Learn: Quiz 3 Cram

Forwarding

Moving a packet from a router's input to the appropriate output.

Routing

Determining the route or path packets take from source to destination.

Data Plane

Per-router function that forwards datagrams from an input link to the correct output link.

Control Plane

Network-wide logic that determines how datagrams are routed from source to destination.

Destination-based forwarding

Forwarding based only on the destination IP address.

Generalized forwarding

Forwarding based on multiple header field values.

Longest Prefix Matching

When multiple forwarding table entries match, use the entry with the longest matching address prefix.

TCAM

Content Addressable Memory used for fast forwarding-table lookups.

Switching Fabric

Transfers packets from a router's input ports to its output ports.

FIFO Scheduling

Packets are transmitted in the same order they arrive.

Priority Scheduling

The highest-priority queued packet is transmitted first.

Round Robin Scheduling

Cyclically scans queues and sends one packet from each available class.

Weighted Fair Queuing (WFQ)

Generalized Round Robin where each class receives a weighted amount of service.

IP Address

A 32-bit identifier associated with a host or router interface.

Interface

The connection between a host/router and a physical link.

IPv4 Address Size

32 bits.

Dotted-Decimal Format

Human-readable representation of an IP address, such as 192.168.1.1.

IP Datagram

The packet used by the Internet Protocol to carry data through a network.

TTL (Time to Live)

Limits how many router hops an IP datagram can make. It decreases at each router.

MTU (Maximum Transmission Unit)

The largest frame size supported by a network link.

IP Fragmentation

Dividing a large IP datagram into smaller datagrams to fit a link's MTU.

Where are IP fragments reassembled?

Only at the final destination.

Fragment Offset

Indicates where a fragment belongs in the original IP datagram.

Subnet Mask

Determines which portion of an IP address represents the network and which represents the host.

Network Portion

The high-order bits of an IP address that identify the network/subnet.

Host Portion

The remaining low-order bits that identify a host within the subnet.

/24 Subnet Mask

The first 24 bits are the subnet portion. Equivalent to 255.255.255.0.

How many total IP addresses are in a /24 network?

256 addresses.

How many valid host addresses are in a /24 network?

254 host addresses.

Why does a /24 have only 254 usable host addresses?

The network address and directed broadcast address cannot be assigned to hosts.

Network Address

Address where all host bits are 0. Example: 192.168.2.0/24.

Directed Broadcast Address

Address where all host bits are 1. Example: 192.168.2.255/24.

Broadcast Address

255.255.255.255.

Private IPv4 Range #1

10.0.0.0 through 10.255.255.255.

Private IPv4 Range #2

172.16.0.0 through 172.31.255.255.

Private IPv4 Range #3

192.168.0.0 through 192.168.255.255.

Loopback Address

127.X.Y.Z, commonly 127.0.0.1.

Multicast IPv4 Range

224.0.0.0 through 239.255.255.255.

Subnet

A group of interfaces that can physically reach each other without passing through an intervening router.

DHCP

Dynamic Host Configuration Protocol. Allows a host to dynamically obtain an IP address from a network server.

DHCP Message Order

DHCP Discover → DHCP Offer → DHCP Request → DHCP ACK.

DHCP Discover

Client broadcasts to find a DHCP server.

DHCP Offer

DHCP server offers an IP address to the client.

DHCP Request

Client requests the offered IP address.

DHCP ACK

Server confirms that the client can use the IP address.

What information can DHCP provide besides an IP address?

First-hop router address, DNS server information, and network mask.

ICANN

Internet Corporation for Assigned Names and Numbers. Allocates IP addresses through regional registries and manages the DNS root zone.

IPv4 Address Exhaustion

IPv4 has limited 32-bit address space. NAT helps conserve addresses and IPv6 provides a larger address space.

IPv6 Address Size

128 bits.

NAT

Network Address Translation. Allows devices on a local network to share a single public IP address.

NAT Translation Table

Stores mappings between private IP/port pairs and the NAT router's public IP/port pairs.

What does NAT change on an outgoing datagram?

The source private IP and port are replaced with the NAT IP and a new port.

What does NAT change on an incoming datagram?

The destination NAT IP and port are replaced with the corresponding private IP and port.

Why is NAT useful?

It reduces the need for public IP addresses and hides internal devices from the outside network.

What computes forwarding and flow tables?

The control plane.