Some common problems in the assessment of network engineers: WLAN, BGP, switch

The process of connecting the host to the Internet

The host by DHCP Get a IP Address and gateway , Through this IP Address online ,

When we go online, we first enter a website , It contains our domain name ,

adopt DHCP The distribution of DNS The server resolves the corresponding domain name IP Address

verification IP Address and host IP Is it a network segment , If it is not a network segment, you need to access the Internet through the gateway

adopt ARP Know the gateway MAC after , Organize data sending to gateway , At this time source IP Host computer , Purpose IP It is the corresponding website IP

Source MAC Is your own , Purpose MAC It's the gateway

The gateway is a three-tier device , Find Baidu's corresponding... By looking up the routing table IP forwarded

establish TCP Three handshakes , send out HTTP request , The server responds ,TCP Four waves

 

About WLAN

Thin AP framework ：AC Yes AP Centralized management ,AC be responsible for WLAN Access control 、 Security 、 Forwarding and statistics 、 roaming 、 Network management agent

School 、 The government 、 Enterprises 、 The mall

Thin AP working process ： It's the same OSPF The process of data exchange AP+AC Empathy ,

AP Belong to AC Part of Management ,AP Request , Request to join AC

AC Verify parameters , If correct, agree ,AP Join in AC,AC Issue management documents , Control AP

1、 framework 1： Three layer switch as gateway （PC gateway +AP gateway ）AC and AP It's not the same segment

So we need a gateway + route ==PC Communication process with layer 3 switch

AP+AC Networking mode ：1、 Layer 2 networking AP Send a broadcast packet to find AC

2、 Three layer networking Unable to broadcast directly AC,DHCP Option43 optional （ contain AC Address ,） Find through unicast AC

CAPWAP： Send through this tunnel AC To AP Parameters of

AC How to connect ：1、 Direct networking , Acting as a layer 3 switch It is more convenient for centralized data management （ A lower cost ）

2、 Side hanging ：AC Only responsible for managing , No data forwarding ,（ Better performance ）

AC adopt CAPWAP Detection and AP The connectivity of

Various data and control messages are communicated through this tunnel

About BGP

Why use BGP？

1、AS Through between IGP Transmission is not secure

2、OSPF、ISIS Cannot carry tens of thousands of routing entries , When the topology becomes larger, the convergence becomes slower , Forwarding performance is degraded

3、BGP It's about routing, not Computing , Capable of supporting large-scale networks

4、 Provide a lot of routing strategies , You can choose the route flexibly

5 Message type 、6 State machine

idle It didn't start at first BGP, Or lack of routing to peers is idle If there is no route all the time, it will always be IDLE

Connect Underway TCP The connection of three handshakes

Active

How to distinguish layer 2 switch and layer 3 switch

1、 see vlan

There are multiple layer 3 switches vlan Interface , And can be activated VLAN And configuration IP Address

Layer 2 switches can create multiple vlan, But there's only one vlan Can be activated as a management address

2、 Look at the forwarding capability

The layer-2 switch works at the data link layer , Only layer 2 forwarding capability , adopt MAC Address forwarding , There is no three-tier routing function

Layer 3 switches work at the network layer , It has three-tier forwarding capability , It has routing function , It is the communication between different network segments

3、 Check the device model

For example, Cisco equipment , With 2 The beginning is the layer-2 switch , With 3 The beginning is the layer 3 switch