Static Routing and Distance Vector Routing Protocols - CCIE Routing and Switching Exam Certification Guide - page 346

The topology entries in Example 7-25 are marked P as being in passive state. A destination is
in passive state when the router is not performing any recomputations for the entry. If the
successor goes down and the route entry has feasible successors, the router does not perform
any recomputations, thus the destination does not go into active state.

The route entry for a destination is placed into active state if the successor goes down and no
feasible successors exist. EIGRP routers send query packets to neighboring routers to find a
feasible successor to the destination. Neighboring routers can send reply packets that indicate
they have a feasible successor or they can send a query packet. The query packet indicates that
the neighboring router does not have a feasible successor and that it is participating in the
recomputation. A route does not return to passive state until it receives a reply packet from each
neighboring router. If the router does not receive all replies before the active-time timer expires,
the route is declared as being in the stuck-in-active (SIA) state. The default active timer is three
minutes.

EIGRP Timers
EIGRP updates are set only when necessary and are sent only to neighboring routers. There is
no periodic update timer.

You use hello packets to learn of neighboring routes. On most networks, the default hello packet
interval is 5 seconds. On multipoint networks with link speeds of T1 and slower, hello packets
are unicast every 60 seconds.

The holdtime to maintain a neighbor adjacency is three times the hello time: 15 seconds. If a
hello is not received in 15 seconds, the neighbor is removed from the table. Hellos are multicast
every 60 seconds on multipoint WAN interfaces (X.25, Frame Relay, ATM) with speeds less
than 1544 Mbps, inclusive. The neighbor holdtime is 180 seconds on these types of interfaces.
If a hello packet is not received within the holdtime, the neighbor is removed from the neighbor
table.

EIGRP updates are not sent using a broadcast address; instead, they are sent to the multicast
address 224.0.0.10 (all EIGRP routers).

NOTE

EIGRP Metrics
EIGRP uses the same composite metric as in IGRP but multiplied by 256 for finer granularity.
The composite metric is based on bandwidth, delay, load, and reliability.