query-source for multiple interfaces

Sam Wilson Sam.Wilson at ed.ac.uk
Fri May 19 09:05:17 UTC 2006

In article <e4j9g9$1i2i$1 at sf1.isc.org>,
 Barry Margolin <barmar at alum.mit.edu> wrote:

> It definitely will *not* use an alias on the loopback address.  If you 
> don't use query-source to force a particular address, the source address 
> of a query is always the address of the interface the query is sent out.  
> Since it should never send queries out the loopback interface, there's 
> no reason why it would ever select that as the source address.  I think 
> the use of query-source in the slide is just being extra cautious, and 
> safe in the case where the server is singly-homed.  But it's not really 
> necessary.

OK - makes perfect sense with hindsight.  Thanks.  I guess I'll take the 
query-source out.

> Also, unless the server is running a routing daemon, it probably won't 
> take much advantage of the fact that it's multihomed.  It will just send 
> most of its queries through its default gateway, so you might as well 
> set query-source to the interface connected to that.

Of course it's running a routing daemon - how else would the anycast 
address be propagated?  Even if it weren't it would get two default 
routes by IRDP - that's how it worked until we decided to try out 
anycast.  No point in being multihomed unless you can use more than one 

Thanks again,

Sam Wilson                             one of hostmaster at ed.ac.uk
Infrastructure Services Division
Computing Services, The University of Edinburgh
Edinburgh, Scotland, UK

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