OSI Layer 3: Routed and Routing Protocols
83
method of maintaining route tables on AppleTalkenabled machines. Look
at the RTMP packets, which are different from other packet structures. They
contain x number of fields called routing tuples. Depending on the type of
network, non-extended or extended, the tuple structure changes.
The example below is a sample from an extended network. The packet
structure is 16 bits long. The packet starts with the router's network number,
which occupies the full 16 bits. Following the network number, the ID
Length
field occupies eight bits. This field specifies the length of the sender's
node address. The next field is used for specifying the actual router's node
address.
After 16 bits of padding, the routing tuples 1 through x follow. Each tuple
contains the same field, as long as it is of the same tuple type. Non-extended
tuples actually follow 16 bits of padding with eight bits of version number
identification. They begin with the network number field, followed by some
padding and a distance field. Extended tuples follow 16 bits of padding, and
then begin with a 16-bit start range. After the start range, there are three
more fields: Distance, Range End, and Version. The version number
becomes part of an extended tuple. It has a default value of 0
Ч82.
RTMP - Routing Table Maintenance Protocol
Router's Net: 106
ID Length: 8
Router's Node ID: 74
RTMP Tuple # 1
Range Start: 100
Range Flag: %100 Extended
Distance: 0
Range End: 110
Version: 0x82
RTMP Tuple # 2
Range Start: 300
Range Flag: %100 Extended
Distance: 1
Range End: 210
Version: 0x82
RTMP Tuple # 3
Range Start: 500
Range Flag: %100 Extended
Distance: 2
Copyright ©2000 SYBEX , Inc., Alameda, CA
www.sybex.com