IPv6 Questions

Note: If you are not sure about IPv6, please read our IPv6 tutorial.

Question 1

Question 2

Question 3

Explanation

The short syntax of static IPv6 route is:

ipv6 route <destination-IPv6-address> {next-hop-IPv6-address | exit-interface}

Question 4

Explanation

Floating static routes are static routes that have an administrative distance greater than the administrative distance (AD) of another static route or dynamic routes. By default a static route has an AD of 1 then floating static route must have the AD greater than 1. Floating static route has a manually configured administrative distance greater than that of the primary route and therefore would not be in the routing table until the primary route fails.

Question 5

Explanation

A IPv6 Unique Local Address is an IPv6 address in the block FC00::/7. It is the approximate IPv6 counterpart of the IPv4 private address. It is not routable on the global Internet.

Note: In the past, Site-local addresses (FEC0::/10) are equivalent to private IP addresses in IPv4 but now they are deprecated.

Link-local addresses only used for communications within the local 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 6

Explanation

The “ipv6 address autoconfig” command causes the device to perform IPv6 stateless address auto-configuration to discover prefixes on the link and then to add the EUI-64 based addresses to the interface. Addresses are configured depending on the prefixes received in Router Advertisement (RA) messages. The device will listen for RA messages which are transmitted periodically from the router (DHCP Server). This RA message allows a host to create a global IPv6 address from:
+ Its interface identifier (EUI-64 address)
+ Link Prefix (obtained via RA)
Note: Global address is the combination of Link Prefix and EUI-64 address

Although answer B seems to be correct but it is missing the prefix-length /64:

Question 7

Explanation

Well-known multicast addresses have the prefix ff00::/12.

FE80::/10 range is used for link-local addresses. 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 8

Explanation

When an interface is configured with IPv6 address, it automatically joins the all nodes (FF02::1) and solicited-node (FF02::1:FFxx:xxxx) multicast groups. The all-node group is used to communicate with all interfaces on the local link, and the solicited-nodes multicast group is required for link-layer address resolution. Routers also join a third multicast group, the all-routers group (FF02::2).

Question 9

Question 10

Explanation

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 to 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 -> Answer C and answer D are not correct.

Let’s take an example of the MAC address of C601.420F.0007. This MAC address is 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. In this case we don’t need to set this bit to 1 because it is already 1 (C6 = 11000110).

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 11

Question 12

Explanation

The short syntax of static IPv6 route is:

ipv6 route <destination-IPv6-address> {next-hop-IPv6-address | exit-interface}

Therefore if we use the destination-IPv6-address, we have to specify the IPv6 address of the remote (next-hop) router, not the local IPv6 address. If we use the exit-interface, we have to use the local exit-interface, not remote interface.

In this question, we have to suppose that all IPv6 addresses of Atlanta ends with .1 and Washington ends with .3

Please notice that this question asks about the command used on NEW York router so answer A is used to reach Atlanta router while answer B is used to reach Washington router.

Question 13

Explanation

Well-known multicast addresses have the prefix ff00::/12.

Reference: https://www.ciscopress.com/articles/article.asp?p=2803866&seqNum=5

Question 14

Explanation

The short syntax of static IPv6 route is:

ipv6 route <destination-IPv6-address> {next-hop-IPv6-address | exit-interface}

Therefore we must configure exit interfaces on Atlanta and Washington routers (their S0/0/0 interfaces) or the next hop IPv6 addresses (which are the IPv6 addresses of S0/0/0 – 2012::2 for Atlanta side and S0/0/1 2023::2 for Washington side).

Note: In an access list, 0.0.0.0/0 is “all possible IPv4 addresses” while ::/0 is the IPv6 equivalent of that.