Time to fine-tune our IP stack:
If you have memore to spare, you can use replace these corresponding settings with:
root@zen-lb:~# vi /etc/sysctl.conf# Performance:
# Turn down swappiness, 0 means no swap on modern kernels, number is percent of free system memory swap will kick in.
vm.swappiness = 2
# Contains, as a percentage of total system memory, the number of pages at which a process which is generating disk writes will start writing out dirty data.
# Defaults to 10 (percent of RAM). Consensus is that 10% of RAM when RAM is say half a GB (so 10% is ~50 MB) is a sane value on spinning disks, but it can be MUCH worse when RAM is larger, say 16 GB (10% is ~1.6 GB), as that's several seconds of writeback on spinning disks. A more sane value in this case is 3 (16*0.03 ~ 491 MB).
vm.dirty_ratio = 3
# Contains, as a percentage of total system memory, the number of pages at which the background kernel flusher threads will start writing out dirty data.
# Defaults to 5 (percent of RAM). It may be just fine for small memory values, but again, consider and adjust accordingly for the amount of RAM on a particular system.
vm.dirty_background_ratio = 2
# Will not change the number of System V IPC message queue resources allowed
# Will not change Kernel semaphores (kernel.sem [semmsl semmns semopm semmni], kernel.shmmax and kernel.shmmin)
# Network Performance:
# Turn off TCP prequeue processing
net.ipv4.tcp_low_latency = 1
# Reuse time-wait sockets, better than recycling
net.ipv4.tcp_tw_reuse = 1
# Fast recycling TIME-WAIT sockets using recycling rather than reusing. Default value is 0. It should not be changed without advice/request of technical experts.
net.ipv4.tcp_tw_recycle = 0
# Maximum time-to-live of entries. Unused entries will expire after this period of time if there is no memory pressure on the pool.
net.ipv4.inet_peer_maxttl = 5
# How often to send out keepalive messages when keepalive is enabled. Default is 7200 seconds.
net.ipv4.tcp_keepalive_time = 512
# How frequent probes are retransmitted, when a probe isn't acknowledged. Default is 75 seconds
net.ipv4.tcp_keepalive_intvl = 15
# Number of keepalive probes to send until the server decides that the connection is broken.
net.ipv4.tcp_keepalive_probes = 5
# Number of outstanding syn requests allowed. This setting tells the system when to start using syncookies. When you have more TCP connection requests in your queue than this number, the system will start using syncookies. Note that syncookies can have an impact on performance.
net.ipv4.tcp_max_syn_backlog = 36000
# Size of the listen queue
net.core.somaxconn = 36000
# Maximum number of timewait sockets held by the system simultaneously.
net.ipv4.tcp_max_tw_buckets = 100000
# Increase TCP default and max receive/send buffer size
net.core.rmem_default = 16777216
net.core.rmem_max = 16777216
net.core.wmem_default = 16777216
net.core.wmem_max = 16777216
# Same for UDP
net.ipv4.udp_rmem_min = 8192
net.ipv4.udp_wmem_min = 8192
# Increase the maximum amount of option memory buffers
net.core.optmem_max= 20480
# Increase Linux autotuning TCP receive/send buffer limit
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216
# Increase the length of the packets queue waiting on an interface until the kernel is ready to process them
# The backlog of pending connections allows the server to hold connections it’s not ready to accept, and this allows it to withstand a larger slow HTTP attack, as well as gives legitimate users a chance to be served under high load. However, a large backlog also prolongs the attack, since it backlogs all connection requests regardless of whether they’re legitimate. If the server supports a backlog, I recommend making it reasonably large to so your HTTP server can handle a small attack.
net.core.netdev_max_backlog = 30000
# This setting determines the time that must elapse before TCP/IP can release a closed connection and reuse its resources.
net.ipv4.tcp_fin_timeout = 30
# Turn connection accounting on
net.netfilter.nf_conntrack_acct = 1
# Maximum number of tracked connections, the toll is 300-350 bytes of unswapped RAM per connection. Hash table should accordingly be hashsize = conntrack_max / 8, that why the options ip_conntrack hashsize=25000 and options nf_conntrack hashsize=25000 in modprobe.conf
net.ipv4.netfilter.ip_conntrack_max = 200000
# Dynamically-assigned ports range; bear in mind that in theory IANA has officially designated the range 49152 - 65535 for dynamic port assignment. The default linux range for modern kernels is 32768 - 61000.
net.ipv4.ip_local_port_range = 10000 65535
# Now that we've increased the ports, we need to increase the number of file handlers as well. This parameter should be at least as twice big as the number of network connections you expect to support. We should also change the number of max number of open files a user can have in /etc/security/limits.conf.
fs.file-max = 1048576
# Increase the number of allowed mmapped files
vm.max_map_count = 1048576
# This setting determines the number of SYN+ACK packets sent in part 2 of a 3-way-handshake before the kernel gives up on the connection. Default is 5.
net.ipv4.tcp_synack_retries = 3
# Number of times initial SYNs for a TCP connection attempt will be retransmitted. This is only the timeout for outgoing connections. Default is 5.
net.ipv4.tcp_syn_retries = 3
# This defines how often an answer to a TCP connection request is retransmitted before it gives up. This is only the timeout for incoming connections. Default is 3.
net.ipv4.tcp_retries1 = 3
# Determines how the TCP stack should behave for memory usage; each count is in memory pages (typically 4KB).
net.ipv4.tcp_mem = 50576 64768 98152
#net.ipv4.tcp_mem = 128000 200000 262144 # Use this for 1Gb+ connections
# The TCP window scale option is an option to increase the receive window size allowed in TCP above its former maximum value of 65535 bytes. See IETF RFC 1323.
# Linux kernels from 2.6.8 have enabled TCP Window Scaling by default
net.ipv4.tcp_window_scaling = 1
# How may times to retry before killing TCP connection, closed by our side. Default 0.
net.ipv4.tcp_orphan_retries = 0
# Security:
# Debian does not have kernel.exec-shield, check that you have NX (Execute Disable) protection: active with dmesg | grep protection. To have NX protection, your BIOS, your CPU, your OS must support it and you must have a 32-bit PAE or 64 bit kernel (NX bit works on the 63rd bit of the address)
#kernel.exec-shield = 1
# Turn on protection and randomize stack, vdso page and mmap + randomize brk base address.
kernel.randomize_va_space = 2
# tcp_syncookies with appropriate tcp_synack_retries and tcp_max_syn_backlog can mitigate SYN flood attacks. Note That without SYN cookies, a much larger value for tcp_max_syn_backlog is required. Default is 1.
net.ipv4.tcp_syncookies = 1
# Protect against tcp time-wait assassination hazards
net.ipv4.tcp_rfc1337 = 1
# Timestamps can provide security by protecting against wrapping sequence numbers (at gigabit speeds) but they also allow uptime detection. Definitely enable for Gb+ speeds, up to the admin to decide what to do for slower speeds.
# 1 is the default value but it has some overhead, use 0 for slightly better performance.
net.ipv4.tcp_timestamps = 0
#net.ipv4.tcp_timestamps = 1 # Use this for 1Gb+ connections
If you have memore to spare, you can use replace these corresponding settings with:
....
net.core.rmem_max=1677721600
net.core.rmem_default=167772160
net.core.wmem_max=1677721600
net.core.wmem_default=167772160
net.core.optmem_max= 2048000
....
net.ipv4.tcp_rmem= 1024000 8738000 1677721600
net.ipv4.tcp_wmem= 1024000 8738000 1677721600
net.ipv4.tcp_mem= 1024000 8738000 1677721600
net.ipv4.udp_mem= 1024000 8738000 1677721600
....
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