ISIS

Intermediate system to intermediate system (ISIS) is  a link-state routing protocol, which like OSPF uses the SPF algorithm. The advantages it has over OSPF is that it is more tunable,  more flexible, handles updates more efficiently, has less design constraints, easier to adapt to IPv6. The only disadvantage is that it is more difficult to understand.

ISIS Routers are members of only one area, Level 1 routers maintain the topology table, Level 2 are considered backbone and L1&L2 are both. the metric cost is 0-63 and the default is 10

some other

NSAP Addressing
NSAP 49.0001.1111.1111.1111.00

Here the ISIS area ID is  49.0001
The System ID is 1111.1111.1111.
and the NSAP Selector byte is 00
Enabling ISIS
R0(config)#router isis
R0(config-router)#net
R0(config-router)#net 49.0001.1111.1111.1111.00
R0(config-router)#is-type level-1-2
R0(config-router)#int lo0
R0(config-if)#ip router isis
R0(config-if)#int s0/0
R0(config-if)#ip router isis
R0(config-if)#
R0(config-if)#

Test Connectivity
R0(config-if)#do ping 192.168.8.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.8.2, timeout is 2 seconds:
.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 4/6/8 ms
R0(config-if)#

Verification commands
R0(config-if)#do sh ip pro
Routing Protocol is “isis”
Invalid after 0 seconds, hold down 0, flushed after 0
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Redistributing: isis
Address Summarization:
None
Maximum path: 4
Routing for Networks:
Loopback0
Serial0/0
Routing Information Sources:
Gateway         Distance      Last Update
192.168.8.2          115      00:01:59
Distance: (default is 115)
R0(config-if)# ^Z
R0#
R0#sh clns neighbors

System Id      Interface   SNPA                State  Holdtime  Type Protocol
R1             Se0/0       *HDLC*              Up     25        L1L2 IS-IS
R0#
R0#sh clns neighbors detail

System Id      Interface   SNPA                State  Holdtime  Type Protocol
R1             Se0/0       *HDLC*              Up     22        L1L2 IS-IS
Area Address(es): 49.0001
IP Address(es):  192.168.1.2*
Uptime: 00:07:05
NSF capable
R0#
R0#sh clns interface
Serial0/0 is up, line protocol is up
Checksums enabled, MTU 1500, Encapsulation HDLC
ERPDUs enabled, min. interval 10 msec.
CLNS fast switching disabled
CLNS SSE switching disabled
DEC compatibility mode OFF for this interface
Next ESH/ISH in 17 seconds
Routing Protocol: IS-IS
Circuit Type: level-1-2
Interface number 0x1, local circuit ID 0x100
Neighbor System-ID: R1
Level-1 Metric: 10, Priority: 64, Circuit ID: R1.00
Level-1 IPv6 Metric: 10
Number of active level-1 adjacencies: 1
Level-2 Metric: 10, Priority: 64, Circuit ID: R0.00
Level-2 IPv6 Metric: 10
Number of active level-2 adjacencies: 1
Next IS-IS Hello in 9 seconds
if state UP
Serial0/1 is administratively down, line protocol is down
CLNS protocol processing disabled
Serial0/2 is administratively down, line protocol is down
CLNS protocol processing disabled
Serial0/3 is administratively down, line protocol is down
CLNS protocol processing disabled
Loopback0 is up, line protocol is up
Checksums enabled, MTU 1514, Encapsulation LOOPBACK
ERPDUs enabled, min. interval 10 msec.
CLNS fast switching disabled
CLNS SSE switching disabled
DEC compatibility mode OFF for this interface
Next ESH/ISH in 38 seconds
Routing Protocol: IS-IS
Circuit Type: level-1-2
Interface number 0x0, local circuit ID 0x1
Level-1 Metric: 10, Priority: 64, Circuit ID: R0.01
Level-1 IPv6 Metric: 10
Number of active level-1 adjacencies: 0
Level-2 Metric: 10, Priority: 64, Circuit ID: R0.01
Level-2 IPv6 Metric: 10
Number of active level-2 adjacencies: 0
Next IS-IS LAN Level-1 Hello in 6 seconds
Next IS-IS LAN Level-2 Hello in 2 seconds
R0#
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

192.168.8.0/32 is subnetted, 2 subnets
C       192.168.8.1 is directly connected, Loopback0
i L1    192.168.8.2 [115/20] via 192.168.1.2, Serial0/0
C    192.168.1.0/24 is directly connected, Serial0/0
R0#

sh runn output
!
!
!
interface Loopback0
ip address 192.168.8.1 255.255.255.255
ip router isis
!
interface Serial0/0
ip address 192.168.1.1 255.255.255.0
ip router isis
!
!
!
!
router isis
net 49.0001.1111.1111.1111.00
!
!
!
!

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