Although not an exhaustive list of CPU impacting data plane traffic, these types of traffic are process switched and can therefore affect the operation of the control plane: This list details several methods to determine which types of traffic are being processed by the Cisco IOS device CPU: Infrastructure ACLs (iACLs) limit external communication to the devices of the network. This makes it possible to correlate and audit network and security events across network devices more effectively. The AAA server then uses its configured policies in order to permit or deny the command for that particular user. This scenario is common in a publicly accessible network or anywhere that servers provide content to untrusted clients. Such encryption is useful in order to prevent casual observers from reading passwords, such as when they look at the screen over the muster of an administrator. This configuration example shows how to enable this feature with the memory free low-watermark global configuration command. The management plane is used in order to access, configure, and manage a device, as well as monitor its operations and the network on which it is deployed. In other words, ICMP redirects should never go beyond a Layer 3 boundary. SNMPv3 consists of three primary configuration options: An authoritative engine ID must exist in order to use the SNMPv3 security mechanisms - authentication or authentication and encryption - to handle SNMP packets; by default, the engine ID is generated locally. Note that ttys can be used for connections to console ports of other devices. This is a list of additional services that must be disabled if not in use: In order to set the interval that the EXEC command interpreter waits for user input before it terminates a session, issue the exec-timeout line configuration command. This configuration example demonstrates how to enable this feature. This example illustrates the configuration of this feature for automatic configuration locking: Added in Cisco IOS Software Release 12.3(8)T, the Resilient Configuration feature makes it possible to securely store a copy of the Cisco IOS software image and device configuration that is currently used by a Cisco IOS device. In a properly functioning IP network, a router sends redirects only to hosts on its own local subnets. Management traffic is permitted to enter a device only through these management interfaces. In order to perform password recovery, an unauthenticated attacker would need to have access to the console port and the ability to interrupt power to the device or to cause the device to crash. You are advised to send logging information to a remote syslog server. Even though patches are a bit of a nuisance, they’re well worth the effort for the protection that they afford. The Enhanced Password Security feature cannot be used with protocols that require the cleartext password to be retrievable, such as CHAP. Note: Dropping traffic from unknown or untrusted IP addresses can prevent hosts with dynamically-assigned IP addresses from connecting to the Cisco IOS device. A secure protocol choice includes the use of SSH instead of Telnet so that both authentication data and management information are encrypted. These known bad prefixes include unallocated IP address space and networks that are reserved for internal or testing purposes by RFC 3330. Peer authentication with MD5 creates an MD5 digest of each packet sent as part of a BGP session. Refer to Configuring Accounting for more information about the configuration of AAA accounting. By default, sessions are disconnected after ten minutes of inactivity. This example illustrates the configuration of this feature: As BGP packets are received, the TTL value is checked and must be greater than or equal to 255 minus the hop-count specified. The repository that you use in order to archive Cisco IOS device configurations needs to be secured. The lowest severity included in the buffer is configured with the logging buffered severity command. This feature can be used in order to protect a device receiving transit traffic where the TTL value is a zero or one. In Cisco IOS Software Release 12.4(6)T and later, the feature Management Plane Protection (MPP) allows an administrator to restrict on which interfaces management traffic can be received by a device. This document describes the information to help you secure your Cisco IOS® system devices, which increases the overall security of your network. An ARP poisoning attack is a method in which an attacker sends falsified ARP information to a local segment. See the Secure Interactive Management Sessions section of this document for more information about the secure management of Cisco IOS devices. Refer to Configuring DHCP features and IP Source Guard for more information on this feature. This configuration example demonstrates the use of GLBP, HSRP, and VRRP MD5 authentication: Although the data plane is responsible for moving data from source to destination, within the context of security, the data plane is the least important of the three planes. Fortunately, newer versions of the popular network operating systems have features that automatically check for updates and let you know when a patch should be applied. Two CPU utilization thresholding methods are supported on Cisco IOS software: Rising Threshold and Falling Threshold. There are two types of ICMP redirect messages: redirect for a host address and redirect for an entire subnet. Additionally, a malicious user can create a denial of service (DoS) condition with repeated attempts to authenticate with a valid username. In Cisco IOS software, ICMP unreachable generation is limited to one packet every 500 milliseconds by default. This kind of communication can allow an attacker to pose as an FHRP-speaking device to assume the default gateway role on the network. One of the most common interfaces that is used for in-band access to a device is the logical loopback interface. However, there are instances where it may be beneficial to perform this filtering on a Cisco IOS device in the network, for example, where filtering must be performed but no firewall is present. Authentication can be enforced through the use of AAA, which is the recommended method for authenticated access to a device, with the use of the local user database, or by simple password authentication configured directly on the vty or tty line. In a dictionary attack, an attacker tries every word in a dictionary or other list of candidate passwords in order to find a match. The requirements of the STIG become effective immediately. CoPP is available in Cisco IOS Software Release trains 12.0S, 12.2SX, 12.2S, 12.3T, 12.4, and 12.4T. Traffic that contains IP options must be process-switched by Cisco IOS devices, which can lead to elevated CPU load. The management plane consists of functions that achieve the management goals of the network. When you revoke a special key, a production image is loaded. This ACL example creates a policy that filters IP packets that contain any IP options: This example ACL demonstrates a policy that filters IP packets with five specific IP options. Every DC has by default the “Default Domain Controllers Policy” in place, but this GPO creates different escalation paths to Domain Admin if you have any members in Backup Operators or Server Operators for example. While this weak encryption algorithm is not used by the enable secret command, it is used by the enable password global configuration command, as well as the password line configuration command. For this reason, TACACS+ should be used in preference to RADIUS when TACACS+ is supported by the AAA server. IP options present a security challenge for network devices because these options must be processed as exception packets. Note that syslog messages are transmitted unreliably by UDP and in cleartext. If this is not feasible due to the large number of prefixes received, a prefix list should be configured to specifically block known bad prefixes. This CPPr policy drops transit packets received by a device where the TTL value is less than 6 and transit or non-transit packets received by a device where the TTL value is zero or one. These sections of this document detail the security features and configurations available in Cisco IOS software that help fortify the management plane. Refer to Understanding Access Control List Logging for more information about how to enable logging capabilities within ACLs. Note: An ATA flash drive has limited disk space and thus needs to be maintained to avoid overwriting stored data. Each device that an IP packet traverses decrements this value by one. The number of users with privilege level 15 must be kept to a minimum. Infrastructure ACLs (iACLs) can be deployed in order to ensure that only end hosts with trusted IP addresses can send SNMP traffic to an IOS device. Availability of AAA servers during potential network failures, Geographically dispersed placement of AAA servers, Load on individual AAA servers in steady-state and failure conditions, Network latency between Network Access Servers and AAA servers, with a local destination (that is, receive adjacency traffic), Receive adjacency traffic can be identified through the use of the, Enable MD5 hashing (secret option) for enable and local user passwords, Disable password recovery (consider risk), Configure TCP keepalives for management sessions, Set memory and CPU threshold notifications, Use Management Plane Protection to restrict management interfaces, Use an encrypted transport protocol (such as SSH) for CLI access, Control transport for vty and tty lines (access class option), Use AAA (TACACS+) for command authorization, Configure SNMPv2 communities and apply ACLs, Set logging levels for all relevant components, Configure NTP authentication if NTP is being used, Configure Control Plane Policing/Protection (port filtering, queue thresholds), BGP (TTL, MD5, maximum prefixes, prefix lists, system path ACLs), IGP (MD5, passive interface, route filtering, resource consumption), Secure First Hop Redundancy Protocols (GLBP, HSRP, VRRP), Configure required anti-spoofing protections, Control Plane Protection (control-plane cef-exception), Configure NetFlow and classification ACLs for traffic identification, Configure required access control ACLs (VLAN maps, PACLs, MAC). Port Security is used in order to mitigate MAC address spoofing at the access interface. Current versions of Cisco IOS software have this functionality disabled by default; however, it can be enabled via the ip directed-broadcast interface configuration command. It is for these reasons that IP fragments are often used in attacks, and why they must be explicitly filtered at the top of any configured iACLs. If there are no protocols in use that require IP options, ACL IP Options Selective Drop is the preferred method to drop these packets. Hence, the user is authenticated or denied access based on the encrypted signature. A malicious user can exploit the ability of the router to send ICMP redirects by continually sending packets to the router, which forces the router to respond with ICMP redirect messages, and results in an adverse impact on the CPU and performance of the router. Cisco IOS software supports the use of a local log buffer so that an administrator can view locally generated log messages. The feature Memory Threshold Notification, added in Cisco IOS Software Release 12.3(4)T, allows you to mitigate low-memory conditions on a device. Information leaks, or the introduction of false information into an IGP, can be mitigated through use of the passive-interface command that assists in controlling the advertisement of routing information. Use the Password Phrase Method: • Choose a phrase that has numbers. As a result, the destination IP address any that is used in the example ACL entries below only refers to the physical or virtual IP addresses of the router. If you ever want to make something nearly impenetrable this is where you'd start. These services include: Although abuse of the small services can be avoided or made less dangerous by anti-spoofing access lists, the services must be disabled on any device accessible within the network. The use of buffered logging is highly recommended versus logging to either the console or monitor sessions. This requires the global configuration command ip dhcp snooping information option; additionally, the DHCP server must support DHCP option 82. Fragmentation is also often used in attempts to evade detection by intrusion detection systems. Refer to ACL Support for Filtering on TTL Value for more information about this functionality. In addition, you must use secure file transfer protocols when you copy configuration data. Configured prefix lists limit the prefixes that are sent or received to those specifically permitted by the routing policy of a network. There are several disadvantages to proxy ARP utilization. Note that some applications and tools such as traceroute use TTL expiry packets for testing and diagnostic purposes. Once a VLAN map is configured, all packets that enter the LAN are sequentially evaluated against the configured VLAN map. This OSPF example uses a prefix list with the OSPF-specific area filter-list command: Routing Protocol prefixes are stored by a router in memory, and resource consumption increases with additional prefixes that a router must hold. Introduced in Cisco IOS Software Release 12.3(8)T1, the Memory Leak Detector feature allows you to detect memory leaks on a device. VACLs, or VLAN maps that apply to all packets that enter the VLAN, provide the capability to enforce access control on intra-VLAN traffic. If a security incident is able to undermine the functions of the management plane, it can be impossible for you to recover or stabilize the network. ICMP unreachable message generation can be disabled with the interface configuration command no ip unreachables. By default, these protocols communicate with unauthenticated communications. The generation of these messages can increase CPU utilization on the device. Failure to secure the exchange of routing information allows an attacker to introduce false routing information into the network. However, the algorithm is subject to dictionary attacks. This command verifies the integrity of image c3900-universalk9-mz.SSA in flash with the keys in the device key store: The Digitally Signed Cisco Software feature was also integrated in Cisco IOS XE Release 3.1.0.SG for the Cisco Catalyst 4500 E-Series Switches. Digitally signed Cisco software keys are identified by the type and version of the key. In the design of a Smart Install architecture, care should be taken such that the infrastructure IP address space is not accessible to untrusted parties. This action is almost certainly unwanted and is another reason to ensure configuration of an enable secret. You can use the show memory debug leaks EXEC command in order to detect if a memory leak exists. 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