Cisco ASA 5505 - Manual (Page 449)

22-3
Cisco ASA 5500 Series Configuration Guide using the CLI
Chapter 22 Configuring Static and Default Routes
Configuring Static and Default Routes
Configuring a Static Route
Static routing algorithms are basically table mappings established by the network administrator before
the beginning of routing. These mappings do not change unless the network administrator alters them.
Algorithms that use static routes are simple to design and work well in environments where network
traffic is relatively predictable and where network design is relatively simple. Because of this fact, static
routing systems cannot react to network changes.
Static routes remain in the routing table even if the specified gateway becomes unavailable. If the
specified gateway becomes unavailable, you need to remove the static route from the routing table
manually. However, static routes are removed from the routing table if the specified interface goes down,
and are reinstated when the interface comes back up.
Note If you create a static route with an administrative distance greater than the administrative distance of the
routing protocol running on the ASA, then a route to the specified destination discovered by the routing
protocol takes precedence over the static route. The static route is used only if the dynamically
discovered route is removed from the routing table.
You can define up to three equal cost routes to the same destination per interface. Equal-cost multi-path
(ECMP) routing is not supported across multiple interfaces. With ECMP, the traffic is not necessarily
divided evenly between the routes; traffic is distributed among the specified gateways based on an
algorithm that hashes the source and destination IP addresses.
To configure a static route, see the following section:
• Adding or Editing a Static Route, page 22-3
Adding or Editing a Static Route
To add or edit a static route, enter the following command:
Command Purpose
route if_name dest_ip mask gateway_ip
[distance]
Example:
hostname(config)# route outside 10.10.10.0
255.255.255.0 192.168.1.1 [1]
Enables you to add a static route.
The dest_ip and mask arguments indicate the IP address for the destination
network, and the gateway_ip argument is the address of the next-hop
router. The addresses you specify for the static route are the addresses that
are in the packet before entering the ASA and performing NAT.
The distance argument is the administrative distance for the route. The
default is 1 if you do not specify a value. Administrative distance is a
parameter used to compare routes among different routing protocols. The
default administrative distance for static routes is 1, giving it precedence
over routes discovered by dynamic routing protocols but not directly
connected routes.
The default administrative distance for routes discovered by OSPF is 110.
If a static route has the same administrative distance as a dynamic route,
the static route takes precedence. Connected routes always take precedence
over static or dynamically discovered routes.