Diffusing Update Algorithm; Eigrp Route Updates; Internal Route Metrics; External Route Metrics - Cisco Nexus 3000 Series Configuration Manual

Chapter 4 Configuring EIGRP
S e n d d o c u m e n t c o m m e n t s t o n e x u s 3 k - d o c f e e d b a c k @ c i s c o . c o m

Diffusing Update Algorithm

The
networks in the topology table. The topology table includes the following information:
•
•
•
DUAL uses the distance metric to select efficient, loop-free paths. DUAL selects routes to insert into the
unicast Routing Information Base (RIB) based on feasible successors. When a topology change occurs,
DUAL looks for feasible successors in the topology table. If there are feasible successors, DUAL selects
the feasible successor with the lowest feasible distance and inserts that into the unicast RIB, avoiding
unnecessary recomputation.
When there are no feasible successors but there are neighbors advertising the destination, DUAL
transitions from the passive state to the active state and triggers a recomputation to determine a new
successor or next-hop router to the destination. The amount of time required to recompute the route
affects the convergence time. EIGRP sends Query messages to all neighbors, searching for feasible
successors. Neighbors that have a feasible successor send a Reply message with that information.
Neighbors that do not have feasible successors trigger a DUAL recomputation.

EIGRP Route Updates

When a topology change occurs, EIGRP sends an Update message with only the changed routing
information to affected neighbors. This Update message includes the distance information to the new or
updated network destination.
The distance information in EIGRP is represented as a composite of available route metrics, including
bandwidth, delay, load utilization, and link reliability. Each metric has an associated weight that
determines if the metric is included in the distance calculation. You can configure these metric weights.
You can fine-tune link characteristics to achieve optimal paths, but we recommend that you use the
default settings for most configurable metrics.
This section includes the following topics:
•
•
•

Internal Route Metrics

Internal routes are routes that occur between neighbors within the same EIGRP autonomous system.
These routes have the following metrics:
•
•
•
Diffusing Update Algorithm
IPv4 address/mask—The network address and network mask for this destination.
Successors—The IP address and local interface connection for all
that advertise a shorter distance to the destination than the current
Feasibility distance (FD)—The lowest calculated distance to the destination. The feasibility distance
is the sum of the advertised distance from a neighbor plus the cost of the link to that neighbor.
Internal Route Metrics, page 4-3
External Route Metrics, page 4-4
EIGRP and the Unicast RIB, page 4-4
Next hop—The IP address of the next-hop router.
Delay—The sum of the delays configured on the interfaces that make up the route to the destination
network. Configured in tens of microseconds.
Bandwidth—The calculation from the lowest configured bandwidth on an interface that is part of
the route to the destination.
Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, NX-OS Release 5.0(3)U1(1)
(DUAL) calculates the routing information based on the destination
Information About EIGRP
or neighbors
feasible successors
feasible distance.
4-3