Floating Static Routes
Floating static routes are static routes that are used to back up dynamic routes learned through configured
routing protocols. A floating static route is configured with a higher administrative distance than the dynamic
routing protocol it is backing up. As a result, the dynamic route learned through the routing protocol is always
preferred to the floating static route. If the dynamic route learned through the routing protocol is lost, the
floating static route is used in its place.
By default, static routes have smaller administrative distances than dynamic routes, so static routes are preferred
to dynamic routes.
Note
Fully Specified Static Routes
In a fully specified static route, both the output interface and next hop are specified. This form of static route
is used when the output interface is multiaccess and it is necessary to explicitly identify the next hop. The
next hop must be directly attached to the specified output interface. The following example shows a definition
of a fully specified static route:
RP/0/RP0/CPU0:router(config)# router static
RP/0/RP0/CPU0:router(config-static)# address-family ipv6 unicast
RP/0/RP0/CPU0:router(config-static-afi)# 2001:0DB8::/32 TenGigE 0/0/0/0 2001:0DB8:3000::1
A fully specified route is valid (that is, a candidate for insertion into the routing table) when the specified
interface, IPv4 or IPv6, is enabled and up.
Recursive Static Routes
In a recursive static route, only the next hop is specified. The output interface is derived from the next hop.
The following example shows how to specify that all destinations with address prefix 2001:0DB8::/32 are
reachable through the host with address 2001:0DB8:3000::1:
RP/0/RP0/CPU0:router(config)# router static
RP/0/RP0/CPU0:router(config-static)# address-family ipv6 unicast
RP/0/RP0/CPU0:router(config-static-afi)# 2001:0DB8::/32 2001:0DB8:3000::1
A recursive static route is valid (that is, it is a candidate for insertion in the routing table) only when the
specified next hop resolves, either directly or indirectly, to a valid output interface, provided the route does
not self-recurse, and the recursion depth does not exceed the maximum IPv6 forwarding recursion depth.
A route self-recurses if it is itself used to resolve its own next hop. If a static route becomes self-recursive,
RIB sends a notification to static routes to withdraw the recursive route.
Assuming a BGP route 2001:0DB8:3000::0/16 with next hop of 2001:0DB8::0104, the following static route
would not be inserted into the IPv6 RIB because the BGP route next hop resolves through the static route and
the static route resolves through the BGP route making it self-recursive:
RP/0/RP0/CPU0:router(config)# router static
RP/0/RP0/CPU0:router(config-static)# address-family ipv6 unicast
RP/0/RP0/CPU0:router(config-static-afi)# 001:0DB8::/32 2001:0DB8:3000::1
Routing Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.3.x
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Implementing Static Routes
Floating Static Routes
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