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<td bgcolor="#336666"><font face="Arial" size="2" color="#FFFFFF"><b>2.</b></font><b><font face="Arial" size="2" color="#FFFFFF">3</font></b></td>
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<font face="Arial" size="2" color="#FFFFFF">WAN Design</font></strong></td>
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<td bgcolor="#669999" height="25"><b><font face="Arial" size="2" color="#FFFFFF">
2.3.6</font></b></td>
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<font face="Arial" size="2" color="#FFFFFF">Other WAN design considerations</font></strong></td>
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Many enterprise WANs will have connections to the Internet. This
poses security problems but also provides an alternative for
inter-branch traffic.<p>Part of the traffic that must be considered during design is going to
or coming from the Internet. Since the Internet probably exists
everywhere that the enterprise has LANs, there are two principal ways
that this traffic can be carried. Each LAN can have a connection to
its local ISP, or there can be a single connection from one of the
core routers to an ISP. The advantage of the first method is that
traffic is carried on the Internet rather than on the enterprise
network, possibly leading to smaller WAN links. The disadvantage of
permitting multiple links, is that the whole enterprise WAN is open to
Internet-based attacks. It is also difficult to monitor and secure the
many connection points. A single connection point is more easily
monitored and secured, even though the enterprise WAN will be carrying
some traffic that would otherwise have been carried on the Internet.<p>If each LAN in the enterprise has a separate Internet connection, a
further possibility is opened for the enterprise WAN. Where traffic
volumes are relatively small, the Internet can be used as the
enterprise WAN with all inter-branch traffic traversing the Internet.
<img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12"> Securing the various LANs will be an issue, but the saving in WAN
connections may pay for the security.<p>Servers should be placed closest to the locations that will access
them most often. Replication of servers, with arrangement for off-peak
inter-server updates, will reduce the required link capacity. Location
of Internet-accessible services will depend on the nature of the
service, anticipated traffic, and security issues. This is a
specialized design topic beyond the scope of this curriculum.
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