Computer Networks: Data Plane (Chapter 4)

• Computer Network Foundations: Chapter 4, Part 1 focuses on the network layers' data plane
• The goal is to understand the principles behind network layer services

Network Layer Goals

• Understand principles behind network layer services, focusing on the data plane
• Network layer service models, forwarding vs. routing, router operation, and addressing
• Instantiation and implementation in the Internet using IP protocol and NAT

"Data Plane" Roadmap

• Overview highlights the data and control planes
• An examination of a router's internal components, including input/output ports and switching
• Explores the Internet Protocol (IP), including IPv4 datagram format, addressing, NAT, and IPv6

Network Layer Services and Protocols

• Network-layer services and protocols cover transport segments from sending to receiving hosts
• Sender: encapsulates segments into datagrams and passes them to the link layer
• Receiver: delivers segments to transport layer protocol
• Hosts and routers have network layer protocols in every Internet device
• Routers principles network layer devices within the network core
• Examining header fields in all IP datagrams passing through
• Moves datagrams from input ports to output ports to transfer datagrams along end-end path

Network-Layer Functions

• Primary network-layer functions include forwarding and routing
• Forwarding moves packets from a router’s input link to the appropriate output link
• Forwarding operates on a timescale of nanoseconds
• Routing determines path packets take from source to destination
• Routing includes routing algorithms
• Routing operates on a timescale of seconds

Data Plane vs Control Plane

• Data plane (forwarding) is a local action performed per-router and determines how incoming datagrams are output
• Control plane (routing) is network-wide logic that determines how datagrams are routed end to end
• Control plane enables end-to-end datagram routing among routers from source to destination
• Traditional routing algorithms in routers manage measurements and forwarding tables
• Software-Defined Networking (SDN) compute routes on remote servers

Routing vs Forwarding Examples

• Forwarding is like "switching" using local action to move packets to the appropriate output
• Routing uses global action to determine source-destination paths with routing algorithms

Per-Router Control vs SDN Control Plane

• The per-router control plane involves individual routing algorithm components interacting in each router
• Software-Defined Networking (SDN) uses a remote controller to compute and install forwarding tables in routers

Router Architecture

• Routers have routing processors, high-speed switching fabric, input ports, and output ports
• The routing, management control plane operates in milliseconds
• The forwarding data plane operates in nanoseconds

Input Port Functions

• Input ports perform line termination, link-layer protocol handling, lookup, and queueing
• Decentralized switching uses header field values to lookup output port
• Decentralized switching lookup forwarding table in input port memory via "match pulse action"
• Decentralized switching has a goal to complete input port processing at 'line speed’
• Input port queueing occurs if datagrams arrive faster than forwarding rate into switch fabric
• Destination-based forwarding forwards based only on destination IP address and is traditional
• Generalized forwarding forwards based on any set of header field values

Internet Protocol

• Path selection algorithms implemented in routing protocols forward datagrams using forwarding tables
• A key protocol is ICMP, used for error reporting and router signaling

IPv4 Datagram Format

• IPv4 datagram format includes a 32-bit length, header length, type of service, 16-bit identifier, flags, fragment offset, time to live, upper-layer protocol, header checksum, source and destination IP addresses, options, and payload data
• "Type of service" can specify differentiated service (diffserv) and Explicit Congestion Notification (ECN)
• Time To Live (TTL) specifies remaining max hops(decremented at each router)
• Payload protocol indicates TCP, UDP, ICMP
• "Overhead" is 20 bytes of TCP + 20 bytes of IP
• "Overhead" is 40 bytes + application layer overhead
• Maximum length should be around 64k bytes

IPv4 Format details

• Version: This is a 4-bit field that specifies the IP Protocol version.
• Header Length: This 4-bit field defines the length of the header
• Type of Service: How the packet should be handled, different services uses this field to differentiate packet types
• Total Length: A 16-bit number which defines the total length of the packet to be bundled in header with bytes
• Identification, Flags, Fragment Offset: When source node issues a unique ID to each packet.
• IP Size is limited to 2 to the power of 16 bytes, or 64 KB.
• In packets, a packet has limited lifetime in the network to avoid circulating forever.
• The protocol field defines the data to which it belongs to.

IPv4 Fragmentation and Reassembly

• Network links have a Maximum Transmission Unit (MTU), so a max link-level frame is transferrable
• Different link types have different MTUs
• A large IP datagram is divided ("fragmented") within net
• One datagram becomes several datagrams and is reassembled at the final destination host
• IP header bits identify and order related fragments

Fields for Fragmentation

• Identification (3-bits)
• Flags
  • Unused bit
  • DF bit (Don't Fragment), meaning if 1 - the router cannot fragment the packet.
  • MF bit (More Fragments), meaning if set to - 1 - tell the destination whether or not more fragments follow
• Offset means to;
• identify sequence of fragments.
• It generally indicates number of data bytes preceding or ahead of the fragment.
• Determine where the fragment fits within the original IP packet
• Use unit of 8-byte chunks
• Determine location between the starting point of the packet and the fragment

Fragmentation and Reassembly

• Fragmentation happens at the sender and the routers.
• Reassembly ( putting back together of parts) always takes place at the receiver host ONLY

IP Addressing

• IP Addresses have structure
• a 32-bit identifier associated with each host or router interface
• An interface is a connection between a host, router and the link
• Routers have multiple interfaces.
• Normally hosts have one or two, could be wired or wireless
• An IP address is related to each interface

IPv4

• The IPv4 space has an address of 2 to the power of 32 (4,294,967,296)

• Some examples of IPv4 notations; -Octet 1 Octet 2 Octet3 Octet 4 10000000 00001011 00000011 00011111

• 128.11.3.31

• There are 32 bits allocated

• It is a hierarchical address, consisting of network on left, and host portion on the right

Subnet Masks

• Subnet mask is the 32-bit number of contiguous 1s followed by 0s
• to find net. ID and host ID by comparing IP Address and the Subnet Mask.
• /8, /16, /24 length- prefix - tells you how many bits in address refer to network portion

Special Addresses

• A network address is an address normally not assigned to a device
• Is used to represent organizations across the world
• ANDin between the IP address and a subunit mask
• Broadcast is an address that is used to broadcast all devices under the network
• The IP addres between NW and BD is called Host address
• Assigned to Host

IP Addressing Summary

• Hosts and Routers each have an IP Address
• Hosts and routers both have interface which are identified via 32 bits
• Some IP address examples
• how interfaces are connected if wired is not yet known
• How devices do not have an interventionary router

Other Address Topics

• IPv4:
• The space of addresse in that version of IP is 2 to the power of 32 4,294,967,296
• It must be of a notated format
  • Can be used in binary fashion
  • It must also be known via dotted decimal notation

Address Structuring

• A 32 bit structed address is useful for device communication
• Has a netowrk portion on left

Hierarchy of addresses

• All devices that are in the IPv4 network need a 32-bit address
• That address also needs to be a hierachal address composed of the network/host
• For Large netorks these ports can be very large ( more space )

IPv4 Details

• Shorthand version of identifying subnet mask
• It is a number ( bits ) set to 1 to be able to read subnet mask
• Written as numbers in slash, can represent how many prefix refers to the network

Address Access

• First address: NW must not assign to device or the org
• The AND between IP address and subnet is what yeilds said network access"
• Broadcast accesss. All devices under the net

IPv4 Communications

• Are done in the following formats;
• Unicast
• Broadcast
• Multiple Cast

IP Address Organization (More than 1 way)

• Each addres can be a 2 level communication device
• The left most bits are for the prefix, the right is for the host
• The amount of bits are what dictate sizes per the 2 categories

IPv4 Address Usage

• You must use the appropraite IPv4 addresses to account for how many can share it!
• Subnetting:
• Allows divides single large networks into smaller known parts
• Then uses block as a smaller sub
• To then use flexible mask
• Supernetting:
• Opposite to the sub method
• Allows routuers to advertise many ports in a single ad!

Sub and Super

• Sunetting, dividing network to small parts with subnet IP, such that site looks like one device ( but routers have access to packets !) Host protions include most and leaste bits in value
• Addres is considered to be the three levels of; Main Subnet Host

Hierarchy

• Mask is changed to fit best with what you hope to be sent as a package in that IP Range

Subnets

• To look at section and where IP is related It should be directly connected via links via tech Addres struct should have
• Netwprk as common upper Bit and Host Part.

Defining Subnets

The goal is to see what each part is by looking at links

CIDR Notation

Address mechanisim is called

• Classless of the
• Inter. Domain
• Routing
• Meaning they must of different amounts
• As well as the notation must have an X where
• X = the bits to hold a net work!

DHCP

• Goal is to dynamic obtains/ sends to Network.

• Can use network as old and be in system, else it joins DHCP overview can be with the following!

• Host broadcasts for any msg that is the discover from the network

• Any server sends with offers what it takes

• Host accepts with what it can request

• Servies can send ack of msg

DCHP

• When to use clients ( to get an id ) with router so that the subnets will have communication with the client
• That also means the client needs id to work in NW

DHCP More info

• More comes with returns such as
• Gateway access
• DNS
• Netmask

Addressing

• As for as knowing Is a very important and good way to send and get allocated parts

Addresses

• This sends the packets

Addresses

• Then makes the protocol much more easy

Address Routing

• Aggregating
• Like in ( SUPER ) where list becomes smalled Longest prefix is the best match for the long type!

CIDR Notes

To perform with networks such that they may communicate!

###Supernetting

• If companies need address numbers The ISP can allocate to the correct group based on if there's any overlapping ( contiguous ) of connections

IPs

• Used for short or small number access to memory for more devices 5 of them which are then delealted and organized into small number count

Data Plane

• Last stop with IPv6 with all functions to be performed!

IPs For All!

• There is both public and private address, such that if you get a normal connection with that data it can't be transferred!
• Meaning it is stuck only to itself!!
• Net translate comes in, such that only local can transfer ( the addresses in the group can then all be seen with the same addresses )

NAT (Translate)

• Need a device to look and send properly!!
• Must
• Send such that a ip address is stored so that others can access ( ip address, ports!)

NAT ( End )

• There's cons of NAT due to;
• shorting issues!
• Only a certain layer or part of device can work
• Argument for what kind or information goes to a protocol

Protocol Information

• If there a protocol and what it can do
• If there a RP and it's reverse As well with boots

ICMP in packet

• Check all

ICMP Tracerout

As with what info that this can all mean to this very important chapter!