ISIS net Address configuration

Unanswered Question
Jun 25th, 2009

Can any please let me know how to configure NET address in ISIS?

Is there any document whcih provide the conversion from IP Address to NET address details?

I have this problem too.
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Giuseppe Larosa Thu, 06/25/2009 - 01:01

Hello Ganpat,

the NET address is a CLNS address and it is unique for the device

(CLNS doesn't use a different L3 address on different interfaces).

There is no corrispondence with IP address(es) on the device.

In designing your IS-IS networks routers in the same area need to be configured with a net with the same area-id.

the net is formed by two parts:



system-id has to be unique in the domain.

So you choice the net on your devices.

systems with same area-id can build L1 adjancencies

systems with different area-id can become L2 neighbors.


Hope to help


marikakis Sat, 06/27/2009 - 15:42

I think Ganpat was asking about the trick of defining a unique SysID by padding a dotted-decimal loopback IP address with zeros. On the URL posted by Guiseppe, you can see this trick occuring in the configuration of

Router 1:

interface Loopback0

ip address


router isis

net 49.0001.1720.1600.1001.00

1) pad loopback with zeros (we pad each octet to 3 digits): --->

2) rearrange the bits to 3 groups of 4 digits:> 1720.1600.1001

3) add area prefix (49.0001) and NSEL suffix (.00)


The same trick has been used in the configuration of Router2, but not in Router 3.

Giuseppe Larosa Sat, 06/27/2009 - 23:21

Hello Mary,

yes Ganpat could be asking this.

Actually, we use something similar in our customer network but we put zeroes on the left:



interface Loopback8

ip address

ip router isis evento


router isis evento

net 49.1011.0080.0034.0015.00

is-type level-1

metric-style wide




Hope to help


visva.ramu1 Fri, 11/14/2014 - 22:48

I got a NET address as like follow


Can i find? which one is area id.


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