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Fundamentals of IPv4 Addressing and Routing


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IP packets
IP focuses on the job of routing data, in the form of __, from the source host to the destination host.
network
The __ layer specifies how packets travel end to end over a TCP/IP network, even when the packet crosses many different types of LAN and WAN links.
hosts
Routers and end-user computers (called __ in a TCP/IP network) work together to perform IP routing.
TCP/IP
The host operating system (OS) has __ software, including the software that implements the network layer.
path selection
The term __ is sometimes used to refer to the routing process, specifically how routing protocols select the best route among the competing routes to the same destination.
default gateway
The default router is also referred to as the __.
routing table networks subnets
All routers use the same general process to route the packet. Each router keeps an IP __. This table lists IP address groupings, called IP __ and IP __.
routing table
When a router receives a packet, it compares the packet’s destination IP address to the entries in the __ and makes a match.
Address Resolution Protocol
An example of how the router determines which data link address to use is the IP __.
ARP
__ dynamically learns the data link address of an IP host connected to a LAN.
Layer 3 protocol data units
The process of routing forwards Layer 3 packets, also called __, based on the destination Layer 3 address in the packet.
encapsulate
The routing process uses the data link layer to __ the Layer 3 packets into Layer 2 frames for transmission across each successive data link.
IP address
Any interface that expects to receive IP packets needs an __, just like you need a postal address before receiving mail from the postal service.
network subnet
A router can list one routing table entry for each IP __ or __, instead of one entry for every single IP address.
default router
Hosts need to know the IP address of their __ so that hosts can send packets to remote destinations.
host
Any device that has at least one interface with an IP address can send and receive IP packets and is called an IP __.
32-bit dotted-decimal notation
IP addresses consist of a __ number, usually written in __.
dots
The four resulting decimal numbers are written in sequence, with “__,” or decimal points, separating the numbers.
octets
Each DDN has four decimal __, separated by periods.
byte
The term octet is just a vendor-neutral term for __. Because each octet represents an 8-bit binary number.
0 255
The range of decimal numbers in each octet is between __ and __.
unique
Finally, note that each network interface uses a __ IP address.
network card
Most people tend to think that their computer has an IP address, but actually their computer’s __ has an IP address.
interface
Similarly, routers, which typically have many network interfaces that forward IP packets, have an IP address for each __.
networks
The original specifications for TCP/IP grouped IP addresses into sets of consecutive addresses called IP __.
first
The addresses in a single IP network have the same numeric value in the __ part of all addresses in the network.
router
All IP addresses in the same group must not be separated from each other by a __.
different groups
IP addresses separated from each other by a router must be in __.
same location
IP routing relies on all addresses in one IP network or IP subnet to be in the __, specifically on a single instance of a LAN or WAN data link.
4 billion
Literally 2^32 different values exist with a 32-bit IP address, for more than __ different numbers.
classes
IP standards first subdivide the entire address space into __, as identified by the value of the first octet.
Class A 1–126
__ gets roughly half of the IPv4 address space, with all DDN numbers that begin with __.
Class B 128–191
__ gets one-fourth(25%) of the address space, with all DDN numbers that begin with __.
Class C 192–223
__ gets one-eighth of the address space, with all numbers that begin with __.
unicast
Classes A, B, and C define __ IP addresses, meaning that the address identifies a single host interface.
multicast experimental
Class D defines __ addresses, used to send one packet to multiple hosts, while Class E defines __ addresses.
16 million
Class A networks each support a very large number of IP addresses (over __ host addresses per IP network).
126
However, because each Class A network is so large, Class A holds only __ Class A networks.
65,534 16,000
Class B defines IP networks that have __ addresses per network, but with space for over __ such networks.
254 2,000,000
Class C defines much smaller IP networks, with __ addresses each and __ networks.
network ID
The __ is just one reserved DDN value per network that identifies the IP network.
first one octet
In a single Class A network, the addresses have the same value in the __.
first two octet
In a single Class B network, the addresses have the same value in the __.
first three octet
In a single Class C network, the addresses have the same value in the __.
classful
The term __ IP network refers to any Class A, B, or C network, because it is defined by Class A, B, and C rules.
subnetting
IP __ defines a flexible way for anyone to take a single Class A, B, or C IP network and further subdivide it into even smaller groups of consecutive IP addresses.
subdivided network
In fact, the name subnet is just shorthand for __.
wasted
A single LAN seldom grows past a few hundred devices, so many of the IP addresses in Class B network 150.1.0.0 would be __.
same IP subnet
If the destination IP address is in the __ as I am, send the packet directly to that destination host.
Step 1
Use the data link Frame Check Sequence (FCS) field to ensure that the frame had no errors; if errors occurred, discard the frame.
Step 2
Assuming that the frame was not discarded at Step 1, discard the old data link header and trailer, leaving the IP packet.
Step 3
Compare the IP packet’s destination IP address to the routing table, and find the route that best matches the destination address. This route identifies the outgoing interface of the router, and possibly the next-hop router IP address.
Step 4
Encapsulate the IP packet inside a new data link header and trailer, appropriate for the outgoing interface, and forward the frame.
routing table
The routing (forwarding) process depends heavily on having an accurate and up-to-date IP __ on each router.
convergence time
The time between losing the route and finding a working replacement route is called __.
routing update
R3 sends a routing protocol message, called a __, to R2, causing R2 to learn about subnet 150.150.4.0.
Domain Name System
TCP/IP needs a way to let a computer find the IP address used by the listed host name, and that method uses the __.
DNS
Enterprises use the __ process to resolve names into the matching IP address.
IP packet
Routers treat the DNS messages just like any other __, routing them based on the destination IP address.
DNS naming standards
The domain names that people use every day when web browsing, which look like www.example.com, follow the __.
distributed
No single DNS server knows all the names and matching IP addresses, but the information is __ across many DNS servers.
queries
The DNS servers of the world work together, forwarding __ to each other, until the server that knows the answer supplies the desired IP address information.
destination MAC address
On Ethernet LANs, whenever a host or router needs to encapsulate an IP packet in a new Ethernet frame, the host or router knows all the important facts to build that header—except for the __.
Address Resolution Protocol
TCP/IP defines the __ as the method by which any host or router on a LAN can dynamically learn the MAC address of another IP host or router on the same LAN.
ARP Request
ARP defines a protocol that includes the __, which is a message that asks the simple request “if this is your IP address, please reply with your MAC address.”
ARP Reply
ARP also defines the __ message, which indeed lists both the original IP address and the matching MAC address.
ARP cache ARP table
Hosts remember the ARP results, keeping the information in their __ or __. A host or router only needs to use ARP occasionally, to build the ARP cache the first time.
ARP cache
Each time a host or router needs to send a packet encapsulated in an Ethernet frame, it first checks its __ for the correct IP address and matching MAC address.
arp -a
You can see the contents of the ARP cache on most PC operating systems by using the __ command from a command prompt.
ping
After you have implemented a TCP/IP internetwork, you need a way to test basic IP connectivity without relying on any applications to be working. The primary tool for testing basic network connectivity is the __ command.
Internet Control Message Protocol echo request echo reply
Ping uses the __, sending a message called an ICMP __ to another IP address. The computer with that IP address should reply with an ICMP __.