IS-IS questions

mikearama

Let's start with this one:

How do companies that employ IS-IS come up with the net address? I get that 49 at the beginning of the area portion denotes a private address. But from there...

For example: 49.0004.30bc.1511.3090.c7d8.00

so 49.0004.30bc is supposed to be the area ID. Where'd that come from? Is it arbitrary, based on the whim of the net admin?

and 1511.3090.c7d8 is the mac, yeah? Fair enough.

The NSEL... 00 denotes a router. What other numbers are usable? Could I pick 12 if I wanted? 24? 69?

Preciate the help, techies.

nicklauscombs

mikearama wrote:

so 49.0004.30bc is supposed to be the area ID. Where'd that come from? Is it arbitrary, based on the whim of the net admin?

I would imagine for the area ID a scheme would be thought up that would make sense in context of seeing the other areas and has some meaning to the administrators, obviously 49.0004 makes more sense for area 4 then 49.0004.30bc

miller811

mikearama wrote:

Let's start with this one:

How do companies that employ IS-IS come up with the net address? I get that 49 at the beginning of the area portion denotes a private address. But from there...

For example: 49.0004.30bc.1511.3090.c7d8.00

so 49.0004.30bc is supposed to be the area ID. Where'd that come from? Is it arbitrary, based on the whim of the net admin?

and 1511.3090.c7d8 is the mac, yeah? Fair enough.

The NSEL... 00 denotes a router. What other numbers are usable? Could I pick 12 if I wanted? 24? 69?

Preciate the help, techies.

You should solve this by starting at the right
The NSEL is always 2 digits (This field is always 00 in a NET address)
The system ID is always the next 12 number (right to left) (used to route inside the area)
The area id is what is remaining (used to route between areas) (the area ID must be at least 2 numbers)

nicklauscombs

miller811 wrote:

mikearama wrote:

Let's start with this one:

How do companies that employ IS-IS come up with the net address? I get that 49 at the beginning of the area portion denotes a private address. But from there...

For example: 49.0004.30bc.1511.3090.c7d8.00

so 49.0004.30bc is supposed to be the area ID. Where'd that come from? Is it arbitrary, based on the whim of the net admin?

and 1511.3090.c7d8 is the mac, yeah? Fair enough.

The NSEL... 00 denotes a router. What other numbers are usable? Could I pick 12 if I wanted? 24? 69?

Preciate the help, techies.

You should solve this by starting at the right
The NSEL is always 2 digits (This field is always 00 in a NET address)
The system ID is always the next 12 number (right to left) (used to route inside the area)
The area id is what is remaining (used to route between areas) (the area ID must be at least 2 numbers)

I think he understands how to read the address, his question seems more to be why would you choose .0004.30bc as your area ID, I think a lot of it has to do with just not being used to seeing IS-IS addressing

tech-airman

mikearama wrote:

Let's start with this one:

How do companies that employ IS-IS come up with the net address? I get that 49 at the beginning of the area portion denotes a private address. But from there...

For example: 49.0004.30bc.1511.3090.c7d8.00

so 49.0004.30bc is supposed to be the area ID. Where'd that come from? Is it arbitrary, based on the whim of the net admin?

and 1511.3090.c7d8 is the mac, yeah? Fair enough.

The NSEL... 00 denotes a router. What other numbers are usable? Could I pick 12 if I wanted? 24? 69?

Preciate the help, techies.

mikearama,

Let's start from the beginning. Intermediate System - Intermediate System or IS-IS for short was originally designed to route the OSI protocol suite. The OSI protocol suite was the application of the OSI reference model. The OSI reference model as well as the OSI protocol suite was created by the ISO organization. The ISO organization is an international organization that has international countries as members, specifically each international country's governmental organizations for standards. For Canada it is the Standards Council of Canada or SCC for short. For the United States of America it is the American National Standards Institute or ANSI for short.

The OSI reference model consists of the following layers:

1. Application Layer
2. Presentation Layer
3. Session Layer
4. Transport Layer
5. Network Layer
6. Data Link Layer
7. Physical Layer

At the Network Layer, the OSI protocol suite uses the ConnectionLess Network Service or CLNS protocol. The CLNS protocol requires Network Service Access Point or NSAP addressing. NSAP address registration is handled by either a subdivision of the national standards organization or a delegated organization. For the case of Canada, the SCC seems to have delegated the authority to manage NSAP adressing to the Public Works and Government Services Canada organization. For non-governmental NSAP addresses, the Canadian OSI Registration Authority handles non-governmental NSAP addressing registrations. For governmental NSAP addresses, the Government OSI Registration Authority handles the governmental NSAP addressing registrations. In the United States of America, ANSI handles non-govermental NSAP addresses and the [U.S.] General Services Administration handles governmental NSAP address registrations.

According to the RFC 1237 - Guidelines for OSI NSAP Allocation in the Internet document, it states that these are the fields within an NSAP address:

1. Initial Domain Part (IDP)
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2. Authority and Format Identifier (AFI)
3. Initial Domain Identifier (IDI)

[*]Domain Specific Part (DSP)

1. High-order DSP (HO-DSP)
2. System Identifier (ID)
3. NSAP Selector (SEL)

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Now, the IDP + HO-DSP parts combine to create the area ID, the System Identifier or System ID for short, and the NSAP Selector or NSEL for short, are the three general parts to a NSAP address.

So in review, the NSAP address' area ID is NOT arbitrarily based on the whim of the network administrator/engineer but it is based on NSAP address registration with the appropriate International Organization for Standardization member nation's standards organization.

According to the "Internet, NSAP, and PSAP Addressing" webpage of the "Multiprotocol Communications Server Reference Guide" at 3com.com, the "NSAP Address Structure" is show in Table B-1. Now, if an NSAP address starts with two hexadecimal numbers like 49. then those two numbers are called the Authority and Format Identifier or AFI for short. The purpose of the AFI is to serve as a "table of contents" to decipher the formatting of the IDI. In the case of an AFI of 49. refers to an IDI defined locally by the network administrator. So only for the case of AFI values of 48. and 49. , the IDI part of the IDP IS at the arbitrary whim of the local network administrator.

Now, technically, any System ID can be used in an NSAP address within the same area ID as long as the System IDs for the Intermediate Systems are unique and not duplicated by two or more Intermediate Systems within the same area or backbone. Since MAC addresses are unique to each networking device, that's where the advice to use the ISIS router's MAC address as the NSAP address' System ID comes from.

For an NSAP address with an NSEL value of '0', that NSAP address is called the Network Entity Title or NET for short. Since routers are considered Intermediate Systems, they have to have an NSEL value of "00." NSEL values other than "00" belong to End Systems or ES for short. Translating "OSI" to "rest of networking" an ES is another name for a Host. So NSEL values like "12", "24", or "69" are used for End Systems' NSAP addresses and NOT for the NSAP addresses for Routers.

I hope this helps.

Source:

1. ISO - International Organization for Standardization - http://www.iso.org/iso/home.htm
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2. ISO members - http://www.iso.org/iso/about/iso_members.htm
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3. Canada - Standards Council of Canada (SCC) - http://www.iso.org/iso/about/iso_members/iso_member_body.htm?member_id=1619
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4. Public Works and Government Services Canada - Canadian OSI Registration Authority/Government OSI Registration Authority (COSIRA*GORA) - http://www.tpsgc-pwgsc.gc.ca/cosira/text/index-e.html

[*]United States of America - American National Standards Institute (ANSI) - http://www.iso.org/iso/about/iso_members/iso_member_body.htm?member_id=2188
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[*]RFC 1237 - Guidelines for OSI NSAP Allocation in the Internet - http://tools.ietf.org/html/rfc1237
[*]"Internet, NSAP, and PSAP Addressing" webpage of the "Multiprotocol Communications Server Reference Guide" at 3Com.com - http://support.3com.com/infodeli/tools/termserv/cs/sw/mcs_rg/mpcsinet.htm

1. Table B-1 shows the relationship between an NSAP address, IDP, and the DSP addressing scheme for the Government Open Systems Interconnection Profile (GOSIP) Version II. - http://support.3com.com/infodeli/tools/termserv/cs/sw/mcs_rg/mpcsinet.htm#4539
2. Table B-2 lists the AFI values and their associated IDI formats, as described in Addendum 2 of the International Standard 8348. - http://support.3com.com/infodeli/tools/termserv/cs/sw/mcs_rg/mpcsinet.htm#4622
3. The IDI format values have the following meanings: - http://support.3com.com/infodeli/tools/termserv/cs/sw/mcs_rg/mpcsinet.htm#4746

[*]"IS Address Assignment" section of the "Integrated IS-IS Routing Protocol Overview [Cisco IOS Software]" webpage at Cisco.com - http://www.cisco.com/en/US/docs/ios/iproute/configuration/guide/isovrvw.html#wp1054976
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