Blacklisting Routes - Bay Networks NauticaRS Reference Manual

NauticaRS 5.5R Reference Guide

Blacklisting Routes

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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-dialed 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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