[CentOS] IPV4 is nearly depleted, are you ready for IPV6?

Steve Clark sclark at netwolves.com
Tue Dec 7 13:01:08 UTC 2010


On 12/07/2010 05:13 AM, David Sommerseth wrote:
> On 07/12/10 02:26, Les Mikesell wrote:
>    
>> On 12/6/10 6:27 PM, Brian Mathis wrote:
>>      
>>> You are enjoying a side-effect of NAT by thinking it
>>> is a firewall.
>>>        
>> The other nice side-effect of NAT is that you get an effectively infinite number
>> of addresses behind it without any pre-arrangement with anyone else.  Even if
>> ISPs hand out what they expect to reasonably-sized blocks, won't it be much
>> harder to deal with when you outgrow your allotment?  We've had the opportunity
>> to move to ipv6 for ages but we haven't (in the US, anyway).  I think the reason
>> is that most people like the way NAT works and don't really want a public
>> address on every device.
>>      
> So you are afraid of out-growing from an assigned /48 net?  Let's do
> some math here ... and I hope I get it right ...
>
> IPv4:  aa:bb:cc:dd  .... that's 32 bit
> IPv6:  aaaa:aaaa:aaaa:: .... this is 48 bits out of 128bits
>
> In the IPv6 scenario, you have been assigned 'aaaa:aaaa:aaaa::' as your
> IPv6 prefix by your ISP.
>
> So that means that you have 128-48 bits available for your own
> addressing scheme.  That is 80 bits you have absolutely full control
> over.  Of course, it's recommended to have subnets no smaller than 64
> bits.  So that makes it:
>
> IPv6 /64 subnets:  aaaa:aaaa:aaaa:bbbb::
>
> That means you have 16 bits for subnets.  2^16 = 65536 subnets, each
> with 64bit addressing.  And if my math doesn't fail me now, a 64 bit
> addressing scheme is doubling the IPv4 address scope 32 times.
>
> What I mean is that from 32 bit to 33 bit, you have 2 * 32 bit
> addressing scope.  from 32 to 34, you have you have 4 * 32 bit
> addressing scope.  For each bit you add, you double what you had.
>
> It is simply insanely many addresses.  And if you fear that ISPs or IANA
> might run out of address spaces.  Remember that they have 48 bits to
> play with, which is the IPv4 address scope doubled 16 times.
>
> Of course some ISP's will probably just hand out /64 networks to most of
> their customers (most probably to home users).  But that's another
> story.  And a /64 network is possible but not so easy to subnet further,
> and is also not recommended.
>
>
>    
ISP's are supposed to hand out /48's so you can move to a new ISP 
without having to disrupt
your internal addressing.


> kind regards,
>
> David Sommerseth
>
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>
>    


-- 
Stephen Clark
*NetWolves*
Sr. Software Engineer III
Phone: 813-579-3200
Fax: 813-882-0209
Email: steve.clark at netwolves.com
http://www.netwolves.com
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