 20.0.2.1, FastEthernet0/0
C 20.20.0.5/32 is directly connected, Loopback0
i L1 20.0.1.0/30 [115/20] via 20.0.2.1, FastEthernet0/0
C 20.0.2.0/30 is directly connected, FastEthernet0/0
i*L1 0.0.0.0/0 [115/10] via 20.0.2.1, FastEthernet0/0
R8:
R8#sh 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
20.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
i L2 20.20.0.4/32 [115/30] via 10.0.5.1, FastEthernet0/0
i L2 20.20.0.5/32 [115/40] via 10.0.5.1, FastEthernet0/0
i L2 20.0.1.0/30 [115/20] via 10.0.5.1, FastEthernet0/0
i L2 20.0.2.0/30 [115/30] via 10.0.5.1, FastEthernet0/0
10.0.0.0/8 is variably subnetted, 11 subnets, 2 masks
i L2 10.10.0.0/32 [115/20] via 10.0.5.1, FastEthernet0/0
i L2 10.10.0.1/32 [115/20] via 10.0.6.1, FastEthernet1/0
i L2 10.10.0.2/32 [115/30] via 10.0.5.1, FastEthernet0/0
i L2 10.10.0.3/32 [115/30] via 10.0.6.1, FastEthernet1/0
C 10.10.0.8/32 is directly connected, Loopback0
i L2 10.0.2.0/30 [115/20] via 10.0.5.1, FastEthernet0/0
i L2 10.0.3.0/30 [115/20] via 10.0.6.1, FastEthernet1/0
i L2 10.0.1.0/30 [115/20] via 10.0.6.1, FastEthernet1/0
[115/20] via 10.0.5.1, FastEthernet0/0
C 10.0.6.0/30 is directly connected, FastEthernet1/0
i L2 10.0.4.0/30 [115/30] via 10.0.6.1, FastEthernet1/0
[115/30] via 10.0.5.1, FastEthernet0/0
C 10.0.5.0/30 is directly connected, FastEthernet0/0
30.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
i L2 30.30.0.6/32 [115/30] via 10.0.6.1, FastEthernet1/0
i L2 30.30.0.7/32 [115/40] via 10.0.6.1, FastEthernet1/0
i L2 30.0.2.0/30 [115/30] via 10.0.6.1, FastEthernet1/0
i L2 30.0.1.0/30 [115/20] via 10.0.6.1, FastEthernet1/0
