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ICND1 – IPv6 Questions 2

June 9th, 2017 in ICND1 100-105 Go to comments

Question 1

Explanation

Answers B E F are correct because A and B are the short form of 0:0:0:0:192:168:0:1 and 2002:c0a8:0101:0:0:0:0:0042 while C are normal IPv6 address.

Answer A is correct because “::” is named the “unspecified” address and is typically used in the source field of a datagram that is sent by a device that seeks to have its IP address configured.

Answer C is not correct because a global-unicast IPv6 address is started with binary 001, denoted as 2000::/3 in IPv6 and it also known as an aggregatable global unicast address. The 2000:: (in particular, 2000::/3) is just a prefix and is not a valid IPv6 address.

In fact answer D is acceptable but it is considered the network portion of an IPv6 address so it is a worse choice than others.

The entire global-unicast IPv6 address range is from 2000::/128 to 3FFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF/128, resulting in a total usable space of over 42,535,295,865,117,307,932,921,825,928,971,000,000 addresses, which is only 1/8th of the entire IPv6 address space!

Question 2

Explanation

Below is the list of common kinds of IPv6 addresses:

Loopback address ::1
Link-local address FE80::/10
Site-local address FEC0::/10
Global address 2000::/3
Multicast address FF00::/8

From the above table, we learn that A and D are correct while B and C are incorrect. Notice that the IPv6 unicast loopback address is equivalent to the IPv4 loopback address, 127.0.0.1. The IPv6 loopback address is 0:0:0:0:0:0:0:1, or ::1.

E is not correct because of anycast addresses which are indistinguishable from normal unicast addresses. You can think of anycast addresses like this: “send it to nearest one which have this address”. An anycast address can be assigned to many interfaces and the first interface receives the packet destined for this anycast address will proceed the packet. A benefit of anycast addressing is the capability to share load to multiple hosts. An example of this benefit is if you are a Television provider with multiple servers and you want your users to use the nearest server to them then you can use anycast addressing for your servers. When the user initiates a connection to the anycast address, the packet will be routed to the nearest server (the user does not have to specify which server they want to use).

Question 3

Question 4

Question 5

Explanation

“6to4 tunneling” is a technique which enables encapsulation of IPv6 packets into IPv4 for transport across an IPv4 network.

Question 6

Explanation

The IPv4 and IPv6 headers are shown below for your comparison. As we can see the Flow Label, Hop Limit, Traffic Class fields are all new but in fact Hop Limit in IPv6 is same as Time to live (TTL) in IPv4. Traffic Class is the equivalent of the DiffServ/DSCP portion of the IPv4 packet (in “Type of service” field) which carries the QoS markings of the packet. Just like in IPv4 the first 6 bits are designated for the DSCP value, and the next 2 bits are for ECN (Explicit Congestion Notifications) capable devices.

Flow-Label: This 20-bit field provides a special service for real-time applications. It can be used to inform routers and switches to maintain the same path for the packet flow so that packets are not reordered.

IPv4_Headers.jpgIPv4 Header fields

IPv6_header.jpgIPv6 Header fields

IPv6 eliminates the Header Checksum field, which handles error checking in IPv4.

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