round robin with over 30 IP

Simon Waters Simon at wretched.demon.co.uk
Fri Feb 14 20:23:25 UTC 2003


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Steffen Krenz wrote:
>
> we have eg following situation
>
> www    IN    A    1.2.3.4
> www    IN    A    2.3.4.5
> .....................
> ...................
> www    IN    A    6.6.6.6 (30 different ip´s)
>
> i ask some nameservers and they gave me all the ip´s in
different order.
> i asked over ten times and the round robin was perfect.
> some nameservers i asked gave me the ip´s every time in the
same order.
>
> could this lead to round robin problems?

Depends what you expect.

If you hand out the records with an appropriate order from your
own servers, with relatively short TTL, it will probably spread
traffic relatively evenly.

> in the answer packet the
> truncated bit is set. is there a maximum amount of A records i
can use
> for a host name?

No, there is a byte limit on the size of DNS packet that can be
handled by UDP (512 bytes), so older servers and those not
supporting EDNS0 may retry with a TCP query depending where in
the packet the truncation occurs.

30 is almost certainly going to be too big, and likely to lead
to slow look-up times and possibly other problems due to
misconfigured firewalls.

Have a look in the archive for discussions on the merits of DNS
based load balancing, and how to achieve it.

What you are trying to do looks highly unusual, and is probably
better achieved using less general purpose tools.

There are tools that will (attempt) to return geographically
close web servers, or update the DNS response to point to
servers on some other criteria (such as system load or response
time, or a combination). Whilst some don't like these tools they
will do a better job than just handing out large numbers of
records in random order.

What is the goal you are trying to achieve? Why so many IP's for
the same domain name?

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