[radvd-devel-l] Running two radvd daemons on the

Pekka Savola pekkas at netcore.fi
Thu Mar 20 03:54:43 EDT 2008

Hello Mark,

On Thu, 20 Mar 2008, Mark Ryden wrote:
> I am new to radvd; I had installed radvd on a machine in a LAN and
> configured and ran it successfully; the other hosts got the prefix from this
> radvd and configured IP addresses according to it.
> Regarding radvd daemon
> According to:
> http://fermiparadox.wordpress.com/2007/02/18/using-radvd/
> ...
> "there should be only one node running it it the whole network."
> ...
> I had tried to install a second radvd on this LAN and I had configured it
> with a different prefix and activated it. The hosts on the LAN had configured
> one more IPV6 address, with the prefix of the second radvd daemon
> My question is:
> - is there a way to prevent such scenario ?
> Is it the responsibility of the radvd daemon to make sure that there
> is no other
> radvd daemons running on the same LAN ? or is there some intention to change the
> ipv6 kernel so that in such a case only the first radvd ROUTER ADVERTISEMENT
> message will be accepted ?

No, preventing this is not easy.  Radvd daemon can't control this. 
The kernel modification you suggest does not work (e.g., in case you 
change the prefix or the router's MAC address changes, how could the 
code handle the scenario)?

It's OK to have multiple routers running radvd on the same LAN, even 
advertising different prefixes.

What is usually a problem, however, that some host thinks it is a 
router and starts advertising a bogus prefix and as a result either 
blackholes traffic or results in hosts generating useless addresses.

The following document describes the problems and potential fixes:


Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

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