Part 14 – WAN

Though topics surrounding WANs (Wide Area Networks) has fallen off in terms of testability, it is still a subject area worth knowing. This section deals with the major forms of WAN connectivity types and protocols. We begin by covering the two types of WAN switching technologies: circuit switching and packet switching. Circuit switching networks send data over the exact same path for all transmitted data. It can be viewed as a direct connection between to endpoints very much like a landline phone connection, which in fact, is an example of a circuit-switched network. Other types of circuit switching networks are ISDN, DSL, and the T-Carriers such as T-1, T-3, etc. It is noted that all though dial-up networking using modems has pretty much disappeared, there are still applications that utilize this type of connection. A prime example is remote access applications. It is also pointed out that ISDN is not really testable, so don't worry too much about knowing the ins and outs. The reason for this is that ISDN has been pretty much supplanted by ADSL, which achieves a faster download speed by trading off for a slower upload speed. Threats targeting circuit-switched networks are then covered. The technique of war dialing is employed against remote access networks which use dial up connections. Several strategies for mitigating war dialing attacks are discussed such as implementing dial back, caller id, and combining strategies into a layered defense. Packet switching is covered next. In packet switching, data is "chunked" into packets and each packet finds its own best way to the destination. This results in faster data delivery. Examples of packet-switched networks are x.25, frame relay, ATM (Asynchronous Transfer Mode), VOIP, and cable networks. We then discuss some of the threats that target packet-switched networks. One of the major benefits of cable networks - an always on connection - is also a major vulnerability. VOIP is vulnerable to some of the same exploits as POTS (Plain Old Telephone System) networks such as phishing, known as "vishing" for VOIP. It is also susceptible to eavesdropping, toll fraud, and SPIT (Spam Over IP Telephony). In addition, performance issues exist with VOIP such as latency and jitter. It's important to be aware that VOIP was never designed to be secure. Protocols such as S/RTP (Secure Real Time Protocol) can be used as a mitigation tactic against some of these threats.
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