The neighbor
establishment and discovering routes processes occur at the same
time in EIGRP. A high-level description of the process is shown in
Figures
-
and defined here:
- A new router (router A) comes up
on the link and sends out a hello through all interfaces.
- Routers receiving the hello
reply with update packets that contain all the routes they have in
their topology tables, except those learned through that interface
(the split horizon process requires that information not be
sent back in the direction it was received). In addition, these
update packets have the Init bit set, indicating that this is the
initialization process.
An update packet includes
information about the routes a neighbor is aware of, including the
metric that the neighbor is advertising for each destination.
- Router A replies to each
neighbor with an Ack (acknowledgment) packet, indicating that it
received the update information.
- Router A puts all update packets
in its topology table.
The topology table includes all
destinations advertised by neighboring (adjacent) routers. It is
organized such that each destination is listed, along with all the
neighbors that can get to the destination, and their associated
metrics.
- Router A then exchanges update
packets with each of its neighbors.
- Upon receiving the update
packets, each neighbor router sends an Ack packet back to router A.
When all updates are received, the
router is ready to choose the primary and backup routes to keep in
the topology table.
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