Arp, RARP, ICMP, Ping

ARP Address Resolution Protocol (data link layer)

ARP provides dynamic ing between IP addresses and corresponding hardware addresses. The message means: If you are the owner of this IP address, please answer your hardware address. Packets are broadcast on the Internet.

The key to ARP high-speed operation is that each host has an ARP high-speed cache. This cache stores the ing records between the nearest Internet address and the hardware address. The lifetime of each item in the cache is generally 20 minutes.

ARP Proxy: If the ARP request is sent from host a of one network to host B of another network, then the router r connecting the two networks can answer the request, this process is called the proxy ARP or ARP proxy ). In this way, the sender of the request can be spoofed to assume that the vro is the destination host, and the destination host is actually the network on the other side of the vro connection. The vro function is equivalent to the proxy of the target host. The group is forwarded from the source host to the target host. In fact, in the ARP cache of host a, the IP addresses of router R and host B are mapped to the port hardware address of router R.

 

RARP Reverse Address Resolution Protocol (data link layer)

RARP is generally usedObtain the IP address when the diskless workstation is started. When a system with a local disk is booted, the IP address is generally read from the local configuration file. However, a diskless workstation needs to obtain its IP address in other ways. It first reads the hardware address of the host's Nic and then sends an RARP request, which is broadcast on the network, the workstation expects a host to respond to the request and specify an IP address for it.

The request packets of RARP and ARP are broadcast, but the response packets are unicast.

 

ICMP Internet Control Packet protocol (Network Layer)

ICMP transmits error messages and control packets between the host and the router. For example, the target host cannot be reached, the port cannot be reached, the Protocol cannot be reached, and the target network cannot be reached. The packets are transmitted in IP packets. The Checksum field covers the entire ICMP packet (the IP packet checksum only covers the IP packet header ).

ICMP is also used,Diskless workstation obtains its own subnet mask during boot.

It is often used for ICMP timestamp requests and responses.

A common ICMP packet is port inaccessibility. One of the UDP rules is that if a UDP datagram is received and the destination port is inconsistent with a process in use, UDP returns an ICMP port inaccessible packet.

 

Ping (Network Layer)

The Ping Command is a network-layer protocol. The ICMP protocol message is used. The ping command can be used to test whether a host can be accessed and the round-trip time (latency) of the host can be measured. It also allows us to view the loss rate and out-of-order of groups. Ping packets do not pass through the transport layer.