On 8/7/24 7:06 AM, Alan Somers wrote:
I'd like to track the rate of packet loss for outbound packets from some production servers. Obviously, that's impossible. But I think that the rate of TCP retransmissions should be a close proxy for packet loss. Currently I can only observe TCP retransmissions by using wireshark, a slow and laborious process. But it seems to me that the network stack should already have that information
The kernel already maintains a VNET-virtualized tcpstat structure for aggregate TCP stats. netstat and systat grab these using the net.inet.tcp.stats sysctl. This might work for you if you're okay with global and not per-interface information.
VNET_PCPUSTAT_DECLARE(struct tcpstat, tcpstat); /* tcp statistics */ $ netstat -sp tcp | grep -iE 'retr|rexm' $ systat -tcp Regards, Navdeep > Would it
be possible to add a sysctl to expose the total number of retransmissions since boot? This information would be very useful. It could reveal for example problems with a model of NIC, or congestion on one network segment but not another, or a regression in the OS. -Alan
