Wildcards in reverse DNS

Clenna Lumina savagebeaste at yahoo.com
Mon Jan 8 17:28:39 UTC 2007

> 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?

If it's connecting to the outside, it would already know which one (the 
domain of the mail it's sending to the destination server, of course... 
it's not exactly magic.) As I've already told you, I've run mail servers 
*behind* (and still do, even my private one on my home network) and 
NEVER had any issues.

You're once again confusing NAT itself with bad implimentations. Your 
way of thinking is just like people who think all modern SUVs are poor 
off road vehicles with bad gas milage, when there are a few that do 
perform exceptionally well off road and have much better fual economy.

>> > 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

Thank you, this helps a lot :)

> Having more than one double-colon abbreviation in an address is
> invalid, as it would make the notation ambiguous.

How so? If such a notation means zero, wouldn't
just essentially translate to

I mean, it would seem pointless of course, although I don't think it 
would be ambiguous if they amount to zero (in other words I would of 
thought extra pairs would be essentially discarded in a manner, as they 
wouldn't really make a difference.

> 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.

Nice. That is exactly what I was hoping for, some way of using old 
adddresses (and with compatibility, may  I assume you mean mapping to 
IPv4 equivlents of the DEC portion (for a IPv4 IP within an IPv6 space 

> Additional information can be found in RFC 4291 - IP Version 6
> Addressing Architecture.

Thank you.

>> 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.

No arguement there.

>>   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.

I see. Not a bad system. I would not say either the German or US system 
is right or wrong, as they oth seem to serve a purpose, though I find 
the German system appears to scale better. 

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