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Interior gateway protocols are used to exchange routing information among routers in an autonomous
network, such as a company’s LAN. A routing protocol determines how routers in a network share and
update information and report changes, enabling a network to be dynamic instead of static. All IP interior
gateway protocols must be specified with a list of associated networks before routing activities can begin on
the switch. The IC35516 supports the Open Shortest Path First (OSPF) and Routing Information Protocol
(RIP) as interior gateway protocols.
Exterior protocols are used to exchange routing information between networks that do not share a common
administration. The supported exterior gateway protocol is Border Gateway Protocol (BGP).
With any of the IP routing protocols, the user must create the routing process, associate networks with the
routing process, and customize the routing protocol for a particular network. In order to configure the IP
routing protocols, perform the following tasks:
• Configure the Static Routes
• Configure RIP
• Configure OSPF
5.3 Configuring Static Routes
Static routes are user-defined routes that cause packets that are moving between a source and a
destination to take a specified path. Static routes can be important if the switch cannot build a route to a
particular destination.
To configure static routes, perform the following task in global configuration mode.
Command
Purpose
ip route {prefix mask | prefix-length}
address | interface} [<1-255>]
Establish a static route.
Note
: The numeric value is the static administrative distance. Enter a number between 1 and 255. See
Table 5-3 for a list of default administrative distances for common routing protocols.
The software retains the configured static routes until they are removed, using the no ip route global
configuration command. However, the user can override the static routes with dynamic routing information
through the assignment of administrative distance values. Each dynamic routing protocol has a default
administrative distance, as listed in Table 5-3. If you would like a static route to be overridden by information
from a dynamic routing protocol, you will need to ensure that the administrative distance of the static route is
higher than that of the dynamic protocol, since the lower value will be used. For example, if a route is known
both by OSPF and RIP, the OSPF route will be used, since its default administrative distance is lower than
RIP.
Note
: Static routes that point to an interface will not be advertised via RIP, nor by other dynamic routing
protocols, unless a redistribute static command is specified for these protocols.
When an interface goes down, all static routes through that interface are removed from the IP routing table.
Also, when the software can no longer find a valid next hop for the specified forwarding router's address in a
static route, the static route is removed from the IP routing table.
Route Source Default Distance
Connected interface 0
Static route 1
External BGP 20
OSPF 110
RIP 120
Internal BGP 200
Unknown 255
Table 5-3: Dynamic Routing Protocol Default Administrative Distances