persistent connections within cisco firewall

Our cisco firewall tears down old connections so I sometimes modify the kernel to send keep alives on tcp connections:

[root@server ~]# tail -2 /etc/sysctl.conf
# keep persistent connection (so firewall doesn't tear down)
net.ipv4.tcp_keepalive_time = 900
[root@server ~]#

redhat hang

If your RedHat system gets really overloaded and hangs here are some things that might help:

• SysRq: SysRq is a key combo you can hit which the kernel will respond to regardless of whatever else it is doing, unless it is completely locked up.
• Hangwatch: Hangwatch periodically polls /proc/loadavg, and echos a user-defined set of characters into /proc/sysrq-trigger if a user-defined load threshold is exceeded.
• NMI: Non-Maskable Interrupt (NMI) is a mechanism to detect system lockups. It enables the built-in kernel deadlock detector. By executing periodic NMI interrupts, the kernel can monitor whether any CPU has locked up and print out debugging messages as needed.