internet protocol

tony2099

2021-07-20 436 words 3 minutes

Contents

IP分片

ping 的工作原理

ip protocol

header size: 20bytes <= ip header size <= 60byte
ip4 range: 0.0.0.0 ~ 255.255.255.255; 2 * 32 ip(4.3billion);
why need ip layer? if we connect all computer, we must group the mac; mac address is hard for group; ip is a virtual address which easy to group , so we can build a big network;

divide the addrees

why? to reach the destination more efficiently
how? divie into two parts: net part and local part using CIDR(classless inter-domain routing)
1. subnet masking
2. CIDR notion ip/n 1~n position : network part; n-32 position: local part;
  
  172.17.100.0/24
  network: 172.17.100; local: 0~255;
  
  172.17.100.0/22
  network: 172.17.10 local: (0~3).255
  
  represent specific ip; 1. 192.168.100.14/24; net: 192.168.100, local: 14
how ip work
1. check destionation;
  1. in same network, 192.168.1.0/24, send directly
  2. in different network 192.168.2.0/24. send to gateway(router)

3. route table

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17



##  host: 192.168.1.1  in first network
   Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
   192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0
   192.168.2.0     192.168.1.1     255.255.255.0   UG    0      0        0 eth0

## routr:   192.168.1.1;  192.168.2.1
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 eth1
192.168.2.0     0.0.0.0         255.255.255.0   U     0      0        0 eth2



##  host: 192.168.2.2  in second network
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.0     192.168.2.1     255.255.255.0   UG    0      0        0 eth0
192.168.2.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0

是什么? 定义各个ip段如何通信； gateway
1. gateway 0.0.0.0 : 直接通信；
2. 其他: 通过router 转发；

4. NAT

network address translation

Source nat

personal host for visit internets 192.1 —[source:192.1 ]–>[ SNAT ] —>[source:45.1] —-> 192.2

Destination nat

websizeHost 192.1 <—[dest: 192.1]–[ NAT ] <— [dest: 45.1]—- 192.2

5. ip fragment

when? upperData > mtu;
fragment: origin: [10000]; ip datagram: {datagram1…datagramN | datagram1.size=mtu}
reassemble:

By id,offset;

Fail: in N Times, reassemble Buffer get all datagram, it send icmp error;

arp protocol

what?

cacheTable{ip:mac}

ip->mac;

1
2


192.168.124.49 (192.168.124.49) at 1a:db:37:87:71:a4 on en0 ifscope [ethernet]
192.168.124.50 (192.168.124.50) at a4:83:e7:6e:1a:f0 on en0 ifscope [ethernet]

icmp protocl

what: internet control message protocol for: 检测目标 ip是否可达，以及原因

type:

sucess request,8 replay,0
erro, unreachable,3 time exceed 11

error code:

网络不可达代码为 0
主机不可达代码为 1
协议不可达代码为 2
端口不可达代码为 3
需要进行分片但设置了不分片位代码为 4

how:

dns resolve
准备icmp packet; send type=8 的请求报文；
通过路由转发到指定host,
1. 指定ip 可达，回复 type=0 回复报文
2. 指定ip 不可达,回复 type=3的错误报文，和 error code