Ch. 4 - Network Layer (Data Plane) Flashcards
What are the key functions of the data plane and the control plane?
Data plane = forwarding - local
Control plane = routing - network-wide
What is a router?
A device that examines header fields in IP datagrams and forwards them between networks.
What are the two control-plane approaches?
Traditional routing algorithms (routers) and
Software-defined networking (SDN) (servers)
What is the difference between forwarding and routing?
In essence, routing is the “brain” that figures out the best path, while forwarding is the “muscle” that moves the packets along that path.
What is the role of a forwarding table within a router?
A router uses a packet’s header to index the forwarding table, which is then used to determine the outgoing link interface.
What is DHCP?
Dynamic Host Configuration Protocol (DHCP) is a network management protocol used to dynamically assign IP addresses to devices on a network.
What is NAT?
Network Address Translation (NAT) is a technique that allows multiple devices on a private network to share a single public IP address.
What is ARP?
Address Resolution Protocol (ARP) is a network communication protocol that translates a computer’s dynamic IP address to its permanent MAC address.
What is HOL blocking? Does it occur in input ports or output ports?
HOL blocking is “Head of the Line” blocking - when a queued datagram at the beginning of a packet prevents others from moving forward. It occurs in input ports
How many IP addresses does a router have?
The router interface has two IP addresses, one public and one private.
What is SDN?
Software-Defined Networking (SDN) - centralized control and configuration management often in public/private cloud
OpenFlow
Protocol for implementing SDN match + action rules.
Quality of Service (QoS)
Guarantees for bandwidth, loss, order, timing.
Best Effort Service Model
No guarantees on delivery, timing, or order of datagrams nor bandwidth available.
Encapsulation
Wrapping data segments into datagrams for transmission.
What is Destination-Based Forwarding?
Forwarding based solely on destination IP address.
What is Input Port Queuing?
Storing datagrams when arrival exceeds processing rate.
What is TCAM?
Ternary Content Addressable Memory (TCAM) is a memory type for fast address retrieval.
What is CIDR?
Classless Inter-Domain Routing (CIDR): A more flexible method using variable-length subnet masks (VLSM).
What is Classful Addressing?
A historical method of dividing IP addresses into classes (A, B, C) based on the first few bits.
Subnetting
Dividing a network into smaller subnetworks to improve network efficiency and security. Uses subnet masks to identify the network and host portions of an IP address.
What are the main differences between IPv4 and IPv6?
IPv4: 32-bit address space, represented in dotted-decimal notation (e.g., 192.168.1.1)
IPv6: 128-bit address space, represented in hexadecimal notation (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334)
Why the switch to IPv6?
Running out of addresses for IPv4 due to the rapid growth of the internet. IPv6 has a vastly larger address space to accommodate future growth.
What is the ARP frame structure?
Hardware Type, Protocol Type, Hardware Address Length, Protocol Address Length, Sender Hardware Address (MAC), Sender Protocol Address (IP), Target Hardware Address (MAC), Target Protocol Address (IP)
What is ICMP?
Internet Control Message Protocol (ICMP) reports errors and other information related to IP packet processing and provides basic network diagnostics.
What are some common ICMP message types?
Echo Request: request an Echo Reply.
Echo Reply: response to an Echo Request.
Destination Unreachable: packet cannot be delivered
Time Exceeded: packet’s Time-to-Live (TTL) expires.
Parameter Problem: packet contains invalid parameters.
Source Quench: host is overloaded and cannot process packets.
What are two ICMP-Based Diagnostics?
Ping: Sends Echo Request messages to a target host to determine reachability and latency.
Traceroute: Sends Echo Request messages with increasing TTL values to identify the path a packet takes to a destination.
What is a Middlebox?
Device that transforms, inspects, filters, and manipulates traffic for purposes other than packet forwarding.
What are the parts of a router’s architecture?
Input/output ports, Switching fabric, Routing processor
What is decentralized switching?
Using header field values to lookup the output port via the forwarding table, with the goal to complete input port processing at ‘line speed’.
Where is the physical layer represented in a router?
Input port line termination - Bit-level reception
Where is the link layer represented in a router?
In the input port, bits are assembled into link layer frames
What is generalized forwarding?
Forwarding based on any set of header field values
What is Longest Prefix Matching?
From the forwarding table, use the longest address prefix that matches the destination address.
What is the purpose of the switching fabric?
To transfer a packet from the input link to the appropriate output link
What is the switching rate?
The rate at which packets can be transferred from inputs to outputs
What is bus contention?
Switching speed is limited by the bus bandwidth
When is buffering required?
When datagrams arrive faster than the link transmission rate.
What is the RFC 3439 Rule of Thumb and what is the more recent recommendation?
RFC 3439: average buffering = “typical” RTT * link capacity C
New recommendation: with N flows, buffering = (RTT * C) / sqrt(N)
Tail drop vs. Priority drop
Tail: drop arriving packet
Priority: drop/remove on priority basis
Packet marking
Packets can be marked to signal congestion (ECN, RED)
What is NFV?
Network functions visualization: programmable services over whitebox networking, computation, storage
