Internet Protocol

Question 24

IP Properties

Answer 24

+ Packet switched connectionless. + Unreliable + Routing + Globally unique, delegated addresses

Question 25

IP (Un)Reliability

Answer 25

+ Routers forward packets on ‘best effort’ basis + IP Packets may get dropped, usually due to congestion. TCP, retransmissions are handled. UDP, application layer must handle. + Quality of Service methods can help.

Question 26

IPv4 Header

Answer 26

Source IP. Destination IP. IHL - Header length ID Field. Fragment Offset Time to live IP header Checksum

Question 27

IP Fragmentation

Answer 27

IP Datagram may be fragmented on it’s path if a link with smaller layer 2 Max Transmission Unit (MTU) is encountered. Ethernet typically has MTU of 1500 bytes. Preferable to avoid frag.

Question 28

Classless Inter-Domain Routing

Answer 28

Allow’s use of any prefix length, not just /8 /16 or /24. ISP’s must give proof of address requirements to RIRs.

Question 29

Network Address Translation (NAT)

Answer 29

Uses private IPv4 address internally to local network, global externally. However, NAT is limited as the number of global IP addresses the router held is the most users connected at one time. Fixed with NAPT

Question 30

Network Address and Port Translation (NAPT)

Answer 30

Keeps record of which hosts are using IP addresses, share 1 global IP address between many hosts by storing TCP/UDP port numbers that map to internet addresses.

Question 31

NAPT downsides:

Answer 31

+Scales poorly as requires state information + Breaks end to end transparency and security model. +Has problems if apps embed IP addresses. +Causes problems if multiple NATed sites merged, if they share common internal private IPs.

Question 32

IPv6: Benefits

Answer 32

128-bit addresses. Supports billions more devices online. Potential to restore end-to-end capability. Removal of the need for NAT Network Plug and Play Streamlined extensible IPv6 header. Fragmentation only at sender

Question 33

IPv6 header

Answer 33

Version Traffic Class Flow Label Payload Length Next Header Hop Limit Source Address Destination Address

Question 34

IPv6 Addressing

Answer 34

Unicast: One to One (as seen in IPv4) Multicast: One to Many NEW: Various scopes of address are defined. + Link local addresses - used only on a local subnet/link +Unique Local Addresses (ULAs) - for use within a site (e.g. campus) +Global Addresses - globally unique and routable

Question 35

Unique Local Addresses

Answer 35

Used only within a site. Devices likely to be multi-addressed. Completely unrelated to ISP, so even switching will mean internal communications are stable over ULA. Use ULA as source address if communicating within the site.

Question 36

Stateless Address Autoconfiguration (SLAAC)

Answer 36

Allows hosts to autoconfig basic network settings without DHCP server. + Stateless - no state info held as no server. + Selects addresses based on network prefix and host’s MAC address

Question 37

Transitioning to IPv6

Answer 37

Dual Stack Mode: Servers and Devices that can communicate with both protocols Translation: Rewriting IP header from one version to another (done at Application Layer) Tunnelling: Encapsulating IPv6 traffic as payload of IPv6 packets. NO ONE BEST METHOD. Focus on Dual Stack Deployment.