Chapter 4: The Network Layer: Data Plane Flashcards
What does the sender in the network layer do?
Encapsulates segments into datagrams and then passes them to the link layer
What does the receiver in the network layer do?
Delivers segments to the transport layer protocol
What do routers do?
Mode datagrams from input ports to output ports to transfer them along the end-end path based on the header fields of the IP datagram
Describe forwarding
Moving packets from a router’s input link to the appropriate router output link
Describe routing
Determining the route taken by packets from source to destination
Describe the data plane
A local, per-router function that determines how arriving datagrams on the router input port are forwarded to the router output port
Which plane is a network-wide logic that determines how datagrams are routed among routers along the end-end path from source host to destination host?
Control plane
Which approach in the control plane has individual routing algorithm components in each and every router that interact in the control plane?
Per-router control plane
Which control plane has a remote controller that computes and installs forwarding tables in routers, to be used by the routers?
Software-Defined Networking (SDN)
What does the physical layer of the input port of a router do?
Terminates incoming physical links at routers
What do the link-layer functions of the input port of a router do?
Interoperate with the link layer at the other side of an incoming link
What does the routing processor of a router do?
Performs control-plane functions
What function is described below?
The forwarding table is consulted to determine the router output port to which an arriving packet will be forwarded via the switching fabric. Control packets are then forwarded from an input port to the routing processor
Lookup function
What sort of queueing occurs when datagrams arrive faster than the forwarding rate into the switch fabric?
Input port queueing
What sort of forwarding is based only on the destination IP address?
Destination-based forwarding
What sort of forwarding is based on any set of header field values?
Generalized forwarding
Give the definition:
When looking for forwarding table entries for given destination addresses, use the longest address prefix that matches the destination address
Longest prefix match
What do switching fabrics do?
Transfer packets from the input link to the appropriate output link
What is the switching rate?
The rate at which packets can be transferred from the input link to the output link
How is the switching rate often measured?
As a multiple of input/output link rate
What are the three major types of switching fabrics?
Memory
Bus
Interconnection network
What sort of switching is done in the following way: packet copied to system’s memory
Switching via memory
What sort of switching is done in the following way: datagram from input port memory to output port memory via a shared bus
Switching via a bus
Give the definition:
When switching speed is limited by bus bandwidth
Bus contention
What sort of switching is done in the following way: scaling using multiple switching planes in parallel to get speedup and scaleup via parallelism
Switching via interconnection networks
What sort of queueing occurs at the input queues when the switch fabric is slower than the input ports combined?
Input port queueing
Give the definition:
Queued datagram at the front of a queue that prevents others in the queue from moving forward
Head-Of-Line blocking (HOL)
Which ports store packets received from the switching fabric and transmit these packets on the outgoing link by performing the necessary link-layer and physical-layer functions?
Output ports
What is required when datagrams arrive from the switching fabric faster than the link transmission rate?
Buffering
To determine which datagrams to drop if there are no free buffers we need a…
drop policy
What discipline chooses among queued datagrams for transmission?
Scheduling discipline
What sort of queueing occurs when there is buffering when the arrival rate via the switch fabric exceeds the output line speed?
Outport port queueing
What happens if there is too much buffering?
Delays increase
Give the definition:
Which packet tot drop when buffers are full
Drop
What sort of drop drops arriving packets when buffers are full?
Tail drop
What sort of drop drops/removes packets on a priority basis when the buffers are full?
Priority drop
What do we call the process of choosing which packets to mark to signal congestion?
Marking
What do we call the deciding of which packet to send next on a link?
Packet scheduling
What do we call the packet scheduling method where packets are transmitted in order of arrival to output port?
First Come, First Serve (FCFS)
What do we call the packet scheduling method when the arriving traffic is classified, then queued by class, and then the packet from the highest priority queue that has buffered packets is sent?
Priority queueing
What do we call the packet scheduling method where the arriving traffic is classified, then queued by class, and the the server cyclically and repeatedly scans class queues, to then send one complete packet from each class in turn?
Round Robin (RR) scheduling
What do we call the packet scheduling method where each class has a weight and gets a weighted amount of service in each cycle?
Weighted Fair Queueing (WFQ)
What do we call the 32-bit identifier associated with each host / router interface?
IP address
What two parts does the IP address consist of?
Subnet and host part
What do we call the connection between host/router and the physical link?
Interface
What are the device interfaces that can physically reach each other without passing through an intervening router?
Subnets
How do we define subnets?
By detaching each interface from its host/router and creating islands of isolated networks, where each isolated network is a subnet
What do we call the routing that enables the subnet portion of an address to be of arbitrary length?
Classless InterDomain Routing (CIDR)
What protocols makes it possible for a host to get an IP address?
Dynamic Host Configuration Protocol (DHCP)
How does an ISP get blocks of addresses?
Through the Internet Corporation for Assigned Names and Numbers (ICANN)
How does the network get the subnet part of an IP address?
Gets allocated a portion of its provider ISPs address space
What sort of protocol is DHCP?
Client-server
What protocol has the following goal:
Host dynamically obtains IP address from network server when it joins the network
DHCP
What DHCP protocol message is on the following format:
host broadcasts [optional]
DHCP discover
What DHCP protocol message is on the following format:
DCHP server response [optional]
DHCP offer
What DHCP protocol message is on the following format:
host requests IP address
DHCP request
What DHCP protocol message is on the following format:
DHCP server sends address
DHCP ack
Is DHCP a client-server protocol?
Yes
What sort of addressing allows efficient advertisement of routing information?
Hierarchical addressing
Give the definition:
All devices in a local network have 32-bit addresses in a “private” IP address space that can only be used in the local network
Network Address Translation (NAT)
What is the main advantage of NAT?
Only 1 IP address is needed from a provider ISP for all devices
What parts of outgoing datagrams does a NAT router replace, and what are the parts replaced with?
source IP address replaced with NAT IP address
old port number replaced with new port number
What parts of incoming datagrams does a NAT router replace, and what are the parts replaced with?
NAT IP address replaced with corresponding source IP address
new port number replaced with port number stored in NAt table
What was the main motivation with IPv6?
The 32-bit address space of IPv4 could be completely allocated
What parts of a IPv6 datagram have been removed in comparison to a IPv4 datagram?
Header checksum
Fragmentation/reassembly
Options
What is the main method used to handle the fact that not all routers have been upgraded to IPv6, and therefore still used IPv4?
Tunneling
Give the definition:
IPv6 datagram carried as payload in IPv4 datagram IPv4 routers - packet within a packet
Tunneling
What are the three cornerstone beliefs of the internet?
Simple connectivity
IP protocols
Intelligence & complexity at network edge
What is the following argument called:
Some network functionality can be implemented in networks or at the network edge
The end-end argument
