9/24 Networking Notes
Domain Name System(DNS)
 Give it the url and it gives you the ip address
 Distributed system
Root
.com .in .us
Google
.org (Dot level domains?)
Wikipedia
www ds
*Has DNS for each site
 If it doesn’t know the ip address, goes up tree and asks domain
 www.wikipedia.org (If org doesn’t know, asks Wikipedia, then asks www to find ip)
*Once you have ip address, can connect to server
 If attack root, you can collapse the whole internet
Packets: DNS queries
OSI architecture: TCP ip is the new version of OSI architecture
 Each layer of this passes information down
Networking: Two computers connecting
Each layer in the stack interact with eachother
*When info goes from one computer to another, goes through routers in other place
*Top 4 layers are not required(look at slides for the layers)
Description of Layers
 Physical Layer:
o Deals with hardware, bits
o Bits across a wire
 Data Link Layer:
o How data should be transferred
o Collects a stream of bits into a larger aggregate called a frame/segment
o Works only on local network
 Network Layer:
o Can work globally
o Uses IP address
o Puts IP into a packet
 Transport Layer:
o Unit of data exchanges in this layer is called a message
o Makes sure each application gets the info it needs
 Session Layer:
o Separates sessions for one single application
 Presentation Layer:
o Not as used
o Concerned about the format of data exchanged between peers
 Application Layer:
o
Standardized common type of exchanges
IP-> network layer
FTP,HTTP,NV,TFTP-> application layer
*IP helps two computers communicate
IP service Model
 Packet delivery model
o Connectionless model for data delivery
Packet Format
 Pieces to address memory
 Every packet that comes to a layer must have a header
o Shows where you send it, where it comes from
 TTL-> how many hops it made
 Length-> bits in a whole packet
ICMP

If a machine cannot do work, sends message to inform the sender
o This message is an ICMP message
 Ping->checks to see if server is alive or not
 If you get no reply, it is not alive
ICMP Attack
 Surf attack(denial of service)
 Overload the server by replies from other servers
Reliable Byte Stream(TCP)
 Transmission control protocol(TCP) offers the following services
o Reliable, connection oriented, byte-stream service
 Streams movies
Flow Control: Preventing senders from overrunning capacity
Congestion Control: Preventing too much data from being injected into network
Sliding window:
 Send packets from A to B then B sends confirmation and update on how many packets it can
receive
 Slide window over in A till all the packets are sent
TCP Segment: Buffers the stack and creates a segment
TCP Header:
 6 bit flags
o SYN, FIN,RESET, PUSH, URG, ACK
*TCP slows packet sending down