Stupid Ipv6 question...
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 -- <Wrin> quick, somebody tell me the moon phase please? <Dan_Wood> Wrin: Plummeting. -Undernet #reboot, 9/11/01 (day of the WTC bombing) --------Dan Mahoney-------- Techie, Sysadmin, WebGeek Gushi on efnet/undernet IRC ICQ: 13735144 AIM: LarpGM Site: http://www.gushi.org ---------------------------
On Fri, Nov 19, 2004 at 03:06:43AM -0500, Dan Mahoney, System Admin <danm@prime.gushi.org> wrote 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?
On Fri, 19 Nov 2004, Stephane Bortzmeyer wrote:
On Fri, Nov 19, 2004 at 03:06:43AM -0500, Dan Mahoney, System Admin <danm@prime.gushi.org> wrote 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 -- "Of course she's gonna be upset! You're dealing with a woman here Dan, what the hell's wrong with you?" -S. Kennedy, 11/11/01 --------Dan Mahoney-------- Techie, Sysadmin, WebGeek Gushi on efnet/undernet IRC ICQ: 13735144 AIM: LarpGM Site: http://www.gushi.org ---------------------------
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
On Fri, 2004-11-19 at 16:36, Stephen Sprunk wrote:
/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.
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. -- Leo Bicknell - bicknell@ufp.org - CCIE 3440 PGP keys at http://www.ufp.org/~bicknell/ Read TMBG List - tmbg-list-request@tmbg.org, www.tmbg.org
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. -- Kevin Loch
Does that mean if we rip them off that we may be prosecuted? ;) Scott -----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On Behalf Of Kevin Loch Sent: Friday, November 19, 2004 1:41 PM To: nanog@merit.edu Subject: Re: Stupid Ipv6 question... 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. -- Kevin Loch
On Fri, 19 Nov 2004, Scott Morris wrote: 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
Does that mean if we rip them off that we may be prosecuted?
;)
Scott
-----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On Behalf Of Kevin Loch Sent: Friday, November 19, 2004 1:41 PM To: nanog@merit.edu Subject: Re: Stupid Ipv6 question...
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.
-- Kevin Loch
-- "We need another cat. This one's retarded." -Cali, March 8, 2003 (3:43 AM) --------Dan Mahoney-------- Techie, Sysadmin, WebGeek Gushi on efnet/undernet IRC ICQ: 13735144 AIM: LarpGM Site: http://www.gushi.org ---------------------------
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 -----Original Message----- From: Dan Mahoney, System Admin [mailto:danm@prime.gushi.org] Sent: Friday, November 19, 2004 2:12 PM To: Scott Morris Cc: 'Kevin Loch'; nanog@merit.edu Subject: Re: [nanog] RE: Stupid Ipv6 question... On Fri, 19 Nov 2004, Scott Morris wrote: 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
Does that mean if we rip them off that we may be prosecuted?
;)
Scott
-----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On Behalf Of Kevin Loch Sent: Friday, November 19, 2004 1:41 PM To: nanog@merit.edu Subject: Re: Stupid Ipv6 question...
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.
-- Kevin Loch
-- "We need another cat. This one's retarded." -Cali, March 8, 2003 (3:43 AM) --------Dan Mahoney-------- Techie, Sysadmin, WebGeek Gushi on efnet/undernet IRC ICQ: 13735144 AIM: LarpGM Site: http://www.gushi.org ---------------------------
On Fri, Nov 19, 2004 at 12:25:10PM -0500, Leo Bicknell wrote:
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.
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 -- James Jun TowardEX Technologies, Inc. Technical Lead Boston IPv4/IPv6 Web Hosting, Colocation and james@towardex.com Network design/consulting & configuration services cell: 1(978)-394-2867 web: http://www.towardex.com , noc: www.twdx.net
Lars Erik Gullerud wrote:
On Fri, 2004-11-19 at 16:36, Stephen Sprunk wrote:
/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.
While that would seem logical for most engineers, used to /30 or /31 ptp links in IPv4 (myself included)
Aren't most engineers used to the fact that point-to-point links are not broadcast links and therefore the concept of a network/netmask for the interface is somewhat useless? In addition, link-local addressing eliminates many situations where you need to allocate tiny blocks for p2p links. -- Crist J. Clark crist.clark@globalstar.com Globalstar Communications (408) 933-4387
Date: Fri, 19 Nov 2004 10:11:36 -0800 From: Crist Clark <crist.clark@globalstar.com> Sender: owner-nanog@merit.edu
Lars Erik Gullerud wrote:
On Fri, 2004-11-19 at 16:36, Stephen Sprunk wrote:
/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.
While that would seem logical for most engineers, used to /30 or /31 ptp links in IPv4 (myself included)
Aren't most engineers used to the fact that point-to-point links are not broadcast links and therefore the concept of a network/netmask for the interface is somewhat useless? In addition, link-local addressing eliminates many situations where you need to allocate tiny blocks for p2p links.
Just to introduce a touch of practicality to this discussion, it might be worth noting that Cisco and Juniper took the RFC stating that the smallest subnet assignments would be a /64 seriously and the ASICs only route on 64 bits. I suspect that they influenced the spec in this area as expending them to 128 bits would have been rather expensive. In any case, if the prefix length is >64, routing is done in the CPU. IPv6 traffic for most tends to be light enough that this is not a big issue today, but the assigning /126 or /127s for P2P links is really, really not a good idea. the use of 127s also ignore the possibility of a anycast address. -- R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: oberman@es.net Phone: +1 510 486-8634
Just to introduce a touch of practicality to this discussion, it might be worth noting that Cisco and Juniper took the RFC stating that the smallest subnet assignments would be a /64 seriously and the ASICs only route on 64 bits. I suspect that they influenced the spec in this area as expending them to 128 bits would have been rather expensive.
darn... and we fought so hard last time we had to expunge classfull addressing asics/hardware in the late 1990s. looks like it crept back into vendor gear. IPv6 was -never- supposed to be classful. --bill
While the concept of classes has changed, I'm not so sure that I agree with the complaint here... Everything I've seen about the multi TLA/SLA concepts always seem to leave 64 bits at the end for the actual host address, so it would be a logical step at that point to have the ASICs spun so that 64 bits was the limit for routing tables. Perhaps I have had the same assumption/misunderstanding that the programmer guys have had then?!?!? Scott -----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On Behalf Of bmanning@vacation.karoshi.com Sent: Saturday, November 20, 2004 9:56 PM To: Kevin Oberman Cc: crist.clark@globalstar.com; Lars Erik Gullerud; Stephen Sprunk; North American Noise and Off-topic Gripes Subject: Re: Stupid Ipv6
Just to introduce a touch of practicality to this discussion, it might be worth noting that Cisco and Juniper took the RFC stating that the smallest subnet assignments would be a /64 seriously and the ASICs only route on 64 bits. I suspect that they influenced the spec in this area as expending them to 128 bits would have been rather expensive.
darn... and we fought so hard last time we had to expunge classfull addressing asics/hardware in the late 1990s. looks like it crept back into vendor gear. IPv6 was -never- supposed to be classful. --bill
On 20 Nov 2004, at 19:13, Kevin Oberman wrote:
In any case, if the prefix length is >64, routing is done in the CPU.
Engineers at Juniper seem to be telling me that this is definitively not the case for their M- and T-series routers. Which routers were you referring to? Joe
From: Joe Abley <jabley@isc.org> Date: Sun, 21 Nov 2004 19:55:10 -0500
On 20 Nov 2004, at 19:13, Kevin Oberman wrote:
In any case, if the prefix length is >64, routing is done in the CPU.
Engineers at Juniper seem to be telling me that this is definitively not the case for their M- and T-series routers. Which routers were you referring to?
Odd. Juniper engineers have assured me that this is th case with M and T series routers (or any router using the IP2 chip). To clarify a bit, if the networks are connected, or "direct" in Juniper-ese. then the CPU is not involved. Only if there is a real "routing decision" made. OS if you have several connected /126s or /127s on a single router, you are OK, but if you are truly sub-netting a prefix longer than a /64 to several routers, then the CPU gets to figure out where a packet goes. I'd love to hear this is wrong, but it was confirmed to m by a rather senor engineer at Juniper, not a JTAC phone droid. Would Tony care to comment? -- R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: oberman@es.net Phone: +1 510 486-8634
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 On Fri, Nov 19, 2004 at 03:06:43AM -0500, Dan Mahoney, System Admin wrote:
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
--
<Wrin> quick, somebody tell me the moon phase please? <Dan_Wood> Wrin: Plummeting.
-Undernet #reboot, 9/11/01 (day of the WTC bombing)
--------Dan Mahoney-------- Techie, Sysadmin, WebGeek Gushi on efnet/undernet IRC ICQ: 13735144 AIM: LarpGM Site: http://www.gushi.org ---------------------------
-- Trent Lloyd <lathiat@bur.st> Bur.st Networking Inc.
participants (13)
-
bmanning＠vacation.karoshi.com -
Crist Clark -
Dan Mahoney, System Admin -
James -
Joe Abley -
Kevin Loch -
Kevin Oberman -
Lars Erik Gullerud -
Leo Bicknell -
Scott Morris -
Stephane Bortzmeyer -
Stephen Sprunk -
Trent Lloyd