ISIS net Address configuration

ganpatspatil · ‎06-25-2009

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?

Giuseppe Larosa · ‎06-25-2009

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:

area-id

system-id

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.

see

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a0080093f38.shtml

Hope to help

Giuseppe

marikakis · ‎06-27-2009

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 172.16.1.1 255.255.255.255

!

router isis

net 49.0001.1720.1600.1001.00

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

172.16.1.1 ---> 172.016.001.001

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

172.016.001.001---> 1720.1600.1001

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

49.0001.1720.1600.1001.00

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

Giuseppe Larosa · ‎06-27-2009

Hello Mary,

yes Ganpat could be asking this.

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

example

!

interface Loopback8

ip address 10.80.34.15 255.255.255.255

ip router isis evento

!

router isis evento

net 49.1011.0080.0034.0015.00

is-type level-1

metric-style wide

log-adjacency-changes

display-route-detail

!

Hope to help

Giuseppe

visva.ramu1 · ‎11-14-2014

I got a NET address as like follow

59.346e.8012.3456.0020.1001.0105

Can i find? which one is area id.

ashifurruet · ‎08-27-2021

u can understand from below example:

A router has a Network Entity Title (NET) of 49.001a.1122.3344.5566.00. To what area does this router belong, and what is its system ID?

The area is 49.001a. The router's system ID is 1122.3344.5566. The easiest way to figure this out is to start from the right and work towards the left. The last two numbers of the NET are the NSEL; they are always 00 on a router. The next 12 numbers (separated into 3 groups of 4 numbers) are the system ID. On Cisco routers, the system ID is always this length—6 bytes. Anything to the left of the system ID is the area ID.

from ref article preview, link below

https://www.ciscopress.com/articles/article.asp?p=101756

ashifurruet · ‎08-27-2021

Hi there, can you share from where or how i can get area prefix number? and if this area prefix is just like area of ospf how do i convert area 165 to area prefix in isis?

ashifurruet · ‎08-27-2021

Example Net Address: 49.0001.1921.6800.1002.00

The IS-IS address consists of three parts:

Area identifier: The first three bytes are the area ID. The first byte of this example — 49 — is the address family identifier (AFI) of the authority, which is equivalent to the IP address space that is assigned to an autonomous system. The AFI value 49 is what IS-IS uses for private addressing, which is the equivalent of RFC 1918 address space for IP protocols.
The second two bytes of the area ID — 0001 — represent the IS-IS area number. In this example, the area number is 1.
System identifier: The next six bytes identify the node (that is, the router) on the network. The system identifier is equivalent to the host or address portion on an IP address.
Although you can choose any value for the system identifier, a commonly used method is to use binary-coded decimal (BCD) which involves taking the router’s IP address (the address you assigned to the lo0 loopback interface), filling in all leading zeros, and then repositioning the decimal points to form three two-byte numbers.
In this example, if you pad the IP address 192.168.1.2 with zeros, the result is 192.168.001.002. Rearranging the decimal points gives you 1921.6800.1002.
NET selector: The final two bytes are the NET selector (NSEL). For IS-IS, they must always be 00, to indicate “this system.