Fabric OS Administrator’s Guide 73
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Routing policies 4
If one ICL is broken but there is a regular ISL, the triangular topology still holds given the ISL cost is
lower than the total cost through the ICL linear topology. If a direct ICL link between two switches is
broken the triangular topology is considered broken when the ISL path between the two switches is
a multiple hop. In this case the triangular topology broken message will still be posted independent
of the cost of the ISL path being lesser or greater than the ICL path between the two switches.
Refer to the Brocade DCX Backbone Hardware Reference Manual and the Brocade DCX-4S
Backbone Hardware Reference Manual for instructions on how to cable ICLs.
FIGURE 11 ICL triangular topology
Virtual Fabrics considerations: In Virtual Fabrics, the ICL ports can be split across the logical
switch, base switch and default switch. The triangular topology requirement still needs to be met
for each fabric individually. The present restriction on ICL being part of only logical switches with
“Allow XISL Use” attribute off still applies.

Routing policies

By default, all routing protocols place their routes into a routing table. You can control the routes
that a protocol places into each table and the routes from that table that the protocol advertises by
defining one or more routing policies and then applying them to the specific routing protocol.
The routing policy is responsible for selecting a route based on one of two user-selected routing
policies:
•Port-based routing
•Exchange-based routing
On the Brocade 300, 4100, 4900, 5000, 5410, 5424, 5450, 5460, 5470, 5480, 5100, 5300,
5424, 7500, 7500E, 7600, 7800, 8000, and VA-40FC switches, the Brocade 48000 director, and
the Brocade DCX and DCX-4S enterprise-class platforms (all 4 Gbps ASICs and later) routing is
handled by the FSPF protocol and either the port-based routing or exchange-based routing policies.
ICL 3
ICL 1 ICL 2
Chassis 2
Chassis 1 Chassis 3