Network Layer

202403192331
Status: #idea
Tags: CN

IP Address

a.b.c.d/x, where $x$ is the number of bits in the network address of the subnet

Note

The rc file stores a static IP for a host UNIX host

Follows DORA (Discover, Offer, Request, Acknowledge)
DHCP returns
- IP address and netmask
- Gateway address
- DNS server host name and IP address

src: 0.0.0.0, 68
dest: 255.255.255.255, 67
yiaddr: 0.0.0.0
Transaction ID: <randomly generated integer = 654>

src: <DHCP server IP>, 67
dest: 255.255.255.255, 68
yiaddr: <IP address offered to the client>
transaction ID: 654
lifetime: 3600 secs

src: 0.0.0.0, 68
dest: 255.255.255.255, 67
yiaddr: <IP offered to the client>
transaction ID: 654
lifetime: 3600 sec

src: <DHCP server IP>, 67
dest: 255.255.255.255, 68
yiaddr: <IP offered to the client>
transaction ID: 654
lifetime: 3600 sec

Warning

For the purpose of this course, do NOT take $n - 2$ (for broadcast and network address)

Have a single IP address for a set of hosts
Can be public-private or private-private
NAT box maps one side to another
Advantages:
- Less number of public IPs needed
- Abstraction/separation between public IP and private IPs
Controversial
- Routers should only process upto layer 3, but sockets are in transport layer
- Violates end-to-end argument
  - NAT possibility should be taken into account by application development
Private IP ranges
- 10.0.0.0/24
- 172.16.0.0/12
- 192.168.0.0/16

Attention

Maps based on port number and IP.

(WAN IP, WAN Port) \to (LAN IP, Private port)

Pasted image 20240321160304.png

Used by hosts and routers to communicate network-level information
Network-layer 'above' IP
- ICMP messages carried in IP datagrams
ICMP message consists of
- Type
- Code
- First 8 bytes of the IP datagram, causing error (Part of the response)