Re: Renumbering

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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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