TCP/IP protocol value IP routing

1. Some network commands in Linux.

(1) ifconfig command is used to view and modify the IP address and MAC address

(2) netstat monitors the network status. netstat-Rn: view the route table in the Local Machine and display it as an IP address.

(3) view ARP and modify the ARP cache

(4) Ping detection of network connection status

(5) traceroute: the router used to detect the data transfer process (the principle is that each time a datagram is sent, the TTL is added to 1 each time, and the port number is inaccessible, then, the vro is detected based on the ICMP response and port inaccessibility report returned by this package)

2. Five Meanings of the flags output by netstat-Rn: U, G, H, D, and M. The G option is used to distinguish between direct routes and indirect routes.

3. ICMP host or network inaccessible error message: Most routers can only work in a local range. Only when they reach the backbone network can they know that the destination is not reachable. Top-level routing domain (VBR) is used to maintain information about most Internet websites without default routing.

4. ICMP redirection packets (corresponding to the above d, m mark)

For example, if an IP data packet is sent to the default route option B in host a, and then B checks the route table to know that the correct route is C, B forwards it to C. At the same time, also, send an ICMP redirection packet to a, indicating that the correct part is C. (Note: These are only the route tables of hosts on the LAN)

5. Dynamic Routing Protocol: (the construction technology of Route tables in routers)

(1) Static Routing means to manually add table items or generate table items with ICMP redirection when sending packets by using the rout command during system configuration. Only for some small networks

(2) dynamic routing is used to build route tables between routers. It mainly refers to rip (routing information protocol, based on Distance Vector Algorithm) and OSPF (Open Shortest Path First, based on the State link algorithm) and BGP (Border Gateway Protocol ).

(3) Internet is organized in a group of Autonomous Systems (AS), such as a university campus or a company. The communication protocol between routers in each autonomous system is called the Internal Gateway Protocol (IGP). The common IGP is Rip and OSPF, and the communication protocol between autonomous systems is called the external Gateway Protocol (EGP ), the BGP protocol is used to replace EGP.

6. Rip: Routing Information Protocol

(1) The port number is usually 520.

(2) Ignore the data format, but understand that it can advertise up to 25 routes. (The request requires other systems to send all or part of the route table, and the response is to send the route table to the requester)

(3) The rip measurement is in Hop (HOP). The maximum value is 15, and 16 indicates infinity (not reachable)

(4) defects: the concept of a subnet does not exist, which may result in "normal reflection is fast, but abnormal reflection is slow.