Chap 4 network Flashcards
Key Aspects of Network Layer
- Routing: to determine the best path for data packets.
- IP Addressing: to uniquely identify devices on a network.
- Fragmentation and Reassembly: fragment large packets into smaller ones at the source and reassembled at the destination.
- Error Handling: to detect and handle errors that may occur during data transmission.
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Logical Addressing: for communication between devices.
1.** Packet Forwarding:** to select the next-hop router or outgoing interface. - Internet Protocol (IP): responsible for addressing, routing, and fragmenting/reassembling packets.
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Virtual Private Networks (VPNs): to encrypt and encapsulate data packets for secure transmission.
1.** Quality of Service (QoS):** to ensure critical applications get sufficient network resources and bandwidth for optimal performance.
1.** Tunneling:** to encapsulate one protocol’s packets within another protocol’s packets for transmission across an intermediary network
network layer and role
The Network Layer is the third layer of the OSI model.
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It plays a crucial role in computer networks by facilitating communication and routing data between different networks.
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It enables the Internet and other interconnected networks to function effectively.
Routing Algorithm
Algorithms used by routers to determine the best path for data packets to travel.
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Consider factors like:
- ◦Network topology (layout)
- ◦Traffic congestion
- ◦Delay (latency)
- ◦Cost (bandwidth)
Goal: Efficiently route data to its destination.
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Categories include Static Routing and Dynamic Routing
Static Routing
Manually configured paths for data packets.
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Simple but inflexible, requires manual updates for network changes.
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Each entry specifies:
- ◦Destination network: The network to which the route applies.
- ◦Next hop: The next router along the path.
- ◦(Optional) Administrative distance: A metric influencing route selection
Advantages of Static Routing
Simple and easy to implement: suitable for small networks or those with clearly defined routing requirements.
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Predictable and reliable:
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Enhanced security: tighter control over network access, restricting unauthorized traffic from entering specific areas
Limitations of Static Routing
Scalability limitations: As a network changes, manually configuring static routes on every device becomes increasingly complex and time-consuming.
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Lack of adaptability:
Increased maintenance overhead: .
When to Use Static Routing
Small, stable networks: patterns are well-defined and unlikely to change frequently.
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Specific control needed: want to manually define allowed routes.
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Limited resources:
Dynamic Routing
Adapts to network changes automatically.
More complex but offers greater flexibility and efficiency.
- Employ algorithms to discover and update network paths.
- Rely on information exchange between routers.
Main types:
- Distance Vector Routing (e.g., RIP)
- Link State Routing (e.g., OSPF)
- Hybrid Routing (combines elements of both)
Distance Vector Routing
Routers exchange information about the “distance” (number of hops) to reach specific destinations with neighboring routers.
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Simple and efficient, but may not always find the optimal path.
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Example: RIP (Routing Information Protocol)
Link State Routing
Routers share information about the entire network topology with all other routers.
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Can discover the optimal path, but requires more processing power and bandwidth.
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Example: OSPF (Open Shortest Path First)
Benefits of Dynamic Routing
- scalability:
- Improved Efficiency:
- Reduced Administrative Overhead:
- Increased Reliability:
Limitations of Dynamic Routing
- Increased network overhead.
- Complexity of configuration and management.
- Convergence time.
- Security concerns.
- Propagation of routing information.
- Impact of route flapping.
- Vendor interoperability issues
Routing Information Protocol (RIP)
A distance vector routing protocol.
Routers exchange information about the “distance” (number of hops) to reach specific destinations.
- Simple and efficient, suitable for small to medium-sized networks.
- Two versions: RIPv1 and RIPv2
Two Main Versions of Routing Info Protocol
RIPv1:
* This is the original version of RIP.
* It utilizes classful routing, which can lead to inefficiencies in networks with varying subnet sizes.
* Lacks certain security features.
RIPv2:
* This version offers several improvements over RIPv1.
* Includes support for classless routing, which enables efficient routing across diverse network configurations.
* Introduces route tagging for better handling of different types of traffic.
* Provides authentication mechanisms to enhance security
RIP Working (Advertisement, Routing Updates, Routing Table Updates, Convergence)
Advertisement: Each router periodically broadcasts its routing table information to neighboring routers through RIP updates.
Routing Updates: These updates include details like:
1. Destination network address
1. Next hop router towards that network
1. Distance (number of hops) required to reach the destination
Routing Table Updates: Upon receiving RIP updates from neighboring routers, each router incorporates the information into its own routing table. The router selects the path with the lowest hop count for each destination network.
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Convergence: Through this process of information exchange and table updates, the network eventually converges to a loop-free routing path, ensuring efficient and reliable data flow
RIP Advantages
- Simple and easy to configure:
- Efficient for small to medium-sized networks:
- Low resource consumption
- Improved security (RIPv2):
Bellman-Ford Algorithm
Finds the shortest paths from a single source vertex to all other reachable vertices in a graph.
- Handles graphs with negative edge weights
- Iterative approach involving repeated relaxation steps to gradually refine the path estimations and eventually reach the optimal solution
Bellman-Ford Working Initialization
The algorithm begins by assigning an initial distance of positive infinity to all vertices in the graph except the source vertex.
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The source vertex is typically assigned a distance of 0, signifying its starting point.
Bellman-Ford Working Relaxation
The core operation of the algorithm lies in the relaxation step.
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This step iterates through each edge in the graph, examining the potential for a shorter path.
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For each edge connecting vertex u to vertex v, the algorithm checks whether the total distance from the source vertex to v through vertex u (distance(source) + weight(u, v)) is shorter than the currently known distance of v.
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If this condition is true, the distance of v is updated to reflect the shorter path, and the predecessor of v is also updated to point to vertex u (as u becomes the preceding vertex in the newly discovered shorter path)
Bellman-Ford Working Iterations
The relaxation step is repeated V-1 times, where V represents the total number of vertices in the graph.
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This repetitive process ensures that the algorithm has sufficient opportunities to discover and update paths throughout the graph, eventually converging to the optimal solution
Bellman-Ford Applications
- Network routing: Finding the shortest paths for data packets to travel across network connections.
- Logistics: Determining the most efficient routes for transportation and delivery services.
- Financial modeling: Calculating the minimum cost paths in financial networks with weighted edges representing risks or benefits.
- Geographic information systems (GIS): Identifying the shortest routes for navigation within a map network
Key Aspects of Network Layer (Quality of Service (QoS): )
to ensure applications get sufficient network resources and bandwidth for optimal performance.
Key Aspects of Network Layer (tunneling)
: to encapsulate one protocol’s packets within another protocol’s packets for transmission across an intermediary network
Key Aspects of Network Layer (VPN)
to encrypt and encapsulate data packets for secure transmission.
IP Addressing
system used to uniquely identify devices (such as computers, servers, routers, etc.) on a network.
It serves** two primary purposes**: Host/Network Identification and Location Addressing.
2 Versions of IP Addresses
The two main versions of IP addresses are IPv4 (Internet Protocol version 4) and IPv6 (Internet Protocol version 6).
2 Purposes of IP Address
Host or Network Identification: IP addresses are used to identify either a network interface (host) or an entire network. A host IP uniquely identifies a specific device within a network. A network IP identifies a group of devices connected to the same network segment.
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Location Addressing: IP addresses help in routing data packets across networks. They indicate the source and destination of data packets, facilitating proper transmission
Breakdown of IPv4 Addresses
Format: Typically represented as X.X.X.X, where each X is an octet (8 bits) ranging from 0 to 255. This is known as dotted-decimal notation.
Uniqueness: Each IPv4 address must be unique within a network or subnetwork.
Classes (Historical): Historically divided into Class A, B, and C based on network size, with Class D for multicasting and Class E reserved. Classful addressing is no longer widely used due to CIDR (Classless Inter-Domain Routing).
Subnet Mask: Used with the IP address to define the network portion and the host portion of the address.
Private vs. Public: Private addresses are for use within private networks and are not routable on the public Internet. Public addresses are globally unique and routable on the Internet.
DHCP (Dynamic Host Configuration Protocol): Commonly used to dynamically assign IPv4 addresses to devices.
NAT (Network Address Translation): A technique used to conserve IPv4 address space by allowing multiple private devices to share a single public IP
3 Key Parts of IPv4 Address
Network address: Identifies the specific network to which a device belongs.
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Subnet mask: Acts like a divider, separating the network and host portions of the address.
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Host address: Uniquely identifies a specific device within a network
IPv4 Advantages
- Familiarity:dominant for a long time,
- Ease of Implementation
- Compatibility: with older networking protocols.
- Large Address Space (for its time): .
- Efficiency in Certain Use Cases: efficient for small-scale
IPv4 Limitations
- Address Exhaustion: 32-bit address space insufficient for the growing # of devices.
- No Built-in Security:
- Fragmentation: Packets may need to be fragmented across networks .
- Limited Support for QoS: challenging to prioritize certain types of traffic.
- Hierarchical Addressing: inefficient allocation.
- Inflexibility: Fixed 32-bit length
Classes in IPv4
Class A: 126 Networks, 1,67,77,214 Hosts per Network. For large numbers of total hosts.
Class B: 16,382 Networks, 65,534 Hosts per Network. For medium to large sized networks.
Class C: 20,97,150 Networks, 254 Hosts per Network. Used in small local area networks (LANs).
Class D: Not allocated to hosts, used for multicasting.
Class E: Not allocated to hosts, reserved for research purposes
IPv6 Breakdown of Addresses
Format: Represented as eight groups of four hexadecimal digits separated by colons
Shorthand Notation: Leading zeros in each group can be omitted, and consecutive groups of zeros can be replaced with a double colon (::) once per address
Hierarchical Structure: The first 64 bits typically represent the network prefix (for routing and subnetting), and the remaining 64 bits represent the interface identifier (uniquely identifies a network interface on a segment)
IPv6 Different Address Types
Unicast Addresses: Identify a single interface. Types include global unicast, link-local (communication within the same network segment), and unique local.
Multicast Addresses: Identify a group of interfaces; packets are sent to multiple recipients simultaneously.
Anycast Addresses: Identify multiple interfaces, but packets are routed to the nearest interface sharing the same address
IPv6 Advantages
- Larger Address Space:
- Address Autoconfiguration (SLAAC): Devices can automatically configure addresses without manual setup
- Efficient Routing and Packet Processing:
- Improved Quality of Service (QoS):
- Enhanced Security Features:
- Simplified Header Structure:
- Support for Mobile Devices and IoT:
- Future-Proofing
IPv6 Limitations
- Compatibility Issues: dual stack (running both IPv4 and IPv6) can be resource-intensive.
- Security Concerns:
- Deployment Challenges:
- Limited Support in Certain Regions:
IPv4 Header
- Version (4 bits): Specifies IP version
- Header Length (4 bits): 32-bit words.
- Type of Service (8 bits): QoS parameters.
- Total Length (16 bits): Total packet length (header + payload).
- Identification (16 bits): For fragmentation/reassembly.
- Flags (3 bits): Control flags for fragmentation.
- Fragment Offset (13 bits): Fragment’s position in the original datagram.
- Time to Live (TTL) (8 bits): Max hops before discarding.
- Protocol (8 bits): Protocol in the payload
- Header Checksum (16 bits): Error detection in the header.
- Source IP Address (32 bits
- Destination IP Address (32 bits)
- Options (Variable): Optional fields.
- Payload (Data): Actual data being transmitted
Ipv4
IPv4 is the older and more widely used version, employing 32-bit numerical values.
Ipv6
IPv6 was developed to address the limitations of IPv4 address exhaustion and uses 128-bit hexadecimal values
OSPF (Open Shortest Path First)
- routing protocol in IP networks, used to find the best path for forwarding data packets across the network.
- link-state routing protocol: routers exchange information about the state of their links with other routers in the network.
- info is used to build a complete topological map of the network.
- uses the Dijkstra algorithm
How does OSPF calculate the shortest path?
Dijkstra algorithm
* calculate the shortest path tree from each router to every other router in the network.
* Each router maintains a database of link state advertisements (LSAs) received from neighboring routers, which is used to calculate the shortest path tree
What are OSPF areas and why are they used?
OSPF networks are typically divided into areas
* to improve scalability
* reduce the amount of routing info that needs to be exchanged.
* Routers within the same area have detailed knowledge of the network topology within that area
* routers in different areas only have summary information about other areas
What is OSPF hierarchical design?
routers organized into a hierarchy of areas.
* reduce the amount of routing information that needs to be exchanged between routers
* improves network scalability
What are OSPF LSAs and what information do they contain?
Each router in an OSPF network generates Link-State Advertisements (LSAs). LSAs contain crucial information about:
*Directly connected networks
*Cost of reaching those networks (e.g., bandwidth, delay)
*Router ID and area ID (if OSPF areas are used)
LSAs are flooded throughout the OSPF area, ensuring every router possesses a complete understanding of the network layout.
What are the benefits of OSPF?
OSPF benefits include:
- Efficient Routing:
- Scalability
- Fast Convergence: network changes, OSPF rapidly adapts: minimizing disruption.
- Loop Prevention
What is Dijkstra’s link-state routing algorithm?
- ensures data packets traverse the network along the most efficient paths.
- employed in protocols like OSPF and IS-IS (Intermediate System to Intermediate System)
How does Dijkstra’s algorithm work?
- start w set of tentative distances for each node,
- initially setting the distance of the
source node to 0
all other nodes to infinity. - It iteratively selects the node with the smallest tentative distance, known as the “current node,” and updates the tentative distances of its neighboring nodes based on
their current distances
the weights of the edges connecting them. - The algorithm continues this process until
all nodes have been visited
until the destination node is reached.
What are the steps in the working of link-state routing with Dijkstra’s algorithm?
1.Topology Discovery: Each router maintains information about its directly connected neighbors and the state of the links to those neighbors.
2.Link-State Advertisement (LSAs):
3.Building Network Topology: use of LSA
4.Shortest Path Calculation
5.Routing Table Construction: based on 4
6.Updating and Maintenance: periodically exchange updated LSAs to reflect network changes. routers recalculate shortest paths
