From: Iljitsch van Beijnum [mailto:iljitsch@xxxxxxxxx]
Sent: Thu 13/09/2007 5:24 PM
To: Keith Moore
Cc: Tony Finch; IETF-Discussion
Subject: Re: Renumbering
On Sep 13, 2007, at 20:52 , Keith Moore wrote:
>>> How do you renumber the IP address stored in the struct
>>> sockaddr_in in a
>>> long running critical application?
Disconnect current session, reconnect.
>> Applications that don't respect DNS TTLs are broken for many
>> reasons, not
>> just network renumbering.
Since when is it the job of applications to manage DNS TTLs?
> Since neither TCP nor UDP respect DNS TTLs it seems a bit of a stretch
> to expect apps to do so.
Right.
> And for that matter, a DNS name is not a host name, and hasn't
> reliably
> been a host name since at least the mid 1980s. Just because you get
> address A1 from doing a lookup on a name at time T1 and an address A1
> from doing the same lookup at time T2, doesn't mean that those
> addresses
> will connect to the same (layer 3 or higher) stack.
> So even if we somehow magically changed our existing transport
> protocols
> to be able to support changes to endpoint addresses on the fly, DNS
> names as they are currently used are not suitable as endpoint
> identifiers for such a purpose. At best, existing DNS names serve as
> identifiers for the initial contact only.
This falls under the heading of "nobody is stopping us from doing
this and it works today so now it's a feature and it can never be
taken away". Giving in to this logic means that it's impossible to
change ANYTHING. As the saying goes, in an infinite universe,
everything that's possible, does indeed exist. The internet is pretty
much an infinite universe these days.
As for renumbering, on a Cisco router, I can make the following
configuration:
!
interface Ethernet1
ipv6 address autoconfig
ipv6 dhcp client pd dhcpv6prefix
!
interface Ethernet2
ipv6 address dhcpv6prefix 0:0:0:A0::/64 eui-64
!
This way, the router obtains an IPv6 prefix dynamically from a DHCPv6
prefix delegation server and then sends out router advertisements
using that prefix. So you can renumber the router and all the hosts
connected through it by changing one entry in a DHCPv6 server config.
However, I don't think this method applies everywhere (such as in
filters) but obviously that's something that would be possible if
desired.
Even with the current state of the art I'd say that renumbering
clients is not a big deal. Renumbering servers is more difficult,
though.
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