эти настройки (/etc/sysctl.conf) с моего сервака с 2.6.26-2-amd64 (debian lenny stock kernel) ядром для меня они вполне подходят - для других, это дело других
net.unix.max_dgram_qlen = 10000
net.ipv4.ip_dynaddr = 0
net.ipv4.ip_local_port_range = 1025 65535
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.conf.all.arp_ignore = 1
net.ipv4.conf.all.arp_filter = 1
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.all.log_martians = 0
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.secure_redirects = 1
net.ipv4.conf.all.send_redirects = 0
net.ipv4.tcp_syncookies = 0
net.ipv4.tcp_workaround_signed_windows = 1
net.ipv4.tcp_rfc1337 = 1
net.ipv4.tcp_no_metrics_save = 1
net.ipv4.tcp_max_syn_backlog = 8192
net.ipv4.tcp_congestion_control = veno
net.ipv4.tcp_timestamps = 0
net.ipv4.tcp_mem = 131072 262144 1048576
net.ipv4.tcp_rmem = 65535 131072 262144
net.ipv4.tcp_wmem = 65535 131072 262144
net.ipv4.tcp_reordering = 9
net.ipv4.tcp_frto = 2
net.ipv4.tcp_frto_response = 2
net.ipv4.tcp_ecn = 0
net.ipv4.tcp_abc = 2
net.ipv4.tcp_max_tw_buckets = 1048576
net.ipv4.tcp_fin_timeout = 5
net.ipv4.tcp_retrans_collapse = 0
net.ipv4.tcp_orphan_retries = 9
net.ipv4.tcp_low_latency = 0
net.ipv4.tcp_max_tw_buckets = 1048576
net.ipv4.icmp_ignore_bogus_error_responses = 1
net.ipv4.icmp_ratelimit = 0
net.ipv4.tcp_tw_recycle = 0
net.ipv4.tcp_app_win = 32
net.ipv4.tcp_tso_win_divisor = 2
net.ipv4.tcp_slow_start_after_idle = 0
net.ipv4.ip_no_pmtu_disc = 0
net.ipv4.ip_default_ttl = 255
net.ipv4.ipfrag_low_thresh = 262144
net.ipv4.ipfrag_high_thresh = 393216
net.core.somaxconn = 65535
net.core.optmem_max = 33554432
net.core.rmem_max = 16777216
net.core.rmem_default = 524288
net.core.wmem_max = 16777216
net.core.wmem_default = 524288
net.core.netdev_max_backlog = 16777216
net.core.netdev_budget = 65535
net.core.dev_weight = 65535
net.ipv4.netfilter.ip_conntrack_max = 16777216
net.netfilter.nf_conntrack_expect_max = 16777216
kernel.sem = 250 256000 100 1024
kernel.threads-max = 32768
kernel.max_lock_depth = 4096
kernel.core_uses_pid = 1
kernel.maps_protect = 1
kernel.domainname = artifica
kernel.printk = 4 4 1 7
vm.mmap_min_addr = 65535
vm.overcommit_memory = 0
vm.swappiness = 5
vm.vfs_cache_pressure = 150
vm.dirty_ratio = 65
vm.dirty_background_ratio = 50
vm.zone_reclaim_mode = 1
vm.min_free_kbytes = 65535
vm.page-cluster = 512
vm.dirty_writeback_centisecs = 300
vm.dirty_expire_centisecs = 900
vm.hugepages_treat_as_movable = 1
vm.min_slab_ratio = 64
vm.drop_caches = 0
fs.file-max = 16777216
fs.aio-max-nr = 16777216
fs.mqueue.msg_max = 16384
fs.mqueue.msgsize_max = 16384
fs.mqueue.queues_max = 32768
fs.inotify.max_queued_events = 16777216
dev.hpet.max-user-freq = 65535
в связи со всё более увеличивающимся опытом использования линукс-систем эти настройки могут видоизменяться.