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550 C
HAPTER
21: A
PPLE
T
ALK
R
OUTING
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A router does not advertise its routing table through an interface until
that interface has an associated network number range.
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An interface is not added to the routing table until it has an associated
network number range.
Changing the zone association for an existing network number involves
the deletion of the existing zone association for that network from all
routers on the segment. For details, see “Changing Zone Names” later in
this chapter.
AppleTalk Routes
Your system maintains a table of local and remote routes to all reachable
AppleTalk networks. The Routing Table Maintenance Protocol (RTMP)
automatically generates the routing table. RTMP defines rules for:
■
Information contained within each routing table — Routers use
the information within this table to determine how to forward data on
the basis of its destination network number.
■
Exchanging information between routers so that the routers
can maintain their routing tables
— All AppleTalk routers
periodically exchange routing tables by broadcasting RTMP packets
onto the network every 10 seconds; each packet contains a router’s
routing table entries. When a router receives the routing table of
another router, it compares its own table to the one it received and
then updates its table with the shortest path to each destination
network.
Each routing table entry contains the following information:
■
Network Range — A range of 16 bit numbers that identifies a
network. Each device on the network selects from this range the
network number with which it identifies itself on the network.
■
Distance — Number of hops to the destination network
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Interface — Interface used to reach the destination network
■
State — Status ( good, suspect, bad, or really bad ) of each route
■
Next Hop — The next-hop Internet router to which the packet must
be sent