Cisco CCNP BSCI 642-901 Certification Exam Review:

Five ISIS Details You Must Know!

By Chris Bryant, CCIE #12933

1. The ISIS backbone is a contiguous collection of L2 and/or L2/L1 routers.  The ISIS backbone is not assigned a number, as the OSPF backbone is.

2. After configuring the ISIS process with a NET address, the interface(s) running ISIS must be configured with ip router isis.  A typical configuration:

interface Serial0/1
 ip address 172.12.123.2 255.255.255.0
 ip router isis
 encapsulation frame-relay
 frame-relay map clns 105 broadcast
 frame-relay map clns 104 broadcast
 frame-relay map ip 172.12.123.4 104 broadcast
 frame-relay map ip 172.12.123.5 105 broadcast
 no frame-relay inverse-arp

router isis
 net 49.0002.2222.2222.2222.00

3. To verify adjacencies, run show clns neighbors.

R2#show clns neighbors
System Id      Interface      SNPA                State  Holdtime  Type Protocol
R4                  Se0/1       DLCI 104                Up     29              L2    IS-IS
R5                  Se0/1       DLCI 105                Up     9                L2     IS-IS

4. ISIS allows route summarization with the summary-address command.

R5(config)#router isis
R5(config-router)#summary-address 148.0.0.0 252.0.0.0

5. There are three ISIS Hello Types:

ESH:  ES Hello – Sent by End Systems to discover a router.

ISH:  IS Hello – Sent by Intermediate Systems to announce their presence.  End Systems listen for these.

IIH:  IS-to-IS Hello – Send by one IS to be heard by another IS. These hellos makes IS-IS adjacencies possible.

To your success,

Chris Bryant

CCIE #12933

chris@thebryantadvantage.com