Tunable parameters

Obsolete networking parameter values

Obsolete general networking parameters

INTTL: Formerly, specified the default time-to-live value for Internet Protocol packets. This is the maximum number of intermediate hops a packet can go through. This parameter value could be overridden by higher-level protocols (see the UDPTTL and TCPTTL parameter descriptions) or by programmer action. This parameter was replaced by ip_ttl.

ARPHASHBCKTCNT: Formerly, specified the number of arp hash table buckets.
ARPHASHBCKTSIZE: Formerly, specified the number of entries per arp hash table bucket.

ICMPMASKREQ: Formerly, controlled whether icmp responds to subnet mask requests. By default, this was turned off (set to zero). When turned on (set to one), the system responded to subnet mask requests using the subnet mask for the interface the request was received on. This parameter was turned on when a system needed to supply subnet mask information to another system (for example, to a diskless workstation). Otherwise it was turned off.

IP_SRCROUTING: Formerly, controlled whether ip rejected (default) or accepted source routed packets. Turning this parameter on (setting it to ``1'') could have compromised the security of your system by making it potentially vulnerable to certain types of attacks that use source routed packets.
IPCKSUM: Formerly, controlled whether IP (Internet Protocol) checksumming was enabled. By default, IP checksumming was turned on (set to ``1''). Except when the underlying hardware guarantees correct and uncorrupted delivery of all packets, this parameter was supposed to remain turned on.
IPFORWARDING: Formerly, if IPFORWARDING was set, hosts acted as gateways. Controlled whether ip forwarded packets; that is, whether it acted as a gateway. This parameter was to be turned on (set to ``1'') only if the machine is intended to be a gateway.
IPSENDREDIRECTS: Formerly, controlled whether ip generated ICMP (Internet Control Message Protocol) redirect messages when forwarding packets to a destination that the sender should be able to reach directly. This was to be turned on (set to ``1'') only if needed to support diskless workstations, or if the machine was acting as a router or gateway.

RTSUBNETSARELOCAL: Formerly, the Internet Protocol limited the size of packets sent through a gateway to 576 bytes (per RFC 1122). If RTSUBNETSARELOCAL was nonzero, this restriction was not applied to destinations that are on non-connected subnets of a network to which the machine is connected. In other words, this assumes that any gateway to a subnet of a connected network could handle large packets. This parameter was to be tuned in a configuration in which all subnets are connected by high-bandwidth gateways and media (such as several networks connected by routers).

ASYHMTU: Formerly, specified the default packet size used during connection initialization.

PPPHIWAT: Formerly, established the STREAMS high water mark for the ppp driver.
PPPMTU: Formerly, specified the default packet size used by ppp for both transmitting and receiving.

TCP_FOREIGN_HASHBKTS: Specified the number of foreign-port hash buckets to allocate. When servers handle a large number of clients and services, you could increase this value to improve performance. Otherwise, the default of 11 was satisfactory.
TCP_LOCAL_HASHBKTS: Specified the number of local-port hash buckets to allocate. When clients connect to a large number of servers and services, you could increase this value to improve performance. Otherwise, the default of 11 was satisfactory.
TCP_SECURE_ISS_BITS: Specified the number of bits to be used for the secure increment of the TCP initial sequence number. The higher the number of bits, the less likely it is that an attacker would be able to guess the TCP initial sequence numbers. The default of 21 bits should have required approximately six days for an attacker to correctly guess a TCP initial sequence number.
TCP_SECURE_ISS_DELTA: Specified whether to use a secure increment for the TCP initial sequence number. For security reasons, it was recommended that this parameter always be left on (the default).
TCPLINGER: Formerly, length of time TCP hung on to an address after a connection has been closed.

UDPCKSUM: Formerly, specified whether udp checksum computation and verification was enabled. Was set to one to enable udp checksum computation and verification. Checksum computation was to be enabled for systems running NFS. The default was not to checksum.
UDPTTL: Formerly, specified the time-to-live value requested by udp (see TCPTTL). The default was ``30'', but it needed to be increased if connections were made to machines that were more than 30 hops away.