Shuffle records and round robin

[Kevin Darcy]

Jon wrote:

> I am running BIND 9.2.2.  Recently I have been looking into using
> round robin to split the traffic over a few servers.  As far as I can
> see, its quite straight forward, just a case of entering each IP for
> the host.
>
> www IN A x.x.x.x
> www IN A z.z.z.z
>
> The question is a "how do they do it".  I notice yahoo.com returns a
> number of IP addresses, so that can't be using round robin, as I
> thought that only returns 1 IP (from the ones you entered).

Different definitions of "round robin" exist. BIND doesn't have any
convenient method of implementing the "shuffle" form of round-robin,
where only 1 address is presented at any given time from a list of
addresses. But many load-balancing products have the ability to do this.
BIND only has "sortlist" (which sorts all addresses lists according to
the source address of the querying client) or "rrset-order" which can
apply a particular ordering to a specific name or pattern of names. But,
BIND always returns the entire list and never "shuffles".

> bbc.co.uk only gives out one IP and if you wait for the TTL to expiry
> and query again, normally you get a different one - this I believe is
> round robin in action.
>
> Is the method yahoo.com use shuffle records, where it trys to order
> the IP addresses in an order which is closer to me (well the IP I am
> querying from).  Is the rrset-order option?

If they're using BIND, "sortlist" would be closer in functionality than
"rrset-order", but actually I think they use a non-BIND product...


- Kevin