What are the two main components of the network layer?
- Data plane: router-level functions that forward datagrams
- Control plane: network-wide logic for routing decisions
What does the network layer protocol enable?
- Logical communication between hosts
- Encapsulation and delivery of transport layer segments
What is the function of the IPv4 version number field?
- Identifies the IP version (e.g., IPv4 or IPv6)
- Guides routers on how to interpret the datagram
Why is the IPv4 header length field needed?
- Indicates where the payload begins
- Accounts for optional header fields
What is the purpose of the TTL (Time To Live) field in IPv4?
- Prevents infinite looping of datagrams
- Decrements at each router; if 0, the datagram is dropped
What does the type of service (TOS) field indicate?
- Differentiates between real-time and non-real-time traffic
- Can prioritize traffic (e.g., low delay, high throughput)
How does IPv4 handle datagram fragmentation?
- Splits large datagrams into fragments based on MTU
- Each fragment has the same ID and includes offset info
How does a receiving host reassemble fragmented IP datagrams?
- Uses identification number and offset field
- Recognizes the final fragment using the flag bit = 0
What happens if fragments are lost during transmission?
- IPv4 is unreliable—missing fragments prevent reassembly
- Entire datagram is dropped if incomplete
What is an IP address technically associated with?
- A network interface, not the host itself
How are IP addresses formatted?
- 32-bit binary values
- Written in dotted-decimal notation (e.g., 192.168.1.1)
What does the /24 in an IP address like 192.168.0.0/24 mean?
- The first 24 bits represent the network portion
- Also called the subnet mask
What is Classless Interdomain Routing (CIDR)?
- Strategy where IP addresses use the format
a.b.c.d/x xdefines the prefix length (network portion)
Define a subnet in IPv4 addressing.
- A logical grouping of connected devices that can communicate without a router
- Devices in the same subnet share a common IP prefix
How are IPv6 addresses different from IPv4?
- 128 bits long
- Includes new anycast address type
- Fixed 40-byte header for faster routing
What layers are present in end systems but not routers?
- Application, Transport layers are present in end hosts only
- Routers only use Network, Data Link, Physical layers
Which layers are found in routers according to the diagram?
- Network
- Data link
- Physical
What does the layering in the diagram imply about packet handling?
- Each router examines only the network layer
- Hosts encapsulate/decapsulate at all layers
In the diagram, what component is responsible for packet forwarding?
- The network layer within each router
What is the purpose of showing multiple paths in the diagram?
- Illustrates routing across different routers and networks
What layers are involved in wireless communication between host and router?
- Physical, Data Link, and Network layers
What difference do you observe between wireless and wired segments in the diagram?
- Wireless hosts connect to routers via wireless access points
- Wired connections are shown using switches and cables
What does the ‘fragment offset’ field represent?
- Position of the fragment within the original datagram
- Helps in reassembly
What is stored in the ‘header checksum’ field?
- A value to detect errors in the IP header
- Recomputed at each router
