In preparation for the upcoming advent of ipv6, I'm playing with a tunnel I've gotten from HE's cool tunnelbroker, and I'm plagued by the question that about an hour of google searching can't answer for me.
I'm having trouble wrapping my head around ipv6 style suffixes -- does anyone have a chart handy? How big is a /64, specifically?
Most of the tutorials I've found seem to be a bit over-the-top on this.
-Dan
a message of 25 lines which said:
I'm having trouble wrapping my head around ipv6 style suffixes --
does anyone have a chart handy? How big is a /64, specifically?
Since an IPv6 address is 128 bits, a /64 holds 2 ** (128 - 64)
addresses, which is 2 ** 64. But it seems too simple. This was really
your question?
Yup. I said it was a stupid question 
Mainly because I've always remembered CIDR's mnemonically rather than mathematically.
-Dan
Thus spake "Dan Mahoney, System Admin" <danm@prime.gushi.org>
I'm having trouble wrapping my head around ipv6 style suffixes -- does anyone have a chart handy? How big is a /64, specifically?
Subnet sizes work a bit differently in IPv6 due to autoconfiguration; nearly all subnets are expected to be /64, which can hold up to 18,446,744,073,709,551,616 hosts. A /48, the minimum assignment to end sites (unless proven to need only a single /64), comprises 65,536 subnets. A /32, the minimum allocation to ISPs, comprises 65,536 /48s. Of course, the minimum allocation sizes may be changed (up or down) in the future by RIR policy actions, and ISPs or end-sites can get shorter prefixes with proper justification.
/127 prefixes are assumed for point-to-point links, and presumably an organization will divide up a single /64 for all ptp links -- unless they have more than 9,223,372,036,854,775,808 of them.
S
Stephen Sprunk "God does not play dice." --Albert Einstein
CCIE #3723 "God is an inveterate gambler, and He throws the
K5SSS dice at every possible opportunity." --Stephen Hawking
While that would seem logical for most engineers, used to /30 or /31 ptp
links in IPv4 (myself included), that does not in fact seem to be the
way things are currently done in IPv6, unless something changed (again)
while I wasn't paying attention... /64 is the minimum subnet size, even
for ptp-links - there was even an RFC published relating to the use of
/127's (or, should I say, the recommendation to "don't to that"), namely
RFC3627 (aka "Use of /127 Prefix Length Between Routers Considered
Harmful"). But, you can still get 65536 ptp links out of a single /48 of
course.
I'm sure Pekka or others will jump in here and correct me if this is now
out-of-date info.
/leg
In a message written on Fri, Nov 19, 2004 at 05:15:26PM +0100, Lars Erik Gullerud wrote:
While that would seem logical for most engineers, used to /30 or /31 ptp
links in IPv4 (myself included), that does not in fact seem to be the
way things are currently done in IPv6, unless something changed (again)
while I wasn't paying attention... /64 is the minimum subnet size, even
for ptp-links - there was even an RFC published relating to the use of
/127's (or, should I say, the recommendation to "don't to that"), namely
RFC3627 (aka "Use of /127 Prefix Length Between Routers Considered
Harmful"). But, you can still get 65536 ptp links out of a single /48 of
course.
FWIW, my test networks have always been configured with /126's, and
have never had an issue.
With the exception of auto-configuration, I have yet to see any
IPv6 gear that cares about prefix length. Configuring a /1 to a
/128 seems to work just fine. If anyone knows of gear imposing
narrower limits on what can be configured I'd be facinated to know
about them.
Lars Erik Gullerud wrote:
Leo Bicknell wrote:
With the exception of auto-configuration, I have yet to see any
IPv6 gear that cares about prefix length. Configuring a /1 to a
/128 seems to work just fine. If anyone knows of gear imposing
narrower limits on what can be configured I'd be facinated to know
about them.
64 bit prefixes are the mattress tags of IPv6 interfaces.
Does that mean if we rip them off that we may be prosecuted?
Scott
No, nobody ever reads that tag. It says "not to be removed except by the consumer".
Which with at least one severly drunk friend of mine, has meant that if you remove it, you have to eat it
-Dan
Very true... But if we are assuming that the ISP isn't the end customer who
may receive an allocation, then who really is the "consumer"?
One has to wonder how much time was spent drunk underneath chairs and/or
mattresses to come up with a rule like that!
Scott
I am seeing the same here. We mostly use /64 as p2p links in 30071, and
also have /127's and /126's and even some /112's with legacy peers.
No problems exhibited in all cases.
But that still doesn't change the fact that /64 is recommended minimum
subnet size. Then again IPv6 gives us lot of *subnets* before we even
talk about gazillion amount of hosts
-J
Hi Dan,
I've got some slides from talks I've done, they cover this sortof stuff.
You can see at http://www.sixlabs.org/talks/
Additionally, the size is 2^(128-prefixlen) [more or less]
But you don't use all of them, obviously, it'd be fairly difficult, best
part about a /64 is EUI-64 works (auto-address allocation based on MAC
address) if you advertise it with radvd [or rtadvd if your freebsd, no
idea about other oss, radvd seems to work in most places]
Cheers,
Trent
Bur.st