Configuring Static Routing
This chapter describes how to configure static routing on the Cisco NX-OS device.
About Static Routing
Routers forward packets using either route information from route table entries that you manually configure or the route information that is calculated using dynamic routing algorithms.
Static routes, which define explicit paths between two routers, cannot be automatically updated; you must manually reconfigure static routes when network changes occur. Static routes use less bandwidth than dynamic routes. No CPU cycles are used to calculate and analyze routing updates.
You can supplement dynamic routes with static routes where appropriate. You can redistribute static routes into dynamic routing algorithms, but you cannot redistribute routing information calculated by dynamic routing algorithms into the static routing table.
You should use static routes in environments where network traffic is predictable and where the network design is simple. You should not use static routes in large, constantly changing networks because static routes cannot react to network changes. Most networks use dynamic routes to communicate between routers but might have one or two static routes configured for special cases. Static routes are also useful for specifying a gateway of last resort (a default router to which all unroutable packets are sent).
This section includes the following topics:
- Administrative Distance
- Directly Connected Static Routes
- Fully Specified Static Routes
- Floating Static Routes
- Remote Next Hops for Static Routes
- BFD
- Virtualization Support
Administrative Distance
An administrative distance is the metric used by routers to choose the best path when there are two or more routes to the same destination from two different routing protocols. An administrative distance guides the selection of one routing protocol (or static route) over another, when more than one protocol adds the same route to the unicast routing table. Each routing protocol is prioritized in order of most to least reliable using an administrative distance value.
Static routes have a default administrative distance of 1. A router prefers a static route to a dynamic route because the router considers a route with a low number to be the shortest. If you want a dynamic route to override a static route, you can specify an administrative distance for the static route. For example, if you have two dynamic routes with an administrative distance of 120, you would specify an administrative distance that is greater than 120 for the static route if you want the dynamic route to override the static route.
Directly Connected Static Routes
You must specify only the output interface (the interface on which all packets are sent to the destination network) in a directly connected static route. The router assumes the destination is directly attached to the output interface and the packet destination is used as the next-hop address. The next hop can be an interface, only for point-to-point interfaces. For broadcast interfaces, the next hop must be an IPv4/IPv6 address.
Fully Specified Static Routes
You must specify either the output interface (the interface on which all packets are sent to the destination network) or the next-hop address in a fully specified static route. You can use a fully specified static route when the output interface is a multi-access interface and you need to identify the next-hop address. The next-hop address must be directly attached to the specified output interface.
Floating Static Routes
A floating static route is a static route that the router uses to back up a dynamic route. You must configure a floating static route with a higher administrative distance than the dynamic route that it backs up. In this instance, the router prefers a dynamic route to a floating static route. You can use a floating static route as a replacement if the dynamic route is lost.
Note
By default, a router prefers a static route to a dynamic route because a static route has a smaller administrative distance than a dynamic route.
Remote Next Hops for Static Routes
You can specify the next-hop address of a neighboring router that is not directly connected to the router for static routes with remote (nondirectly attached) next-hops. If a static route has remote next hops during data forwarding, the next hops are recursively used in the unicast routing table to identify the corresponding directly attached next hops that have reachability to the remote next hops.
BFD
This feature supports bidirectional forwarding detection (BFD). BFD is a detection protocol designed to provide fast forwarding-path failure detection times. BFD provides subsecond failure detection between two adjacent devices and can be less CPU-intensive than protocol hello messages because some of the BFD load can be distributed onto the data plane on supported modules. See the Cisco Nexus 9000 Series NX-OS Interfaces Configuration Guide for more information.
Virtualization Support
Static routes support virtual routing and forwarding (VRF) instances.
Licensing Requirements for Static Routing
The following table shows the licensing requirements for this feature:
Prerequisites for Static Routing
Default Settings
Table 12-1 lists the default settings for static routing parameters.
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Configuring Static Routing
This section includes the following topics:
- Configuring a Static Route
- Configuring a Static Route over a VLAN
- Configuring Virtualization
- Verifying the Static Routing Configuration
Note If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature might differ from the Cisco IOS commands that you would use.
Configuring a Static Route
SUMMARY STEPS
2. ip route { ip-prefix | ip-addr/ip-mask } {[ next-hop | nh-prefix ] | [ interface next-hop | nh-prefix ]} [ name nexthop-name] [ tag tag-value] [ pref ]
ipv6 route ip6-prefix { nh-prefix | link-local-nh-prefix } | { nh-prefix [ interface ] | link-local-nh-prefix [ interface ]} [ name nexthop-name] [ tag tag-value] [ pref ]
DETAILED STEPS
This example shows how to configure a static route for a null interface:
switch(config)# ip route 1.1.1.1/32 null 0
switch(config)# copy running-config startup-config
Use the no { ip | ipv6 } route command to remove the static route.
Configuring a Static Route over a VLAN
You can configure a static route without next hop support over a VLAN.
BEFORE YOU BEGIN
SUMMARY STEPS
DETAILED STEPS
This example shows how to configure a static route without a next hop over an SVI:
Configuring Virtualization
SUMMARY STEPS
3. ip route { ip-prefix | ip-addr ip-mask } { next-hop | nh-prefix | interface } [ name nexthop-name] [ tag tag-value] [ pref ]
ipv6 route ip6-prefix { nh-prefix | link-local-nh-prefix } | { next-hop [ interface ] | link-local-next-hop [ interface ]} [ name nexthop-name] [ tag tag-value] [ pref ]
DETAILED STEPS
This example shows how to configure a static route:
switch(config)# vrf context StaticVrf
Verifying the Static Routing Configuration
To display the static routing configuration, perform one of the following tasks:
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Displays information about the IPv4 or IPv6 static-route track table. |
Configuration Example for Static Routing
This example shows how to configure static routing:
ip route 192.0.2.0/8 192.0.2.10
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