Kluge delegation of a single host

[Michael Voight]

Jim Reid wrote:
> 

> 
>     Christine> www.jelly.com.  IN NS CDD.jelly.com.
>     Christine> cdd.jelly.com.  IN A 1.2.3.4
> 
>     Christine> I have not seen this before, is it legal? and workable
>     Christine> in BIND 8.2?  If not, can I mimic this dynamic load
>     Christine> balancing within BIND somehow?
> 
> The RRs are certainly legal. However you might expect problems with
> browsers who lookup www.jelly.com and get a SOA record returned
> instead of an A or CNAME record.

Why would they get an SOA record????
The Distributed Director would return an A record.

> 
> As for load balancing, you get that for free in BIND8. The name server
> will round-robin between N "equivalent" resource records:
>         www.jelly.com. IN A 1.2.3.4
>         www.jelly.com. IN A 1.2.3.5
>         www.jelly.com. IN A 1.2.3.6
>         www.jelly.com. IN A 1.2.3.7
> 

This is not the same functionality as DD.  Cisco DistributedDirector
only responds with a single A record based on a predictor value. DD also
does polling so it would not offer the address of a dead machine.

While it can do load balancing similar to round robin, it also can
return an address based on drp metric distance from client to server, as
well as allow portioning. You can give fast machines a portion value of
2 and they would have their address advertise twice as much as a machine
with a value of 1. DD is sold with Cisco 2500 or 4700-M routers, but you
can not simply buy the software for an existing router. It must be
purchased as a hw/sw combination.

Not an ad, just trying to clarify what DD is. Functionally, it is
configured into the network as a subdomain server (i.e. pointed to by a
higher level domain server via NS)

Michael Voight
Cisco System








> The first lookup of www.jelly.com will get answers with the IP
> addresses in the sequence 4, 5, 6 and 7. The next 5, 6, 7 and 4. And
> so on. This will mean that on average a quarter of the browsers will
> go to 1.2.3.4 because that was the first IP address in the answer
> section of quarter of the replies. For the same reason, a quarter will
> go to 1.2.3.5, another quarter to 1.2.3.6 and another to 1.2.3.7.
> This gives crude but effective (and simple!) load balancing.
> 
> However it does not take account of the respective capacities or the
> load on the 4 web servers (let's assume the addresses are on different
> systems). And it doesn't care about network topology either. Some
> users might go to 1.2.3.7 even though 1.2.3.4 was a better choice in
> networking terms: bandwidth, hop count, etc. If you want/need that
> functionality you probably need to use something like Cisco's
> Distributed Director or lbnamed - a "load-balancing" name server
> written in perl. Even so, for most circumstances the default
> round-robin mechanism in BIND8 should be good enough.