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radvd or dhcp

 
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Martin Marcher
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Since: Mar 23, 2007
Posts: 6



PostPosted: Fri May 18, 2007 8:10 pm    Post subject: radvd or dhcp
Archived from groups: linux>debian>maint>ipv6 (more info?)

Hello,

I preparing to carry out ipv6 in our network. A thing I don't get is
the actual difference between radvd and dhcp in ipv6 networks. If
radvd can do all the autoconfiguration stuff (and from what i learned
by now it is just built-in in ipv6) why would i need dhcp
(http://tldp.org/HOWTO/Linux+IPv6-HOWTO/).

I couldn't really find a comparison of when to use which of those demons.

I'm probably stuck in ipv4 thinking (or making that up in my mind) but
I still stick with something like:

set up dhcp, tell the clients to do dhcp configuration (ipv6 still
needs a dhcp client afaik - radvd doesn't need a client, correct me if
i'm wrong)

the dhcp server will certain hosts to fixed addresses (servers) and
also serve a dynamic pool to workstations, tell about timeservers etc.

so why is there radvd? is it intended for a small setup, a large one I
just can't think of, or something totally different. Maybe the
question is why is there still dhcp, I'm quite confused atm and would
be gratefull for an overall answer, if I have the right terms to
google for I'll probably figure out the details by myself Smile

thanks
martin


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Stephane Bortzmeyer
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Since: Nov 24, 2004
Posts: 36



PostPosted: Fri May 18, 2007 8:50 pm    Post subject: Re: radvd or dhcp [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

On Fri, May 18, 2007 at 04:04:08PM +0200,
Martin Marcher wrote
a message of 33 lines which said:

> A thing I don't get is the actual difference between radvd and dhcp
> in ipv6 networks. If radvd can do all the autoconfiguration stuff
> (and from what i learned by now it is just built-in in ipv6) why
> would i need dhcp

RA allows only to distribute the prefix and the prefix length. It does
not allow you to distribute other information (like the DNS server or
the NTP server) and it does not allow you to have fixed centralized
IPv6 addresses.

> so why is there radvd?

Good question.


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Wouter Verhelst
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Since: Nov 08, 2004
Posts: 663



PostPosted: Mon May 21, 2007 3:50 am    Post subject: Re: radvd or dhcp [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

On Fri, May 18, 2007 at 04:44:24PM +0200, Stephane Bortzmeyer wrote:
> > so why is there radvd?
>
> Good question.

RA is a stateless protocol; as a result, it does not require as much CPU
power as is the case for DHCP, and also unlike DHCP doesn't need to keep
a database of leases which it's sent out. If you don't need all the
time/DNS/whatever server configuration synchronized in a large network
(because, say, you have a setup that allows you to synchronize
configuration when it actually changes, rather than only when your lease
expires), then running radvd (or another implementation of router
advertisement) can help you get rid of a maintenance and processor time
overhead that you don't need anyway.

Ultimately, what you use depends very much on what you want and what
your requirements are. Personally, I use DHCP for v4 addresses (because
there's no other modern way of distributing IP address configuration for
v4); and since I use that already anyway, I also use it to distribute
DNS server configuration. As such, I have no need to distribute DNS
server configuration for v6 anymore, so I prefer to do that through RA.

--
Shaw's Principle:
Build a system that even a fool can use, and only a fool will
want to use it.


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Juliusz Chroboczek
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Since: Apr 18, 2005
Posts: 37



PostPosted: Wed May 30, 2007 10:20 am    Post subject: Re: radvd or dhcp [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

> RA is a stateless protocol; as a result, it does not require as much
> CPU power as is the case for DHCP, and also unlike DHCP doesn't need
> to keep a database of leases which it's sent out.

This latter point bears repeating.

A DHCP server must keep track of the addresses that it has given out
to clients. Hence, it must save to persistent storage every single
lease it gives out, which makes it difficult to implement DHCP on
diskless routers.

With RA, the router simply multicasts prefix information, and nodes
choose an IP address for themselves. There is no state in the router,
so when the router crashes, there is no state to recover.

Note that in IPv6 you can combine RA with DHCPv6: use RA for address
configuration, and DHCPv6 for configuring other data (such as DNS
servers).


Juliusz


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Martin Marcher
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Since: Mar 23, 2007
Posts: 6



PostPosted: Wed May 30, 2007 6:50 pm    Post subject: Re: radvd or dhcp [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

sorry, gmail doesn'T quite get this list and i hit reply to fast

---------- Forwarded message ----------
From: Martin Marcher
Date: May 30, 2007 2:47 PM
Subject: Re: radvd or dhcp
To: Juliusz Chroboczek


On 5/30/07, Juliusz Chroboczek wrote:
> Note that in IPv6 you can combine RA with DHCPv6: use RA for address
> configuration, and DHCPv6 for configuring other data (such as DNS
> servers).

That sounds interesting,

so (naively said) I'd use RA for simple address assignments
(preferrably a client pool) and have a dhcp server that tells those
clients where the time server dns server whatever dns option i want
are but not the address.

Fixed address assignments still need pure dhcp (like certain dhcp
clients that need to have the same ip address at all times - static
configuration put aside)


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aeriksson
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Since: May 02, 2004
Posts: 2



PostPosted: Fri Jun 01, 2007 12:30 am    Post subject: Re: radvd or dhcp [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

said:
> On 5/30/07, Juliusz Chroboczek wrote:
> Note that in IPv6 you can combine RA with DHCPv6: use RA for address
> configuration, and DHCPv6 for configuring other data (such as DNS
> servers).

Nope. What you really want to do is to run zeroconf (switching to avahi right
now). It multicasts dns RRs on the ethernet segment which contains announced
services, e.g. dns, ntp etc... Quite elegant.

/A





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Wouter Verhelst
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Since: Nov 08, 2004
Posts: 663



PostPosted: Sun Jun 03, 2007 10:00 pm    Post subject: Re: radvd or dhcp [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)

On Thu, May 31, 2007 at 08:26:46PM +0200, aeriksson@fastmail.fm wrote:
> said:
> > On 5/30/07, Juliusz Chroboczek wrote:
> > Note that in IPv6 you can combine RA with DHCPv6: use RA for address
> > configuration, and DHCPv6 for configuring other data (such as DNS
> > servers).
>
> Nope. What you really want to do is to run zeroconf (switching to avahi right
> now). It multicasts dns RRs on the ethernet segment which contains announced
> services, e.g. dns, ntp etc... Quite elegant.

Elegant for small networks, perhaps, but not for large ones; that would
generate too much multicast traffic so that it'd drown out the regular
traffic in the end.

--
Shaw's Principle:
Build a system that even a fool can use, and only a fool will
want to use it.


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