[PATCH] DFS referral shuffling

Robin McCorkell rmccorkell at karoshi.org.uk
Tue Feb 24 12:37:13 MST 2015

On 23/02/2015 11:19 PM, Steve French wrote:
> On Mon, Feb 23, 2015 at 1:23 PM, Richard Sharpe
> <realrichardsharpe at gmail.com <mailto:realrichardsharpe at gmail.com>> wrote:
>     On Mon, Feb 23, 2015 at 11:20 AM, Robin McCorkell
>     <rmccorkell at karoshi.org.uk <mailto:rmccorkell at karoshi.org.uk>> wrote:
>     > Hi,
>     >
>     > Any chance of getting this patch reviewed? DFS referral
>     shuffling allows
>     > load balancing of a DFS share for dumb clients, which is one of the
>     > primary uses of DFS, so I'd imagine it'd be useful for many people.
>     Shouldn't we fix smbclient and mount.cifs to have the correct
>     behavior?
> Makes sense to me to fix the clients - probably should shuffle, but
> not clear whether nearness should be a factor (same subnet at least?)
> and what criteria to use (or to allow to be configured) on client to
> decide which share to try first.
> Also (at least for mount.cifs) but also for smbclient presumably need
> to fix it so we cache some of the other referrals so we can reconnect
> to a copy if the network connection to the first one fails and we
> can't reconnect to the first one.

Actually, referral shuffling is mentioned in the spec, [MS-DFSC]

> The DFS server places the target servers in the referral response in
the following order:
> - Targets in the same site as the client are listed at the top of the
referral response in random order.
> - Targets outside the client's site are appended to the response in
random order.

Besides, implementing referral shuffling on the server side makes the
admin's life much easier - load balancing is guaranteed by the server
configuration, rather than relying on updated clients. But I agree: the
clients should perform heuristics to determine the best server to
connect to, rather than blindly picking the first one that works.
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