Understanding Linux Network Internals

Tuning via /proc Filesystem

As we saw in an earlier chapter, the neighboring protocols follow the common kernel practice of offering a convenient interface in the /proc directory to let administrators tune the subsystem's parameters. The neighboring subsystem 's parameters reside in four directories, two for IPv4 and two for IPv6:

/proc/sys/net/ipv4/neigh

/proc/sys/net/ipv6/neigh

Generic parameters of the neighboring subsystem, such as the timers used to control when cache operations take place

/proc/sys/net/ipv4/conf

/proc/sys/net/ipv6/conf

Particular behaviors within the protocol, such as the ones described in the section "Tunable ARP Options" in Chapter 28

Each directory contains a subdirectory for each NIC device on the system, a default subdirectory, and (in the case of the conf directory) an all subdirectory that can be used to apply a change to all the devices at once. Under conf, the default subdirectory shows the global status of each feature, while under neigh, the default subdirectory shows the default setting (i.e., configuration parameters) of each feature. The values of the default subdirectories are used to initialize the per-device subdirectories when the latter are created.

The directories for individual devices take precedence over the more general directories. But not all devices pay attention to all the parameters; if a parameter is not relevant to a device, the associated directory contains a file for the parameter but the kernel ignores it. For instance, ...