Westermo RedFox Series - Manual (Page 593)

Westermo OS Management Guide
Version 4.17.0-0
Example
#Router2
ip
route 0.0.0.0/0 192.168.33.1 200
end
router
ospf
network 192.168.35.0/24 area 0.0.0.0
distribute-default
end
end
Router 3 has no static routes, i.e., it only uses OSPF.
Example
#Router3
router
ospf
network 192.168.34.0/24 area 0.0.0.0
network 192.168.35.0/24 area 0.0.0.0
end
end
26.1.4.3 Blackhole routes
WeOS has a blackhole interface referred to as ”null0”. This interface is hidden
in the sense that it cannot be configured (no IP address, management settings,
etc.). The blackhole interface is useful to avoid routing loops in networks with
incomplete subnetting.
An example is shown in fig. 26.2 . R1 has set a static route for the ”192.168.0.0/22”
range towards R2. R2 only has routes to a part of this range, i.e., the directly con-
nected subnets ”192.168.0.0/24”, ”192.168.1.0/24” and ”192.168.2.0/24”, while
”192.168.3.0/24” is currently unused. As R2 has defined R1 as its default route, a
packet sent towards e.g., ”192.168.3.11” would bounce back and forth between
R1 and R2, unless R2 defines a blackhole route.
Note
In this example, the static blackhole route for ”192.168.0.0/22” has a shorter
prefix than the directly connected routes. Therefore only traffic in range
”192.168.3.0/24” will be sent to ”null0” as long as the interfaces to the
directly connected subnets are up.
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