Cisco CCNA Study Guide - Router Alley

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CCNA Study Guide v2.62 – Aaron Balchunas 206 EIGRP Packet Types EIGRP employs five packet types: • Hello packets - multicast • Update packets – unicast or multicast • Query packets – multicast • Reply packets – unicast • Acknowledgement packets - unicast Hello packets are used to form neighbor relationships, and were explained in detail previously. Hello packets are always multicast to address 224.0.0.10. Update packets are sent between neighbors to build the topology and routing tables. Updates sent to new neighbors are sent as unicasts. However, if a route’s metric is changed, the update is sent out as a multicast to address 224.0.0.10. Query packets are sent by a router when a Successor route fails, and there are no Feasible Successors in the topology table. The router places the route in an Active state, and queries its neighbors for an alternative route. Query packets are sent as a multicast to address 224.0.0.10. Reply packets are sent in response to Query packets, assuming the responding router has an alternative route (feasible successor). Reply packets are sent as a unicast to the querying router. Recall that EIGRP utilizes the Reliable Transport Protocol (RTP) to ensure reliable delivery of most EIGRP packets. Delivery is guaranteed by having packets acknowledged using…..Acknowledgment packets! Acknowledgment packets (also known as ACK’s) are simply Hello packets with no data, other than an acknowledgment number. ACK’s are always sent as unicasts. The following packet types employ RTP to ensure reliable delivery via ACK’s: • Update Packets • Query Packets • Reply Packets Hello and Acknowledgments (ha!) packets do not utilize RTP, and thus do not require acknowledgement. * * * All original material copyright © 2013 by Aaron Balchunas (aaron@routeralley.com), unless otherwise noted. All other material copyright © of their respective owners. This material may be copied and used freely, but may not be altered or sold without the expressed written consent of the owner of the above copyright. Updated material may be found at http://www.routeralley.com.
CCNA Study Guide v2.62 – Aaron Balchunas 207 EIGRP Route States An EIGRP route can exist in one of two states, in the topology table: • Active state • Passive State A Passive state indicates that a route is reachable, and that EIGRP is fully converged. A stable EIGRP network will have all routes in a Passive state. A route is placed in an Active state when the Successor and any Feasible Successors fail, forcing the EIGRP to send out Query packets and reconverge. Multiple routes in an Active state indicate an unstable EIGRP network. If a Feasible Successor exists, a route should never enter an Active state. Routes will become Stuck-in-Active (SIA) when a router sends out a Query packet, but does not receive a Reply packet within three minutes. In other words, a route will become SIA if EIGRP fails to re-converge. To view the current state of routes in the EIGRP topology table: Router# show ip eigrp topology IP-EIGRP Topology Table for AS(10)/ID(172.19.1.1) Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status P 10.3.0.0/16, 1 successors, FD is 2297856 via 172.16.1.2 (2297856/128256), Serial0 P 172.19.0.0/16, 1 successors, FD is 281600 via Connected, Serial 1 To view only active routes in the topology table: Router# show ip eigrp topology active IP-EIGRP Topology Table for AS(10)/ID(172.19.1.1) Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - Reply status A 172.19.0.0/16, 1 successors, FD is 23456056 1 replies, active 0:00:38, query-origin: Multiple Origins (Reference: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008010f016.shtml) * * * All original material copyright © 2013 by Aaron Balchunas (aaron@routeralley.com), unless otherwise noted. All other material copyright © of their respective owners. This material may be copied and used freely, but may not be altered or sold without the expressed written consent of the owner of the above copyright. Updated material may be found at http://www.routeralley.com.
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