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Re: curl DSCP option?
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From: Ronan Pigott via curl-users <curl-users_at_lists.haxx.se>
Date: Wed, 22 May 2024 07:05:35 +0000
> I don't know much about DSCP, but from what I understand it you are
> (almost?)
>
> asking for this:
>
> https://github.com/curl/curl/pull/13606
Wow, what lucky timing. This looks like just what I had in mind.
DSCP is just the top 6 bits of what used to be the IP type-of-service field in
the IP header. Now the bottom two bits are used for ECN and the top 6 for
differentiated service.
In my case, I am interested because the cake qdisc "diffserv" configuration
uses this field to help select a traffic category for various flows, and cake
is the qdisc of choice for implementing QoS/SQM in OpenWRT and other home
routers. With very constrained upload bandwidth, the ability to mark some
transfers as "background" traffic with the LE (Lower Effort) codepoint is
useful to help maintain low latency on the link under load, and I expect that
is mostly how it will be used in curl.
Linux or custom netfilter may also use this field to set the internal sk
priority, which in turn is used by drivers to determine, e.g. 802.1p VLAN
priority, or 802.11e User Priority / Access Category if it traverses a Wi-Fi
network. I have observed some odd issues apparently related to 802.11e with my
laptop wi-fi card, and this could be useful to produce affected traffic on
demand for debugging purposes, similar to ping -Q.
Cheers,
Ronan
Date: Wed, 22 May 2024 07:05:35 +0000
> I don't know much about DSCP, but from what I understand it you are
> (almost?)
>
> asking for this:
>
> https://github.com/curl/curl/pull/13606
Wow, what lucky timing. This looks like just what I had in mind.
DSCP is just the top 6 bits of what used to be the IP type-of-service field in
the IP header. Now the bottom two bits are used for ECN and the top 6 for
differentiated service.
In my case, I am interested because the cake qdisc "diffserv" configuration
uses this field to help select a traffic category for various flows, and cake
is the qdisc of choice for implementing QoS/SQM in OpenWRT and other home
routers. With very constrained upload bandwidth, the ability to mark some
transfers as "background" traffic with the LE (Lower Effort) codepoint is
useful to help maintain low latency on the link under load, and I expect that
is mostly how it will be used in curl.
Linux or custom netfilter may also use this field to set the internal sk
priority, which in turn is used by drivers to determine, e.g. 802.1p VLAN
priority, or 802.11e User Priority / Access Category if it traverses a Wi-Fi
network. I have observed some odd issues apparently related to 802.11e with my
laptop wi-fi card, and this could be useful to produce affected traffic on
demand for debugging purposes, similar to ping -Q.
Cheers,
Ronan
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