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

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ip_ire_gw_probe_interval:
Controls the probe interval for Dead Gateway Detection.
IP periodically probes active and dead gateways.
ip_ire_gw_probe_interval controls the frequency of probing.
With retries, the maximum time to detect a dead gateway is
ip_ire_gw_probe_interval + 10000 milliseconds. Maximum time
to detect that a dead gateway has come back to life is
ip_ire_gw_probe_interval. [15000,- ]
Default: 180000 (3 minutes)
A gateway probe is an ICMP echo request sent by the host to the gateway's IP address. If the gateway has
been configured to ignore ICMP echo requests, a host will mistakenly think the gateway is dead, and traffic
will stop flowing from the host through the gateway, unless gateway probing is disabled by setting
ip_ire_gw_probe to zero.
ip_ire_pathmtu_interval:
Every ip_ire_pathmtu_interval milliseconds, IP will scan
its routing table for entries that have an MTU less than the
MTU for the first hop interface. For each, it will increase
the value to the next highest value in its internal table of
common MTU sizes. In this way, if the path to a remote host
has changed, and a larger MTU is now usable, the new MTU
will be discovered. If this value is made too small, then
excessive lost packets can result. [5000, - ]
Default: 600000 (10 minutes)
ip_ire_redirect_interval:
All routing table entries resulting from ICMP "Redirect"
messages are deleted after this much time has elapsed,
whether or not the entry has been recently used.
[60000, - ] Default: 300000 (5 minutes)
An ICMP "Redirect" is sent to a host when it uses a gateway that believes there is a "better" way for that
host to send IP datagrams to their final destination. This occurs when one relies on default routes and there
are multiple routers on the local subnet, each going to different destinations.
ip_pmtu_strategy:
Set the Path MTU Discovery strategy:
0 Disables Path MTU Discovery. For any destination not directly
connected to the host, a maximum MTU of 576 is used;
1 Enables Path MTU Discovery;
2 Obsoleted, must not be used;
3 Disables Path MTU Discovery. For any destination not directly
connected to the host, the maximum MTU of the link is used.
When Path MTU Discovery is enabled all outbound datagrams have
the "Don't Fragment" bit set. This should result in notification
from any intervening gateway that needs to forward a datagram
down a path that would require additional fragmentation. When the
ICMP "Fragmentation Needed" message is received, IP updates its
MTU for the remote host. If the responding gateway implements the