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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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demilitarized zone (DMZ) between the external <strong>and</strong> internal network so that the<br />

outer router only permits access from the outside to the bastion host (possibly to<br />

the information server) <strong>and</strong> the inner router only permits access from the internal<br />

network to the bastion host. The routers force all inbound <strong>and</strong> outbound traffic<br />

through the bastion host. This provides strong security because an intruder has<br />

to penetrate three separate systems to reach the internal network.<br />

Internal<br />

DNS <strong>and</strong><br />

mail server<br />

Secure network<br />

private.organization.com<br />

Client1 Client2<br />

Router<br />

Packet<br />

filter<br />

Figure 22-22 Screened subnet firewall<br />

One of the significant benefits of the DMZ is that because the routers force the<br />

systems on both external <strong>and</strong> internal networks to use the bastion host, there is<br />

no need for the bastion host to be a dual-homed host. This provides much faster<br />

throughput than achieved by a dual-homed host. Of course, this is complicated<br />

<strong>and</strong> some security problems might be caused by improper router configurations.<br />

22.4 <strong>IP</strong> Security Architecture (<strong>IP</strong>Sec)<br />

Bastion host gateway<br />

Proxy<br />

servers<br />

Packet<br />

filter<br />

Modems<br />

SOCKS<br />

server<br />

External<br />

DNS<br />

Public<br />

server<br />

Untrusted network<br />

Internet<br />

Router<br />

Packet<br />

filter<br />

WWW<br />

FTP<br />

This section examines, in detail, the <strong>IP</strong>Sec framework <strong>and</strong> its three main<br />

components, Authentication Header (AH), Encapsulated Security Payload<br />

(ESP), <strong>and</strong> Internet Key Exchange (IKE). We discuss the header formats, the<br />

specific cryptographic features, <strong>and</strong> the different modes of application.<br />

Chapter 22. <strong>TCP</strong>/<strong>IP</strong> security 809

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