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IPv6 Questions 4

October 28th, 2018 Go to comments

Question 1


Let’s see an example of IPv6 prefix: 2001:0A3C:5437:ABCD::/64:


In this example, the RIR has been assigned a 12-bit prefix. The ISP has been assigned a 32-bit prefix and the site is assigned a 48-bit site ID. The next 16-bit is the subnet field and it can allow 216, or 65536 subnets. This number is redundant for largest corporations on the world!

The 64-bit left (which is not shown the above example) is the Interface ID or host part and it is much more bigger: 64 bits or 264 hosts per subnet!

Therefore in this question 4079 is the subnet ID. The FD14 prefix belongs to FC00::/7 which is an IPv6 Unique Local Address (The address block fc00::/7 is divided into two /8 groups which are FC00::/8 & FD00::/8)

Question 2


Below lists some reserved and well-known IPv6 multicast address in the reserved multicast address range:

FF01::1 All IPv6 nodes within the node-local scope
FF01::2 All IPv6 routers within the node-local scope
FF02::1 All IPv6 nodes within the link-local scope
FF02::2 All IPv6 routers within the link-local scope
FF02::5 All OSPFv3 routers within the link-local scope
FF02::6 All OSPFv3 designated routers within the link-local scope
FF02::9 All RIPng routers within the link-local scope
FF02::A All EIGRP routers within the link-local scope
FF02::D All PIM routers within the link-local scope
FF02::1:2 All DHCPv6 agents (servers and relays) within the link-local scope
FF05::2 All IPv6 routers within the site-local scope
FF02::1:FF00:0/104 IPv6 solicited-node multicast address within the link-local scope

Question 3


Any IPv6 address that begins with the 2002::/16 prefix is known as a 6to4 address. A 6to4 gateway adds its IPv4 address to this 2002::/16, creating a unique /48 prefix (because an IPv4 consists of 32 bits).

For example: In the IPv6 address 2002:ab10:beef::/48, “ab10:beef” is equivalent to (convert “ab” in hexadecimal to “171” in decimal; “10” in hexadecimal to “16” in decimal…). Therefore the corresponding IPv4 address can be globally routed.

Question 4


On inter-router point-to-point links, it is useful, for security and other reasons, to use 127-bit IPv6 prefixes. Such a practice parallels the use of 31-bit prefixes in IPv4.

Reference: https://tools.ietf.org/html/rfc6164

Question 5

Question 6


Link-local addresses only used for communications within the local subnetwork (automatic address configuration, neighbor discovery, router discovery, and by many routing protocols). It is only valid on the current subnet. It is usually created dynamically using a link-local prefix of FE80::/10 and a 64-bit interface identifier (based on 48-bit MAC address).

Question 7

Question 8


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, 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 9


Extended Unique Identifier (EUI) allows a host to assign itself a unique 64-Bit IPv6 interface identifier (EUI-64). This feature is a key benefit over IPv4 as it eliminates the need of manual configuration or DHCP as in the world of IPv4. The IPv6 EUI-64 format address is obtained through the 48-bit MAC address. The MAC address is first separated into two 24-bits, with one being OUI (Organizationally Unique Identifier) and the other being NIC specific. The 16-bit 0xFFFE is then inserted between these two 24-bits for the 64-bit EUI address. IEEE has chosen FFFE as a reserved value which can only appear in EUI-64 generated from the an EUI-48 MAC address.

For example, suppose we have the MAC address of C601.420F.0007. It would be divided into two 24-bit parts, which are “C60142” (OUI) and “0F0007” (NIC). Then “FFFE” is inserted in the middle. Therefore we have the address: C601.42FF.FE0F.0007.

Then, according to the RFC 3513 we need to invert the Universal/Local bit (“U/L” bit) in the 7th position of the first octet. The “u” bit is set to 1 to indicate Universal, and it is set to zero (0) to indicate local scope.

Therefore with the subnet of 2001:DB8:0:1::/64, the full IPv6 address is 2001:DB8:0:1:C601:42FF:FE0F:7/64

Question 10

Question 11

Question 12


A packet sent to an all-router multicast group is received and processed by all IPv6 routers on the link or network

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