Network Time Protocol (NTP) is a networking protocol for clock synchronization between devices in a network. NTP is implemented using User Datagram Protocol (UDP), which in turn runs over an IP. An NTP network usually gets its time from an authoritative time source, such as a radio clock or an atomic clock attached to a time server. NTP then distributes this time across the network. NTP is extremely efficient; no more than one packet per minute is necessary to synchronize two devices within a millisecond of one another.

Secure Shell (SSH) is a cryptographic network protocol for secure data communication, remote command line login, remote command execution, and other secure-network services between two networked computers. It connects an SSH server and SSH client through a secure channel over a network that is not secure. SSH is typically used to log in to remote machines and execute commands.

Remote shell protocols send information, such as password, in plaintext making the networks susceptible to interception and disclosure. SSH is designed as a replacement for Telnet and other remote shell protocols that are not secure.

A VLAN is a switched network that is logically segmented by function, project team, or application, irrespective of the physical location of users. A VLAN has the same attributes as the physical LAN. However, you can group the end stations in a VLAN even if they are not physically located on the same LAN segment. A switch module port can belong to a VLAN, but the unicast, broadcast, and multicast packets are forwarded only to the end stations in the VLAN. A VLAN is often associated with IP subnetworks. For example, all the end stations in a particular IP subnet belong to the same VLAN.

Interface VLAN membership on a switch module is assigned manually on an interface-by-interface basis and is known as interface-based or static VLAN membership. Traffic between the VLANs must be routed. VLANs are identified with a number ranging from 1 to 4094.

A port channel bundles up to eight individual interfaces into a group to provide increased bandwidth and redundancy. If a member port within a port channel fails, the traffic that is carried over a failed link switches to one of the remaining member ports within the port channel. This traffic switch facilitates the load and balances the traffic across the physical interfaces. A port channel is operational as long as at least one physical interface within the port channel is operational.

You can create a port channel by bundling compatible interfaces. You can configure and run either static port channels or the port channels that run the Link Aggregation Control Protocol (LACP). Any configuration change that you apply to a port channel is applied to each member interface of that port channel.

Use a static port channel with no associated protocol for a simplified configuration. To use a port channel efficiently, you can use LACP, which is defined in IEEE 802.3ad.

Address Resolution Protocol (ARP) provides IP communication within a Layer 2 broadcast domain by mapping an IP address to a MAC address. It can be used in the following scenario:

­­Host B wants to send information to Host A, but does not have the MAC address of Host A in the ARP cache. Host B generates a broadcast message for all the hosts within the broadcast domain to obtain the MAC address associated with the IP address of Host A. All the hosts within the broadcast domain receive the ARP request and Host A responds with its MAC address.

Dynamic Host Configuration Protocol (DHCP) snooping is a security feature that acts like a firewall between untrusted hosts and trusted DHCP servers. The DHCP snooping feature validates DHCP messages that are received from the untrusted sources and filters the invalid messages. It limits the rate of DHCP traffic that is sent or received from trusted and untrusted sources. It builds and maintains the DHCP snooping binding database which contains information about untrusted hosts with leased IP addresses. It utilizes the DHCP snooping binding database to validate subsequent requests from the untrusted hosts. DHCP snooping is enabled on a per VLAN basis. By default, the feature is inactive on all VLANs. You can enable the feature on a single VLAN or on a range of VLANs.

Domain Name System (DNS) is a hierarchical distributed naming system that maps hostnames to IP addresses. When you configure DNS on your switch, you can substitute the hostname for the IP address with the IP commands, such as ping, telnet, connect, and related Telnet support operations. IP defines a hierarchical naming scheme that allows a device to be identified by its location or domain. Domain names are pieced together with periods (.) as delimiting characters. For example, Cisco Systems is a commercial organization that the IP identifies by a com domain name. Therefore, its domain name is cisco.com. To keep track of domain names, IP has defined the concept of a domain name server that holds a cache (or database) of names mapped to IP addresses. If you need to map the domain name to the IP addresses, you must identify the hostname, specify the server name that is present on your network, and then enable the DNS.

To map a domain name to an IP address, use the following command on your network and enable the DNS:

serverservpresent