| Thus far, you have seen how OSPF
operates within a single area. What issues would arise if this
single area ballooned into 400 networks? The issues shown in the main figure, at a minimum, would need
to be addressed.
The issues shown in the Figure are described as follows:
- Frequent SPF calculations
--- With such a large network,
network changes are inevitable, so the routers will spend many
more CPU cycles recalculating the routing table.
Large routing table --- Each router needs to maintain at least
one entry for every network; that is, at least 400 networks.
Assuming there are multiple paths to just 25 percent of the networks
adds another 100 entries!
Large link-state table --- Because the link-state table
includes the complete topology of the network, each router needs to
maintain an entry for every network in the area, even routes that
are not used.
Luckily, OSPF was created to solve many of these network scaling
issues previously left unanswered by earlier routing protocols. OSPF allows large areas to be separated into smaller, more
manageable areas that can still exchange routing information. By
splitting the network into manageable pieces, the routers can handle
the traffic and the network can grow efficiently.
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