Re: PTR for IPv6 clients (Re: IPv6 NAT?)

Harald Alvestrand wrote:
> Mark Andrews skrev:
> > You also don't want to do it as you would also need massive churn in
> > the DNS.
> >
> > Microsoft gets this wrong as they don't register the privacy addresses
> > in the DNS which in turn causes services to be blocked because there
> > is no address in the DNS.
>
> perhaps the advent of IPv6 will result in people finally (*finally*)
> giving up on this sorry excuse for a security blanket? (calling it a
> "mechanism" is too kind)
>
> Or perhaps it'll just make people register wildcard records at the /64
> level in ip6.arpa :-(
>
>              Harald(_at_)162(_dot_)80-203-220(_dot_)nextgentel(_dot_)com (MY, 
> what an useful
> reverse map!)
Like a lot of things, "it depends".

For SMTP/SSH and for management-alike protocols requiring proper
reverse -> forward -> reverse mapping is IMHO a good thing.

Clients & servers using these protocols  should be on stable & trackable 
addresses. (of course you an set a low TTL etc, that is why one should 
always log the name + IP, the more information the better). With 
management I mean for instance reverses on router IP addresses, as it 
makes traceroute so much more informative, also reverses on servers etc.
For SSH you will most likely have firewall rules in place anyway. SMTP 
should similarly only be allowed to clients that are in your client 
list. One doesn't have to require r->f->r if the client is in your 
client-list of course. Your server, which talks to other SMTP servers 
outside of your control, should be on a stable IP and have functioning 
r->f->r. For SMTP the current track of mind is: no reverse, no 
communication. Which stops most of the spam already, as that client is 
clearly not configured correctly to do inter-domain SMTP.
For that matter anything that is 'stable' should (note should) IMHO have 
a proper r->f->r.
For any other protocol _requiring_ reverse is silly IMHO.
You don't need it for HTTP, you don't need it for BitTorrent etc.
Having reverse in those cases is nice, as it might give extra 
information (eg the remote is most likely dsl as it contains 'dsl' in 
the reverse), but it is always a guess and might quite well be faked.
The biggest issue with the use of reverses tends to be with applications 
which only lookup a reverse, but don't check if the r->f->r link is 
complete.
Greets,
 Jeroen

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