Probe Interval; Probe Timeout; Path Mtu Black Hole Detection And Recovery - Novell NETWARE 6-DOCUMENTATION Manual

Probe Interval

Probe Timeout

Path MTU Black Hole Detection and Recovery

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NetWare TCP/IP Administration Guide
This configured parameter lets you fine-tune the performance of the Dead
Gateway Detection feature by modifying the time interval (in seconds) at
which probes are sent to the default gateway to determine whether it is
functional or not.
For more information on this, see
This configured parameter sets the time interval (in seconds) after which the
next probe is sent to the default gateway, when there is no reply received by
the gateway for the previously sent probe.
For more information on this, see
This feature provides the facility to detect a connection failure due to black
hole routers and helps to recover such connections.
Whenever a router gets a datagram with Don't Fragment (DF) bit set in its
header and the packet size is greater than the next MTU the router cannot
forward the packet. In such a case, the router sends an ICMP Destination
Unreachable DF bit set message to the host.
Often routers do not send such a message. Instead they ignore the datagram.
Typically, an IP datagram cannot be forwarded because its maximum segment
size is too large for the receiving server and the Don't Fragment bit is set in the
header of the datagram. Routers that ignore these datagrams and send no
message are called PMTU black hole routers. Some routers might silently
drop large frames, even when the DF bit is not set. Firewalls are often
misconfigured to suppress all ICMP messages.
To respond effectively to black hole routers, the Novell TCP/IP stack now
provides a Path MTUBH Detect feature. Path MTUBH Detect recognizes
repeated unacknowledged transmissions and responds by turning off the Don't
Fragment bit. After a datagram is transmitted successfully, the MTUBH
Detect feature reduces the maximum segment size and turns the Don't
Fragment bit on again.
"Configuring Probe Interval" on page
"Configuring Probe Timeout" on page
74.
75.