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The reason your PIX should have an external address is for simplicity in things such as port forwarding into your network from outside. &nbsp;I'm sure it's possible to use private addresses to do this if you really wanted to (although convoluted). &nbsp;Having your outside router doing routing to forward to your PIX which then forwards it again is adding another point of confusion on the network to deal with when tracking down problems.<br />
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PS &nbsp;Cisco PIX is end of life so they have or will soon stop supporting it....if you are strapped for cash look into open source free alternatives such as:<br />
IPCop<br />
Smoothwall<br />
or even Astaro if you don't need more than 10 nodes on your network.
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What is the purpose of having your firewall have a public IP?<br />
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We have a setup like this:<br />
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s0 Router e0--------e0 PIX e1--------------internal<br />
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The router's interfaces have public IPs and the pix's outside interface has a public IP. What is the point of doing this, can't we use private Ip addressing in between the pix and router?
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What is the purpose of having your firewall have a public IP?

We have a setup like this:

s0 Router e0--------e0 PIX e1--------------internal

The router's interfaces have public IPs and the pix's outside interface has a public IP. What is the point of doing this, can't we use private Ip addressing in between the pix and router?

Router and Firewall both having public IP

Networking hardware includes the physical devices facilitating the use of a computer network. Typically, networking hardware includes gateways, routers, network bridges, modems, wireless access points, networking cables, line drivers, switches, hubs, and repeaters. But it also includes hybrid network devices such as multilayer switches, protocol converters, bridge routers, proxy servers, firewalls, network address translators, multiplexers, network interface controllers, wireless network interface controllers, ISDN terminal adapters and other related hardware.