E.6 4.4BSD

4.4BSD is the first of the Berkeley releases to provide dynamic configuration for numerous kernel parameters. The sysctl (8) command is used. The names for the parameters were chosen to look like MIB names from SNMP. To examine a parameter we type:

 vangogh %  sysctl net.inet.ip.forwarding  net.inet.ip.forwarding = 1

To change a parameter we need superuser privilege and then type:

 vangogh #  sysctl -w net.inet.ip.ttl=128

The following parameters can be changed.

`net.inet.ip.forwarding`

If 0 (default), IP datagrams are not forwarded. If 1, forwarding is enabled.

`net.inet.ip.redirect`

If 1 (default), the host will send ICMP redirects when forwarding IP datagrams. If 0, ICMP redirects are not sent.

`net.inet.ip.ttl`

The default TTL for both TCP and UDP. The default is 64.

`net.inet.icmp.maskrepl`

If 0 (default), the host does not respond to ICMP address mask requests . If 1, it does respond.

`net.inet.udp.checksum`

If 1 (default), UDP checksums are calculated for outgoing UDP datagrams, and incoming UDP datagrams containing nonzero checksums have their checksum verified . If 0, outgoing UDP datagrams do not contain a checksum, and no checksum verification is performed on incoming UDP datagrams, even if the sender calculated a checksum.

Additionally, numerous variables that we've described earlier in this appendix are scattered among various source files ( tcp_keepidle, subnetsarelocal, etc.) and can be modified.