[j-nsp] IPv6 subnetting

[snort bsd]

Here is from rfc4291:

2.6.1.  Required Anycast Address

   The Subnet-Router anycast address is predefined.  Its format is as
   follows:





Hinden                      Standards Track                    [Page 12]

RFC 4291              IPv6 Addressing Architecture         February 2006



   |                         n bits                 |   128-n bits   |
   +------------------------------------------------+----------------+
   |                   subnet prefix                | 00000000000000 |
   +------------------------------------------------+----------------+

   The "subnet prefix" in an anycast address is the prefix that
   identifies a specific link.  This anycast address is syntactically
   the same as a unicast address for an interface on the link with the
   interface identifier set to zero.

   Packets sent to the Subnet-Router anycast address will be delivered
   to one router on the subnet.  All routers are required to support the
   Subnet-Router anycast addresses for the subnets to which they have
   interfaces.

   The Subnet-Router anycast address is intended to be used for
   applications where a node needs to communicate with any one of the
   set of routers.
So the statements above is what you refer to?
The "subnet prefix" in an anycast address is the prefix that identifies a specific link. This anycast address is syntactically the same as a unicast address for an interface on the link with the interface identifier set to zero.

Then how 
does 
that 
calculate/126? It should 
give 
me 
four 
addresses 
with 
first 
one 
being 
network 
ID/anycast address and 
I 
could 
use 
rest 
of 
three, 
right? honestly, it doesn't sound right to me:

So, we subnet the address fec0::/126 according the rules of IPv4; 0~3, 
4~7, 
8~11, 
12~15, 
and 
so 
on... fec0::14/126 is not the first address of that subnet.

Or 
am 
I 
missing 
something?

Dave


----- Original Message ----
From: Mark Kamichoff <prox at prolixium.com>
To: a. r.isnaini. rangkayo sutan <risnaini at netsoft.net.id>
Cc: snort bsd <snortbsd at yahoo.com.au>; juniper-nsp <juniper-nsp at puck.nether.net>
Sent: Saturday, 2 February, 2008 12:42:52 PM
Subject: Re: [j-nsp] IPv6 subnetting

On 
Fri, 
Feb 
01, 
2008 
at 
01:32:49PM 
+0700, 
a. 
r.isnaini. 
rangkayo 
sutan 
wrote:
> 
Yes, 
you 
cannot 
assign 
10::14/126 
which 
4 
I 
believe 
is 
network 
ID 
for
> 
/126  
(/30 
in 
ipv4), 
before 
10::14/126 
there 
should 
10::/126.

The 
first 
address 
in 
any 
IPv6 
subnet 
is 
reserved 
for 
subnet-router
anycast.  
Section 
2.6.1 
of 
RFC 
2373 
defines 
this.

This 
also 
includes 
the 
first 
address 
of 
/127's.  
Reading 
RFC 
3627 
(Use
of 
/127 
Prefix 
Length 
Between 
Routers 
Considered 
Harmful) 
is 
probably
worthwhile.

- 
Mark

-- 
Mark 
Kamichoff
prox at prolixium.com
http://prolixium.com/
Rensselaer 
Polytechnic 
Institute, 
Class 
of 
2004





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