[Pdns-users] pdns-recursor + heartbeat

[Chris Foote]

On Wed, 27 Dec 2006, Kai wrote:

> On Thu, Dec 21, 2006 at 12:07:58PM +1030, Chris Foote wrote:
>>
>> I was in a similar situation with getting pdns listening on IP aliases
>> that aren't available at daemon startup.  I wanted to have pdns running
>> and responding successfully to test queries and then bring up IP aliases
>> which were then advertised via OSPF to routers.  The obvious way to do
>> this was to configure pdns to listen on 0.0.0.0, however pdns responses
>> contain the source IP of the main ethernet interface, not that of the IP
>> alias.
>
> We run our instances on a locally configured address (lo0 or lo1), and use
> ospf or openbgp to signal availability to routers.
>
> No need to bind to 0.0.0.0 in that case, and this works across other OSes
> too.

Hi Kai.

That's exactly the situation I was trying to explain, with the exception
that `ifconfig lo:0 down` is used so that OSPF sends a change in link
state immediately to all neighbours.

If you didn't take the interface/IP-alias/loopback down as you are
suggesting, then you would either need to reconfigure your OSPF/BGP to
stop advertising the address, or kill the OSPF/BGP process.  In the
later, you would be relying on the neighbour-dead timeout period
if there's no clean shutdown implemented.  If you were reconfiguring an
access-list/route-map/etc in BGP or OSPF, then I suppose that could be
a reasonable workaround, but it can be rather inconvenient compared to
simply taking an interface down.  e.g. When using config files, the ospfd
process under Quagga has to be killed and started as it has no external
'reload' functionality.  To make a change without killing the process,
you would have to interface with the interactive version of the 'vtysh'
terminal process, something which is accident-prone, and takes some
time.

Cheers,
Chris