[email protected] wrote:
I have been working through a timeless topic: p2p transit link addressing.
After reading http://tools.ietf.org/tools/rfcmarkup/rfcmarkup.cgi?rfc=3627
and http://tools.ietf.org/html/draft-ietf-ipv6-addr-arch-v4-04 as well a
networkers presentation, various blogs, etc. I thought it was time to
consult people who might actually be dealing with this in production today
in hopes that I can learn from any potential mistakes.
Can I simply avoid the problem of p2p links altogether with unnumbered from
an ipv6 loopback address?
I fear that link local addressing will ruin traceroute information.
Any definitive answers would be greatly appreciated. I would prefer not to
burn up all of my routable address space with p2p /64's however.
Thanks for your time,
John
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There has been some heated debates on the subject with no real
definitive answer; I have seen /64s, /112, /120, /126 and /127s.
Steve Leibson takes a shot at putting it in real world terms:
*/ So we could assign an IPV6 address to EVERY ATOM ON THE SURFACE OF
THE EARTH, and still have enough addresses left to do another 100+
earths. It isn't remotely likely that we'll run out of IPV6 addresses at
any time in the future! */
The point being is that this analogy is simply to show that there are an
awful lot of addresses and that you should not be too concerned with
conserving address space; however, this is to be taken with a grain of
salt. I would highly recommend that your address policies should avoid
the assignments in a unnecessarily wasteful fashion because it does
start to deteriorate from 2128 to 264 (from 340,282,366,920,938,463,46
3,374,607,431,768,211,456 to 18,446,744,073,709,551,616. In all
honestly, if you are a large network, then you were more than likely
allocated a /32 which only gives you a 8-16 bit improvement (16 bit
improvement if all you assign are /48s). Once you start planning a
practical address plan, the IPv6 allocation that you were assigned is
not that big; nothing more than a class B from the v4 land.
Here is some additional reading and references:
*In RFC5375 Section 2.4.1 and 2.4.2*
"Address conservation requirements are less stringent in IPv6, but they
should still be observed."
*In RFC5375 B.2. Considerations for Subnet Prefixes Longer than /64*
"The following subsections describe subnet prefix values that should be
avoided - B.2.1. /126 Addresses"
*In RFC3177 Section 3 (Address Delegation Recommendations) *
"/64 when it is known that one and only one subnet is needed by design."
*http://www.getipv6.info/index.php/IPv6_Addressing_Plans
<http://www.getipv6.info/index.php/IPv6_Addressing_Plans> - Point 10*.
"IETF expects that you will assign a /64 for point-to-point links"
In my professional opinion, allocate a /64 and assign a /126 to a point
to point link; do not assign anything else out of that /64.
I am sure there will be tons of response to your question and you will
not get on definitive answer; you as an engineer will need
to take all the information and based on your design and topology will
need to make that decision.
Good Luck
Billy
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