[Dibbler-devel] help

[Tomasz Mrugalski]

On Sat, 13 Jan 2007 somebody known as aparna.srinivasamurthy at wipro.com wrote:

> Perhaps, I don't need prefix delegation feature of the dibbler. Actually 
>I want to know the "prefix Length" of the IPv6 address delegated by the 
>Dibbler server. Currently I'm hard coding the prefix length as 64 in my 
>client code. Hence wanted to know if I can get the length (like subnet 
>mask in IPv4) too from server. In the config file i could not set the 
>length in pool. Please have a look at my config file contents below,
Did you read Frequenty Asked Question in the Dibbler User's Guide? I mean 
the very first question. I suppose you didn't :)

Ok, here come the answer (again):
DHCPv6 protocol was intended (among other things) to provide addresses. As 
for the prefix length, you should use a feature called router 
advertisements. THERE IS NO WAY TO SPECIFY PREFIX LENGTH VIA DHCPv6.
It's rather odd, but that's the way DHCPv6 protocol has been designed - to 
provide addresses. For prefix/routing configuration, router advertisements 
should be used. There is a nice radvd daemon for Linux. In Windows 
environment you can use ipv6.exe or netsh.exe tools to start RA 
announcements.

As this is a very common issue, i have implemented a workaround for this, 
but it is direct VIOLATION OF THE RFC3315. However, it works quite nice. 
When dibbler-client receives and address it also configures routing for 
it. It uses default prefix length set to 64. If you don't like it, you can 
switch dibbler back to default mode (as specified in RFC3315) by putting 
strict-rfc-no-routing directive in the client.conf file.

Prefix length is defined in Misc/DHCPConst.h (CLIENT_DEFAULT_PREFIX_LENGTH 
constant). If you want to change this, you must recompile dibbler client.

> Please let me know if my understanding is correct. And do let me know 
>does the server gives the prefix length or not!!
No, you understanding is not correct.
No, server does not provide prefixes.
Yes, I know that it is weird, but that's the way it was designed (by the 
RFC authors, not by me).

Best regards,

-- 
Tomasz Mrugalski,              | "We all know Linux is great...it does    |
thomson(at)klub(dot)com(dot)pl |  infinite loops in 5 seconds."           |
                                |                           Linus Torvalds |