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Static Routes

Static routes can be configured for IPv4 and IPv6. Both protocols support the following types of static routes: standard static route, default static route, floating static route, and summary static route. Static routes are configured using the ip route and ipv6 route global configuration commands. When configuring a static route, the next hop can be identified by an IP address, exit interface, or both. How the destination is specified creates one of the three following types of static route: next-hop, directly connected, and fully specified. IPv4 static routes are configured using the following global configuration command: ip route network-address subnet-mask { ip-address | exit-intf [ip=address] } [distance]. IPv6 static routes are configured using the following global configuration command: ipv6 route ipv6-prefix/prefix-length { ipv6-address | exit-intf [ipv6-address]} [distance]. The command to start an IPv4 routing table is show ip route | begin Gateway. The command to start an IPv6 routing table is show ipv6 route | begin C.

Configure IP Static Routes

In a next-hop static route, only the next-hop IP address is specified. The exit interface is derived from the next hop. When configuring a static route, another option is to use the exit interface to specify the next-hop address. Directly connected static routes should only be used with point-to-point serial interfaces. In a fully specified static route, both the exit interface and the next-hop IP address are specified. This form of static route is used when the exit interface is a multi-access interface and it is necessary to explicitly identify the next hop. The next hop must be directly connected to the specified exit interface. In a fully specified IPv6 static route, both the exit interface and the next-hop IPv6 address are specified. Along with show ip routeshow ipv6 routeping and traceroute, other useful commands to verify static routes include: show ip route staticshow ip route network, and show running-config | section ip route. Replace ip with ipv6 for the IPv6 versions of the command.

Configure IP Default Static Routes

A default route is a static route that matches all packets. A default route does not require any far-left bits to match between the default route and the destination IP address. Default static routes are commonly used when connecting an edge router to a service provider network, and a stub router. The command syntax for an IPv4 default static route is similar to any other IPv4 static route, except that the network address is 0.0.0.0 and the subnet mask is 0.0.0.0. The 0.0.0.0 0.0.0.0 in the route will match any network address. The command syntax for an IPv6 default static route is similar to any other IPv6 static route, except that the ipv6-prefix/prefix-length is ::/0, which matches all routes. To verify an IPv4 default static route, use the show ip route static command. For IPV6 use the show ipv6 route static command.

Configure Floating Static Routes

Floating static routes are static routes that are used to provide a backup path to a primary static or dynamic route in the event of a link failure. The floating static route is configured with a higher administrative distance than the primary route. By default, static routes have an administrative distance of 1, making them preferable to routes learned from dynamic routing protocols. The administrative distances of some common interior gateway dynamic routing protocols are EIGRP = 90, OSPF = 110, and IS-IS = 115. IP floating static routes are configured by using the distance argument to specify an administrative distance. If no administrative distance is configured, the default value (1) is used. The show ip route and show ipv6 route output verifies that the default routes to a router are installed in the routing table.

Configure Static Host Routes

A host route is an IPv4 address with a 32-bit mask or an IPv6 address with a 128-bit mask. There are three ways a host route can be added to the routing table: automatically installed when an IP address is configured on the router, configured as a static host route, or automatically obtained through other methods not covered in this module. Cisco IOS automatically installs a host route, also known as a local host route, when an interface address is configured on the router. A host route can be a manually configured static route to direct traffic to a specific destination device. For IPv6 static routes, the next-hop address can be the link-local address of the adjacent router; however, you must specify an interface type and an interface number when using a link-local address as the next hop. To do this, the original IPv6 static host route is removed, then a fully specified route is configured with the IPv6 address of the server and the IPv6 link-local address of the ISP router.

15.6.4 Module Quiz – IP Static Routing