[EXTERNAL] Re: Proxy issue - Failing proxied request for user error

Winfield, Alister Alister.Winfield at sky.uk
Thu Jul 18 10:21:28 CEST 2019

Sigh basic network tuning on Linux.

Yes and on high rate systems I've even managed to wrap the default NIC's ring-buffer mostly due to the kernel not processing enough per-interrupt. (Took a while to work out how you can get malformed packets in userland that definitely should have failed the checksums).

On how big.... that depends.

If what you are really seeing is short bursts of high rates and the server can easily keep up feel free to make the buffer HUGE. Latency might go up when the burst arrives but assuming it's all processed before timeouts start occurring you are good. If you are really starved for resource then increasing the buffers is bad news and might mean you process nothing before timeout essentially creating a total service failure rather than handling some percentage of requests. (This is especially true for DHCP, so much so that random drops to keep the queue short actually works better than answering everything when overloaded).


´╗┐On 18/07/2019, 06:52, "Freeradius-Users on behalf of James Wood" <freeradius-users-bounces+alister.winfield=sky.uk at lists.freeradius.org on behalf of james.wood at purplewifi.com> wrote:

    Found it.

    I checked `cat /proc/net/udp` and could see some packets being dropped in
    the UDP buffer queue; and whilst monitoring the dropped packets we're
    seeing from the clients, the numbers were going up in line with this.

    So I increased the `net.core.rmem` and `net.core.wmem` values a little on
    the server via sysctl, to increase the default UDP buffer size which has
    stopped the timeouts from occurring.

    I guess out the box the server has am appropriate value for the UDP buffer
    queue but when using FreeRADIUS it fills it up if there's enough traffic
    (and its all UDP) and then the kernel starts dropping packets.

    Whist I appreciate it's not FreeRADIUS related, is there any advice around
    the best sysctl values to use for a large FreeRADIUS server? Has anyone
    come across this before?


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