2023-11-09
Introduction
Summary
keywords
TODO
HW
Exercise*
Next time
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 routerIP 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.
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
255.255.255.0:67IP.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.
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