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Routing
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• 'black-hole' : packets routed to a black-hole are silently dropped. 'Silent' refers to the lack of any ICMP
response back to the sender.
• 'no-where' (also called 'dead-end') : packets routed to 'no-where' are also dropped but the FB6000 generates
ICMP error responses back to the sender.
The
blackhole
and
nowhere
top-level objects are used to specify prefixes which are routed to these special
targets. In the User Interface, these objects can be found under the Routes category icon.
7.3. Dynamic route creation / deletion
For data links that have an Up/Down state, such as L2TP or FB105 tunnels, or PPP links, the ability to actually
send traffic to the route target will depend on the state of the link. For such links, you can specify route(s)
to automatically create each time the link comes up - when the link goes down these routes are removed
automatically. Refer to Chapter 11 for details on how to achieve this via the
routes
attribute on the tunnel
definition objects.
Note
Routes to subnets on Ethernet interfaces do not support this functionality.
This can be useful where a link such as PPPoE is defined with a given
localpref
value, and a separate
route is defined with a lower
localpref
value (i.e. less preferred), and therefore acts as a fallback route if
the PPPoE link drops.
7.4. Routing tables
The conventional routing logic described above operates using one of possibly many routing tables that the
FB6000 can support simultaneously. Routing tables are numbered, with the default being routing table 0 (zero).
The various ways to add routes allow the routing table to be specified, and so allow completely independent
routing for different routing tables. The default table (table zero) is used when optional routing-table
specification attributes or CLI command parameters are omitted.
Each
interface
is logically in a routing table and traffic arriving on it is processed based on the routes in
that routing table. Tunnels like FB105 and L2TP allow the wrapped tunnel packets to work on one routing table
and the tunnel payload packets to be on another. In firewalling models, it is possible to jump between routing
tables using a rule in a rule-set.
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