The network should be
accessible, particularly at the access layer. Access routers need to
connect to a variety of WAN services, yet be secure, as shown in the
figure.
Support for a variety of WAN technologies is important because
the technologies are not all available throughout the world. In many
cases, not only is usage a consideration when selecting a WAN
technology, but so is geographical availability.
IP access routers must also allow telecommuters to dial in, but
be able to differentiate between legitimate and hostile connection
attempts. Cisco IOS features that support access include:
Dedicated and Switched WAN Support
- Dedicated access --- Cisco routers can be directly connected to
basic telephone service or digital services such as T1/E1. This
means that you can create a core WAN infrastructure for heavy
traffic loads, and then use other access services for sporadic
traffic requirements.
- Switched access --- Cisco routers support Frame Relay, X.25,
Switched Multimegabit Data Service (SMDS), and ATM. With this
variety of support, you can determine which switched service, or
combination of switched services, to use, based on cost,
location, and traffic requirements.
Exterior Protocol Support
Cisco IOS software supports several exterior protocols, including
EGP and BGP. EGP is an older exterior gateway protocol that provides
connection between separate autonomous systems. BGP is often used by
Internet service providers (ISPs) and by organizations that want to
connect to ISPs.
Features that support network security include:
Access lists --- Access lists, which are lists containing
information about which type of traffic should be forwarded, can be
defined to prevent user traffic from accessing portions of the
network. Access lists can also assist in providing security because
when they block user traffic effectively, the users themselves are
being denied access to sensitive areas of the network. Access lists
can be used to filter access to certain locations, but this is not a
security feature.
Authentication protocols