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Introduction

Summary

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TODO

HW

Exercise*

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IP

IP datagram​

TTL : prevent looping. (not usually occurs because network is hierarchical) type of service

Overheads

  • 20 bytes of IP header,
  • 20 bytes of TCP header.

IP fragmentation​

Network links have max transfer size (MTU) IP fragmentation can occur at any router IP assembly always happen only at the last router.

3 fields on header 16 identifier, flags, offset fragflag 0 indicates the last fragment. fragmentation was about the flow capacity. offset - size

where fragmentation happens? depended on the size?

IP addressing​

32 bit identifier with each host or router interface IP address is associated with an interface, not a device.

router also has interface. #test: prefix matching problems

  • virtual network interfaces By default, 192.168.56.1 is the IP address assigned for Ethernet adapter to virtual box.

There's Layer 2 device (called hub) on blue areas network example

subnets​

223.1.1.X, 223.1.3.X,223.1.2.X is a subnet address part.

subnet is indicated by subnet mask. one device can be in several subnet, each adapter to each subnet.

for 223.1.3.0/24, /24 part means 24 bits in front are for subnet address.

CIDR (Classless InterDomain Routing)

subnet portion can be of arbitrary length

a.b.c.d/x

How do you get IP address?​

  • How does host get their IP?

    • Option 1) Hard Coded in config file
    • Option 2) Dynamic Host Configuration Protocol(DHCP)

  • How does network get their IP?

    • gets allocated portion of its provider ISP's address space

DHCP​

It is a Application layer protocol. Goal

  • can renew its lease(time duration of borrowing) on address in use

  • allows reuse of address.

  • support for mobile users who join/leave network.

  • discover, offer, request, ack

DHCP scenario​

  • There's a DHCP server connected in the network.

  • DHCP broadcast : broadcast send to 255.255.255.0:67 IP.

    • src:0.0.0.0,68
    • dest:255.255.255.0,67
    • yladdr: 0.0.0.0
    • transaction ID:654

  • DHCP server serves at port 67.

  • DHCP Offer : How about <address on yladdr> this IP?

    • src:223.1.2.5,67
    • dest:255.255.255.0,68
    • yladdr: 223.1.2.4
    • transaction ID:654
    • lifetime: 3600 secs

  • destination is till broadcasting.

  • The client recognizes the offer by transaction

  • there is a lifetime

  • DHCP request : OK, can I use it?

    • src:0.0.0.0,68
    • dest:255.255.255.255,67
    • yladdr: 223.2.3.4
    • transaction ID:654
    • lifetime: 3600 secs

  • DHCP Ack : yes, you can

      • src:.0.0.0,68
    • dest:255.255.255.0,67
    • yladdr: 0.0.0.0
    • transaction ID:654
    • asdfaf?

normal mobile device only uses request, ack. They only use their address saved in client device. They only confirms if the

DHCP sends more info other than IP.​

  • first-hop router
  • local DNS server IP
  • network mask

How does network get subnet part of IP?​

  • ISP bought a portion of address space. ex. 11001000 00010111 00010000 00000000
  • ISP divides them into subnets into however they like. ex. 11001000 00010111 00010010 00000000/23 ex. 11001000 00010111 00010020 00000000/23

This way, IP is a natural Hierarchical Addressing Space.