HP-UX TCP/IP Performance White Paper, March 2008

ip_forward_directed_broadcasts:

Set to 1 to have IP forward subnet broadcasts.

Set to 0 to inhibit forwarding. [0,1] Default: 1

A directed broadcast datagram has the broadcast IP address of a remote IP subnet as its destination IP

address. Directed broadcasts will only be forwarded if ip_forward_directed_broadcasts is set to

one and ip_forwarding is set to one or two. If either ip_forward_directed_broadcasts or

ip_forwarding are set to zero, directed broadcasts will not be forwarded.

ip_forward_src_routed:

Set to 1 to forward source-routed packets; set to 0 to

disable forwarding. If disabled, an ICMP Destination

Unreachable message is sent to the sender of source-routed

packets needing to be forwarded. [0,1] Default: 1

In a source-routed datagram, the source of the datagram specifies explicit options that indicate which

intermediate hops the datagram must take. Source-routed datagrams will only be forwarded if both

ip_forward_src_routed is set to one and ip_forwarding set to one or two. If either

ip_forward_src_routed or ip_forwarding are set to zero, no source-routed datagrams will be

forwarded.

ip_forwarding:

Controls how IP hosts forward packets: Set to 0 to inhibit

forwarding; set to 1 to always forward; set to 2 to forward

only if the number of logical interfaces on the system is 2

or more. [0,2] Default: 2

The ip_forwarding tunable can be thought-of as the "master forwarding switch." If it is set to zero, no IP

datagrams will be forwarded outside the box. If it is set to one or two, IP datagrams may be forwarded

outside the box.

If ip_forwarding is set to zero, the system will still "internally forward" datagrams received on the

"wrong" (does not have the matching IP address) interface. If you want to limit the receipt of IP datagrams

to only the interface with the matching IP address, you should consider setting ip_strong_es_model.

ip_fragment_timeout:

Set the amount of time IP fragments are held while waiting for

missing fragments.

RFC1122 specifies 60 seconds as the time-out period for reassembly

of IP datagrams. This is a long time, but may be appropriate for

reassembling datagrams that have traversed an internet. On local

file server systems, on the other hand, fragmentation reassembly

will either take place very quickly, or not all, i.e., if all

fragments are not received at about the same time, it is likely

that one was dropped by the local interface, and will never

arrive. In this case, holding fragments for 60 seconds may only