Wildcards in reverse DNS

Marc Haber mh+bind-users at zugschlus.de
Sat Jan 6 20:16:34 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

> > 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


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.


Marc Haber         | "I don't trust Computers. They | Mailadresse im Header
Mannheim, Germany  |  lose things."    Winona Ryder | Fon: *49 621 72739834
Nordisch by Nature |  How to make an American Quilt | Fax: *49 621 72739835

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