Re: using named with CARP

[Dave Tyson <dtyson%liv.ac.uk@localhost>]

On Thu, 25 Feb 2010 23:17:20 +1100 Malcolm Herbert wrote:

> As far as I can recall, an application (such as named) cannot bind
> directly to a CARP-managed virtual IP and listen for connections. Is
> this the case?
>
> I've seen CARP virtual IPs used to provide reliable routing services for
>a network but haven't seen them in use with an application listening on
>them directly, hence the question ...
>
>My thoughts for getting around that restriction (if it exists) would be
>to have the application listen on lo0 and configure pf to redirect or
>NAT incoming connections on the CARP VIP to the application on lo0.
>
>This sounds like it should work, although it seems to be a lot of extra
>effort to me ... is it really necessary?
>
>Can an application cope with having an IP interface suddenly disappear
>or re-appear after it has started? Or am I simply making things too hard
>for myself and everything should Just Work if the application binds to
>all network interfaces?
>
>What would I do in situations where I want the application to bind to
>the CARP interface only and then can't make use of the dynamic nature
>of an 'all interfaces' bind? I guess I could use pf to drop incoming
>connections from those interfaces I'm not interested in if this were the
>case ...
>
>Has anyone set up CARP in this manner with applications listening on
>the CARP VIP?

>Regards,
>Malcolm

I have a couple of servers which use carp to allow redundant operation to 
cover crashes or server failure. Both servers run bind and apache and bind to 
all interfaces include the carp one. The carp virtual address is configured in 
the ADSL firewall and so the only route into the boxes from outside is via the 
carp address. Everything works fine for both apache and named (and a few other 
services). 

Feb 25 19:02:19 forglen2 named[7948]: listening on IPv4 interface fxp0, 
192.168.0.222#53
Feb 25 19:02:19 forglen2 named[7948]: listening on IPv4 interface lo0, 
127.0.0.1#53
Feb 25 19:02:19 forglen2 named[7948]: listening on IPv4 interface carp0, 
192.168.0.220#53

Dave

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