Page 819 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

operating at layer 2 are part of the same broadcast domain but are in
different collision domains. Brouters are used to connect network

segments that use the same protocol.

Gateways A gateway connects networks that are using different
network protocols. A gateway is responsible for transferring traffic
from one network to another by transforming the format of that traffic
into a form compatible with the protocol or transport method used by
each network. Gateways, also known as protocol translators, can be

stand-alone hardware devices or a software service (for example, an
IP-to-IPX gateway). Systems on either side of a gateway are part of
different broadcast domains and different collision domains. Gateways
are used to connect network segments that use different protocols.
There are many types of gateways, including data, mail, application,
secure, and internet. Gateways typically operate at OSI layer 7.

Proxies A proxy is a form of gateway that does not translate across

protocols. Instead, proxies serve as mediators, filters, caching servers,
and even NAT/PAT servers for a network. A proxy performs a function
or requests a service on behalf of another system and connects
network segments that use the same protocol. Proxies are most often
used in the context of providing clients on a private network with
internet access while protecting the identity of the clients. A proxy
accepts requests from clients, alters the source address of the

requester, maintains a mapping of requests to clients, and sends the
altered request packets out. This mechanism is commonly known as
Network Address Translation (NAT). Once a reply is received, the
proxy server determines which client it is destined for by reviewing its
mappings and then sends the packets on to the client. Systems on
either side of a proxy are part of different broadcast domains and

different collision domains.

Network Infrastructure Inventory

If you can gain approval from your organization, perform a general
survey or inventory of the significant components that make up
your network. See how many different network devices you can

locate within your network. Also, do you notice any patterns of