Specifications

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4-2
Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, Release 5.0(3)U2(2)
OL-25782-02
Chapter 4 Configuring EIGRP
Information About EIGRP
• Advanced EIGRP, page 4-4
EIGRP Components
EIGRP has the following basic components:
• Reliable Transport Protocol, page 4-2
• Neighbor Discovery and Recovery, page 4-2
• Diffusing Update Algorithm, page 4-3
Reliable Transport Protocol
The Reliable Transport Protocol guarantees ordered delivery of EIGRP packets to all neighbors. (See
the “Neighbor Discovery and Recovery” section on page 4-2.) The Reliable Transport Protocol supports
an intermixed transmission of multicast and unicast packets. The reliable transport can send multicast
packets quickly when unacknowledged packets are pending. This provision helps to ensure that the
convergence time remains low for various speed links. See the “Configuring Advanced EIGRP” section
on page 4-13 for details about modifying the default timers that control the multicast and unicast packet
transmissions.
The Reliable Transport Protocol includes the following message types:
• Hello—Used for neighbor discovery and recovery. By default, EIGRP sends a periodic multicast
Hello message on the local network at the configured hello interval. By default, the hello interval is
5 seconds.
• Acknowledgement—Verify reliable reception of Updates, Queries, and Replies.
• Updates—Send to affected neighbors when routing information changes. Updates include the route
destination, address mask, and route metrics such as delay and bandwidth. The update information
is stored in the EIGRP topology table.
• Queries and Replies—Sent as necessary as part of the Diffusing Update Algorithm used by EIGRP.
Neighbor Discovery and Recovery
EIGRP uses the Hello messages from the Reliable Transport Protocol to discover neighboring EIGRP
routers on directly attached networks. EIGRP adds neighbors to the neighbor table. The information in
the neighbor table includes the neighbor address, the interface it was learned on, and the hold time, which
indicates how long EIGRP should wait before declaring a neighbor unreachable. By default, the hold
time is three times the hello interval or 15 seconds.
EIGRP sends a series of Update messages to new neighbors to share the local EIGRP routing
information. This route information is stored in the EIGRP topology table. After this initial transmission
of the full EIGRP route information, EIGRP sends Update messages only when a routing change occurs.
These Update messages contain only the new or changed information and are sent only to the neighbors
affected by the change. See the “EIGRP Route Updates” section on page 4-3.
EIGRP also uses the Hello messages as a keepalive to its neighbors. As long as Hello messages are
received, Cisco NX-OS can determine that a neighbor is alive and functioning.