Page 749 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

modern networks by devising NetBIOS over TCP/IP (NBT). This in

turn supports the Windows sharing protocol of Server Message
Block (SMB), which is also known as Common Internet File
System (CIFS). NetBEUI is no longer supported as a lower-layer
protocol; only its SMB and CIFS variants are still in use.

A potential security risk exists when non-IP protocols are in use in
a private network. Because non-IP protocols are rare, most
firewalls are unable to perform packet header, address, or payload

content filtering on those protocols. Thus, when it comes to non-IP
protocols, a firewall typically must either block all or allow. If your
organization is dependent on a service that operates over only a
non-IP protocol, then you may have to live with the risk of passing
all non-IP protocols through your firewall. This is mostly a concern
within a private network when non-IP protocols traverse between
network segments. However, non-IP protocols can be encapsulated
in IP to be communicated across the internet. In an encapsulation

situation, IP firewalls are rarely able to perform content filtering
on such encapsulation and thus security has to be set to an allow-
all or deny-all configuration.

Routers and bridge routers (brouters) are among the network
hardware devices that function at layer 3. Routers determine the best
logical path for the transmission of packets based on speed, hops,
preference, and so on. Routers use the destination IP address to guide
the transmission of packets. A brouter, working primarily in layer 3

but in layer 2 when necessary, is a device that attempts to route first,
but if that fails, it defaults to bridging.

Routing Protocols

There are two broad categories of routing protocols: distance
vector and link state. Distance vector routing protocols maintain a

list of destination networks along with metrics of direction and
distance as measured in hops (in other words, the number of
routers to cross to reach the destination). Link state routing
protocols maintain a topography map of all connected networks