Female Voice: “Don’t tell me which zone’s for stopping and which zone’s for loading!
Male Voice: “Listen, Betty, don’t start your white zone sh*t again. There is just no stopping in the white zone.” – Airplane 1980
In an earlier blog post, we introduced you to the IOS Zone-Based Firewall from Cisco Systems. You can find that post here if you need it.
This post will walk you through an example of the Zone-Based Firewall at the command line. Here is the simple topology we will use in this example:

For this example, we will pretend the R1 device is in the Inside, private, protected network. R3 represents a device in the Outside, public, unprotected Internet. R2 in the middle will be our IOS Zone-Based Firewall. We want to inspect Telnet traffic sourced from the Inside network traveling to the Outside network, and we want to dynamically permit return traffic back in from the Outside based on session information.
From our first blog post on this topic, we recall the four steps of this configuration:

• Step 1 – Define and populate zones.
• Step 2 – Define the class maps that identify traffic that is permitted between zones.
• Step 3 – Configure a policy map that specifies actions for the traffic.
• Step 4 – Configure the zone pair and apply the policy.

Now that we have reviewed the steps of this configuration, let us begin.
Step 1: Define and populate our zones:

R2(config)#zone security ZONE_PRIVATE
R2(config-sec-zone)#zone security ZONE_INTERNET
R2(config-sec-zone)#interface fa0/0
R2(config-if)#zone-member security ZONE_PRIVATE
R2(config-if)#interface fa0/1
R2(config-if)#zone-member security ZONE_INTERNET

Step 2: Define the class maps that identify traffic that is permitted between zones:

R2(config)#class-map type inspect match-any CM_INTERNET_TRAFFIC
R2(config-cmap)#match protocol telnet

Step 3: Configure a policy map which specifies the action for the class map:

R2(config)#policy-map type inspect PM_PRIVATE_TO_INTERNET
R2(config-pmap)#class type inspect CM_INTERNET_TRAFFIC
R2(config-pmap-c)#inspect

Step 4: Configure the zone pair and apply your policy:

R2(config)#zone-pair security ZONEP_PRIV_INT source ZONE_PRIVATE destination ZONE_INTERNET
R2(config-sec-zone-pair)#service-policy type inspect PM_PRIVATE_TO_INTERNET

Now it is time for some verification. Can we ping through the firewall (R2) and get a response from R3? We would expect this to fail since we are not inspecting ICMP traffic.

R1#ping 10.20.20.3

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.20.20.3, timeout is 2 seconds:

.....

Success rate is 0 percent (0/5)

Can we Telnet to this same address on R3? We would expect this to work thanks to the inspection of Telnet traffic.

R1#telnet 10.20.20.3

Trying 10.20.20.3 ... Open

User Access Verification

Password:

R3>

Can we Telnet from R3 (Outside) into R1 (Inside)? No we cannot:

R3#telnet 10.10.10.1 

Trying 10.10.10.1 ...

%
Connection timed out; remote host not responding

R3#

Now for a further verification, let us examine R2.
We will use a very powerful command:

R2#show policy-map type inspect zone-pair
Zone-pair: ZONEP_PRIV_INT
Service-policy inspect : PM_PRIVATE_TO_INTERNET
Class-map: CM_INTERNET_TRAFFIC (match-any)
Match: protocol telnet
5 packets, 120 bytes
30 second rate 0 bps
Inspect
Packet inspection statistics [process switch:fast switch]
tcp packets: [0:40]

Looking for more information on this Version 4.X feature, or many others? check out these products:

• Advanced Technologies Class On Demand
• Open Lecture Series
• CCIE R&S Audio Bootcamp