2023-11-14

Introduction

Summary

keywords

TODO

HW

Exercise*

Next time

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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.