Re: ipv6 addressing question for subnetting...

From: Edwards, Andrew M (andrew.m.edwards@boeing.com)
Date: Fri Sep 23 2005 - 14:08:05 GMT-3


Sounds like a dumb question but here goes.

I was working on a vendor lab.

The requirement was to address interfaces over frame using site-local
addressing.
Use an SLA of B. All hosts are on subnet 2A. Use the router id as the
host IP.

The answer key used:

FEC0::B:0:0:2A:1/125
FEC0::B:0:0:2A:3/125
FEC0::B:0:0:2A:2/125

My thoughts:

The SLA is known as a 16 bit value before host-id. We also know
site-local addressing FEC0:/10 is defined.

So I have no qualms with: FEC0::B.....

If the subnet is just a masked off portion of the host id like in IPv4,
would there be a problem in using the following subnets?

FEC0::B:2A:0:0:1/80
FEC0::B:2A:0:0:3/80
FEC0::B:2A:0:0:2/80

Granted, my alternative answer is a larger single subnet, but aren't
they basically the same?

Just looking to make sure I understand V6 subnetting because their
answer threw me... I was under the impression that last 64 bits were all
for the host and SLA/subnetID was for subnetting. Their answer key made
me rethink this understanding to mean that I could use the SLA bits for
subnetting and I could further subnet within the host bits portion of
the v6 address space.

Thanks in advance,

andy



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