Catalyst 6500 Release 12.2SX Software Configuration Guide

Using AutoSecure

This chapter describes how to use the AutoSecure function. Release 12.2(33)SXH and later releases support the AutoSecure function.

Note For complete syntax and usage information for the commands used in this chapter, see the Cisco IOS Master Command List, at this URL:

http://www.cisco.com/en/US/docs/ios/mcl/allreleasemcl/all_book.html

Tip For additional information about Cisco Catalyst 6500 Series Switches (including configuration examples and troubleshooting information), see the documents listed on this page:

http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html

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This chapter consists of these sections:

•Understanding AutoSecure

•Configuring AutoSecure

•AutoSecure Configuration Example

Understanding AutoSecure

You can easily secure the switch without understanding all the security capabilities of the switch by using the AutoSecure feature. AutoSecure is a simple security configuration process that disables nonessential system services and enables a basic set of recommended security policies to ensure secure networking services.

Caution Although AutoSecure helps to secure a switch, it does not guarantee the complete security of the switch.

The following sections describe how AutoSecure works:

•Benefits of AutoSecure

•Securing the Management Plane

•Securing the Forwarding Plane

•AutoSecure Guidelines and Restrictions

Benefits of AutoSecure

AutoSecure provides a variety of mechanisms to enhance security of the switch.

Simplified Switch Security Configuration

AutoSecure automates a thorough configuration of security features of the switch. AutoSecure disables certain features that are enabled by default that could be exploited for security holes.

You can execute AutoSecure in either of two modes, depending on your individual needs:

•Interactive mode—Prompts with options to enable and disable services and other security features, suggesting a default setting for each option.

•Noninteractive mode—Automatically executes the recommended Cisco default settings.

Enhanced Password Security

AutoSecure provides the following mechanisms to improve the security of access to the switch:

•You can specify a required minimum password length, which can eliminate weak passwords that are prevalent on most networks, such as "lab" and "cisco."

To configure a minimum password length, use the security passwords min-length command.

•You can cause a syslog message to be generated after the number of unsuccessful login attempts exceeds the configured threshold.

To configure the number of allowable unsuccessful login attempts (the threshold rate), use the security authentication failure rate command.

System Logging Message Support

System logging messages capture any subsequent changes to the AutoSecure configuration that are applied on the running configuration. As a result, a more detailed audit trail is provided when AutoSecure is executed.

Securing the Management Plane

AutoSecure provides protection for the switch management interfaces (the management plane) and the data routing and switching functions (the forwarding plane, described in the "Securing the Forwarding Plane" section.) Securing the management plane is done by turning off certain global and interface services that can be potentially exploited for security attacks and turning on global services that help minimize the threat of attacks. Secure access and secure logging are also configured for the switch.

Caution If your device is managed by a network management (NM) application, securing the management plane could turn off some services such as the HTTP server and disrupt the NM application support.

The following sections define how AutoSecure helps to secure the management plane:

•Disables Global Services

•Disables Per-Interface Services

•Enables Global Services

•Secures Access to the Switch

•Enhances Logging for Security

Disables Global Services

AutoSecure will disable the following global services on the switch without prompting the user:

•Finger—Collects information about the system (reconnaissance) before an attack.

•PAD—Enables all packet assembler and disassembler (PAD) commands and connections between PAD devices and access servers.

•Small servers—Causes TCP and User Datagram Protocol (UDP) diagnostic port attacks: a sender transmits a volume of fake requests for UDP diagnostic services on the switch, consuming all CPU resources.

•Bootp server—Bootp is an insecure protocol that can be exploited for an attack.

•HTTP server—Without secure-HTTP or authentication embedded in the HTTP server with an associated ACL, the HTTP server is insecure and can be exploited for an attack. (If you must enable the HTTP server, you will be prompted for the proper authentication or access list.)

Note If you are using Security Device Manager (SDM), you must manually enable the HTTP server using the ip http server command.

•Identification service—An unsecure protocol (defined in RFC 1413) that allows an external host to query a TCP port for identification. An attacker can access private information about the user from the ID server.

•CDP—If a large number of Cisco Discovery Protocol (CDP) packets are sent to the switch, the available memory of the switch can be consumed, which causes the switch to crash.

Note NM applications that use CDP to discover network topology will not be able to perform discovery.

•NTP—Without authentication or access control, Network Time Protocol (NTP) is insecure and can be used by an attacker to send NTP packets to crash or overload the switch.

If you require NTP, you must configure NTP authentication using Message Digest 5 (MD5) and the ntp access-group command. If NTP is enabled globally, disable it on all interfaces on which it is not needed.

•Source routing—Source routing is provided only for debugging purposes, and should be disabled in all other cases. Otherwise, packets may avoid some of the access control mechanisms of the switch.

Disables Per-Interface Services

AutoSecure will disable the following per-interface services on the switch without prompting the user:

•ICMP redirects—Disabled on all interfaces. Does not add a useful functionality to a correctly configured network, but could be used by attackers to exploit security holes.

•ICMP unreachables—Disabled on all interfaces. Internet Control Management Protocol (ICMP) unreachables are a known method for some ICMP-based denial of service (DoS) attacks.

•ICMP mask reply messages—Disabled on all interfaces. ICMP mask reply messages can give an attacker the subnet mask for a particular subnetwork in the internetwork.

•Proxy-arp—Disabled on all interfaces. Proxy-arp requests are a known method for DoS attacks because the available bandwidth and resources of the switch can be consumed in an attempt to respond to the repeated requests sent by an attacker.

•Directed broadcast—Disabled on all interfaces. Potential cause of SMURF attacks for DoS.

•Maintenance Operations Protocol (MOP) service—Disabled on all interfaces.

Enables Global Services

AutoSecure will enable the following global services on the switch without prompting the user:

•The service password-encryption command—Prevents passwords from being visible in the configuration.

•The service tcp-keepalives-in and service tcp-keepalives-out commands—Ensures that abnormally terminated TCP sessions are removed.

Secures Access to the Switch

Caution If your device is managed by an NM application, securing access to the switch could turn off vital services and may disrupt the NM application support.

AutoSecure will make the following options available for securing access to the switch:

•If a text banner does not exist, you will be prompted to add a banner. This feature provides the following sample banner:

Authorized access only

This system is the property of ABC Enterprise

Disconnect IMMEDIATELY if you are not an authorized user!

Contact abc@example.com +1 408 5551212 for help.

•The login and password (preferably a secret password, if supported) are configured on the console, AUX, vty, and tty lines. The transport input and transport output commands are also configured on all of these lines. (Telnet and secure shell (SSH) are the only valid transport methods.) The exec-timeout command is configured on the console and AUX as 10.

•When the image on the device is a crypto image, AutoSecure enables SSH and secure copy (SCP) for access and file transfer to and from the switch. The timeout seconds and authentication-retries integer options for the ip ssh command are configured to a minimum number. (Telnet and FTP are not affected by this operation and remain operational.)

•If the user specifies that the switch does not use Simple Network Management Protocol (SNMP), one of the following functionalities will occur:

–In interactive mode, the user is asked whether to disable SNMP regardless of the values of the community strings, which act like passwords to regulate access to the agent on the switch.

–In noninteractive mode, SNMP will be disabled if the community string is public or private.

Note After AutoSecure has been enabled, tools that use SNMP to monitor or configure a device will be unable to communicate with the device using SNMP.

•If authentication, authorization, and accounting (AAA) is not configured, AutoSecure configures local AAA. AutoSecure will prompt the user to configure a local username and password on the switch.

Enhances Logging for Security

AutoSecure provides the following logging options, which allow you to identify and respond to security incidents:

•Sequence numbers and time stamps for all debug and log messages. This option is useful when auditing logging messages.

•Logging messages for login-related events. For example, the message "Blocking Period when Login Attack Detected" will be displayed when a login attack is detected and the switch enters quiet mode. (Quiet mode means that the switch will not allow any login attempts using Telnet, HTTP, or SSH.)

•The logging console critical command, which sends system logging (syslog) messages to all available TTY lines and limits messages based on severity.

•The logging buffered command, which copies logging messages to an internal buffer and limits messages logged to the buffer based on severity.

•The logging trap debugging command, which allows all commands with a severity higher than debugging to be sent to the logging server.

Securing the Forwarding Plane

To minimize the risk of attacks on the switch forwarding plane, AutoSecure provides the following functions:

•Cisco Express Forwarding (CEF)—AutoSecure enables CEF or distributed CEF (dCEF) on the switch whenever possible. Because there is no need to build cache entries when traffic starts arriving for new destinations, CEF operates more predictably than other modes when presented with large volumes of traffic addressed to many destinations. Switches configured for CEF perform better under SYN attacks than switches using the traditional cache.

Note CEF consumes more memory than a traditional cache.

•If strict Unicast Reverse Path Forwarding (uRPF) is available, it can be configured on the switch to help mitigate problems that are caused by the introduction of forged (spoofed) IP source addresses. uRPF discards IP packets that lack a verifiable IP source address.

•Hardware rate limiting—AutoSecure will enable hardware rate-limiting of the following types of traffic without prompting the user:

–IP errors

–RPF failures

–ICMP no-route messages

–ICMP acl-drop messages

–IPv4 multicast FIB miss messages

–IPv4 multicast partially switch flow messages

AutoSecure will provide the option for hardware rate-limiting of the following types of traffic:

–ICMP redirects

–TTL failures

–MTU failures

–IP unicast options

–IP multicast options

–Ingress and egress ACL bridged packets

Note Rate-limiting of ingress and egress ACL bridged packets can interfere with ACL logging and can increase session setup rates for hardware accelerated features such as NAT, Layer 3 WCCP, and TCP intercept.

AutoSecure Guidelines and Restrictions

When configuring AutoSecure, follow these guidelines and restrictions:

•Because there is no command to undo configuration changes made by AutoSecure, always save your running configuration before configuring AutoSecure.

•The AutoSecure configuration can be configured at run time or setup time. If any related configuration is modified after AutoSecure has been enabled, the AutoSecure configuration may not be fully effective.

•After AutoSecure has been enabled, tools that use SNMP to monitor or configure a device will be unable to communicate with the device using SNMP.

•If your device is managed by a network management (NM) application, securing the management plane could turn off some services such as HTTP server and disrupt the NM application support.

•If you are using Security Device Manager (SDM), you must manually enable the HTTP server using the ip http server command.

•NM applications that use CDP to discover network topology will not be able to perform discovery.

Configuring AutoSecure

These sections describe how to configure AutoSecure:

•Using the AutoSecure Command

•Configuring Additional Security

•Verifying AutoSecure

Using the AutoSecure Command

The auto secure command guides you through a semi-interactive session (also known as the AutoSecure session) to secure the management and forwarding planes. You can use this command to secure just the management plane or the forwarding plane; if neither option is selected in the command line, you can choose to configure one or both planes during the session.

This command also allows you to go through all noninteractive configuration portions of the session before the interactive portions. The noninteractive portions of the session can be enabled by selecting the optional no-interact keyword.

The AutoSecure session will request the following information from you:

•Is the device going to be connected to the Internet?

•How many interfaces are connected to the Internet?

•What are the names of the interfaces connected to the Internet?

•What will be your local username and password?

•What will be the switch hostname and domain name?

At any prompt you may enter a question mark (?) for help or Ctrl-C to abort the session.

In interactive mode, you will be asked at the end of the session whether to commit the generated configuration to the running configuration of the switch. In noninteractive mode, the changes will be automatically applied to the running configuration.

Note There is no undo command for configuration changes made by AutoSecure. You should always save the running configuration before executing the auto secure command.

To execute the AutoSecure configuration process, beginning in privileged EXEC mode, perform this task:

For an example of the AutoSecure session, see the "AutoSecure Configuration Example" section.

Configuring Additional Security

After completing the AutoSecure configuration, you can further enhance the security of management access to your switch by performing this task:

The following example shows how to configure the switch for a minimum password length of 10 characters and a threshold of 3 password failures in one minute. The example also shows how to set a hidden local password.

Router# configure terminal

Router(config)# security passwords min-length 10

Router(config)# security authentication failure rate 3

Router(config)# enable password 7 elephant123

Verifying AutoSecure

To verify that the AutoSecure feature has executed successfully, perform this task:

AutoSecure Configuration Example

The following example is a sample AutoSecure session. After you execute the auto secure command, the feature will automatically prompt you with a similar response unless you enable the no-interact keyword. (For information on which features are disabled and which features are enabled, see the "Securing the Management Plane" section and the "Securing the Forwarding Plane" section.)

Router# auto secure

                --- AutoSecure Configuration ---

*** AutoSecure configuration enhances the security of

the router, but it will not make it absolutely resistant

to all security attacks ***

 AutoSecure will modify the configuration of your device.

All the configuration changes will be shown. For a detailed

explanation of how the configuration changes enhance security

and any possible side effects, please refer to Cisco.com for

AutoSecure documentation.

At any prompt you may enter '?' for help.

Use ctrl-c to abort this session at any prompt.

If this device is being managed by a network management station,

AutoSecure configuration may block network management traffic.

Continue with AutoSecure? [no]: y

Gathering information about the router for AutoSecure

Is this router connected to internet? [no]: y

Enter the number of interfaces facing the internet [1]: 1

Interface              IP-Address      OK? Method Status                Protocol

Vlan1                  unassigned      YES NVRAM  administratively down down    

Vlan77                 77.1.1.4        YES NVRAM  down                  down    

GigabitEthernet6/1     unassigned      YES NVRAM  administratively down down    

GigabitEthernet6/2     21.30.30.1      YES NVRAM  up                    up      

Loopback0              3.3.3.3         YES NVRAM  up                    up      

Tunnel1                unassigned      YES NVRAM  up                    up            

Enter the interface name that is facing the internet: Vlan77

Securing Management plane services...

Disabling service finger

Disabling service pad

Disabling udp & tcp small servers

Enabling service password encryption

Enabling service tcp-keepalives-in

Enabling service tcp-keepalives-out

Disabling the cdp protocol

Disabling the bootp server

Disabling the http server

Disabling the finger service

Disabling source routing

Disabling gratuitous arp

Here is a sample Security Banner to be shown

at every access to device. Modify it to suit your

enterprise requirements.

Authorized Access only

  This system is the property of <Name of Enterprise>.

  UNAUTHORIZED ACCESS TO THIS DEVICE IS PROHIBITED.

  You must have explicit permission to access this

  device. All activities performed on this device

  are logged. Any violations of access policy will result

  in disciplinary action.

Enter the security banner {Put the banner between

k and k, where k is any character}:

k

banner     

k

Enter the new enable secret: 

Confirm the enable secret : 

Enable password is not configured or its length

is less than minimum no. of charactersconfigured

Enter the new enable password: 

Confirm the enable password: 

Configuration of local user database

Enter the username: cisco

Enter the password: 

Confirm the password: 

Configuring AAA local authentication

Configuring Console, Aux and VTY lines for

local authentication, exec-timeout, and transport

Securing device against Login Attacks

Configure the following parameters

Blocking Period when Login Attack detected (in seconds): 5

Maximum Login failures with the device: 3

Maximum time period for crossing the failed login attempts (in seconds): ?

% A decimal number between 1 and 32767.

Maximum time period for crossing the failed login attempts (in seconds): 5

Configure SSH server? [yes]: no

Configuring interface specific AutoSecure services

Disabling mop on Ethernet interfaces

Securing Forwarding plane services...

Enabling unicast rpf on all interfaces connected

to internet

The following rate-limiters are enabled by default:

  mls rate-limit unicast ip errors 100 10

  mls rate-limit unicast ip rpf-failure 100 10

  mls rate-limit unicast ip icmp unreachable no-route 100 10

  mls rate-limit unicast ip icmp unreachable acl-drop 100 10

  mls rate-limit multicast ipv4 fib-miss 100000 100

  mls rate-limit multicast ipv4 partial 100000 100

Would you like to enable the following rate-limiters also?

mls rate-limit unicast ip icmp redirect 100 10

mls rate-limit all ttl-failure 100 10

mls rate-limit all mtu-failure 100 10

mls rate-limit unicast ip options 100 10

mls rate-limit multicast ipv4 ip-options 100 10

Enable the above rate-limiters also? [yes/no]: yes

Would you like to enable the rate-limiters for Ingress/EgressACL bridged packets also?

NOTE: Enabling the ACL in/out rate-limiters can affect ACL logging

      and session setup rate for hardware accelerated features such

      as NAT, Layer 3 WCCP and TCP Intercept

mls rate-limit unicast acl input 100 10

mls rate-limit unicast acl output 100 10

Enable the ACL in/out rate-limiters also? [yes/no]: no

This is the configuration generated:

no service finger

no service pad

no service udp-small-servers

no service tcp-small-servers

service password-encryption

service tcp-keepalives-in

service tcp-keepalives-out

no cdp run

no ip bootp server

no ip http server

no ip finger

no ip source-route

no ip gratuitous-arps

no ip identd

banner k

banner

k

security passwords min-length 6

security authentication failure rate 10 log

enable secret 5 $1$30kP$f.KDndYPz/Hv/.yTlJStN/

enable password 7 08204E4D0D48574446

username cisco password 7 08204E4D0D48574446

aaa new-model

aaa authentication login local_auth local

line console 0

 login authentication local_auth

 exec-timeout 5 0

 transport output telnet

line vty 0 15

 login authentication local_auth

 transport input telnet

login block-for 5 attempts 3 within 5

service timestamps debug datetime msec localtime show-timezone

service timestamps log datetime msec localtime show-timezone

logging facility local2

logging trap debugging

service sequence-numbers

logging console critical

logging buffered

int Vlan1

 no ip redirects

 no ip proxy-arp

 no ip unreachables

 no ip directed-broadcast

 no ip mask-reply

 no mop enabled

int Vlan77

 no ip redirects

 no ip proxy-arp

 no ip unreachables

 no ip directed-broadcast

 no ip mask-reply

 no mop enabled

int GigabitEthernet6/1

 no ip redirects

 no ip proxy-arp

 no ip unreachables

 no ip directed-broadcast

 no ip mask-reply

 no mop enabled

int GigabitEthernet6/2

 no ip redirects

 no ip proxy-arp

 no ip unreachables

 no ip directed-broadcast

 no ip mask-reply

 no mop enabled

interface Vlan77

 ip verify unicast source reachable-via rx

mls rate-limit unicast ip icmp redirect 100 10

mls rate-limit all ttl-failure 100 10

mls rate-limit all mtu-failure 100 10

mls rate-limit unicast ip options 100 10

mls rate-limit multicast ipv4 ip-options 100 10

!

end

Apply this configuration to running-config? [yes]: yes

Applying the config generated to running-config

Router#

Tip For additional information about Cisco Catalyst 6500 Series Switches (including configuration examples and troubleshooting information), see the documents listed on this page:

http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html

Participate in the Technical Documentation Ideas forum