HP 200 Series Services And Applications page 201

Table 1. Packet Types for Random Circuit Assignment
Protocol
AppleTalk Zone Information Protocol (ZIP)
AppleTalk Routing Table Maintenance Protocol (RTMP)
AppleTalk Name Binding Protocol (NBP)
AppleTalk Address Resolution Protocol (AARP)
AppleTalk Echo Protocol (AEP)
DECnet Routing Protocol
Learning Bridge multicast/broadcast packets
Novell IPX all packet types
XNS all packet types
Circuit Assignment Algorithm #2: Indexed
The second circuit assignment algorithm is referred to as "indexed". The
indexed algorithm typically MODs the sum of the source and destination
addresses by the number of available circuits in the circuit group. Recall that
the MOD function returns the remainder of a division. The following
example illustrates this algorithm.
The indexed circuit assignment algorithm is used for all IP data packets. In
figure 2 (above), assume that a computer at site A with IP address
15.8.128.210 sent a packet to a computer at site B with IP address
15.8.64.173. To determine which of the two circuits to use for sending the
packet, the circuit group manager adds the two IP addresses. The result in
hexadecimal is 1E10C17F. This value is then MODed by 2 (the number of
available circuits in the circuit group). The result is 1 (the remainder when
1E10C17F is divided by 2). A MOD value of 0 indicates that the packet must
be transmitted on circuit 1 and the MOD value of 1 indicates that the packet
must be transmitted on circuit 2.
Suppose one of the coterminus circuits fail. What happens? Again, consider
the network depicted in figure 2. When a packet with the IP addresses given
above is received by router A, the two addresses are MODed by 1 instead of
2. This causes the packet to be transmitted on the one remaining circuit.
When the failed circuit is restored, the indexed algorithm will operate as
before.
Improving Network Availability
Circuit Group Manager
Packet Type
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