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Precept 5

Precept 5. Router & Assignment 2. Peng Sun. How VNS works. Just informational You don’t have to know it to finish assignment. How VNS works. Virtual Router Client. Raw Ethernet Frame. A. B. Virtual Router Server. Firewall. A pplication S ervers. Your VR Client.

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Precept 5

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  1. Precept 5 Router & Assignment 2 Peng Sun

  2. How VNS works • Just informational • You don’t have to know it to finish assignment

  3. How VNS works Virtual Router Client Raw Ethernet Frame A B Virtual Router Server Firewall Application Servers

  4. Your VR Client • Receive a Raw Ethernet Frame • Analyze headers to decide actions • Modify the frame • e.g., decrement TTL, update checksum • Or generate new frame • e.g., ARP reply, ICMP echo reply • Specify interface & Send the new frame to VR server

  5. How Router works • Scenario: • A TCP connection to one application server

  6. 1. ARP Request on eth0: How has IP3? Routing Table Your Client A IP3 IP1 eth1 A IP5 IP0 eth0 ARP Table IP2 eth2 IP4 Firewall A Virtual Router Server Application Servers

  7. 2. ARP Reply on eth0: eth0 HW has IP3 Routing Table Your Client A IP3 IP1 eth1 A IP5 IP0 eth0 ARP Table IP2 eth2 IP4 Firewall A Virtual Router Server Application Servers

  8. 3. IP packet on eth0: destined for IP3 Routing Table Your Client A IP3 IP1 eth1 A IP5 IP0 eth0 ARP Table IP2 eth2 IP4 Firewall A Virtual Router Server Application Servers

  9. 4. ARP request on eth1: Who has IP3? Routing Table Your Client A IP3 IP1 eth1 A IP5 IP0 eth0 ARP Table IP2 eth2 IP4 Firewall A Virtual Router Server Application Servers

  10. 5. ARP reply on eth1: HW3 has IP3 Routing Table Your Client A IP3 IP1 eth1 A IP5 IP0 eth0 ARP Table IP2 eth2 IP4 Firewall A Virtual Router Server Application Servers

  11. IP packet on eth1: HW3 in Ethernet header. Destined for IP3 Routing Table Your Client A IP3 IP1 eth1 A IP5 IP0 eth0 ARP Table IP2 eth2 IP4 Firewall A Virtual Router Server Application Servers

  12. Big / Little endian • Network order: big endian • Host order: usually little endian (x86) • Functions: • htonl, htons • ntohl, ntohs

  13. Some Exam Questions • Spring’11 Midterm Q1 • Spring’10 Midterm Q1 • Spring’09 Midterm Q4 • etc.

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