How much use is IPTOS_LOWDELAY

David Holder david.holder at
Mon Jan 4 11:21:49 UTC 2016

Hi Richard,

Happy New Year!

I didn't see you get a response to this one so here are my thoughts.

IPTOS_LOWDELAY is historic. It refers to a time prior to Differentiated 
Services (DiffServ) when the Type of Service field in the IP header had 
bit flags indicating the quality of service required.

Today, with the advent of DiffServ, the Differentiated Services Code 
Point (DSCP) value for the required level of service should be set 
instead. The appropriate value will vary from network to network 
depending on the network's QoS policy.

See RFC 2474 for DiffServ.

To set the DSCP field use the the IP_TOS socket option in legacy IPv4 
(if you are still using v4) or the IPV6_TCLASS socket option in IPv6.

Hope that helps!

Best Regards,

Dr David Holder CEng FIET MIEEE

Erion Ltd, An Cala, Inverkirkaig, Lochinver, Sutherland, IV27 4LR, UK

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On 27/12/2015 19:02, Richard Sharpe wrote:
> Hi folks,
> I see a lot of noise out there on the internet about using
> IPTOS_LOWDELAY with Samba.
> Is there any data on how useful this is in terms of performance improvements?

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