Linux network basic notes router

A Router is a device that works on a layer-3 network. compared with a Switch, the Router splits data packets, changes the mac address, and

A Router is a device that works on a layer-3 network. compared with a Switch, the Router splits data packets, changes the mac address, and decreases the TTL time.

Router steps:

1: The PC first sets the destination IP address and subnet mask to determine whether the destination IP address is in the same broadcast domain.

2: In the same broadcast domain, the mac address buffer table is queried. If yes, it is unicast. If no, it is broadcast.

3: If the destination IP address is not in the same broadcast domain or is not in the same LAN, check whether the mac address of the Gateway exists in the mac table. If yes, send the data to the Gateway. If no IP address is displayed, the mac address of the Gateway is obtained.

4: The Gateway routes the data and queries the destination IP address and port subnet mask. if there is a corresponding network number, the packet is sent to the port. If no matching network number exists, check whether the default route is used. if not, the data packet is discarded.

Configuration of the Router:

1. Static route configuration

Each port of the Router must be configured with a specific ip address. the configuration command is ip address 192.168.1.1 255.255.255.0.

Manual static routing configuration command:

Ip route 192.168.4.0 (next hop network address) 255.255.255.0 192.168.1.1 (this is the IP address of the router data egress port)

Default route configuration: ip route 0.0.0.0 0.0.0.0 ip_address (route interface ip address)

2: configure multiple network numbers when the number of vro ports is small. you can use loopback.

Configuration command: enter configure mode. input command: interface loopback 0 starts from 0 by default.

Router product and device interface type

WIC slot: WAN interface card, which can be inserted into various WAN modules to achieve flexible networking

NM slot: network module, which can be inserted into various network modules to expand the number of interfaces of devices.

Router components:

Cpu rom nvrom Flash interface

The operating system of Switch and Router is IOS (network operating system). the format of the system name is as follows:

Naming format: AAAAA--BBBB--CCC--DDDD. bin

AAAA: indicates the applicable platform

BBBB: feature set included in IOS

CC: IOS software running format and compression format

DDDD: IOS software version

Bin: the suffix of the operating system file.

Router system loading process:

1: boot programs stored in ROM are first loaded into memory.

2: The Boot program first goes to Flash to check whether there are operating system files.

3: If there is no operating system in Flash, the boot program will install the system from the network through TFTP.

Router configuration file loading:

1: The system first looks for the configuration file from NVRAM.

2: If there is no configuration file in NVRAM, try to find whether there is a configuration file from TFTP.

3: If not, the ROUTER will be configured through the console line.