Expand Configuration and Management Manual (G06.24+)

Subsystem Description
Expand Configuration and Management Manual—523347-008
18-30
Routing Algorithms
Split Horizon (SH)
When the split horizon (SH) algorithm is used, $NCP tells its neighbor $NCP the best-
path route or the second-best route to a destination node. If the best-path route leads
through the neighbor being updated, $NCP will tell its neighbor $NCP its second-best
route as long as that route does not lead directly through the neighbor being updated.
Figure 18-10 shows the routing information known by node \D when the SH algorithm
has been selected. Each entry indicates the TF and HC to each node from the
perspective of node \D. Notice that with the SH algorithm, node \C reports to node \D
that a path does exist from itself to node \B; this is its second-best path.
The advantage of the SH algorithm is that alternate paths are immediately known
(temporary discontinuity never occurs).
Figure 18-10. Routing Information With the SH Algorithm
019CDT .CDD
Node \A
TF 4
TF 1 TF 1
TF 1 TF 1
\C \B \E
\A
\B
\C
\E
NRT
2 (2)
1 (1)
1 (1)
1 (1)
6 (3)
5 (2) --
6 (3) --
--
8 (5) 8 (5)
Node \B
Node \C Node \ENode \D
To
Nodes
Via Nodes