SO I have been turning up v6 with multiple providers now and notice that
some choose /64 for numbering interfaces but one I came across use a /126. A
/126 is awfully large (for interface numbering) and I am curious if there is
some rationale behind using a /126 instead of a /64.
Zaid
You mean to say that a /126 is 'small' actually as it is only
2^(128-126) = 2^2 = 4 IP addresses while a /64 is......
For this discussion, please go through the archives.
In short: Personal preference of operators involved.
Greets,
Jeroen
http://www.google.com/search?q=nanog+126+64 would be a good place to
start...
(And I'm guessing you mean that /64 is "awfully large", not /126)
Scott.
There are 4 general choices of netmask for ipv6 point to point interface
numbering schemes:
/64: the default ipv4 subnet. many people feel that this is a waste of
addressing space. others feel that there is so much ipv6 address space out
there that it's simpler to keep all interfaces on /64.
/112: /112 is 16-bit aligned, which means that it's easy to read because 16
bits implies that the last 4 octets are link-specific. Also, your entire
PoP point-to-point addressing scheme can be held within a single /64, which
means good address conservation
/126: this is the same as we use in ipv4: it's less easy to read, as the
link-specific digits are not octet-aligned. Your entire PoP point-to-point
addressing scheme can be held within a single /64, which means good address
conservation
/127: this is used on POS links where there is no link-layer address
resolution protocol available (like ARP/ND) and consequently you can end up
with unknown traffic looping between each side if you're not careful.
None of these is the right or the wrong approach, unless you're using
POS/STM. Otherwise all of them have their merits and demerits.
Nick
Bahh had my head turned around and brain fried on a Friday. I was more
curious about /64 vs /126 from management perspective. Thanks everyone for
answering offline as well, I got my questions answered.
Zaid
Hi,
SO I have been turning up v6 with multiple providers now and notice that
some choose /64 for numbering interfaces but one I came across use a /126. A
/126 is awfully large (for interface numbering) and I am curious if there is
some rationale behind using a /126 instead of a /64.
If you're not going to follow the IPv6 Addressing Architecture, which
says /64s for everything, then the prefix length decision is
pretty much arbitrary - there is nothing that special
about /112s, /126s, /127s or /128s (or /120s or /80s) - they all break
something in the existing IPv6 RFCs so once you've passed that threshold
then you're really only choosing your poison. If you're going to go
down that latter path, I'd suggest reserving a /64 for each link, and
then using a longer prefix length out of that /64 when you configure
the addressing, to make it easier if you decided to change back to /64s
at a later time.
Regards,
Mark.
but then, can't we use ip unumbered on p2p links on cisco?
Drafts are drafts, and nothing more, aren't they?
Since we are on the topic of IPv6. I'd like to know if anyone has books/articles they recommend on fully
understanding IPv6 adoption in the work place. I will need to contact ARIN shortly to request a v6 block.
I'm assuming I would be asking for a /64 being an ISP. But I'd like to read up as much as possible before
requesting the block....
I think our approach will be to use dual-stack on the routers and let the clients themselves handle how they want to use IPv6...
Ultimately, it is up to them, their network, and their applications on how to use v6...
Thanks guys!
Since we are on the topic of IPv6. I'd like to know if anyone has books/articles they recommend on fully
understanding IPv6 adoption in the work place. I will need to contact ARIN shortly to request a v6 block.I'm assuming I would be asking for a /64 being an ISP. But I'd like to read up as much as possible before
requesting the block....
No, as an ISP, you should get at least a /32. A /64 is a single subnet in IPv6.
I think our approach will be to use dual-stack on the routers and let the clients themselves handle how they want to use IPv6...
Seems reasonable. FWIW, you should plan for assigning clients a /48 per end-site.
Ultimately, it is up to them, their network, and their applications on how to use v6...
Yep.
Owen
Joel's widget number 2
Since we are on the topic of IPv6. I'd like to know if anyone has books/articles they recommend on fully
understanding IPv6 adoption in the work place. I will need to contact ARIN shortly to request a v6 block.I'm assuming I would be asking for a /64 being an ISP. But I'd like to read up as much as possible before
requesting the block....
An ISP requesting an assignment would typically request a /32
For policy, I'd read the ARIN nrpm's section on v6 assignment.
I'd also get a book, for background, something like:
Then move on to the Internet which as with most things is where the most cuurent if not helpful information resides.
Eric Vyncke's IPv6 security book is definitely worthwhile, as well, in combination with Schudel & Smith's infrastructure security book (the latter isn't IPv6-specific, but is the best book out there on infrastructure security):
<http://www.ciscopress.com/bookstore/product.asp?isbn=1587055945>
<http://www.ciscopress.com/bookstore/product.asp?isbn=1587053365>
Thanks everyone who responded. This list is such a valuable wealth of information.
Apparently I was wrong about the /64 as that should be /32 so thanks for that correction....
Thanks again especially on a Saturday weekend!
You give a /64 to the end users (home/soho), and /48 to multi homed organization (or bigger orgs that use more than one network internally) and get a /32 if you are an ISP.
See also the discussion about what to use in p2p links.
You give a /64 to the end users (home/soho), and /48 to multi homed organization (or bigger orgs that use more than one network internally) and get a /32 if you are an ISP.
Please DON'T do that. End users (home/soho) should get at least a /56 and ideally a /48. The standards and the RIR policies both allow for end-users/sites to get /48s.
If you are an ISP, you get AT LEAST a /32.
See also the discussion about what to use in p2p links.
Yep. Personally, I like the /64 per subnet including p2p link approach. Others have different opinions.
Owen
"Dobbins, Roland" <rdobbins@arbor.net> writes:
Eric Vyncke's IPv6 security book is definitely worthwhile,
A good companion to Eric's book is Deploying IPv6 Networks
<Deploying IPv6 Networks | Cisco Press;
Jens
This 'get a /32' BAD ADVICE has got to stop. There are way too many people
trying to force fit their customers into a block that is intended for a
start-up with ZERO customers.
Develop a plan for /48 per customer, then go to ARIN and get that size
block. Figure out exactly what you are going to assign to customers later,
but don't tie your hands by asking for a block that is way too small to
begin with. Any ISP with more than 30k customers SHOULD NOT have a /32, and
if they got one either trade it in or put it in a lab and get a REAL block.
Tony
This 'get a /32' BAD ADVICE has got to stop. There are way too many people
trying to force fit their customers into a block that is intended for a
start-up with ZERO customers.
+1
Develop a plan for /48 per customer, then go to ARIN and get that size
block. Figure out exactly what you are going to assign to customers later,
More accurately... A /48 per customer end-site...
but don't tie your hands by asking for a block that is way too small to
begin with. Any ISP with more than 30k customers SHOULD NOT have a /32, and
if they got one either trade it in or put it in a lab and get a REAL block.
But otherwise, yes, Tony is right.
Owen
Unfortunately, it is not as easy as that in practice.
I recently worked with a customer that has ~60,000 customers currently. We tried to get a larger block, but were denied. ARIN said they would only issue a /32, unless immediate usage could be shown that required more than that. Their guidelines also state /56 for end-users. I am a big proponent of nibble boundaries, too. I think if you are too big to use only a /32, you should get a /28, /24, and so forth. It would make routing so much nicer to deal with. /31 and such is just nasty.
-Randy