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). Alister On 18/07/2019, 06:52, "Freeradius-Users on behalf of James Wood" <freeradius-users-bounces+alister.winfield=sky.uk@lists.freeradius.org on behalf of james.wood@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? Thanks J - List info/subscribe/unsubscribe? See https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.freeradius.org%2Flist%2Fusers.html&data=02%7C01%7Calister.winfield%40sky.uk%7C671716d463054c78e42a08d70b442e11%7C68b865d5cf184b2b82a4a4eddb9c5237%7C0%7C0%7C636990259784198618&sdata=caG8ueU%2FpTo1CqI9d%2BJwyPKd%2BLqobLyXIGgW17ZxO38%3D&reserved=0 -------------------------------------------------------------------- This email is from an external source. Please do not open attachments or click links from an unknown or suspicious origin. Phishing attempts can be reported by sending them to phishing@sky.uk as attachments. Thank you -------------------------------------------------------------------- Information in this email including any attachments may be privileged, confidential and is intended exclusively for the addressee. The views expressed may not be official policy, but the personal views of the originator. If you have received it in error, please notify the sender by return e-mail and delete it from your system. You should not reproduce, distribute, store, retransmit, use or disclose its contents to anyone. Please note we reserve the right to monitor all e-mail communication through our internal and external networks. SKY and the SKY marks are trademarks of Sky Limited and Sky International AG and are used under licence. Sky UK Limited (Registration No. 2906991), Sky-In-Home Service Limited (Registration No. 2067075), Sky Subscribers Services Limited (Registration No. 2340150) and Sky CP Limited (Registration No. 9513259) are direct or indirect subsidiaries of Sky Limited (Registration No. 2247735). All of the companies mentioned in this paragraph are incorporated in England and Wales and share the same registered office at Grant Way, Isleworth, Middlesex TW7 5QD