Cisco Systems VC-289 manual Proxy Outside the Firewall, Proxies and NAT, VC-300

Configuring H.323 Gatekeepers and Proxies

H.323 Proxy Features

Proxy Outside the Firewall

To place the proxy and gatekeeper outside the firewall, two conditions must exist. First, the firewall must support H.323 dynamic access control. Second, Network Address Translation (NAT) must not be in use.

If NAT is in use, each endpoint must register with the gatekeeper for the duration of the time it is online. This will quickly overwhelm the firewall because a large number of relatively static, internal-to-external address mappings will need to be maintained.

If the firewall does not support H.323 dynamic access control, the firewall can be configured with static access lists that allow traffic from the proxy or gatekeeper through the firewall. This can present a security risk if an attacker can spoof, or simulate, the IP addresses of the gatekeeper or proxy and use them to attack the network. Figure 60 illustrates proxy outside the firewall.

Figure 60 Proxy Outside the Firewall

Terminals Firewall

Edge router

Gatekeeper

Proxy
Outside
devices	S6915

Proxies and NAT

When a firewall is providing NAT between an internal and an external network, proxies may allow H.323 traffic to be handled properly, even in the absence of a firewall that can translate addresses for H.323 traffic. Table 24 and Table 25 provide guidelines for proxy deployment for networks that use NAT.

Table 24	Guidelines for Networks That Use NAT
For Networks Using NAT		Firewall with H.323 NAT	Firewall Without H.323 NAT
Firewall with dynamic access		Gatekeeper and proxy inside the	Co-edge gatekeeper and proxy
control		firewall
Firewall without dynamic access		Gatekeeper and proxy inside the	Co-edge gatekeeper and proxy
control		firewall, with static access lists
		on the firewall

Cisco IOS Voice, Video, and Fax Configuration Guide

VC-300