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Introduction

Summary

keywords

TODO

HW

Exercise*

Next time

DHCP

#test : fill-in-the-blank problem in DCHP client-server scenario

ipconfig /renew command refreshes DCHP transactions that is done in prior.

Hierarchical nature of IP address

How it is made​

  • ISP reserves a address space. /20
  • The ISP can allocate address subnets. /23 -> made $2^3$ subnets available under this ISP.

Benefits​

  • allows efficient route advertisement of routing information.
    • Only the subnet part is advertised in routing tables.
    • "You don't need to know my whole address. To get to me, just send it to my subnet gateway".
    • The subnet gateway has the forwarding table for the rest of the IP address info.
    • Consequently, the forwarding tables are reduced efficiently.
  • if new IP is added in the subnet, that is not inside the current subnet IP range, advertise that additionally.
  • At the higher level router, they compute longest address prefix computing.

ETC​

  • ICANN : Highest level of system organization above all the ISP.

    • allocates IP addresses through 5 Regional registries (RRs)
    • manages DNS root zone.

  • NAT helps IPv4 address space exhausion.

NAT

Network address translation

  • A network-layer software unit allowing to expand its subnet.

This network devices share a single global IP address.

  • Interior devices is routed by the gateway router, by port number.

  • all devices in local network have 32-bit address in a private IP address space.

    • 10/8, 172,16/12,192.168/16 prefixes.

Benefits​

  • just one IP address for all devices.
  • can change address of devices in local network at will.
  • can change ISP without changing local device addresses.
  • Security : every devices are not directly accessible.

Implementation​

  1. Outgoing
  • replace every datagram IP by NAT IP
  1. Incoming
  • replace every datagram IP+port by NAT table.

Controversy on NAT​

  • router should only process up to layer 3, but port is a transport layer property.
  • should be solved by IPv6 instead.
  • violates end-to-end argument modularity.
  • NAT traversal : What if client wants to connect to server behind NAT?

IPv6

  • out of 40 bytes header, 32 bytes are used for source IP, destination IP.
  • Fragmentation header fields are omitted.
  • How do they handle big MTU fragmentation? The router sends back a request of a smaller MTU. fragmentation is done in the end user device.
  • option fields are omitted. The header size is now fixed.
  • flow level number will be used in the future.
  • no TTL, no header Length, asdlfkasdmlsadkfamdlck.