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DGS-3600 Series Layer 3 Gigabit Ethernet Managed Switch CLI Manual
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101
UNICAST ROUTE COMMANDS
Route Preference is a way for routers to select the best path when there are two or more different routes to the same
destination from two different routing protocols. The majority of routing protocols are not compatible when used in
conjunction with each other. This Switch supports and may be configured for many routing protocols, as a stand alone
switch or more importantly, in utilizing the stacking function and Single IP Management of the Switch. Therefore the ability
to exchange route information and select the best path is essential to optimal use of the Switch and its capabilities.
The first decision the Switch will make in selecting the best path is to consult the Route Preference Settings table of the
Switch. This table can be viewed using the show route preference command, and it holds the list of possible routing
protocols currently implemented in the Switch, along with a reliability value which determines which routing protocol will
be the most dependable to route packets. Below is a list of the default route preferences set on the Switch.
Route Type Validity Range Default Value
Default 1-999 1
Local 0 – Permanently set on the Switch and not configurable. 0
Static 1 – 999 60
RIP 1 – 999 100
OSPF Intra 1 – 999 80
OSPF Inter 1 – 999 90
OSPF ExtT1 1 – 999 110
OSPF ExtT2 1 – 999 115
EBGP 1 – 999 70
IBGP 1 – 999 130
As shown above, Local will always be the first choice for routing purposes and the next most reliable path is Static due to
the fact that its has the next lowest value. To set a higher reliability for a route, change its value to a number less than the
value of a route preference that has a greater reliability value using the config route preference command. For example,
if the user wishes to make RIP the most reliable route, the user can change its value to one that is less than the lowest
value (Static - 60) or the user could change the other route values to more than 100.
The user should be aware of three points before configuring the route preference.
• No two route preference values can be the same. Entering the same route preference may cause the Switch to
crash due to indecision by the Switch.
• If the user is not fully aware of all the features and functions of the routing protocols on the Switch, a change in
the default route preference value may cause routing loops or black holes.
• After changing the route preference value for a specific routing protocol, that protocol needs to be restarted
because the previously learned routes have been dropped from the Switch. The Switch must learn the routes
again before the new settings can take affect.