Blacklisting Routes - Bay Networks Nautica 200 Reference Manual

NauticaRS Release 4.1 Reference Guide

Blacklisting Routes

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When an external packet is received by the path, with a
destination address equal to the NAT address for the path, the
table is searched for a match on the path and port number. The
destination address and port number in the IP header and higher
protocols is replaced with the internal information from the table
before the packet is passed onwards.
With a packet from the internal network going out, the source
address is translated to the NAT address of the router. The source
port address is also translated to a unique value so that replies can
be passed back to the correct internal device. This translation is
added to the table for when the reply is received.
In both directions some of the higher level protocols are
translated as they contain both IP addresses and port addresses.
The NAT implementation in the Nautica routers has knowledge
of these higher level protocols, which types of packets need
translating and where the fields are in these packets. Also, most
packets have a form of checksum which is also recalculated.
Blacklisting is a mechanism used to denote paths in a router that
are unavailable for various reasons. A blacklisted path is kept on
the blacklist table for a specified time period. All routes
associated with a blacklisted path are set to an infinite
(unreachable) metric. After a definable period of time, the path
will be re-dialled and is either brought up or re-blacklisted,
depending on the success of the call.
Path blacklisting provides Dial Around Dead Site (DADS)
functionality in mesh networks. If a call to a remote site fails, then
the path called to that remote site is blacklisted. As the associated
routes are set to an infinite metric, other, higher metric, routes
become available for the router to use.
when the remote site comes back on line, the automatic re-dial of
the path makes a connection and the original, lower, metric routes
are re-enabled, allowing the backup path to close down.
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