Configure NTP on a Cisco router

NTP (Network Time Protocol) is an application layer protocol used for time synchronization between hosts on a TCP/IP network. The goal of NTP is to ensure that all devices on a network agree on the time, since even a small difference can cause problems. NTP uses a client-server architecture; usually with one host being configured as the NTP server, and other hosts on the network are configured as NTP clients.Cisco routers can be configured as both NTP clients and NTP servers. To configure a Cisco Read more [...]

TCP three-way handshake

Since TCP is a connection-oriented protocol, a connection needs to be established before two devices can communicate. TCP uses a process called three-way handshake to negotiate the sequence and acknowledgment fields and start the session. Here is a graphical representation of the process:As the name implies, the three way handshake process consists of three steps:Host A initiates the connection by sending the TCP SYN packet to the destination host. The packet contains the random sequence number (e.g. Read more [...]

Configure ROAS

To allow interVLAN communication, you can divide a single physical interface on a router into logical interfaces that will be configured as trunk interfaces. This method of interVLAN communication is called router on a stick (ROAS) and enables all VLANs to communicate through a single physical interface. The physical interface is divided into logical interfaces (known as subinterfaces), one for each VLAN.A subinterface is created with the interface TYPE NUMBER.SUBINTERFACE command. The subinterface Read more [...]

Configure interVLAN routing

Each VLAN is its own subnet and broadcast domain, which means that frames broadcasted onto the network are switched only between the ports within the same VLAN. For interVLAN communication, an OSI layer 3 device (usually a router) is needed. This layer 3 device needs to have an IP address in each VLAN and have a connected route to each of those subnets. The hosts in each subnet can then be configured to use the router’s IP addresses as their default gateway.Three options are available for Read more [...]

Configure Cisco router as DHCP server

Dynamic Host Configuration Protocol (DHCP) is an application layer protocol used to distribute various network configuration parameters to devices on a TCP/IP network. – IP addresses, subnet masks, default gateways, DNS servers, etc. DHCP employs a client-server architecture; a DHCP client is configured to request network parameters from a DHCP server on the network. A DHCP server is configured with a pool of available IP addresses and assigns one of them to the DHCP client.A Cisco router Read more [...]

Types of memory on a Cisco device

Cisco devices usually have four types of memory that are being used for different purposes. These four types are:ROM (Read-only memory) – stores a bootstrap program that is used to initialize a boot process. This is a read-only type of memory, so it can’t be altered.RAM (Random Access Memory) – the running configuration and routing tables of the device are stored here. This type of memory loses its content when a device is restarted.Flash memory – used to store IOS software Read more [...]