When increasing net.inet.udp.recvspace on a server (FreeBSD 13.2), I noticed I can no longer SSH into that server if I set the value higher than 1.86 MB. The current SSH session is kept alive, but if I initiate another simultaneous ssh connection, I get the following error message: kex_exchange_identification: Connection closed by remote host Connection closed by 172.31.29.181 port 22 Also, if I close the current SSH session, I am locked out of the server. In /var/log/messages, I notice the following: Jan 11 16:57:23 server-1 sshd[14120]: fatal: bad addr or host: <NULL> (Name does not resolve) I then checked the ena0 interface: #ifconfig ena0 -v ifconfig: socket(family 2,SOCK_DGRAM): No buffer space available Finally, I checked the network memory buffer space: #netstat -m 3984/2376/6360 mbufs in use (current/cache/total) 0/1270/1270/1004997 mbuf clusters in use (current/cache/total/max) 0/1270 mbuf+clusters out of packet secondary zone in use (current/cache) 3982/1352/5334/502498 4k (page size) jumbo clusters in use (current/cache/total/max) 0/0/0/148888 9k jumbo clusters in use (current/cache/total/max) 0/0/0/83749 16k jumbo clusters in use (current/cache/total/max) 16924K/8542K/25466K bytes allocated to network (current/cache/total) 0/0/0 requests for mbufs denied (mbufs/clusters/mbuf+clusters) 0/0/0 requests for mbufs delayed (mbufs/clusters/mbuf+clusters) 0/0/0 requests for jumbo clusters delayed (4k/9k/16k) 0/0/0 requests for jumbo clusters denied (4k/9k/16k) 0 sendfile syscalls 0 sendfile syscalls completed without I/O request 0 requests for I/O initiated by sendfile 0 pages read by sendfile as part of a request 0 pages were valid at time of a sendfile request 0 pages were valid and substituted to bogus page 0 pages were requested for read ahead by applications 0 pages were read ahead by sendfile 0 times sendfile encountered an already busy page 0 requests for sfbufs denied 0 requests for sfbufs delayed As far as I can tell, it doesn't look like network memory buffers are close to full. I also found that if I increase kern.ipc.maxsockbuf to 3 MB, I am able to increase the net.inet.udp.recvspace to 2 MB and SSH on the server. Apparently, the kern.ipc.maxsockbuf must be set a little higher than the net.inet.udp.recvspace, which makes sense. The command I used to increase/decrease udp socket buffer space: #sysctl net.inet.udp.recvspace=value Server specs: FreeBSD server-1 13.2-RELEASE-p8 FreeBSD 13.2-RELEASE-p8 GENERIC amd64 I'm not sure whether this is a bug or not, but I have no idea why this happens. This is a reference to the following discussion on the FreeBSD forums: https://forums.freebsd.org/threads/cant-connect-with-ssh-after-changing-net-inet-udp-recvspace.91874/