Cisco ASR 9000 Series Routing Configuration Guide

Configuring a Fixed Default Route: Example
A default static route is often used in simple router topologies. In the following example, a route is configured
with an administrative distance of 110.
configure
router static
address-family ipv4 unicast
0.0.0.0/0 2.6.0.1 110
end
Configuring a Floating Static Route: Example
A floating static route is often used to provide a backup path if connectivity fails. In the following example,
a route is configured with an administrative distance of 201.
configure
router static
address-family ipv6 unicast
2001:0DB8::/32 2001:0DB8:3000::1 201
end
Configure Native UCMP for Static Routing
In a network where traffic is load balanced on two or more links, configuring equal metrics on the links would
create Equal Cost Multipath (ECMP) next hops. Because the bandwidth of the links is not taken into
consideration while load balancing, the higher bandwidth links are underutilized. To avoid this problem, you
can configure Unequal Cost Multipath (UCMP), either locally (local UCMP), or natively (native UCMP) so
that the higher bandwidth links carry traffic in proportion to the capacity of the links. UCMP supports IPv4
and IPv6 static VRF routes.
Local UCMP: All static routes are configured with the same link metrics. The static IGP calculates the load
metric based on the bandwidth of the links and load balances the traffic across the links. However, local UCMP
does not consider bandwidth while load balancing across links that are closer to the destination (multiple hops
away).
Native UCMP: Static routes over higher bandwidth links are configured with lower link metrics so that they
are preferred to routes over lower bandwidth links. The static IGP calculates the load metric based on the
bandwidth of the links and determines the percentage of traffic going out of the higher and lower bandwidth
links. By matching the configured link metrics with end-to-end available bandwidth, native UCMP is able to
effectively load balance traffic across links that are closer to the destination (multiple hops away).
Configuration Example
Consider the topology in the following figure. For load balancing traffic out of Router A1, if local UCMP is
used, then both 10G and 100G links will have equal link metrics. The static IGP decides to send more traffic
out of the 100G link because of the higher load metric. However, for load balancing traffic out of Router A2,
local UCMP works only on links to Routers C1 and C2. For load balancing traffic from Router C1 to Router
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
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Implementing Static Routes
Configuring a Fixed Default Route: Example

Cisco ASR 9000 Series Specifications

General

Brand	Cisco
Model	ASR 9000 Series
Category	Network Router
Language	English