链路层

数据帧(Data Frame)

MAC SRC (6 Octets)
MAC DEST (6 Octets)

1 Octet = 8 bits (0 ~ 256)

ARP

Address Resolution Protocol

通过 IP 找 MAC

• 从 ARP 缓存表中找 IP 对应的 MAC
• 没有找到则发送广播 ARP Request
• 目标单播 ARP Response
• 写入缓存表

网络层

IP

ICMP

传输层

TCP

UDP

应用层

HTTP

VPN

Virtual Private Network

PPTP

• PPP (Point-to-Point Protocol)
  • 在两个节点间创建链接，可提供认证、传输加密、压缩的功能
  • 认证
    • CHAP (Challenge-Handshake Authentication Protocol)

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sudo apt install pptpd

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# sudo vim /etc/pptpd.conf
localip 192.168.3.1
remoteip 192.168.3.100-200

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# sudo vim /etc/ppp/pptpd-options
ms-dns 1.1.1.1
ms-dns 8.8.8.8

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# sudo vi /etc/ppp/chap-secrets
# client server secret IP
username * password *

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sudo systemctl restart pptpd.service

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# sudo vim /etc/sysctl.conf
net.ipv4.ip_forward=1
# sudo sysctl -p

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sudo iptables -t nat -A POSTROUTING -s 192.168.3.0/24 -o eth0 -j MASQUERADE
sudo iptables -A FORWARD -p tcp --syn -s 192.168.3.0/24 -j TCPMSS --set-mss 1356