Wildcards in reverse DNS

Sten Carlsen ccc2716 at vip.cybercity.dk
Sat Jan 6 20:55:25 UTC 2007

As for 128bit adressing; as far as I can see (which may not be far
enough) the lower 64bits are meant for the MAC-address, the rest is
useful as addresses.

This reduces the number of addresses from the very astronomical numbers
normally discussed to a 64 bit address space. This will probably be ok,
but claims of 128bit addressing are a little bit oversold.

What is the reason for this use of the lower 64 bits? Can you get rid of
ARP? Is this so much better than the self-assigned IPv4 addresses in use
today? On top of this, there are now attempts of hiding the MAC-address
to help privacy, which would otherwise be gone.

I still doubt if IPv6 is really as good as promised, it may be good
enough though.

Marc Haber wrote:
> On Sat, Jan 06, 2007 at 11:15:32AM -0800, Clenna Lumina wrote:
>> Marc Haber wrote:
>>>> so if it's generating a bad HELO, then thats the fault of the
>>>> foreign mail server, which is likely not configured correctly to
>>>> begin with.
>>>> My personal mail server which sits behind my home NAT, has never
>>>> failed to get a proper HELO from proper foreign hosts.
>>> It's the connecting server who says HELO, not the server connected to.
>> That *is* what I said - s/foreign/connecting/
>> " so if it's generating a bad HELO, then thats the fault of the
>>   foreign mail server "
>>   ^^^^^^^
> I am talking about connecting via SMTP to the outside. How is a server
> behind NAT supposed to know which HELO to use when connecting to the
> outside?
>>> and 2001:1b18:f:4::4/128 is not _that_ bad. Yes, that's an actually
>>> workin address.
>> How does that equate to a full 16 octet IPv6 address? I'm not all the 
>> keen on all forms of IPv6 ips, but I've never seen it written like you 
>> have. If you can connect to an IP using a short hand like this (withotu 
>> breaking anything) that would be great. It's a new concept to get used 
>> to, but (if it pans out), a welcome one.
> Quoting from Wikipedia:
> IPv6 addresses are normally written as eight groups of four
> hexadecimal digits. For example,
> 2001:0db8:85a3:08d3:1319:8a2e:0370:7334 is a valid IPv6 address.
> If a four-digit group is 0000, the zeros may be omitted. For example,
> 2001:0db8:85a3:0000:1319:8a2e:0370:1337 can be shortened as
> 2001:0db8:85a3::1319:8a2e:0370:1337. Following this rule, any group of
> consecutive 0000 groups may be reduced to two colons, as long as there
> is only one double colon used in an address. Leading zeros in a group
> can also be omitted. Thus, the addresses below are all valid and
> equivalent:
> 2001:0db8:0000:0000:0000:0000:1428:57ab
> 2001:0db8:0000:0000:0000::1428:57ab
> 2001:0db8:0:0:0:0:1428:57ab
> 2001:0db8:0:0::1428:57ab
> 2001:0db8::1428:57ab
> 2001:db8::1428:57ab
> Having more than one double-colon abbreviation in an address is
> invalid, as it would make the notation ambiguous.
> A sequence of 4 bytes at the end of an IPv6 address can also be
> written in decimal, using dots as separators. This notation is often
> used with compatibility addresses (see below). Thus, ::ffff: is
> the same address as ::ffff:102:304.
> Additional information can be found in RFC 4291 - IP Version 6
> Addressing Architecture.
>> If you could suggest a good page to look at that desribes these sorts of 
>> things, I would appreciate it.
> The Wikipedia page on ipv6 is not that bad.
>>>> Can you really tell me you can easily remember an address that long?
>>>> I can remebmer a 4 section IP with out any trouble. Remembering an
>>>> IPv6 address might be possible, no doubt, but you'd likely have to
>>>> known it rather well, and have a rather good memory.
>>> If DNS is properly used, you don't need to remember IPv6 addresses.
>>> And, usually, you only need to remember the prefix anyway.
>> Well you still need to enter them at _some_ point or another into DNS 
> yes, once. And one is well advised to use cut&paste for ipv4 as well.
>>   While I like how the Germans did it, there is an
>>   obvious benefit to using area codes, especially in a country the
>>   size of the US. When you see a phone number with an area code,
>>   you can easily deduce or determine where it may actually be located.
> Actually, we have area codes. They are longer for rural areas, and
> shorter for the big cities, to allow the actual subscriber number to
> vary in length according to the size of the local network.
> Greetings
> Marc

Best regards

Sten Carlsen

No improvements come from shouting:


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