|
|
This section covers the following Cisco IOS Firewall information:
Firewalls are often placed in between the internal network and an external network such as the Internet. With a firewall between your network and the Internet, all traffic coming from the Internet must pass through the firewall before entering your network.
Firewalls can also be used to control access to a specific part of your network. For example, you can position firewalls at all the entry points into a research and development network to prevent unauthorized access to proprietary information.
The most basic function of a firewall is to monitor and filter traffic. Firewalls can be simple or elaborate, depending on your network requirements. Simple firewalls are usually easier to configure and manage. However, you might require the flexibility of a more elaborate firewall.
Cisco IOS software provides an extensive set of security features, allowing you to configure a simple or elaborate firewall, according to your particular requirements. You can configure a Cisco device as a firewall if the device is positioned appropriately at a network entry point. Security features that provide firewall functionality are listed in the section "Create a Customized Firewall."
In addition to the security features available in standard Cisco IOS feature sets, there is a Cisco IOS Firewall feature set that gives your router additional firewall capabilities.
The Cisco IOS Firewall feature set is designed to prevent unauthorized, external individuals from gaining access to your internal network, and to block attacks on your network, while at the same time allowing authorized users to access network resources.
You can use the Cisco IOS Firewall feature set to configure your Cisco IOS router as:
The Cisco IOS Firewall feature set provides the following benefits:
As well as configuring these features, you should follow the guidelines listed in the section "Other Guidelines for Configuring Your Firewall." This section outlines important security practices to protect your firewall and network. Table 1 describes Cisco IOS security features and lists the related chapter of the Security Configuration Guide.
| Feature | Chapter | Comments |
|---|---|---|
"Access Control Lists: Overview and Guidelines" in the Cisco IOS Release 12. Security Configuration Guide. | Standard and static extended access lists provide basic traffic filtering capabilities. You configure criteria that describe which packets should be forwarded, and which packets should be dropped at an interface, based on each packet's network layer information. For example, you can block all UDP packets from a specific source IP address or address range. Some extended access lists can also examine transport layer information to determine whether to block or forward packets. Additionally, it is possible to implement access lists based on the time of day, providing network administrators with more control over permitting or denying a user access to resources. To configure a basic firewall, you should at a minimum configure basic traffic filtering. You should configure basic access lists for all network protocols that will be routed through your firewall, such as IP, IPX, AppleTalk. | |
Lock-and-Key (Dynamic Access Lists)
| "Configuring Lock-and-Key Security (Dynamic Access Lists)" in the Cisco IOS Release 12.0 Security Configuration Guide. | Lock-and-Key provides traffic filtering with the ability to allow temporary access through the firewall for certain individuals. These individuals must first be authenticated (by a username/password mechanism) before the firewall allows their traffic through the firewall. Afterwards, the firewall closes the temporary opening. This provides tighter control over traffic at the firewall than with standard or static extended access lists. |
"Configuring IP Session Filtering (Reflexive Access Lists)" in the Cisco IOS Release 12.0 Security Configuration Guide. | Reflexive access lists filter IP traffic so that TCP or UDP "session" traffic is only permitted through the firewall if the session originated from within the internal network. You would only configure Reflexive Access Lists when not using Context-based Access Control. | |
"Configuring TCP Intercept (Prevent Denial-of-Service Attacks)" in the Cisco IOS Release 12.0 Security Configuration Guide. | TCP Intercept protects TCP servers within your network from TCP SYN-flooding attacks, a type of denial-of-service attack. You would only configure TCP Intercept when not using Context-based Access Control. | |
|
| "Configuring Context-based Access Control" in this document. | Context-based Access Control (CBAC) examines not only network layer and transport layer information, but also examines the application-layer protocol information (such as FTP information) to learn about the state of TCP and UDP connections. CBAC maintains connection state information for individual connections. This state information is used to make intelligent decisions about whether packets should be permitted or denied, and dynamically creates and deletes temporary openings in the firewall. CBAC is only available in the Cisco IOS Firewall Feature Set. |
|
| "Configuring TACACS+," "Configuring TACACS and Extended TACACS," "Configuring RADIUS," and "Configuring Kerberos" in the Cisco IOS Release 12.0 Security Configuration Guide. | The Cisco IOS Firewall feature set can be configured as a client of the following supported security servers:
You can use any of these security servers to store a database of user profiles. To gain access into your firewall or to gain access through the firewall into another network, users must enter authentication information (such as a username and password), which is matched against the information on the security server. When users pass authentication, they are granted access according to their specified privileges. |
"Configuring IP Addressing" chapter in the Network Protocols Configuration Guide, Part 1. | You can use Network Address Translation (NAT) to hide internal IP network addresses from the world outside the firewall. NAT was designed to provide IP address conservation and for internal IP networks that have unregistered (not globally unique) IP addresses: NAT translates these unregistered IP addresses into legal addresses at the firewall. NAT can also be configured to advertise only one address for the entire internal network to the outside world. This provides security by effectively hiding the entire internal network from the world. NAT gives you limited spoof protection because internal addresses are hidden. Additionally, NAT removes all your internal services from the external name space. NAT does not work with the application-layer protocols RPC, VDOLive, or SQL*Net "Redirected." (NAT does work with SQL*Net "Bequeathed.") Do not configure NAT with networks that will carry traffic for these incompatible protocols. | |
"Configuring Cisco Encryption Technology" in the Security Configuration Guide.
| Cisco Encryption Technology (CET) selectively encrypts IP packets that are transmitted across unprotected networks such as the Internet. You specify which traffic is considered sensitive and should be encrypted. This encryption prevents sensitive IP packets from being intercepted and read or tampered with. | |
"Configuring IPSec Network Security" in the Security Configuration Guide. | IPSec is a framework of open standards developed by the Internet Engineering Task Force (IETF) that provides security for transmission of sensitive information over unprotected networks such as the Internet. IPSec acts at the network layer, protecting and authenticating IP packets between participating IPSec devices ("peers") such as Cisco routers. IPSec services are similar to those provided by Cisco Encryption Technology, a proprietary security solution introduced in Cisco IOS Software Release 11.2. (The IPSec standard was not yet available at Release 11.2.) However, IPSec provides a more robust security solution, and is standards-based. | |
"Neighbor Router Authentication: Overview and Guidelines" in the Security Configuration Guide. | Neighbor router authentication requires the firewall to authenticate all neighbor routers before accepting any route updates from that neighbor. This ensures that the firewall receives legitimate route updates from a trusted source.
| |
|
| "Troubleshooting the Router" chapter in the "System Management" part of the Configuration Fundamentals Configuration Guide. | Event logging automatically logs output from system error messages and other events to the console terminal. You can also redirect these messages to other destinations such as virtual terminals, internal buffers, or syslog servers. You can also specify the severity of the event to be logged, and you can configure the logged output to be timestamped. The logged output can be used to assist real-time debugging and management, and to track potential security breaches or other nonstandard activities throughout a network. |
"Configuring Authentication" and | Authentication and authorization help protect your network from access by unauthorized users. |
You should also consider the following recommendations:
For a complete description of the CBAC commands used in this section, refer to the "Context-based Access Control Commands" chapter in the Security Command Reference.
This section describes:
CBAC intelligently inspects TCP and UDP packets based on application-layer protocol session information and can be used for intranets, extranets, and the Internet. You can configure CBAC to permit specified TCP and UDP traffic through a firewall only when the connection is initiated from within the network you want to protect. (In other words, CBAC can inspect traffic for sessions that originate from the external network.) However, while this example discusses inspecting traffic for sessions that originate from the external network, CBAC can inspect traffic for sessions that originate from either side of the firewall.
Without CBAC, traffic filtering is limited to access list implementations that examine packets at the network layer, or at most, the transport layer. However, CBAC examines not only network layer and transport layer information but also examines the application-layer protocol information (such as FTP connection information) to learn about the state of the TCP or UDP session. This allows support of protocols that involve multiple channels created as a result of negotiations in the control channel. Most of the multimedia protocols as well as some other protocols (such as FTP, RPC, and SQL*Net) involve multiple channels.
CBAC inspects traffic that travels through the firewall to discover and manage state information for TCP and UDP sessions. This state information is used to create temporary openings in the firewall's access lists to allow return traffic and additional data connections for permissible sessions (sessions that originated from within the protected internal network).
Inspecting packets at the application layer and maintaining TCP and UDP session information provides CBAC with the ability to detect and prevent certain types of network attacks such as SYN-flooding. A SYN-flooding attack occurs when a network attacker floods a server with a barrage of requests for connection and does not complete the connection. The resulting volume of half-open connections can overwhelm the server, causing it to deny service to valid requests.
Denial-of-Service (DoS) detection and prevention inspects packet sequence numbers in TCP connections. If they are not within expected ranges, the router drops suspicious packets. When the router detects unusually high rates of new connections, it issues an alert message. The router drops half-open TCP connection state tables to prevent system resource depletion.
Additional features include Java blocking and real-time alerts and audit trails. Java blocking can be configured to filter based on the server address or completely deny access to Java applets that are not embedded in an archived or compressed file.
Enhanced audit trail features use syslog to track all transactions; recording time stamps, source host, destination host, ports used, and the total number of transmitted bytes, for advanced, session-based reporting.
Real-time alerts send syslog error messages to central management consoles upon detecting suspicious activity. Network managers have the ability to respond immediately to intrusions.
CBAC protects against certain attacks but should not be considered a perfect, impenetrable defense. Determined, skilled attackers might be able to launch effective attacks. While there is no such thing as a perfect defense, CBAC detects and prevents most of the popular attacks on your network.
You should understand the material in this section before you configure CBAC. If you do not understand how CBAC works, you might inadvertently introduce security risks by configuring CBAC inappropriately.
In Figure 1, the inbound access lists at S0 and S1 are configured to block Telnet traffic, and there is no outbound access list configured at E0. When the connection request for User1's Telnet session passes through the firewall, CBAC creates a temporary opening in the inbound access list at S0 to permit returning Telnet traffic for User1's Telnet session. (If the same access list is applied to both S0 and S1, the same opening would appear at both interfaces.) If necessary, CBAC would also have created a similar opening in an outbound access list at E0 to permit return traffic.
This section describes how CBAC inspects packets and maintains state information about sessions to manage the traffic flow through the interface.
Packets entering the firewall are inspected by CBAC only if they first pass the inbound access list at the interface. If a packet is denied by the access list, the packet is simply dropped and not inspected by CBAC.
CBAC inspects and monitors only the control channels of connections; the data channels are not inspected. For example, during FTP sessions both the control and data channels (which are created when a data file is transferred) are monitored for state changes, but only the control channel is inspected (that is, the CBAC software parses the FTP commands and responses).
CBAC inspection tracks sequence numbers in all TCP packets, and drops those packets with sequence numbers that are not within expected ranges.
CBAC inspection recognizes application-specific commands (such as illegal SMTP commands) in the control channel, and detects and prevents certain application-level attacks.
When CBAC suspects an attack, the DoS feature can take several actions:
CBAC uses timeout and threshold values to manage session state information, helping to determine when to drop sessions that do not become fully established. Setting timeout values for network sessions helps prevent DoS attacks by freeing up system resources, dropping sessions after a specified amount of time. Setting threshold values for network sessions helps prevent DoS attacks by controlling the number of half-open sessions, which limits the amount of system resources applied to half-open sessions. When a session is dropped, CBAC sends a reset message to the devices at both end points (source and destination) of the session. When the system under DoS attack receives a reset command, it releases, or frees up, processes and resources related to that incomplete session.
CBAC provides three thresholds against DoS attacks:
If a threshold is exceeded, CBAC has two options: send a reset message to the end points of the oldest half-open session, making resources available to service newly arriving SYN packets; or block all SYN packets temporarily for the duration configured by the threshold value. When the router blocks a SYN packet, the TCP three-way handshake is never initiated, which prevents the router from using memory and processing resources needed for valid connections.
DoS detection and prevention requires that you create a CBAC inspection rule and apply that rule on an interface. The inspection rule must include the protocols that you want to monitor against DoS attacks. For example, if you have TCP inspection enabled on the inspection rule, then CBAC can track all TCP connections to watch for DoS attacks. If the inspection rule includes FTP protocol inspection but not TCP inspection, CBAC tracks only FTP connections to watch for DoS attacks on FTP servers.
For detailed information about setting timeout and threshold values in CBAC to detect and prevent DoS attacks, refer to the section "Configure Global Timeouts and Thresholds".
Return traffic will only be permitted back through the firewall if the state table contains information indicating that the packet belongs to a permissible session. Inspection controls the traffic that belongs to a valid session and forwards the traffic it does not know. When return traffic is inspected, the state table information is updated as necessary.
The temporary access list entries are never saved to NVRAM.
Use CBAC when the firewall will be passing TCP, UDP, and common application traffic.
Use CBAC for applications if you want the application's traffic to be permitted through the firewall only when the traffic session is initiated from a particular side of the firewall (usually from the protected internal network).
In many cases, you will configure CBAC in one direction, in or out, at a single interface. This configuration causes traffic to be permitted back into the internal network only if the traffic is part of a permissible (valid, existing) session. This is a typical configuration for protecting your internal networks from traffic that originates on the Internet.
You can also configure CBAC in both directions on the same interface if you want to inspect sessions initiated on either side of the interface. Configuring CBAC in both directions can be useful in a corporate intranet or extranet environment where you want to manage sessions between different groups of users or between corporate partners.
In this example, a TCP packet exits the internal network through the firewall's external interface. The TCP packet is the first packet of a Telnet session, and Telnet is configured for CBAC inspection.
1. The packet reaches the firewall's external interface.
2. The packet is evaluated against the interface's existing outbound access list, and the packet is permitted. (A denied packet would simply be dropped at this point.)
3. The packet is inspected by CBAC to determine and record information about the state of the packet's connection. This information is recorded in a new state table entry created for the new connection.
(If the packet's application---Telnet---was not configured for CBAC inspection, the packet would simply be forwarded out the interface at this point without being inspected by CBAC. See the section "Define an Inspection Rule" for configuring CBAC inspection information.)
4. Based on the obtained state information, CBAC creates a temporary access list entry which is inserted at the beginning of the external interface's inbound extended access list. This temporary access list entry is designed to permit inbound packets that are part of the same connection as the outbound packet just inspected.
5. The outbound packet is forwarded out the interface.
6. Later, an inbound packet reaches the interface. This packet is part of the same Telnet connection previously established with the outbound packet. The inbound packet is evaluated against the inbound access list, and it is permitted because of the temporary access list entry previously created.
7. The permitted inbound packet is inspected by CBAC, and the connection's state table entry is updated as necessary. Based on the updated state information, the inbound extended access list temporary entries might be modified in order to permit only packets that are valid for the current state of the connection.
8. Any additional inbound or outbound packets that belong to the connection are inspected to update the state table entry and to modify the temporary inbound access list entries as required, and they are forwarded through the interface.
9. When the connection terminates or times out, the connection's state table entry is deleted, and the connection's temporary inbound access list entries are deleted.
In the sample process just described, the firewall access lists are configured as follows:
You can configure CBAC to inspect the following types of sessions:
You can also configure CBAC to specifically inspect certain application-layer protocols. The following application-layer protocols can all be configured for CBAC:
When a protocol is configured for CBAC, the protocol's traffic will be inspected, state information will be maintained, and in general, packets will be allowed back through the firewall only if they belong to a permissible session.
You can use the Cisco IOS Firewall feature set to configure your Cisco IOS router as:
Sometimes CBAC must evaluate long access lists, which might have presented a negative impact to performance. However, this impact is avoided, because CBAC evaluates access lists using an accelerated method (CBAC hashes access lists and evaluates the hash).
The Cisco IOS Firewall feature set is supported on the following platforms:
None.
None.
To configure CBAC, complete the tasks described in the following sections:
You can also perform the tasks described in the following sections. These tasks are optional.
For CBAC configuration examples, refer to the "Configuration Examples" section.
You must decide whether to configure CBAC on an internal or external interface of your firewall.
"Internal" refers to the side where sessions must originate for their traffic to be permitted through the firewall. "External" refers to the side where sessions cannot originate (sessions originating from the external side will be blocked).
If you will be configuring CBAC in two directions, you should configure CBAC in one direction first, using the appropriate "internal" and "external" interface designations. When you configure CBAC in the other direction, the interface designations will be swapped. (CBAC is rarely configured in two directions, and usually only when the firewall is between two networks that need protection from each other, such as with two partners' networks connected by the firewall.)
The firewall is most commonly used with one of two basic network topologies. Determining which of these topologies is most like your own can help you decide whether to configure CBAC on an internal interface or on an external interface.
The first topology is shown in Figure 2. In this simple topology, CBAC is configured for the external interface Serial 1. This prevents specified protocol traffic from entering the firewall and the internal network, unless the traffic is part of a session initiated from within the internal network.
---CBAC Configured at the External Interface
The second topology is shown in Figure 3. In this topology, CBAC is configured for the internal interface Ethernet 0. This allows external traffic to access the services in the Demilitarized Zone (DMZ), such as DNS services, but prevents specified protocol traffic from entering your internal network---unless the traffic is part of a session initiated from within the internal network.
---CBAC Configured at the Internal Interface
Using these two sample topologies, decide whether to configure CBAC on an internal or external interface.
Follow these two general rules when evaluating your IP access lists at the firewall:
Here are some tips for your access lists when you will be configuring CBAC on an external interface:
Here are some tips for your access lists when you will be configuring CBAC on an internal interface:
You can use the default timeout and threshold values, or you can change to values more suitable to your security requirements. You should make any changes to the timeout and threshold values before you continue configuring CBAC.
All the available CBAC timeouts and thresholds are listed in the following table, along with the corresponding command and default value.
| Timeout or Threshold Value to Change | Command | Default |
|---|---|---|
The length of time the software waits for a TCP session to reach the established state before dropping the session. | 30 seconds | |
The length of time a TCP session will still be managed after the firewall detects a FIN-exchange. | 5 seconds | |
The length of time a TCP session will still be managed after no activity (the TCP idle timeout).1 | 3600 seconds (1 hour) | |
The length of time a UDP session will still be managed after no activity (the UDP idle timeout).1 | 30 seconds | |
The length of time a DNS name lookup session will still be managed after no activity. | 5 seconds | |
The number of existing half-open sessions that will cause the software to start deleting half-open sessions.2 | 500 existing half-open sessions | |
The number of existing half-open sessions that will cause the software to stop deleting half-open sessions.2 | 400 existing half-open sessions | |
The rate of new unestablished sessions that will cause the software to start deleting half-open sessions.2 | 500 half-open sessions per minute | |
The rate of new unestablished sessions that will cause the software to stop deleting half-open sessions.2 | 400 half-open sessions per minute | |
The number of existing half-open TCP sessions with the same destination host address that will cause the software to start dropping half-open sessions to the same destination host address.3 | ip inspect tcp max-incomplete host number block-time minutes | 50 existing half-open TCP sessions; 0 minutes |
| 1The global TCP and UDP idle timeouts can be overridden for specified application-layer protocols' sessions as described in the ip inspect name (global configuration) command description, found in the "Context-based Access Control Commands" chapter of the Security Command Reference. 2See the following section, "Half-Open Sessions," for more information. 3Whenever the max-incomplete host threshold is exceeded, the software will drop half-open sessions differently depending on whether the block-time timeout is zero or a positive non-zero number. If the block-time timeout is zero, the software will delete the oldest existing half-open session for the host for every new connection request to the host and will let the SYN packet through. If the block-time timeout is greater than zero, the software will delete all existing half-open sessions for the host, and then block all new connection requests to the host. The software will continue to block all new connection requests until the block-time expires. |
To return any threshold or timeout to the default value, use the no form of the command in the preceding table.
CBAC measures both the total number of existing half-open sessions and the rate of session establishment attempts. Both TCP and UDP half-open sessions are counted in the total number and rate measurements. Measurements are made once per minute.
When the number of existing half-open sessions rises above a threshold (the max-incomplete high number), the software will delete half-open sessions as required to accommodate new connection requests. The software will continue to delete half-open requests as necessary, until the number of existing half-open sessions drops below another threshold (the max-incomplete low number).
When the rate of new connection attempts rises above a threshold (the one-minute high number), the software will delete half-open sessions as required to accommodate new connection attempts. The software will continue to delete half-open sessions as necessary, until the rate of new connection attempts drops below another threshold (the one-minute low number). The rate thresholds are measured as the number of new session connection attempts detected in the last one-minute sample period. The firewall router reviews the "one-minute" rate on an ongoing basis, meaning that the router reviews the rate more frequently than one minute and does not keep deleting half-open sessions for one-minute after a DoS attack has stopped---it will be less time.
An inspection rule should specify each desired application-layer protocol as well as generic TCP or generic UDP if desired. The inspection rule consists of a series of statements each listing a protocol and specifying the same inspection rule name.
To define an inspection rule, follow the instructions in the following sections:
| Command | Purpose |
|---|---|
Configure CBAC inspection for an application-layer protocol (except for RPC and Java). Use one of the protocol keywords defined in Table 2, following. Repeat this command for each desired protocol. Use the same inspection-name to create a single inspection rule. | |
ip inspect name inspection-name rpc program-number number [wait-time minutes] [timeout seconds] | Enable CBAC inspection for the RPC application-layer protocol. You can specify multiple RPC program numbers by repeating this command for each program number. Use the same inspection-name to create a single inspection rule. |
Refer to the description of the ip inspect name (global configuration) command in the "Context-based Access Control Commands" chapter in the Security Command Reference for complete information about how the command works with each application-layer protocol.
To enable CBAC inspection for Java, see the following section, "Configure Java Inspection."
Table 2 identifies application protocol keywords.
| Application Protocol | protocol Keyword |
|---|---|
CU-SeeMe | cuseeme |
FTP | ftp |
H.323 | h323 |
UNIX R commands (rlogin, rexec, rsh) | rcmd |
RealAudio | realaudio |
SMTP | smtp |
SQL*Net | sqlnet |
StreamWorks | streamworks |
TFTP | tftp |
VDOLive | vdolive |
Java applet filtering distinguishes between trusted and untrusted applets by relying on a list of external sites that you designate as "friendly." If an applet is from a friendly site, the firewall allows the applet through. If the applet is not from a friendly site, the applet will be blocked. (Alternately, you could permit applets from all external sites except for those you specifically designate as hostile.)
| Step | Command | Purpose | ||
|---|---|---|---|---|
| ip access-list standard name or access-list access-list-number {deny | permit} source [source-wildcard] | Create a standard access list that permits traffic only from friendly sites, and denies traffic from hostile sites. If you want all internal users to be able to download friendly applets, use the any keyword for the destination as appropriate---but be careful to not misuse the any keyword to inadvertently allow all applets through. | ||
| ip inspect name inspection-name http [java-list access-list] [timeout seconds] | Block all Java applets except for applets from the friendly sites defined previously in the access list. Java blocking only works with standard access lists. Use the same inspection-name as when you specified other protocols, to create a single inspection rule. |
Any application-layer protocol that is inspected will take precedence over the TCP or UDP packet inspection. For example, if inspection is configured for FTP, all control channel information will be recorded in the state table, and all FTP traffic will be permitted back through the firewall if the control channel information is valid for the state of the FTP session. The fact that TCP inspection is configured is irrelevant to the FTP state information.
With TCP and UDP inspection, packets entering the network must exactly match the corresponding packet that previously exited the network. The entering packets must have the same source/destination addresses and source/destination port numbers as the exiting packet (but reversed); otherwise, the entering packets will be blocked at the interface. Also, all TCP packets with a sequence number outside of the window are dropped.
With UDP inspection configured, replies will only be permitted back in through the firewall if they are received within a configurable time after the last request was sent out. (This time is configured with the ip inspect udp idle-time command.)
To configure CBAC inspection for TCP or UDP packets, use one or both of the following global configuration commands:
| Command | Purpose |
|---|---|
ip inspect name inspection-name tcp [timeout seconds] | Enable CBAC inspection for TCP packets. Use the same inspection-name as when you specified other protocols, to create a single inspection rule. |
ip inspect name inspection-name udp [timeout seconds] | Enable CBAC inspection for UDP packets. Use the same inspection-name as when you specified other protocols, to create a single inspection rule. |
After you define an inspection rule, you apply this rule to an interface.
Normally, you apply only one inspection rule to one interface. The only exception might occur if you want to enable CBAC in two directions as described earlier in the section "When and Where to Configure CBAC." For CBAC configured in both directions at a single firewall interface, you should apply two rules, one for each direction.
If you are configuring CBAC on an external interface, apply the rule to outbound traffic.
If you are configuring CBAC on an internal interface, apply the rule to inbound traffic.
To apply an inspection rule to an interface, use the following interface configuration command:
| Command | Purpose |
|---|---|
Apply an inspection rule to an interface. |
You can view certain CBAC information by using one or more of the following EXEC commands:
| Command | Purpose |
|---|---|
show ip inspect name inspection-name | |
show ip inspect config | |
show ip inspect interfaces | Show interface configuration with regards to applied inspection rules and access lists. |
show ip inspect session [detail] | Show existing sessions that are currently being tracked and inspected by CBAC. |
show ip inspect all | Show all CBAC configuration and all existing sessions that are currently being tracked and inspected by CBAC. |
To turn on audit trail messages, use the following global configuration command:
| Command | Purpose |
|---|---|
Turn on CBAC audit trail messages. |
If required, you can also use the CBAC debug commands listed in this section. (Debugging can be turned off for each of the commands in this section by using the no form of the command. To disable all debugging, use the privileged EXEC commands no debug all or undebug all.)
The available debug commands are listed in the following categories:
For a complete description of the debug commands, refer to the Debug Command Reference.
You can use the following generic debug commands, entered in privileged EXEC mode:
| Command | Purpose |
|---|---|
debug ip inspect function-trace | Display messages about software functions called by CBAC. |
debug ip inspect object-creation | Display messages about software objects being created by CBAC. Object creation corresponds to the beginning of CBAC-inspected sessions. |
debug ip inspect object-deletion | Display messages about software objects being deleted by CBAC. Object deletion corresponds to the closing of CBAC-inspected sessions. |
debug ip inspect events | Display messages about CBAC software events, including information about CBAC packet processing. |
debug ip inspect timers | Display messages about CBAC timer events such as when a CBAC idle timeout is reached. |
debug ip inspect detail | Enable the detailed option, which can be used in combination with other options to get additional information. |
You can use the following transport-level debug commands, entered in privileged EXEC mode:
| Command | Purpose |
|---|---|
debug ip inspect tcp | Display messages about CBAC-inspected TCP events, including details about TCP packets. |
debug ip inspect udp | Display messages about CBAC-inspected UDP events, including details about UDP packets. |
You can use the following application protocol debug command, entered in privileged EXEC mode:
| Command | Purpose |
|---|---|
debug ip inspect protocol | Display messages about CBAC-inspected protocol events, including details about the protocol's packets. Refer to Table 3 to determine the protocol keyword. |
Table 3 identifies application protocol keywords for the debug ip inspect command.
| Application Protocol | protocol keyword |
|---|---|
CU-SeeMe | cuseeme |
FTP commands and responses | ftp-cmd |
FTP tokens (enables tracing of the FTP tokens parsed) | ftp-tokens |
H.323 | h323 |
Java applets | http |
UNIX R commands (rlogin, rexec, rsh) | rcmd |
RealAudio | realaudio |
RPC | rpc |
SMTP | smtp |
SQL*Net | sqlnet |
StreamWorks | streamworks |
TFTP | tftp |
VDOLive | vdolive |
CBAC provides syslog messages, console alert messages and audit trail messages. These messages are useful because they can alert you to network attacks and because they provide an audit trail that provides details about sessions inspected by CBAC. While they are generally referred to as error messages, not all error messages indicate problems with your system.
The following types of error messages can be generated by CBAC:
For explanations and recommended actions related to the error messages mentioned in this section, refer to the Cisco IOS Software System Error Messages.
%FW-4-ALERT_ON: getting aggressive, count (550/500) current 1-min rate: 250 %FW-4-ALERT_OFF: calming down, count (0/400) current 1-min rate: 0
When %FW-4-ALERT_ON and %FW-4-ALERT_OFF error messages appear together, each "aggressive/calming" pair of messages indicates a separate attack. The preceding example shows one separate attack.
Error messages such as the following may indicate that a denial-of-service attack has occurred on a specific TCP host:
%FW-4-HOST_TCP_ALERT_ON: Max tcp half-open connections (50) exceeded for host 172.21.127.242. %FW-4-BLOCK_HOST: Blocking new TCP connections to host 172.21.127.242 for 2 minutes (half-open count 50 exceeded) %FW-4-UNBLOCK_HOST: New TCP connections to host 172.21.127.242 no longer blocked
%FW-4-SMTP_INVALID_COMMAND: Invalid SMTP command from initiator (192.168.12.3:52419)
%FW-4-HTTP_JAVA_BLOCK: JAVA applet is blocked from (172.21.127.218:80) to (172.16.57.30:44673).
%FW-3-FTP_PRIV_PORT: Privileged port 1000 used in PORT command -- FTP client 10.0.0.1 FTP server 10.1.0.1 %FW-3-FTP_SESSION_NOT_AUTHENTICATED: Command issued before the session is authenticated -- FTP client 10.0.0.1 %FW-3-FTP_NON_MATCHING_IP_ADDR: Non-matching address 172.19.148.154 used in PORT command -- FTP client 172.19.54.143 FTP server 172.16.127.242
%FW-6-SESS_AUDIT_TRAIL: tcp session initiator (192.168.1.13:33192) sent 22 bytes -- responder (192.168.129.11:25) sent 208 bytes %FW-6-SESS_AUDIT_TRAIL: http session initiator (172.16.57.30:44673) sent 1599 bytes -- responder (172.21.127.218:80) sent 93124 bytes
You can turn off CBAC, with the no ip inspect global configuration command.
In most situations, turning off CBAC has no negative security impact because CBAC creates "permit" access lists. Without CBAC configured, no "permit" access lists are maintained. Therefore, no derived traffic (returning traffic or traffic from the data channels) can go through the firewall. The exception is SMTP and Java blocking. With CBAC turned off, unacceptable SMTP commands or Java applets may go through the firewall.
This section provides three configuration examples:
The first example develops a CBAC inspection rule and supporting ACL, and applies that inspection rule on ATM interface. This example focuses on how to configure CBAC and does not provide a complete router configuration.
The other examples provide more complete firewall configurations, illustrating different ways to apply CBAC in branch office environments with LAN and serial interfaces.
In this example, firewall protection is required for inbound traffic on an ATM interface. This example might apply to sites where local hosts require access to hosts or services on a remote network. Additionally, the security policy for this site uses Access Control Lists (ACL) to restrict outbound traffic on the ATM interface to IP and ICMP protocol traffic, denying outbound access for TCP and UDP protocol traffic. Outbound access for specific TCP and UDP protocol traffic is provided through dynamic access lists, which are generated according to CBAC inspection rules.
For information on how to select the interface on which to apply CBAC, refer to the section "Pick an Interface.
!------------------------- !Create the Inspection Rule !------------------------- ! !Create the CBAC inspection rule "test", allowing inspection of the protocol traffic !specified by the rule. This inspection rule sets the timeout value to 30 seconds for !each protocol (except for RPC). The timeout value defines the maximum time that a !connection for a given protocol can remain active without any traffic passing through !the router. When these timeouts are reached, the dynamic ACLs that are inserted to !permit the returning traffic are removed, and subsequent packets (possibly even valid !ones) are not permitted. ip inspect name test cuseeme timeout 30 ip inspect name test ftp timeout 30 ip inspect name test h323 timeout 30 ip inspect name test realaudio timeout 30 ip inspect name test rpc program-number 100000 ip inspect name test streamworks timeout 30 ip inspect name test vdolive timeout 30 ! !------------------------------ !Create the Access Control List !------------------------------ ! !In this example, ACL 105 denies all TCP and UDP protocol traffic. IP traffic is !permitted to allow access for routing and control traffic. This means that only the !return traffic for protocols defined in the inspection rule is allow access through !the interface where this rule is applied. access-list 105 deny TCP any any access-list 105 deny UDP any any access-list 105 permit ip any any ! !--------------------------------- !Apply the Inspection Rule and ACL !--------------------------------- ! !In this example, the inspection rule "test" is applied at ATM interface 3/0 for !connections initiated in the outbound direction; that is, from hosts that are located !on a local network. ACL 105 is applied at ATM interface 3/0 in the inbound direction; !that is, return traffic in response to local host initiated connections. If inbound !traffic at the interface matches an inspection rule, CBAC creates a dynamic access !list allowing inbound (returning) traffic for that connection. This combination of the !ACL and CBAC inspection rules means that TCP and UDP traffic that is not part of a !connection that initiated from a local host is not permitted access through the !interface. interface ATM3/0 ip address 10.1.10.1 255.0.0.0 ip access-group 105 in no ip directed-broadcast ip nat outside ip inspect test out no shutdown atm clock INTERNAL atm pvc 7 7 7 aal5snap map-group atm
The firewall has two interfaces configured:
!---------------------------------------------------------------------- ! This first section contains some configuration that is not required for CBAC, ! but illustrates good security practices. Note that there are no ! services on the Ethernet side. Email is picked up via POP from a server on the ! corporate side. !---------------------------------------------------------------------- ! hostname fred-examplecorp-fr ! boot system flash c1600-fw1600-l enable secret 5 <elided> ! username fred password <elided> ip subnet-zero no ip source-route ip domain-name example.com ip name-server 172.19.2.132 ip name-server 198.92.30.32 ! ! !---------------------------------------------------------------------- !The next section includes configuration required specifically for CBAC !---------------------------------------------------------------------- ! !The following commands define the inspection rule "myfw", allowing !the specified protocols to be inspected. Note that Java applets will be permitted !according to access list 51, defined later in this configuration. ip inspect name myfw cuseeme timeout 3600 ip inspect name myfw ftp timeout 3600 ip inspect name myfw http java-list 51 timeout 3600 ip inspect name myfw rcmd timeout 3600 ip inspect name myfw realaudio timeout 3600 ip inspect name myfw smtp timeout 3600 ip inspect name myfw tftp timeout 30 ip inspect name myfw udp timeout 15 ip inspect name myfw tcp timeout 3600 ! !The following interface configuration applies the "myfw" inspection rule to !inbound traffic at Ethernet 0. Since this interface is on the internal network !side of the firewall, traffic entering Ethernet 0 is actually !exiting the internal network. Applying the inspection rule to this interface causes !inbound traffic (which is exiting the network) to be inspected; return traffic will !only be permitted back through the firewall if part of a session which began from !within the network. !Also note that access list 101 is applied to inbound traffic at Ethernet 0. !Any traffic that passes the access list will be inspected by CBAC. !(Traffic blocked by the access list will not be inspected.) !interface Ethernet0 description ExampleCorp Ethernet chez fred ip address 172.19.139.1 255.255.255.248 ip broadcast-address 172.19.131.7 no ip directed-broadcast no ip proxy-arp ip inspect myfw in ip access-group 101 in no cdp enable ! interface Serial0 description Frame Relay (Telco ID 22RTQQ062438-001) to ExampleCorp HQ no ip address ip broadcast-address 0.0.0.0 encapsulation frame-relay IETF no arp frame-relay bandwidth 56 service-module 56k clock source line service-module 56k network-type dds frame-relay lmi-type ansi ! !Note that the following interface configuration applies access list 111 to !inbound traffic at the external serial interface. (Inbound traffic is !entering the network.) When CBAC inspection occurs on traffic exiting the !network, temporary openings will be added to access list 111 to allow returning !traffic that is part of existing sessions. ! interface Serial0.1 point-to-point ip unnumbered Ethernet0 ip access-group 111 in bandwidth 56 no cdp enable frame-relay interface-dlci 16 ! ip classless ip route 0.0.0.0 0.0.0.0 Serial0.1 ! !The following access list defines "friendly" and "hostile" sites for Java !applet blocking. Because Java applet blocking is defined in the inspection !rule "myfw" and references access list 51, applets will be actively denied !if they are from any of the "deny" addresses and allowed only if they are from !either of the two "permit" networks. ! access-list 51 deny 172.19.1.203 access-list 51 deny 172.19.2.147 access-list 51 permit 172.18.0.0 0.1.255.255 access-list 51 permit 192.168.1.0 0.0.0.255 access-list 51 deny any ! !The following access list 101 is applied to interface Ethernet 0 above. !This access list permits all traffic that should be CBAC inspected, and also !provides anti-spoofing. The access list is deliberately set up to deny unknown !IP protocols, because no such unknown protocols will be in legitimate use. ! access-list 101 permit tcp 172.19.139.0 0.0.0.7 any access-list 101 permit udp 172.19.139.0 0.0.0.7 any access-list 101 permit icmp 172.19.139.0 0.0.0.7 any access-list 101 deny ip any any !The following access list 111 is applied to interface Serial 0.1 above. !This access list filters traffic coming in from the external side. When !CBAC inspection occurs, temporary openings will be added to the beginning of !this access list to allow return traffic back into the internal network. !This access list should restrict traffic that will be inspected by !CBAC. (Remember that CBAC will open holes as necessary to permit returning traffic.) !Comments precede each access list entry. These entries aren't all specifically related !to CBAC, but are created to provide general good security. ! !Anti-spoofing. access-list 111 deny ip 172.19.139.0 0.0.0.7 any ! !Sometimes EIGRP is run on the Frame Relay link. When you use an !input access list, you have to explicitly allow even control traffic. !This could be more restrictive, but there would have to be entries !for the EIGRP multicast as well as for the office's own unicast address. access-list 111 permit igrp any any ! !These are the ICMP types actually used... !administratively-prohibited is useful when you're trying to figure out why !you can't reach something you think you should be able to reach. access-list 111 permit icmp any 172.19.139.0 0.0.0.7 administratively-prohibited ! !This allows network admins at headquarters to ping hosts at the field office: access-list 111 permit icmp any 172.19.139.0 0.0.0.7 echo ! !This allows the field office to do outgoing pings access-list 111 permit icmp any 172.19.139.0 0.0.0.7 echo-reply ! !Path MTU discovery requires too-big messages access-list 111 permit icmp any 172.19.139.0 0.0.0.7 packet-too-big ! !Outgoing traceroute requires time-exceeded messages to come back access-list 111 permit icmp any 172.19.139.0 0.0.0.7 time-exceeded ! ! Incoming traceroute access-list 111 permit icmp any 172.19.139.0 0.0.0.7 traceroute ! !Permits all unreachables because if you are trying to debug !things from the remote office, you want to see them. If nobody ever did !any debugging from the network, it would be more appropriate to permit only !port unreachables or no unreachables at all. access-list 111 permit icmp any 172.19.139.0 0.0.0.7 unreachable ! !These next two entries permit users on most ExampleCorp networks to telnet to !a host in the field office. This is for remote administration by the network admins. access-list 111 permit tcp 172.18.0.0 0.1.255.255 host 172.19.139.1 eq telnet access-list 111 permit tcp 192.168.1.0 0.0.0.255 host 172.19.139.1 eq telnet ! !Final deny for explicitness access-list 111 deny ip any any ! no cdp run snmp-server community <elided> RO ! line con 0 exec-timeout 0 0 password <elided> login local line vty 0 exec-timeout 0 0 password <elided> login local length 35 line vty 1 exec-timeout 0 0 password 7 <elided> login local line vty 2 exec-timeout 0 0 password 7 <elided> login local line vty 3 exec-timeout 0 0 password 7 <elided> login local line vty 4 exec-timeout 0 0 password 7 <elided> login local ! scheduler interval 500 end
The branch office has this sample network configuration:
! ------------------------------------------------------------------ ! This first section contains some configuration that is not required ! for CBAC, but illustrates good security practices. ! ------------------------------------------------------------------ !Add this line to get timestamps on the syslog messages. service timestamps log datetime localtime show-timezone ! hostname Router1 ! boot system flash c3600-fw3600-l ! ! Configure AAA user authentication. aaa new-model aaa authentication login lista tacacs+ enable ! enable secret 5 <elided> ip subnet-zero ! ! Disable source routing to help prevent spoofing. no ip source-route ! ! Set up the domain name and server IP addresses. ip domain-name example.com ip name-server 192.168.55.132 ip name-server 192.168.27.32 ! ! The audit-trail command enables the delivery of specific CBAC messages ! through the syslog notification process. ip inspect audit-trail ! ! Establish the time-out values for DNS queries. When this idle-timer expires, ! the dynamic ACL entries that were created to permit the reply to a DNS request ! will be removed and any subsequent packets will be denied. ip inspect dns-timeout 10 ! !---------------------------------------------------------------------- !The next section includes configuration statements required !specifically for CBAC. !---------------------------------------------------------------------- ! Define the CBAC inspection rule "inspect1", allowing the specified protocols to be ! inspected. The first rule enables SMTP specific inspection. SMTP inspection causes ! the exchange of the SMTP session to be inspected for illegal commands. Any packets ! with illegal commands are dropped, and the SMTP session will hang and eventually ! time out. ip inspect name inspect1 smtp timeout 300 ! ! In the next two lines of inspect1, define the maximum time that each of the udp and ! tcp sessions are allowed to continue without any traffic passing ! through the router. When these timeouts are reached, the dynamic ACLs that ! are inserted to permit the returning traffic are removed and subsequent packets ! (possibly even valid ones) will not be permitted. ip inspect name inspect1 udp timeout 300 ip inspect name inspect1 tcp timeout 300 ! ! Define the CBAC inspection rule "inspect2", allowing the specified protocols to be ! inspected. These rules are similar to those used in the inspection rule "inspect1," ! except that on the interfaces where this rule is applied, SMTP sessions are not ! expected to go through; therefore, the SMTP rule element is not applied here. ip inspect name inspect2 udp timeout 300 ip inspect name inspect2 tcp timeout 3600 ! !---------------------------------------------------------------------- ! The next section shows the Ethernet interface configuration statements for each ! interface, including access lists and inspections rules. !---------------------------------------------------------------------- ! Apply the "inspect1" inspection rule to sessions that are initiated in the outbound ! direction (toward the LAN) at Ethernet interface 0/0. All packets in these sessions ! will be inspected by CBAC. Provided that network traffic passes the Access Control ! List (ACL) restrictions, traffic is then inspected by CBAC for access through the ! IOS Firewall. Traffic blocked by the access list is not inspected by CBAC. Access ! list 110 is applied to outbound traffic on this interface. interface Ethernet0/0 description HR_Server Ethernet ip address 172.16.110.1 255.255.255.0 ip access-group 110 out no ip directed-broadcast no ip proxy-arp ip inspect inspect1 out no cdp enable ! ! Apply access list 120 to inbound traffic on Ethernet interface 0/1. ! Applying access list 120 to inbound traffic provides anti-spoofing on this interface ! by dropping traffic with a source address matching the IP address on a network other ! than Ethernet 0/1. The IP helper address lists the IP address of the DHCP server on ! Ethernet interface 1/0. interface Ethernet0/1 description HR_client Ethernet ip address 172.16.120.1 255.255.255.0 ip access-group 120 in ip helper-address 172.16.130.66 no ip directed-broadcast no ip proxy-arp no cdp enable ! ! Apply the "inspect2" inspection rule to sessions that are initiated in the outbound ! direction (toward the LAN) at Ethernet interface 1/0. Provided that network traffic ! passes the Access Control List (ACL) restrictions, traffic is then inspected by CBAC ! through the IOS Firewall. Traffic blocked by the access list is not inspected by ! CBAC. Access list 130 is applied to outbound traffic on this interface. interface Ethernet1/0 description Web_server Ethernet ip address 172.16.130.1 255.255.255.0 ip access-group 130 out no ip directed-broadcast no ip proxy-arp ip inspect inspect2 out no cdp enable ! ! Apply access list 140 to inbound traffic at Ethernet interface 1/1. This ! provides anti-spoofing on the interface by dropping traffic with a source address ! matching the IP address of a network other than Ethernet 1/1. The IP helper address ! lists the IP address of the DHCP server on Ethernet interface 1/0. interface Ethernet1/1 description Everyone_else Ethernet ip address 172.16.140.1 255.255.255.0 ip access-group 140 in ip helper-address 172.16.130.66 no ip directed-broadcast no ip proxy-arp no cdp enable ! !---------------------------------------------------------------------- ! The next section configures the serial interfaces, including access lists. !---------------------------------------------------------------------- ! Apply access list 150 to Serial interfaces 0/0. This provides anti-spoofing on the ! serial interface by dropping traffic with a source address matching the IP address ! of a host on Ethernet interface 0/0, 0/1, 1/0, or 1/1. interface Serial0/0 description T1 to HQ ip address 192.168.150.1 255.255.255.0 ip access-group 150 in bandwidth 1544 ! interface Serial1/1 description T1 to HQ ip address 192.168.160.1 255.255.255.0 ip access-group 150 in bandwidth 1544 ! ! ------------------------------ ! Configure routing information. ! ------------------------------- router igrp 109 network 172.16.0.0 network 192.168.150.0 network 192.168.160.0 ! ! Define protocol forwarding on the firewall. When you turn on a related command, ! ip helper-address, you forward every IP broadcast in the ip forward protocol ! command list, including several which are on by default: TFTP (port 69), ! DNS (port 53), Time service (port 37), NetBIOS Name Server (port 137), ! NetBIOS Datagram Server (port 138), BOOTP client and server datagrams ! (ports 67 and 68), and TACACS service (port 49). One common ! application that requires helper addresses is Dynamic Host Configuration ! Protocol (DHCP). DHCP protocol information is carried inside of BOOTP packets. The ! "no ip forward protocol" statements turn off forwarding for the specified protocols. no ip forward-protocol udp netbios-ns no ip forward-protocol udp netbios-dgm no ip forward-protocol udp tacacs no ip forward-protocol udp tftp ip forward-protocol udp bootpc ! ! Add this line to establish where router SYSLOG messages are sent. This includes the ! CBAC messages. logging 192.168.55.131 ! ! --------------------------------------------------------------- ! Define the configuration of each access list. ! --------------------------------------------------------------- ! Defines Telnet controls in access list 12. access-list 12 permit 192.168.55.0 0.0.0.255 ! ! Defines snmp controls in access list 13. access-list 13 permit 192.168.55.12 access-list 13 permit 192.168.55.19 ! ! Access list 110 permits TCP and UDP protocol traffic for ! specific ports and with a source address on Ethernet interface 0/1. The access list ! denies IP protocol traffic with any other source and destination address. The ! access list permits ICMP access for any source and destination ! address. Access list 110 is deliberately set up to deny unknown IP protocols ! because no such unknown protocols will be in legitimate use. Access list ! 110 is applied to outbound traffic at Ethernet interface 0/0. In ACL 110, ! network traffic is being allowed access to the ports on any server on the HR server ! network. In less trusted environments, this can be a security problem; however, you ! can limit access more severely by specifying specific destination addresses in the ! ACL statements. access-list 110 permit tcp 172.16.120.0 0.0.0.255 any eq smtp access-list 110 permit tcp 172.16.120.0 0.0.0.255 any eq pop3 access-list 110 permit tcp 172.16.120.0 0.0.0.255 any eq 110 access-list 110 permit udp any any eq 137 access-list 110 permit udp any any eq 138 access-list 110 permit udp any any eq 139 access-list 110 permit icmp any any access-list 110 deny ip any any! ! ! Access-list 120 permits TCP, UDP, and ICMP protocol traffic with a source address ! on Ethernet interface 0/1, but denies all other IP protocol traffic. Access list ! 120 is applied to inbound traffic on Ethernet interface 0/1. access-list 120 permit tcp 172.16.120.0 0.0.0.255 any access-list 120 permit udp 172.16.120.0 0.0.0.255 any access-list 120 permit icmp 172.16.120.0 0.0.0.255 any access-list 120 deny ip any any ! ! Access list 130 permits TCP, UDP, and ICMP protocol traffic for specific ports and ! with any source and destination address. It opens access to the web server and to ! all NBT services to the rest of the company, which can be controlled through the ! trust relations on the NT servers. The bootpc entry permits access to the DHCP ! server. Access list 130 denies all other IP protocol traffic. Access list 130 is ! applied to outbound traffic at Ethernet interface 1/0. access-list 130 permit tcp any any eq www access-list 130 permit tcp any any eq 443 access-list 130 permit tcp any any eq 110 access-list 130 permit udp any any eq 137 access-list 130 permit udp any any eq 138 access-list 130 permit udp any any eq 139 access-list 130 permit udp any any eq bootpc access-list 130 permit icmp any any access-list 130 deny ip any any ! ! Access list 140 permits TCP, UDP, and ICMP protocol traffic with a source address on ! Ethernet interface 1/1, and it denies all other IP protocol traffic. Access list 140 ! is applied to inbound traffic at Ethernet interface 1/1. access-list 140 permit tcp 172.16.140.0 0.0.0.255 any access-list 140 permit udp 172.16.140.0 0.0.0.255 any access-list 140 permit icmp 172.16.140.0 0.0.0.255 any access-list 140 deny ip any any ! ! Access list 150 denies IP protocol traffic with a source address on Ethernet ! interfaces 0/0, 0/1, 1/0, and 1/1, and it permits IP protocol traffic with any other ! source and destination address. Access list 150 is applied to inbound traffic ! on each of the serial interfaces. access-list 150 deny ip 172.16.110.0 0.0.0.255 any access-list 150 deny ip 172.16.120.0 0.0.0.255 any access-list 150 deny ip 172.16.130.0 0.0.0.255 any access-list 150 deny ip 172.16.140.0 0.0.0.255 any access-list 150 permit ip any any ! ! Disable Cisco Discovery Protocol. no cdp run ! snmp-server community <elided> ro 13 tacacs-server host 192.168.55.2 tacacs-server key <elided> ! ! ----------------------------------------------------------------------------------- ! Configures the router console port and the virtual terminal line interfaces, ! including AAA authentication at login. Authentication is required for users defined ! in "lista." Access-class 12 is applied on each line, restricting Telnet access to ! connections with a source address on the network management network. ! ----------------------------------------------------------------------------------- line console 0 exec-timeout 3 00 login authentication lista line aux 0 exec-timeout 3 00 login authentication lista line vty 0 exec-timeout 1 30 login authentication lista access-class 12 in line vty 1 exec-timeout 1 30 login authentication lista access-class 12 in line vty 2 exec-timeout 1 30 login authentication lista access-class 12 in line vty 3 exec-timeout 1 30 login authentication lista access-class 12 in line vty 4 exec-timeout 1 30 login authentication lista access-class 12 in ! end
None. Cisco IOS Firewall feature set command descriptions are included in the Security Command Reference.
Posted: Tue May 4 08:04:29 PDT 1999
Copyright 1989-1999©Cisco Systems Inc.
