search for: tcp_max_syn_backlog

...3306. Sending cookies. possible SYN flooding on port 3306. Sending cookies. possible SYN flooding on port 3306. Sending cookies. possible SYN flooding on port 3306. Sending cookies. I adapted already following: # sysctl -a |grep -E 'maxconn|syn_backlog' net.core.somaxconn = 2048 net.ipv4.tcp_max_syn_backlog = 2048 but ListenOverflows and ListenDrops values are still high # cat /proc/net/netstat | awk '{print $21 "-" $22 }' ListenOverflows-ListenDrops 13568-13568 any suggestion? -- Thanks, LF

...essage is emitted when the SYN backlog of a socket is full." http://blog.dubbelboer.com/2012/04/09/syn-cookies.html Furthermore: "While you see SYN flood warnings in logs not being really flooded, your server is seriously misconfigured." *A potential fix* - increase the net.ipv4.tcp_max_syn_backlog kernel parameter. Or tune some more parameters like tcp_synack_retries and netdev_max_backlog *My question *- to fix this SYN flooding problem should I modify net.ipv4.tcp_max_syn_backlog, net.core.somaxconn and the backlog size passed to the listen() syscall or might there be an alternative easie...

...ng into a behavior that I wouldn''t expect. I''d like to confirm an entry in sysctl.conf by changing the value if necessary or appending the key/value if it doesn''t exist in the file. This seems like a common scenario. However, the following example does not add net.ipv4.tcp_max_syn_backlog if it doesn''t already exist in sysctl.conf. class sysctl { file { "sysctl_conf": name => $operatingsystem ? { default => "/etc/sysctl.conf" }, } config { "net.ipv4.tcp_max_syn_backlog": ensure => 4096 } exec { "sysctl -p&q...

...gt; possible SYN flooding on port 3306. Sending cookies. >> possible SYN flooding on port 3306. Sending cookies. >> >> >> I adapted already following: >> >> # sysctl -a |grep -E 'maxconn|syn_backlog' >> net.core.somaxconn = 2048 >> net.ipv4.tcp_max_syn_backlog = 2048 >> >> >> but ListenOverflows and ListenDrops values are still high >> >> # cat /proc/net/netstat | awk '{print $21 "-" $22 }' >> ListenOverflows-ListenDrops >> 13568-13568 >> >> any suggestion? > > Use tools...

...0 vm.min_free_kbytes = 65536 net.core.rmem_default = 262144 net.core.rmem_max = 262144 net.core.wmem_default = 262144 net.core.wmem_max = 262144 net.core.netdev_max_backlog = 25000 net.ipv4.tcp_reordering = 127 net.ipv4.tcp_rmem = 4096 87380 16777216 net.ipv4.tcp_wmem = 4096 65536 16777216 net.ipv4.tcp_max_syn_backlog = 8192 net.ipv4.tcp_no_metrics_save = 1 The {r,w}mem_{max,default} values are twice what they were previously; changing these had no effect. The number of dirty pages is nowhere near the dirty_ratio when the hangs occur; there may be only 50MB of dirty memory. A local process on the NFS server...

...ng on port 3306. Sending cookies. > possible SYN flooding on port 3306. Sending cookies. > possible SYN flooding on port 3306. Sending cookies. > > > I adapted already following: > > # sysctl -a |grep -E 'maxconn|syn_backlog' > net.core.somaxconn = 2048 > net.ipv4.tcp_max_syn_backlog = 2048 > > > but ListenOverflows and ListenDrops values are still high > > # cat /proc/net/netstat | awk '{print $21 "-" $22 }' > ListenOverflows-ListenDrops > 13568-13568 > > any suggestion? Use tools like tcpdump/wireshark? and further examination...

If I execute these via command line, will they persist after a reboot? Or, should I be putting these into a file like /etc/sysctl.conf? --------------snip-------------- /sbin/sysctl -w net.ipv4.tcp_max_syn_backlog=2048 /sbin/sysctl -w net.ipv4.tcp_fin_timeout=30 /sbin/sysctl -w net.ipv4.tcp_keepalive_intvl=10 /sbin/sysctl -w net.ipv4.tcp_keepalive_probes=7 /sbin/sysctl -w net.ipv4.tcp_keepalive_time=1800 /sbin/sysctl -w net.ipv4.tcp_max_tw_buckets=360000 /sbin/sysctl -w net.ipv4.tcp_synack_retries=3 /sbin/sy...

I get these errors from the following settings in /etc/sysctl.conf file: # Custom Settings: net.ipv4.tcp_max_syn_backlog=2048 net.ipv4.tcp_fin_timeout=30 net.ipv4.tcp_keepalive_intvl=10 net.ipv4.tcp_keepalive_probes=7 net.ipv4.tcp_keepalive_time=1800 net.ipv4.tcp_max_tw_buckets=360000 net.ipv4.tcp_synack_retries=3 net.ipv4.tcp_rmem="4096 87380 16777216" net.ipv4.tcp_wmem="4096 87380 16777216" net....

i all I use linux as GiGE router and have 6 NIC on it Those days the NIC interrupt takes around 100% CPU but the system is 4G memroy and 8 CPU. I can't see any error packet in this NIC interface too After I block the udp, the %CPU drops. but the UDP only takes around 8M in general We use UDP traffic for voice. Do you have any suggestion ? increase the kernel parameter? Thank you so much

...shared memory segments, in pages kernel.shmall = 4294967296 ########### add by operation V1.0 begin ############ net.ipv4.ip_local_port_range = 32768 65000 net.core.rmem_max = 8388608 net.core.wmem_max = 8388608 net.ipv4.tcp_rmem = 4096 87380 8388608 net.ipv4.tcp_wmem = 4096 65536 8388608 net.ipv4.tcp_max_syn_backlog = 8192 net.ipv4.tcp_window_scaling = 0 net.ipv4.tcp_sack = 0 net.ipv4.tcp_timestamps = 0 kernel.panic = 5 vm.swappiness = 51 ########### add by operation V1.0 end ############ net.bridge.bridge-nf-call-ip6tables = 0 net.bridge.bridge-nf-call-iptables = 0 net.bridge.bridge-nf-call-arptables = 0...

...4.icmp_ignore_bogus_error_responses = 1 net.ipv4.conf.all.log_martians = 0 net.ipv4.conf.default.log_martians = 0 net.ipv4.conf.default.accept_source_route = 0 net.ipv4.conf.all.accept_redirects = 0 net.ipv4.conf.default.accept_redirects = 0 vm.vfs_cache_pressure = 35 vm.nr_hugepages = 512 net.ipv4.tcp_max_syn_backlog = 2048 fs.aio-max-nr = 1048576 vm.dirty_background_ratio = 3 vm.dirty_ratio = 40 After making changes, do you have any recommendations on which tools to use to monitor those changes and see how they perform? I have noatime set in fstab in the guest for the /var partition, where much of the spamas...

Hello, I current have a FreeBSD 4.8 bridge firewall that sits between 7 servers and the internet. The servers are being attacked with syn floods and go down multiple times a day. The 7 servers belong to a client, who runs redhat. I am trying to find a way to do some kind of syn flood protection inside the firewall. Any suggestions would be greatly appreciated. -- Ryan James ryan@mac2.net

...tcp_mem echo 400000 400000 400000 > /proc/sys/net/ipv4/tcp_rmem echo 400000 400000 400000 > /proc/sys/net/ipv4/tcp_wmem echo 1 > /proc/sys/net/ipv4/tcp_tw_recycle echo 0 > /proc/sys/net/ipv4/tcp_sack echo 8192 > /proc/sys/net/ipv4/tcp_max_syn_backlog echo 500000 > /proc/sys/net/ipv4/tcp_max_tw_buckets echo 0 > /proc/sys/net/ipv4/tcp_timestamps Linux-Linux ftp 251000kbit/s Linux-XP ftp 40000kbit/s Linux-Linux smbclient 236000kbit/s (3.0.20pre1-1) Linux-XP Explorer 22000kbit/s (3.0.20pre1-1) Linux-X...

https://bugzilla.netfilter.org/cgi-bin/bugzilla/show_bug.cgi?id=40 laforge@netfilter.org changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |ASSIGNED ------- Additional Comments From laforge@netfilter.org 2003-02-03 16:49 ------- We haven't seen this