IP Addressing and Fragmentation Quiz
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Questions and Answers

What is the purpose of IP fragmentation?

  • To increase the data transfer speed.
  • To encrypt data during transmission.
  • To ensure compatibility with different MTU sizes. (correct)
  • To reduce the overall size of the data packet.

What determines how a network acquires its subnet part of an IP address?

  • It is randomly generated by the network.
  • It gets allocated from its provider's address space. (correct)
  • It is predetermined by global standards.
  • It is derived from the network's internal configuration.

How much overhead is typically added by the TCP layer?

  • 30 bytes
  • 10 bytes
  • 20 bytes (correct)
  • 40 bytes

Which of the following correctly identifies an IP address?

<p>A 32-bit identifier for a host or router interface. (C)</p> Signup and view all the answers

What is the address notation used for Organization 1 based on the provided content?

<p>200.23.18.0/23 (A)</p> Signup and view all the answers

What occurs to the headers when a datagram is fragmented?

<p>Each fragment retains a copy of the original header. (A)</p> Signup and view all the answers

How does hierarchical addressing benefit routing advertisement?

<p>It allows for efficient advertisement of routing information. (C)</p> Signup and view all the answers

What is the maximum data field length in a packet if the MTU is 1500 bytes and the IP header is 20 bytes?

<p>1480 bytes (C)</p> Signup and view all the answers

In an IP header, what does the 'offset' represent during fragmentation?

<p>The position of the fragment within the original datagram. (B)</p> Signup and view all the answers

What type of address space does the ISP provide to its organizations?

<p>A portion of its allocated address space. (A)</p> Signup and view all the answers

What is the least specific route indicated in the address space provided?

<p>200.23.16.0/20 (C)</p> Signup and view all the answers

What can be a consequence of IP fragmentation in data transmission?

<p>Higher chances of packet loss. (B)</p> Signup and view all the answers

Which statement about maximum transmission unit (MTU) is true?

<p>MTU can vary between different network links. (D)</p> Signup and view all the answers

Which organization has an address of 200.23.20.0/23?

<p>Organization 2 (C)</p> Signup and view all the answers

What is the purpose of sending requests to the ISP with address specifications?

<p>To receive anything with specified address beginnings. (B)</p> Signup and view all the answers

How many bits are used to represent an IPv4 address?

<p>32 bits (C)</p> Signup and view all the answers

Which of the following best describes the 'options' field in an IP header?

<p>It can contain additional routing or timing information. (B)</p> Signup and view all the answers

What organization is responsible for allocating IP address blocks to ISPs?

<p>ICANN (D)</p> Signup and view all the answers

What is the primary function of NAT in the context of a local network?

<p>To hide internal IP addresses from the outside world (C)</p> Signup and view all the answers

Which of the following is NOT a motivation for using NAT?

<p>Improved network speed for local devices (D)</p> Signup and view all the answers

How does a NAT router modify outgoing datagrams?

<p>It replaces the source IP address with the NAT IP address (D)</p> Signup and view all the answers

What IP address format is used in a typical local network managed by NAT?

<p>10.0.0.0/24 (D)</p> Signup and view all the answers

What happens to the visibility of devices in a local network when using NAT?

<p>They are entirely hidden from external networks (B)</p> Signup and view all the answers

Which of the following statements about the IP address 200.23.30.0/23 is correct?

<p>It is part of a larger block allocated to an organization. (B)</p> Signup and view all the answers

What key task does ICANN perform besides address allocation?

<p>Assigns domain names (B)</p> Signup and view all the answers

What is a primary motivation for transitioning from IPv4 to IPv6?

<p>The 32-bit address space of IPv4 is nearly exhausted (D)</p> Signup and view all the answers

What is one criticism of Network Address Translation (NAT)?

<p>It violates the end-to-end argument principle (A)</p> Signup and view all the answers

In an IPv6 datagram format, what must be noted about fragmentation?

<p>No fragmentation is allowed in the IPv6 datagram format (B)</p> Signup and view all the answers

Which field in an IPv6 packet header identifies priority among datagrams in a flow?

<p>Traffic Class (C)</p> Signup and view all the answers

What does NAT facilitate in network architecture?

<p>Multiple simultaneous connections using a single external IP address (B)</p> Signup and view all the answers

What aspect must application designers consider due to NAT?

<p>Potential issues with NAT traversal for client communications (D)</p> Signup and view all the answers

What is a benefit of the fixed-length IPv6 header format?

<p>Simplifies the processing and forwarding of packets (A)</p> Signup and view all the answers

What does the flow label in an IPv6 datagram indicate?

<p>Datagrams belonging to the same 'flow' (D)</p> Signup and view all the answers

What significant aspect was removed in IPv6 to enhance processing time at each hop?

<p>Checksum (A)</p> Signup and view all the answers

Which protocol was introduced in IPv6 to accommodate additional message types?

<p>ICMPv6 (D)</p> Signup and view all the answers

What is the purpose of the 'Next Header' field in IPv6?

<p>To indicate options outside of the header (A)</p> Signup and view all the answers

How do IPv4 and IPv6 routers manage the transition between the two protocols?

<p>Through tunneling (D)</p> Signup and view all the answers

Which of the following statements regarding the adoption of IPv6 is correct?

<p>One-third of all US government domains are IPv6 capable. (D)</p> Signup and view all the answers

Which component is NOT part of the IPv6 header structure?

<p>Multicast address (B)</p> Signup and view all the answers

What does tunneling allow during the IPv4 to IPv6 transition?

<p>IPv6 packets to be forwarded as IPv4 packets (C)</p> Signup and view all the answers

What mode allows for the inclusion of options in IPv6 packet transmission?

<p>Next Header Mode (D)</p> Signup and view all the answers

Which of the following is a feature of the IPv4 header not present in IPv6?

<p>Checksum (A)</p> Signup and view all the answers

What is a common challenge faced during the transition from IPv4 to IPv6?

<p>Simultaneous upgrade of all routers (A)</p> Signup and view all the answers

What is the action taken when the source IP matches 1.2.. and the destination IP matches 3.4.5.*?

<p>Drop the packet (A)</p> Signup and view all the answers

Which action is associated with packets destined to IP address 51.6.0.8?

<p>Forward to output port 6 (C)</p> Signup and view all the answers

What happens to all datagrams destined to TCP port 22 according to firewall rules?

<p>Drop them (C)</p> Signup and view all the answers

In the OpenFlow abstraction, what type of addresses do firewalls match against?

<p>IP addresses and TCP/UDP port numbers (D)</p> Signup and view all the answers

What is the forwarding decision when the ingress port is 1 and IP source is 10.3..?

<p>Forward to port 3 (B)</p> Signup and view all the answers

Which operation is not part of the possible actions in an OpenFlow flow table?

<p>Rearrange packet header fields (C)</p> Signup and view all the answers

What type of forwarding is associated with layer 2 (switch) according to the content?

<p>MAC address-based forwarding (C)</p> Signup and view all the answers

In the context of OpenFlow, what does a match rule for NAT typically include?

<p>IP address and port (C)</p> Signup and view all the answers

Which statement best describes the action taken for packets originating from host 128.119.1.1?

<p>They are dropped (D)</p> Signup and view all the answers

What type of match does a router typically use according to the forwarding rules?

<p>Longest destination IP prefix (A)</p> Signup and view all the answers

When sending packets from hosts h5 and h6 through the switch s1, what is the forwarding action taken?

<p>Forward to s2 (B)</p> Signup and view all the answers

What is the main purpose of the stats column in the OpenFlow flow table?

<p>To keep track of packet and byte counters (C)</p> Signup and view all the answers

What does the action 'forward' mean in the context of OpenFlow?

<p>Send packets out on specified ports (B)</p> Signup and view all the answers

What does the 'x' represent in the address format a.b.c.d/x?

<p>The subnet prefix length (C)</p> Signup and view all the answers

Which of the following ranges represents non-routable IP addresses?

<p>10.0.0.0 - 10.255.255.255 (C)</p> Signup and view all the answers

How is the subnet part determined in a CIDR address?

<p>By the binary representation of the address (D)</p> Signup and view all the answers

What IP address would be part of the non-routable range for private networks?

<p>192.168.100.1 (A), 172.16.0.1 (B), 10.1.1.1 (D)</p> Signup and view all the answers

Which statement regarding the subnet portion of an IP address in CIDR is correct?

<p>It can vary in length as specified by 'x'. (B)</p> Signup and view all the answers

What is the primary method used in FIFO scheduling?

<p>Send packets in the order they arrive (D)</p> Signup and view all the answers

What does the term 'tail drop' refer to in the context of packet scheduling?

<p>Discarding the packet that arrives last when the queue is full (A)</p> Signup and view all the answers

In priority scheduling, what factor determines which packets are sent first?

<p>Assigned priority levels of different classes (A)</p> Signup and view all the answers

What is the core principle of Round Robin scheduling?

<p>All classes are given equal time to send one packet each (C)</p> Signup and view all the answers

What characteristic may influence the class of a packet in priority scheduling?

<p>The packet's header information and markings (B)</p> Signup and view all the answers

Which of the following is NOT a recognized discard policy in the context of scheduling mechanisms?

<p>Last in last out (A)</p> Signup and view all the answers

What happens when packets are classified into multiple classes in priority scheduling?

<p>Each class gets a sequenced priority for sending packets (D)</p> Signup and view all the answers

What is a common outcome when a packet arrives at a full FIFO queue?

<p>The arriving packet is dropped based on the tail drop policy (A)</p> Signup and view all the answers

What is the source IP address of the DHCP Offer message?

<p>223.1.2.5 (D)</p> Signup and view all the answers

Which of the following best describes the purpose of the DHCP ACK message?

<p>To acknowledge that the client has received an IP address. (B)</p> Signup and view all the answers

What is the main advantage of using longest prefix matching in routing?

<p>It optimizes the selection of the most specific route for forwarding. (B)</p> Signup and view all the answers

What is the transaction ID in the DHCP Request message?

<p>654 (B)</p> Signup and view all the answers

What is a characteristic of ternary content addressable memories (TCAMs)?

<p>They enable retrieval of addresses in a single clock cycle. (A)</p> Signup and view all the answers

What IP address is being offered to the client in the DHCP Offer message?

<p>223.1.2.4 (A)</p> Signup and view all the answers

Which of the following best describes a switching fabric?

<p>It determines how packets are transferred from input buffers to output buffers. (B)</p> Signup and view all the answers

What limitation does the bus switching method encounter?

<p>The switching speed is limited by the bus bandwidth. (B)</p> Signup and view all the answers

What is the lifetime of the IP address assigned in the DHCP messages?

<p>3600 secs (A)</p> Signup and view all the answers

In switching via interconnection networks, what is a key advantage?

<p>It can overcome bandwidth limits experienced in bus systems. (C)</p> Signup and view all the answers

What is a common characteristic of memory switching?

<p>It is constrained by the memory's bandwidth and CPU control. (B)</p> Signup and view all the answers

When implementing longest prefix matching, which interface would the following address use: 11001000 00010111 00011000 10101010?

<p>Interface 1 (A)</p> Signup and view all the answers

Which of the following statements about packet switching speed is accurate?

<p>Switching speed is measured as a factor of input/output rates. (B)</p> Signup and view all the answers

What is a potential drawback of using older routers with memory-based switching?

<p>They face limitations due to inadequate memory capacity. (B)</p> Signup and view all the answers

What is the primary function of a crossbar switching network?

<p>To route packets based on destination addresses with minimal collisions. (B)</p> Signup and view all the answers

What defines a flow in the OpenFlow data plane abstraction?

<p>Header fields (C)</p> Signup and view all the answers

Which of the following best describes the role of a control plane in networking?

<p>Manages routing tables and flow tables (D)</p> Signup and view all the answers

What does the 'match' component in generalized forwarding involve?

<p>Pattern matching values in packet header fields (D)</p> Signup and view all the answers

How do routers utilize the flow table derived from the logically centralized routing controller?

<p>To define match+action rules for packet handling (B)</p> Signup and view all the answers

What is a necessary feature of the action component in the OpenFlow flow table?

<p>Drop or forward matched packets (C)</p> Signup and view all the answers

Which of the following actions is NOT defined in the generalized forwarding rules?

<p>Create new packets (B)</p> Signup and view all the answers

When prioritizing patterns in a flow table, what purpose does priority serve?

<p>To disambiguate overlapping patterns (A)</p> Signup and view all the answers

What is the function of counters in the OpenFlow flow table?

<p>To monitor #bytes and #packets for statistics (B)</p> Signup and view all the answers

How does an organization obtain its subnet part of an IP address?

<p>By getting an allocated portion from its ISP's address space (D)</p> Signup and view all the answers

Which of the following is an example of a less specific route?

<p>200.23.16.0/20 (C)</p> Signup and view all the answers

What does hierarchical addressing facilitate in network routing?

<p>Efficient advertisement of routing information (B)</p> Signup and view all the answers

Which organization address format corresponds to Organization 1 in the provided information?

<p>200.23.18.0/23 (D)</p> Signup and view all the answers

What is the primary function of ISPs regarding IP address allocation?

<p>They distribute their allocated address space to organizations (C)</p> Signup and view all the answers

Which of the following correctly describes the hierarchical model in the context of routing?

<p>It enables aggregation of routing information for efficient management (B)</p> Signup and view all the answers

What information is typically sent to ISPs regarding address specifications?

<p>Instructions to send all addresses starting with specific prefixes (B)</p> Signup and view all the answers

Which address block represents the least specific routing for the organizations listed?

<p>200.23.16.0/20 (C)</p> Signup and view all the answers

Flashcards

Subnet Allocation

An ISP allocates a portion of its address space (a subnet) to an organization.

Hierarchical Addressing

Organizing IP addresses in a way that groups related addresses together, enabling efficient routing information.

IP Address Subnetting

Dividing a large IP address range into smaller networks known as subnets.

Route Aggregation

Combining multiple routes into a single, more general route.

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Address Space

The total range of available IP addresses.

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ISP

Internet Service Provider

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Organization

A company, entity or group receiving a subnet for internal use.

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Route

A path or instruction to get packets to their destination.

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IP Datagram Format

The structure of an IP datagram, containing header information like source/destination IP addresses, length, and flags for fragmentation.

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IP Fragmentation

Dividing a large IP datagram into smaller pieces (fragments) to fit on smaller network links.

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IP Reassembly

Putting together the fragments of an IP datagram in the correct order at the destination.

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MTU (Maximum Transfer Unit)

The largest size of a data packet that a network link can handle.

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IP Address

A unique 32-bit identifier for a host or router interface, used for routing data.

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Interface (Networking)

The connection point between a host/router and a physical link (e.g., Ethernet cable).

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IP Header

The overhead portion of an IP datagram containing information about the packet, like source/dest. addresses, length, and flags.

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Header Overhead

The amount of extra data added by TCP and IP headers, typically around 40 bytes.

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Network Layer

The layer in the network model responsible for logical addressing (IP addresses) and routing data.

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IP Datagram

Fundamental unit of data transfer in the Internet Protocol.

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IP Addressing allocation

ICANN (Internet Corporation for Assigned Names and Numbers) allocates IP addresses and manages DNS, assigning domain names and resolving disputes.

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NAT (Network Address Translation)

NAT allows a local network to use a single IP address for all devices facing the internet, masking internal addresses.

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Motivation for NAT

NAT reduces the need for IP addresses from the ISP, enables changing devices' addresses internally without outside notification, and changes ISPs without affecting internal devices' addresses. It also provides additional security by hiding internal devices.

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NAT Implementation: Outgoing Datagrams

NAT routers change the source IP address and port number of outgoing datagrams, replacing them with a NAT IP address and a new port number.

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200.23.30.0/23

An example IP address range or network.

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199.31.0.0/16

Another example IP address range or network or address block.

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200.23.18.0/23

Another example IP address range or network or address block.

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Local Network IP Addresses

Addresses inside a local network (e.g., home network) like 10.0.0.0/24.

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IPv4 addressing

The original 32-bit addressing scheme for the Internet Protocol(IP).

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Network address translation

Replacing one IP address with another to connect to remote networks.

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Address shortage

The potential problem of running out of IP addresses.

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IPv6 Header Fields

IPv6 header fields include version, priority, flow label, payload length, next header, and hop limit, along with source and destination addresses (128 bits each).

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IPv6 Checksum Removal

The IPv6 header omits the checksum field to reduce processing time at each network hop.

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IPv6 Options

IPv6 allows options but places them outside the header, using the 'Next Header' field to identify them.

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IPv6 Tunneling

Method to transmit IPv6 packets over an IPv4 network. An IPv6 datagram is encapsulated within an IPv4 datagram, enabling IPv6 connectivity through IPv4 routers.

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IPv6 Transition Challenges

Simultaneous upgrade of all routers is impossible, creating a mixed IPv4/IPv6 network requiring tunneling and other techniques.

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ICMPv6

New version of Internet Control Message Protocol (ICMP). ICMPv6 provides additional message types, including 'Packet Too Big' and multicast group management functions.

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IPv6 Deployment Status

IPv6 adoption has been gradual, with limited deployment in services and networks. However, organizations like Google and NIST have seen partial adoption.

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Logical View of Tunneling

The intended view of the network, where the IPv6 routers appear to be directly connected, as if they were on an IPv6 network.

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Physical View of Tunneling

The actual physical view of how the network is set up, showing routers as connected through an IPv4 infrastructure.

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IPv6 Adoption Rate

The gradual and slow rate of adoption of IPv6 in comparison to the anticipated timescale. This is shown by examples such as Google and NIST, but has taken over 20 years.

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Flow Table

A table within a network device (like a switch or router) that stores rules for forwarding network traffic. Each rule specifies matching criteria (e.g., source IP, destination port) and actions to take (e.g., forward, drop).

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Match + Action

The core principle of OpenFlow, where a rule in the flow table defines a set of matching criteria (match) and an action to be taken based on that match.

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OpenFlow Abstraction

A standardized protocol that allows network devices to be controlled and managed in a unified way, regardless of their physical implementation. It simplifies network management and allows for more flexible traffic control.

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Packet Drop

An action in a flow table that discards a network packet without forwarding it. It's used to block undesirable traffic.

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Forward Packet

An action in a flow table that sends a network packet to a specified destination, such as an output port or another network device.

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Encapsulate & Forward to Controller

An action in a flow table that wraps a packet in a new header (encapsulation) and sends it to a central controller for further processing or decision-making.

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Modify Fields

An action in a flow table that changes specific fields within a network packet, such as source or destination IP address, port numbers, or VLAN identifier.

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Destination-Based Forwarding

A type of forwarding where traffic is routed based on the destination IP address, allowing for direct forwarding to the correct destination without the need for complex routing protocols.

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Firewall Rule

A specific rule configured to block or permit network traffic based on certain criteria, such as source, destination IP addresses, and port numbers.

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Layer 2 Forwarding

Forwarding traffic based on MAC addresses (Media Access Control), typically within a local network or within a specific VLAN. It handles communication between devices on the same network segment.

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Ingress Port

The port on a network device where a packet arrives from the outside network.

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Egress Port

The port on a network device through which a packet exits to reach its destination.

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Network Layer: Data Plane

The part of the network that handles forwarding and routing data packets according to network layer protocols (e.g., IP).

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Generalized Forwarding

A flexible traffic forwarding approach that allows for complex decision-making and actions based on various matching criteria, empowering network administrators to tailor traffic flow according to specific needs.

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Longest Prefix Matching

When a router needs to forward a packet, it looks up the destination IP address in its forwarding table. Longest prefix matching means using the address prefix (a portion of the IP address) that matches the destination address most specifically. This allows for more precise routing, ensuring packets reach their right destinations.

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Ternary Content Addressable Memory (TCAM)

A specialized type of memory used for very fast lookups in network devices. TCAMs are 'content addressable' - you give it an address, and it instantly retrieves the corresponding data. They are often used for longest prefix matching in routers, ensuring efficient and fast packet forwarding.

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Why is Longest Prefix Matching Used?

Longest prefix matching helps routers route packets efficiently. It ensures packets reach their correct destinations by choosing the most specific route, minimizing the chance of sending packets through unnecessary hops or incorrect paths.

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Switching Fabric

A hardware component within a network device that allows for high-speed transfer of packets between different input and output ports. It acts as a 'middleman' between incoming data from different ports and ensures that it gets delivered efficiently to the right outgoing port.

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Switching via Memory

An older method of packet switching where packets are first copied into the router's main memory before being forwarded. This is slower than other techniques because it involves copying data and accessing memory, causing delays.

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Switching via Bus

A packet switching method where a shared bus connects various ports. Packets travel over this shared bus to their respective destinations. This technique is faster than memory-based switching but can become congested if multiple devices share the bus.

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Switching via Interconnection Network

An advanced packet switching technique that uses specialized interconnection networks, like crossbar structures, to connect multiple input and output ports. This method overcomes the limitations of bus-based switching and offers high-speed packet forwarding.

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Crossbar Switching

A type of switching fabric with a direct connection between each input port and each output port. This allows for high-speed and flexible packet routing. This approach is ideal for connecting different components within a network device.

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Why are switching fabrics important?

Switching fabrics are essential for high-speed data forwarding. They allow network devices to process and route enormous amounts of data rapidly without bottlenecks. This is crucial for modern networks that handle large volumes of traffic.

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Packet Scheduling

The process of choosing the next packet to be sent on a network link.

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FIFO Scheduling

Packets are sent in order of arrival to the link. The first packet to arrive is the first to leave.

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Tail Drop

If a packet arrives to a full queue, the packet is dropped. This is a simple, common packet discarding policy.

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Priority Scheduling

Packets are classified into multiple priority classes. Higher priority packets are sent first, offering priority to certain traffic types.

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Round Robin (RR) Scheduling

Packets are sent from multiple classes in a cyclic pattern. Each class gets a turn to send one packet before the next class gets its turn.

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Real-World Example of FIFO

A queue at a checkout counter, where the first customer arrives first.

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Real-World Example of Priority

Emergency calls getting priority in a call center.

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Real-World Example of Round Robin

A printing queue where each user takes turns printing their documents.

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Non-Routable IP Address

An IP address reserved for private networks and not meant to be routed on the public internet. These addresses are used within organizations or homes to conserve public IP addresses.

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How does a host get an IP address?

A host typically obtains an IP address through a process called Dynamic Host Configuration Protocol (DHCP). A DHCP server assigns IP addresses to devices on a network, ensuring uniqueness and efficient management of the address space.

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What are Private Networks?

Private networks use a dedicated range of IP addresses for internal communication and are not routable on the public internet. They provide security, efficient management, and address conservation.

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What is the motivation for NAT?

Network Address Translation (NAT) helps conserve public IP addresses, enhances security by hiding internal devices from the public internet, and provides flexibility in managing internal network configurations.

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DHCP Offer

A message sent by a DHCP server to a client, proposing an IP address, subnet mask, and other network configuration information.

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DHCP Request

A message sent by a client to a DHCP server, acknowledging the offer and requesting the proposed IP address.

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DHCP ACK

A message sent by a DHCP server to a client, confirming that the client has been assigned the requested IP address.

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DHCP Transaction ID

A unique identifier used to track a DHCP conversation between a client and server.

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DHCP Lifetime

The duration for which a client can use an IP address assigned by a DHCP server.

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OpenFlow

A standardized protocol that allows network devices to be controlled and managed in a unified way, regardless of their physical implementation. It simplifies network management and allows for more flexible traffic control.

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Why do ISPs use hierarchical addressing?

Hierarchical addressing allows ISPs to efficiently advertise routing information to the internet. They can send a single advertisement to the internet for all networks within their address space.

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What is a switching fabric?

A high-speed network component that allows for rapid and efficient packet forwarding between various input and output ports within a network device.

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What is packet scheduling?

The process of deciding which packet to send out of a network link next, like managing a queue of packets.

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Study Notes

Chapter 4: Network Layer: The Data Plane

  • This chapter focuses on the data plane of the network layer, emphasizing the principles behind network layer services, specifically concentrating on the data plane.
  • The use of PowerPoint slides is freely available to all, and can be modified, modified and deleted to suit needs but the source must be noted (with copyright) if used.
  • Key points about uses for slides:
    • Citation of the slide source when used in classroom settings
    • Acknowledging the copyright, and source of the slide material, when posting on a website.
  • The slides cover generalized forwarding and Software Defined Networking (SDN) concepts.
  • Examples of match-plus-action in routers are also covered.
  • Key Network Layer Functions:
    • Forwarding: The process of moving packets from a router's input to appropriate output ports. Think of it like navigating a single interchange in a road trip.
    • Routing: The process of planning a trip from source to destination, determining the route a packet takes. This includes routing algorithms.
  • Network Layer Data Plane, Control Plane:
    • Data plane: This operates locally per router determining how arriving datagrams are forwarded to the output port.
    • Control plane: This operates across the entire network, determining how datagrams are routed between routers along the source-to-destination path. Includes traditional routing algorithms implemented in routers and Software Defined Networking (SDN) implemented remotely.

Network Layer Service Models

  • Datagram Services:
    • Guaranteed delivery
    • Guaranteed delivery with less than 40 msec delay
  • Flow Services:
    • In-order datagram delivery
    • Guaranteed minimum bandwidth
    • Restrictions on changes in inter-packet spacing

Router Architecture Overview

  • High-level view of a generic router's architecture. Includes routing processor for processing logic, high speed switching fabric, input ports, & output ports.

Input Port Functions

  • The physical layer handles bit-level reception.
  • The data link layer (e.g., Ethernet) handles the link protocol for sending and receiving data.
  • Decentralized switching uses IP header values for lookup and forwarding, using a "match plus action" mechanism in the input port hardware.
  • Destination-based forwarding focuses on destination IP addresses.
  • Generalized forwarding allows for forwarding based on header values.

Longest Prefix Matching

  • This is often used for finding entries in forwarding tables using a suitable address prefix.
  • Uses ternary content addressable memories (TCAMs) that allow retrieval of addresses in one clock cycle, regardless of the table size.
  • TCAMs can be helpful in router design with very large tables.

Switching Fabrics

  • Switching fabrics transfer packets from input buffers to appropriate output buffers.
  • Speed is often measured in multiples of input/output line rates.
  • Three types include memory-based, bus-based, and crossbar-based.
    • Memory based relies on CPU intervention.
    • Bus-based transfer packets from memory for an output port using a shared bus.
    • Crossbar use interconnection networks for switching.

Input Port Queuing

  • Queueing may happen at high traffic volume, when traffic from one or several ports exceeds the rate capacity via the switching fabric. This can cause delays or packets loss.
  • Head-of-line (HOL) blocking happens when the first packet in a queue prevents or delays other packets from proceeding.

Output Ports

  • Datagrams may arrive at output port buffers faster than they can be transmitted (causing delays).
  • There is a need for buffering or scheduling to manage queues to avoid delays in transfers.
  • Priority scheduling methods aim to prioritize different data packets (eg. high-priority datagrams vs lower).

Network Layer's IP Datagram Format

  • It includes header fields for version, header length, type of service, total length, identification, flags, offset, and more (options are available).
  • Each router along a path decrements the time to live field. Forwarded to the next hop until zero to discard the packet.

IP Fragmentation and Reassembly

  • Networks may employ MTU (maximum transmission unit) limits due to the maximum size of data frames possible.
  • IP datagrams may need to be fragmented into smaller pieces that can be carried by the next hop/router.
  • The receiving router is responsible for reassembling fragments back into the original, larger datagram.

IPv4 Addressing

  • 32 bits identify a host or router interface.
  • Interfaces on a host or router is a connection between the host/router and a physical link.
  • Routers usually have multiple interfaces.
  • Hosts typically have one or more interfaces.

Subnets

  • Subnets are logical groupings of networks or interfaces.
  • Dividing networks into subnets ensures logical network organization.
  • When identifying subnets, interfaces are detached from hosts and/or routers creating isolated networks

IP Addresses: CIDR

  • Classless InterDomain Routing (CIDR) uses subnets with flexible variable length.
  • Address format: a.b.c.d/x with 'x' being the number of subnet bits.

Non-Routable IP Addresses

  • Specific sets of IP addresses are not routed over the Internet ( eg. 10.0.0.0/8; 172.16.0.0/12; 192.168.0.0/16), used primarily as private networks.

IP Addresses: How To Get One?

  • IP addresses can be hardcoded for each host, and dynamically obtained from a Dynamic Host Configuration Protocol (DHCP) server.

DHCP: Dynamic Host Configuration Protocol

  • A standard protocol for dynamically assigning IP addresses. The DHCP server can provide the client with IP addresses, the the address of the first-hop router, the DNS server address and the network mask (network vs host) information.

DHCP Client-Server Scenario

  • A client requesting an IP address can obtain an address from the DHCP server through a series of messages.

DHCP: More Than IP Addresses

  • DHCP can also return more than IP address; also includes information such as address of first-hop router, name & IP address of DNS server .

OpenFlow Data Plane Abstraction

  • A method for representing and distributing network forwarding rules.

  • Defines flows using header fields.

  • Flow table entries include a pattern and associated actions.

  • Examples include forwarding datagrams to particular ports, dropping datagrams (firewall rules).

Match+Action

  • This framework unifies various networking elements (routers, firewalls, and switches) into a common way of expressing rules to manage data packets.
  • Various actions include forwarding to particular port, dropping or rewriting address and port.

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Description

Test your knowledge on IP addressing and fragmentation concepts. This quiz covers topics such as TCP overhead, subnetting, and hierarchical addressing. Challenge yourself with questions related to IP header and data transmission.

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