KB.15.15

Configured

Provides a route that is used as a backup route for discarding traffic where the primary

route is unavailable. A configured null route consists of:

• Destination network address or host and a corresponding network mask

• Either the reject keyword (traffic dropped with ICMP notification to the sender) or

blackhole keyword (traffic dropped without any ICMP notification).

Non-default null routes created with the reject or blackhole keywords use a gateway of

zero (0).

Figure 15 (page 185) illustrates the default and configured null route entries in the switch's routing

table.

Static routing default settings

The routing switch applies default administrative distance and metric values to ensure that static

routes are preferred over dynamic routes to the same destination.

Administrative distance

In the case of static routes, this is the value the routing switch uses to compare a static route to

routes from other route sources to the same destination before placing a route in the routing

table. The default administrative distance for static routes is 1, but can be configured to any

value in the range of 1 to 255.

Metric

In the case of static routes, this is the value the routing switch uses when comparing a static

route to routes in the routing table from any dynamic routes to the same destination. The metric

for static routes is fixed, that is, always set to "1".

Static route states follow VLAN states

Static routes remain in the routing table only while the interface link to the next-hop router is up. If

the next-hop router interface link goes down, the software removes the static route from the routing

table. If the next-hop interface comes up again, the software adds the route back to the routing

table.

This feature allows the routing switch to adjust to changes in network topology. The routing switch

does not continue trying to use routes on unreachable paths, but instead uses routes only when

their paths are reachable.

Static routes for ECMP applications

Equal-cost multi-path routing (ECMP) is a routing strategy where next-hop packet forwarding to a

single destination can occur over multiple "best paths." Each path has the same cost as the other

paths, but a different next-hop router. In static routing, load-balancing can be achieved through

ECMP. Figure 15 (page 185) illustrates static routes applied to an ECMP topology.

184 IPv6 Static Routing