Subject: RE: [Isis-wg] Addressing Routers in IS-IS Packets

From: "Nurit Sprecher" <[email-masked]>
Date: Mon, 8 Nov 2004 20:36:21 +0200

Thanks Jeff for your response.

Your answer is correct as long as the OSI style address is
administratively configured. In such a case it is the ISP's
responsibility to guarantee the uniqueness. But if iit is required from
the network element to map between IP address and the OSI style address
it is matter. This should be done in a consistent way by all network
elements.

Nurit.

  _____  

From: Jeff Parker [mailto:[email-masked]] 
Sent: Thursday, November 04, 2004 7:30 PM
To: Nurit Sprecher; [email-masked]
Subject: Re: [Isis-wg] Addressing Routers in IS-IS Packets

Nurit -
    The short answer is that it doesn't matter.  
    If these addresses, IS-IS System IDs, were visible outside an ISP,
it would matter.  But as long as the values are unique within the
domain, which is typically interior to an ISP, it doesn't matter how
they are allocated.  

- jeff parker

On 11/4/04 6:31 AM, "Nurit Sprecher"
<[email-masked]> wrote:

Hi,
 
I have a question on the OSI-style addresses of IP routers, and I'll
appreciate a response.
 
RFC 1195 suggests two ways in which NSAP addresses may be obtained for
use with the IS-IS protocol.
When using the algorithmically generating a valid OSI style address from
existing IP address, RFC 1195 suggests that the System ID is based on
the System's IP address. The hex value "02 00" is used prepended to the
IP address of the router.
 
However I could see that Cisco claims that most ISPs do it in another
way. Each of the four bytes of the IP address is prepended by zeros if
necessary. Then, the resulting 12 decimal digits are re-divided into
three groups of 4 decimal digits, each group occupying 2 bytes.  
 
Since the mapping needs to be defined coherently network wide, I would
like to know which of the methods is the common and used one, and maybe
other methods are in use.
 
Thanks in advance,
Nurit.

  _____  

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---

From: Tony Li <[email-masked]>
Date: Tue, 9 Nov 2004 08:46:41 -0800

There is currently no such global requirement.  Thus, this remains a 
local matter.

Tony

On Nov 8, 2004, at 10:36 AM, Nurit Sprecher wrote:

> responsibility to guarantee the uniqueness. But if iit is required 
> from the network element to map between IP address and the OSI style 
> address it is matter. This should be done in a consistent way by all 
> network elements.
>
>  
>
> Nurit.
>
>  
>
>
>      The short answer is that it doesn’t matter.  
>      If these addresses, IS-IS System IDs, were visible outside an 
> ISP, it would matter.  But as long as the values are unique within the 
> domain, which is typically interior to an ISP, it doesn’t matter how 
> they are allocated.  
>
>  - jeff parker
>
>
>  RFC 1195 suggests two ways in which NSAP addresses may be obtained 
> for use with the IS-IS protocol.
>  When using the algorithmically generating a valid OSI style address 
> from existing IP address, RFC 1195 suggests that the System ID is 
> based on the System’s IP address. The hex value "02 00" is used 
> prepended to the IP address of the router.
>   
>  Since the mapping needs to be defined coherently network wide, I 
> would like to know which of the methods is the common and used one, 
> and maybe other methods are in use.
>   
>  Thanks in advance,
>  Nurit.
>   
>   
>   
>   
>
>

---

From: Dave Katz <[email-masked]>
Date: Tue, 9 Nov 2004 09:02:29 -0800

It is never "required" of the network element to do the address 
mapping.  If a vendor chooses to provide such a function, it is 
nonstandard, and of course there is some risk of address collision.  In 
general this would, at best, be silly, as there is so much other 
configuration information necessary for a router that providing a 
function so that one less line of configuration is required would not 
provide significant return.