1.4 Given a scenario, configure a subnet and use appropriate IP addressing schemes.

Question 1

Networking with IPv4

Answer 1

• IP Address, e.g., 192.168.1.165
  – Every device needs a unique IP address
• Subnet mask, e.g., 255.255.255.0
  – Used by the local device to determine what subnet it’s on
  – The subnet mask isn’t (usually) transmitted
  across the network
  – You’ll ask for the subnet mask all the time
  – What’s the subnet mask of this network?
• Default gateway, e.g., 192.168.1.1
  – The router that allows you to communicate
  outside of your local subnet
  – The default gateway must be an
  IP address on the local subnet

Question 2

Special IPv4 addresses

Answer 2

• Loopback address
  – An address to yourself
  – Ranges from 127.0.0.1 through 127.255.255.254
  – An easy way to self-reference (ping 127.0.0.1)
• Reserved addresses
  – Set aside for future use or testing
  – 240.0.0.1 through 254.255.255.254
• Virtual IP addresses (VIP)
  – Not associated with a physical network adapter
  – Virtual machine, internal router address

Question 3

DHCP

Answer 3

• IPv4 address configuration used to be manual
  – IP address, subnet mask, gateway,
  DNS servers, NTP servers, etc.
• Dynamic Host Configuration Protocol
  – Provides automatic addresses and
  IP configuration for almost all devices

Question 4

APIPA - Automatic Private IP Addressing

Answer 4

• A link-local address - No forwarding by routers
• IETF has reserved
  169.254.0.1 - through 169.254.255.254
  – First and last 256 addresses are reserved
  – Functional block of
  169.254.1.0 through 169.254.254.255

Question 5

NAT (Network Address Translation)

Answer 5

• It is estimated that there are over 20 billion devices
  connected to the Internet (and growing)
  – IPv4 supports around 4.29 billion addresses
• The address space for IPv4 is exhausted
  – There are no available addresses to assign
• How does it all work?
  – Network Address Translation
• This isn’t the only use of NAT
  – NAT is handy in many situations

Question 6

RFC 1918 Private IPv4 Addresses

Answer 6

Question 7

Static NAT

Answer 7

Question 8

NAT Overload / Port Address Translation (PAT)

Answer 8

Question 9

Unicast

Answer 9

• One station sending information to another station
• Send information between two systems
• Web surfing, file transfers
• Does not scale optimally for streaming media

Question 10

Broadcast

Answer 10

• Send information to everyone at once
• One packet, received by everyone
• Limited scope - the broadcast domain
• Routing updates, ARP requests
• Not used in IPv6 - focus on multicast

Question 11

Multicast

Answer 11

• Delivery of information to interested systems
  – One to many
• Multimedia delivery, stock exchanges
• Very specialized
  – Difficult to scale across large networks
• Used in both IPv4 and IPv6
  – Extensive use in IPv6

Question 12

Anycast

Answer 12

• Single destination IP address has
  multiple paths to two or more endpoints
  – One-to-one-of-many
  – Used in IPv4 and IPv6
• Configure the same anycast address on different devices
  – Looks like any other unicast address
• Packets sent to an anycast address are delivered to the closest interface
  – Announce the same route out of multiple data centers,
  clients use the data center closest to them
  – Anycast DNS

Question 13

Classful Subnetting

Answer 13

• Very specific subnetting architecture
  – Not used since 1993
  – But still referenced in casual conversation
• Used as a starting point when subnetting
  – Standard values

Question 14

The construction of a subnet

Answer 14

• Network address
  – The first IP address of a subnet - Set all host bits to 0 (0 decimal)
• First usable host address
  – One number higher than the network address
• Network broadcast address
  – The last IP address of a subnet - Set all host bits to 1 (255 decimal)
• Last usable host address
  One number lower than the broadcast address

Question 15

VLSM (Variable Length Subnet Masks)

Answer 15

• Class-based networks are inefficient
  – The subnet mask is based on the network class
• Allow network administrators to define their own masks
  – Customize the subnet mask to specific network requirements
• Use different subnet masks in the same classful network
  – 10.0.0.0/8 is the class A network - 10.0.1.0/24 and 10.0.8.0/26 would be VLSM

Question 16

Four Important Addresses

Answer 16

• Network address / subnet ID
  – The first address in the subnet
• Broadcast address
  – The last address in the subnet
• First available host address
  – One more than the network address
• Last available host address
  – One less than the broadcast address

Question 17

Magic number subnetting

Answer 17

• Very straightforward method
  – Can often perform the math
  in your head
• Subnet with minimal math
  – Still some counting involved
• Some charts might help
  – But may not be required
  – CIDR to Decimal
  – Host ranges

Question 18

The magic number process

Answer 18

• Convert the subnet mask to decimal
• Identify the “interesting octet”
• Calculate the “magic number”
  – 256 minus the interesting octet
  – Calculate the host range
• Identify the network address
  – First address in the range
• Identify the broadcast address
  Last address in the range

Question 19

Seven second subnetting

Answer 19

• Convert IP address and subnet mask to decimal
  – Use chart to convert between CIDR-block notation and decimal
  – Same chart also shows the number of devices per subnet
• Determine network/subnet address
  – Second chart shows the
  starting subnet boundary
• Determine broadcast address
  – Chart below shows the
  ending subnet boundary
• Calculate first and last usable IP address
  – Add one from network address,
  subtract one from broadcast address

Question 20

IPv6 addresses

Answer 20

• Internet Protocol v6 - 128-bit address
  – 340,282,366,920,938,463,463,374,607,431,768,211,456
  addresses (340 undecillion)
  – 6.8 billion people could have
  5,000,000,000,000,000,000,000,000,000 addresses each

Question 21

IPv6 address compression

Answer 21

• Your DNS will become very important!
• Groups of zeros can be abbreviated
  with a double colon ::
  – Only one of these abbreviations
  allowed per address
• Leading zeros are optional

Question 22

Configuring IPv6 with a modified EUI-64

Answer 22

• Static addressing can be useful
  – The IP address never changes
• What other address never changes?
  – The MAC address
• Extended Unique Identifier (64-bit)
• Combined a 64-bit IPv6 prefix and the MAC address
  – Wait, the MAC address is only 48-bits long!
• You’re going to need some extra bits
  – And a minor change to the MAC address

Question 23

Converting EUI-48 to EUI-64

Answer 23

• Split the MAC
  – Two 3-byte (24 bit) halves
• Put FFFE in the middle
  – The missing 16 bits
• Invert the seventh bit
  – Changes the address from globally unique/universal
  – Turns the burned-in address (BIA) into a locally
  administered address
  – This is the U/L bit (universal/local)

Question 24

IPV6 Addressing: Shortcut for flipping the 7th bit

Answer 24

• Quickly convert the MAC address - create a chart
• Count from 0 to F in hex - two columns, groups of four
• Quickly convert the second character of the first hex byte
  – Change it to the other value

Question 25

Assigning IPv6 Addresses

Answer 25

• Internet Assigned Numbers Authority (IANA) provides address blocks to RIRs (Regional Internet Registries)
• RIRs assigns smaller subnet blocks to ISPs (Internet Service Providers)
• ISP assigns a /48 subnet to the customer

Question 26

Tunneling IPv6

Answer 26

• 6 to4 addressing
  – Send IPv6 over an existing IPv4 network
  – Creates an IPv6 based on the IPv4 address
  – Requires relay routers
  – No support for NAT
• 4in6 - Tunnel IPv4 traffic on an IPv6 network

Question 27

Teredo/Miredo

Answer 27

• Tunnel IPv6 through NATed IPv4
  – End-to-end IPv6 through an IPv4 network
  – No special IPv6 router needed
  – Temporary use - We’ll have IPv6 native networks soon (?)
• Miredo - Open-source Teredo for Linux,
• BSD Unix, and Mac OS X - Full functionality

Question 28

Dual-stack routing

Answer 28

• Dual-stack IPv4 and IPv6 - Run both at the same time
  – Interfaces will be assigned multiple address types
• IPv4
  – Configured with IPv4 addresses
  – Maintains an IPv4 routing table
  – Uses IPv4 dynamic routing protocols
• IPv6 - Configured with IPv6 addresses
  – Maintains a separate IPv6 routing table
  – Uses IPv6 dynamic routing protocols

Question 29

Howdy Neighbor

Answer 29

• There’s no ARP in IPv6
  – So how do you find out the MAC address of a device?
• Neighbor Solicitation (NS) -Sent as a multicast
• Neighbor Advertisement (NA)

Question 30

NDP (Neighbor Discovery Protocol)

Answer 30

• No broadcasts! - Operates using multicast over ICMPv6
• Neighbor MAC Discovery - Replaces the IPv4 ARP
• SLAAC (Stateless Address Autoconfiguration)
  – Automatically configure an IP address
  without a DHCP server
• DAD (Duplicate Address Detection) - No duplicate IPs!
• Discover routers
  – Router Solicitation (RS) and Router Advertisement (RA)