3Com CoreBuilder 3500, Руководство по внедрению

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460 C
HAPTER
16: A
PPLE
T
ALK
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 containing 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, 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 it will use to identify itself on the network.
■
Distance — Number of hops to the destination network.
■
Interface — Interface used to reach the destination network.
■
State — Status ( good, suspect, bad, or r eally bad ) of each route.
■
Next Hop — The next-hop Internet router to which the packet must
be sent.
Important
Considerations
Before administering AppleTalk routes, review the following guidelines
and considerations:
■
The RTMP table supports a maximum of 514 entries.
■
AppleTalk supports a maximum distance of 15 hops.
■
A hop count of 0 represents a network directly connected to a router.
■
When an AppleTalk router starts up on the network, the first entries in
its routing table are the network numbers to which it is directly
attached.
■
Node numbers are dynamically assigned and often change when the
router restarts.
■
Each 16 bit number within a network range is capable of supporting
253 network nodes.