Cisco LAN switch configuration

3.1 LAN switch configuration overview

Shared Ethernet, physical address, conflict domain, broadcast domain. Bridging, switching, MAC address table, VLAN. VLAN relay, and VLAN relay protocols. The concept of Spanning Tree Protocol is particularly important. This section briefly introduces these concepts.

Shared Ethernet
Shared Ethernet is an Ethernet built on a bus topology. You can directly connect a computer to a shared Ethernet using a thin or crude cable. You can also use a Hub) it is connected to a twisted pair computer to form a shared Ethernet.

Shared Ethernet is a network that strictly complies with the CSMA/CD algorithm, and Carrier has the Sense MultipleAccess/Collision Detect Algorithm, the working characteristics of the CSMA/CD algorithm determine the half-duplex characteristics of the shared network. On shared Ethernet, when a host sends data, other hosts can only receive the Ethernet frame. At this time, no data can be sent from other hosts on the Internet.

Physical address

When the host system over Ethernet communicates with each other, it must be used to identify the host's identifier, that is, the physical address, also known as the Media Access Control (MAC. media Access Control) address, the MAC address on the host is fixed on the NIC, so as the NIC inserted in the host changes, its MAC address will also change accordingly. The MAC address on a network card is the only one in the world.

Conflict domain

Shared Ethernet built with coaxial cables or built with Hub as the core. All nodes on the shared Ethernet are in the same conflict domain, the Ethernet frames sent by different devices in a conflicting domain conflict with each other. At the same time, a host in the conflicting domain sends data, and other hosts in the same domain can receive the data. Too many hosts in a conflicting domain may cause three major consequences: the available bandwidth of each host is very low, and the number of online conflicts increases exponentially. And the security of information transmission is not guaranteed.

Broadcast domain

A broadcast domain is a collection of devices on the Internet. When one of these devices sends a broadcast, all other devices can receive the broadcast frame.

Broadcast domains and conflicting domains are particularly confusing concepts. We can distinguish them as follows: all devices connected to the two hubs constitute a conflict domain and a broadcast domain; the devices connected to each port on a vswitch without VLAN division belong to different conflict domains (each exchange port constitutes a conflict domain), but belong to the same broadcast domain.

Bridging

The so-called "bridging" mainly refers to transparent bridging in the ccna tutorial. A transparent bridge connects two or more shared Ethernet CIDR blocks. Different CIDR blocks belong to their respective conflicting domains, and all CIDR blocks are in the same broadcast domain. The working mode of bridging should be carefully understood, which is the basis for understanding the working principle of the switch.

Exchange

The concept of LAN switching comes from bridging. In terms of basic functions, it uses the same algorithm as transparent bridging, but the implementation of switching is implemented by dedicated hardware, traditional bridging is implemented by software. Ethernet switches provide a wide range of functions, such as VLAN division, spanning tree Protocol, multicast support, and service quality.

MAC Address Table

A mac address table is provided in the vswitch to store the information about the MAC address and port number of the device connected to the vswitch port. The MAC address table is the basis for the normal operation of the switch. Its generation process is also the content we should master.

VLAN

VLAN technology is one of the important advances in the exchange technology. Currently, all smart switches support VLAN, which is used to logically divide physically directly connected networks into multiple subnets. Each VLAN corresponds to a) broadcast domain. L2 switches do not have the routing function and cannot forward frames between VLANs. Therefore, hosts on different VLANs cannot communicate. Only layer-3 switches (Inter-VLAN Routing) are introduced) after technology, communication between VLANs becomes possible.

VLAN Relay

VLAN Relay (VLAN Trunk) is also known as the VLAN Trunk. It refers to configuring the relay mode on the port connecting a switch to a vswitch or connecting a vswitch to a vro, this enables data frames belonging to different VLANs to be transmitted through this relay link.

The frame format of VLAN relay is divided into two types: ISL (Inter-Switch Link, connection between switches) and 802.1Q. The former is the protocol unique to the Cisco Switch, and the latter is the international standard protocol, supported by almost all network equipment manufacturers.

VLAN relay Protocol

For a Cisco device, the VLAN relay protocol (VTP) helps the switch set a VLAN. The VTP protocol can maintain the network-wide consistency of VLAN information.

VTP has three working modes. That is, the server mode, customer mode, and transparent mode. Accurate differentiation of the three modes is one of the key points of exchange technology.

Among the three modes, it is hard to understand the features of the transparent mode. The so-called "Transparent" means that a switch in the transparent mode ignores any VTP information sent from other switches, but forwards the information to other switches so that other switches can use it. Another important feature of transparent mode is that it can create, delete, and modify VLANs and their attributes, but these settings are not transmitted to other switches, only the vswitches in the transparent mode are affected.

Spanning Tree Protocol

STP (Spanning Tree Protocl) is an important concept and Technology in switched Ethernet. The purpose of this Protocol is to achieve redundant connections between switches while avoiding the emergence of network loops, achieve high network reliability.

The STP Protocol transmits BPDU (Bridge Protocol Data Unit) between switches to inform each other of the Bridge ID (number) and link nature of the switch. Root Bridge ID and other information to determine the Root Bridge and determine which ports are in the forwarding status and which ports are in the blocking status to avoid network loops.

It is important for CCNA to understand the causes of network loops and the working principle of STP.