The board is available with three different relay coil voltages (5, 12, 24 VDC), allowing you to choose whichever is most conveniently available for your project. Suitable wall power supplies for the 5V and 12V models are available below. Please note that the relay coil voltage you select has no effect whatsoever on the voltages you can switch with the relay contacts. Also note that the relay coil voltage you select does NOT affect what voltage is needed for the input control signals. For any of the coil voltage options (5, 12, or 24V), an input control signal from 2.5VDC up through 25VDC will activate the relay. See datasheet for input current requirements.
Patented by James Buie of Pacific Semiconductor in 1961, TTL (Transistor Transistor Logic) emerged as the most popular logic configuration of the next two decades. Unaware of Buie's work but inspired by an "all transistor" logic circuit described by Ruegg and Beeson of Fairchild, Thomas Longo led the design of the first TTL family, Sylvania Universal High-level Logic (SUHL) in 1963. Encouraged by SUHL's success in winning a high-profile Hughes military design (the Phoenix missile), TI introduced the competing SN5400 Series TTL family the following year. The company announced the SN7400 Series in low cost plastic packages for industrial customers in 1966 and quickly gained a greater than 50% share of the logic market.
Ttl Data For Design Engineers.pdf
By 1968 lithography advances significantly increased the number of transistors that could be integrated on a chip. Eager to win a share of the TTL business, Fairchild (9300 Series) and Signetics (8200 Series) pioneered the design of TTL-MSI (Medium Scale Integration - up to 100 logic gates per chip) functions such as counters, shift registers, and arithmetic logic units. Many vendors applied Schottky (1969 Milestone) and CMOS (1963 Milestone) technology to build larger, faster, and lower power TTL-compatible functions that extended the useful life and range of applications of this popular logic configuration.
After centralized logging is implemented, you must develop a structured approach to log analysis and incident tracking. Based on the needs of your organization, this approach can range from a simple diligent review of log data to advanced rule-based analysis.
Many protocols are used in order to carry sensitive network management data. You must use secure protocols whenever possible. A secure protocol choice includes the use of SSH instead of Telnet so that both authentication data and management information are encrypted. In addition, you must use secure file transfer protocols when you copy configuration data. An example is the use of the Secure Copy Protocol (SCP) in place of FTP or TFTP.
You can use configuration archives to roll back changes that are made to network devices. In a security context, configuration archives can also be used in order to determine which security changes were made and when these changes occurred. In conjunction with AAA log data, this information can assist in the security auditing of network devices.
The service password-encryption global configuration command directs the Cisco IOS software to encrypt the passwords, Challenge Handshake Authentication Protocol (CHAP) secrets, and similar data that are saved in its configuration file. 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. However, the algorithm used by the service password-encryption command is a simple Vigen re cipher. The algorithm is not designed to protect configuration files against serious analysis by even slightly sophisticated attackers and must not be used for this purpose. Any Cisco IOS configuration file that contains encrypted passwords must be treated with the same care that is used for a cleartext list of those same passwords.
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. In releases that do not support the vstack command, ensure that only the Smart Install director has TCP connectivity to all Smart Install clients on port 4786.
Once created, the iACL must be applied to all interfaces that face non-infrastructure devices. This includes interfaces that connect to other organizations, remote access segments, user segments, and segments in data centers.
The Internet Control Message Protocol (ICMP) is designed as an IP control protocol. As such, the messages it conveys can have far-reaching ramifications to the TCP and IP protocols in general. While the network troubleshooting tools ping and traceroute use ICMP, external ICMP connectivity is rarely needed for the proper operation of a network.
Cisco IOS Software Release 12.4(2)T added ACL support to filter IP packets based on the Time to Live (TTL) value. The TTL value of an IP datagram is decremented by each network device as a packet flows from source to destination. Although initial values vary by operating system, when the TTL of a packet reaches zero, the packet must be dropped. The device that decrements the TTL to zero, and therefore drops the packet, is required in order to generate and send an ICMP Time Exceeded message to the source of the packet.
Because information can be disclosed in an interactive management session, this traffic must be encrypted so that a malicious user cannot gain access to the data that is transmitted. Traffic encryption allows a secure remote access connection to the device. If the traffic for a management session is sent over the network in cleartext, an attacker can obtain sensitive information about the device and the network.
An administrator is able to establish an encrypted and secure remote access management connection to a device with the SSH or HTTPS (Secure Hypertext Transfer Protocol) features. Cisco IOS software supports SSH Version 1.0 (SSHv1), SSH Version 2.0 (SSHv2), and HTTPS that uses Secure Sockets Layer (SSL) and Transport Layer Security (TLS) for authentication and data encryption. SSHv1 and SSHv2 are not compatible. SSHv1 is insecure and not standardized, so it is not recommended if SSHv2 is an option.
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.
A vty and tty should be configured in order to accept only encrypted and secure remote access management connections to the device or through the device if it is used as a console server. This section addresses ttys because such lines can be connected to console ports on other devices, which allow the tty to be accessible over the network. In an effort to prevent information disclosure or unauthorized access to the data that is transmitted between the administrator and the device, transport input ssh should be used instead of clear-text protocols, such as Telnet and rlogin. The transport input none configuration can be enabled on a tty, which in effect disables the use of the tty line for reverse-console connections.
A method list is a sequential list that describes the authentication methods to be queried in order to authenticate a user. Method lists enable you to designate one or more security protocols to be used for authentication, and thus ensure a backup system for authentication in case the initial method fails. Cisco IOS software uses the first listed method that successfully accepts or rejects a user. Subsequent methods are only attempted in cases where earlier methods fail due to server unavailability or incorrect configuration.
Originally designed in order to allow quick decryption of stored passwords, Type 7 passwords are not a secure form of password storage. There are many tools available that can easily decrypt these passwords. The use of Type 7 passwords should be avoided unless required by a feature that is in use on the Cisco IOS device.
This section highlights several methods that can be used in order to secure the deployment of SNMP within IOS devices. It is critical that SNMP be properly secured in order to protect the confidentiality, integrity, and availability of both the network data and the network devices through which this data transits. SNMP provides you with a wealth of information on the health of network devices. This information should be protected from malicious users that want to leverage this data in order to perform attacks against the network.
Community strings are passwords that are applied to an IOS device to restrict access, both read-only and read-write access, to the SNMP data on the device. These community strings, as with all passwords, should be carefully chosen to ensure they are not trivial. Community strings should be changed at regular intervals and in accordance with network security policies. For example, the strings should be changed when a network administrator changes roles or leaves the company.
SNMP Views are a security feature that can permit or deny access to certain SNMP MIBs. Once a view is created and applied to a community string with the snmp-server community community-string view global configuration commands, if you access MIB data, you are restricted to the permissions that are defined by the view. When appropriate, you are advised to use views to limit users of SNMP to the data that they require.
The Management Plane Protection (MPP) feature in Cisco IOS software can be used in order to help secure SNMP because it restricts the interfaces through which SNMP traffic can terminate on the device. The MPP feature allows an administrator to designate one or more interfaces as management interfaces. Management traffic is permitted to enter a device only through these management interfaces. After MPP is enabled, no interfaces except designated management interfaces accept network management traffic that is destined to the device. 2ff7e9595c
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