v6 & DSL / Cable modems [was: Private use of non-RFC1918 IP space (IPv6-MW)]

Ricky Beam jfbeam at gmail.com
Mon Feb 9 17:16:28 CST 2009


On Fri, 06 Feb 2009 09:39:01 -0500, Iljitsch van Beijnum  
<iljitsch at muada.com> wrote:
>> If you want the machine to always have the same address, either enter  
>> it manually or set your DHCP server to always give it the same address.
>
> Manual configuration doesn't scale. With IPv4, it's quite hard to make  
> this work with DHCP, but mostly because of a lack of IPv4 addresses.  
> With IPv6 it's easier, but you're still limiting the uptime of your  
> system to that of the DHCPv6 server. Router advertisements is much more  
> robust.

As I read it, you don't want to use DHCP because "it's an other service to  
fail."  Well, what do you think is broadcasting RA's?  My DHCP servers  
have proven far more stable than my routers. (and one of them is a windows  
server :-))  Most dhcp clients that keep any state will continue using the  
previously assigned address if the server is unavailable (and nothing else  
is using it.)  Configuring a static address in a DHCP server is a pretty  
trivial task.

My point is simply, this whole mess with RA's should never have been on  
the table.  DHCP has been around and used for years to provide IPv4 hosts  
with an address, gateway, and MANY other configuration options.  It exists  
because (in many cases) hosts need more than just an address.  Yet the  
protocol designers, staunch haters of DHCP, refused to see any value in  
DHCP for IPv6 and rolled back the clock 3 decades dooming us ALL to  
repeating the same bull.  DHCPv6 can do everything SLAAC can plus  
infintely more.  And an "it just works" configurationless setup could have  
been part of the standard instead; yet here we are... nobody 100% happy  
and a considerable amount of work being poured into reinventing the DHCP  
wheel.

Manual static configuration is indeed a pain.  That's why we have DHCP...  
set aside a range of addresses for machines that can move around (client  
workstations, etc.) and a pool of persistant addresses for servers,  
printers, etc. that you want to stay in one place -- some applications  
record addresses instead of names, *sigh*.  Everything is in one, easy to  
manage location.  For an ISP where a lot necessarily has to be manually  
configured, it can be more work, but is still simple -- even in the days  
of the "NOC NOTEBOOK" where only one person could be assigning addresses  
at a time. (we've had web based stuff for years now; feed rwhois directly,  
'tho not automatic.)

> Isn't remembering stuff what we have computers for?

If you aren't accessing machines by number, why do you care if it always  
has the same number?  As long as the name always maps to the right number,  
it doesn't matter.

> I have a lot of problems with DHCP and most people don't _need_ it.  
> Still, very many people _want_ it and some people do in fact need it. I  
> have no problem with that, as long as it doesn't lead to the situation  
> where I have to run it.

And I, likewise, don't want the utterly useless "RA" forced on my  
networks.  Hosts need much more than just a unique address.  And I don't  
want to have to walk around to every one of them to change anything.

--Ricky




More information about the NANOG mailing list