Chapter 31 - Implementing IPv6 Addressing on Hosts Flashcards
PC1, PC2, and Router R1 all connect to the same VLAN and IPv6 subnet. PC1 wants to send its first IPv6 packet to PC2. What protocol or message will PC1 use to discover the MAC address to which PC1 should send the Ethernet frame that encapsulates this IPv6 packet?
a. ARP
b. NDP NS
c. NDP RS
d. SLAAC
B.
PC1 needs to discover PC2’s MAC address. Unlike IPv4, IPv6 does not use ARP, instead using NDP. Specifically, PC1 uses the NDP Neighbor Solicitation (NS) message to request that PC2 send back an NDP Neighbor Advertisement (NA). SLAAC relates to address assignment, and not to discovering a neighbor’s MAC address.
PC1 and Router R1 connect to the same VLAN and IPv6 subnet. The user of PC1 pings the IPv6 address of a host that sits at a remote site, so that the packets flow through R1, PC1’s default router. PC1 does not statically configure its default router setting. Which of the following answers lists a protocol or message that PC1 could have used when trying to learn what IPv6 address to use as its default router?
a. EUI-64
b. NDP NS
c. DAD
d. NDP RS
D.
Hosts can ask for (solicit) all routers to identify themselves by sending an NDP Router Solicitation (RS) message, with the routers sending back an NDP Router Advertisement (RA) message. PC1 can also use NDP Neighbor Solicitation (NS), but not for the purpose of learning its default router IPv6 address. DAD is a function that happens to use NDP NS and NA messages, but its function does not include the discovery of the default router address. Finally, EUI-64 does not define a protocol or message.
Which of the following pieces of information does a router supply in an NDP Router Advertisement (RA) message?
(Choose two answers.)
a. Router IPv6 address
b. Host name of the router
c. IPv6 prefix(es) on the link
d. IPv6 address of DHCP server
A and C.
The NDP RA lists the router IPv6 address, the IPv6 prefixes known on the link, and the matching prefix lengths. When using DHCPv6, the host learns the IPv6 address of the DNS server through DHCPv6 messages. For MAC addresses of on-link neighbors, hosts use NDP NS and NA messages.
Host PC1 dynamically learns its IPv6 settings using Stateless Address Auto Configuration (SLAAC). Which one of PC1’s settings is most likely to be learned from the stateless DHCPv6 server?
a. Host address
b. Prefix length
c. Default router address
d. DNS server address(es)
D.
SLAAC gives the host a means to choose its unicast address. The host also uses NDP to learn its prefix length, plus the address(es) of any default routers. It then uses stateless DHCP to learn the addresses of the DNS server(s).
Host PC1 dynamically learns its IPv6 settings using Stateless Address Auto Configuration (SLAAC). Think about the host’s unicast address as two parts: the prefix and the interface ID. Which of the answers list a way that SLAAC learns or builds the value of the interface ID portion of the host’s address?
(Choose two answers.)
a. Learned from a DHCPv6 server
b. Built by the host using EUI-64 rules
c. Learned from a router using NDP RS/RA messages
d. Built by the host using a random value
B and D.
With SLAAC, the host learns the prefix from a router using NDP RS/RA messages, and then the host builds the rest of the address (the interface ID). The host can use EUI-64 rules or use a defined process to randomly generate the interface IDvalue. The host does not learn the interface ID from any other device, which helps make the process stateless because no other device needs to assign the host its full address.
Three routers connect to the same VLAN and IPv6 subnet. All three routers have sent NDP RA messages, in reply to various IPv6 hosts’ NDP RS messages, asking to learn about the available IPv6 routers in the subnet. A network engineer issues the show ipv6 neighbors command on R1. Which of the answers best describes the kind of NDP information held in this output?
a. IPv6 neighbors (both routers and hosts) plus their MAC addresses, without noting which are routers
b. IPv6 neighbors (both routers and hosts) plus their MAC addresses, and also noting which are routers
c. IPv6 routers, with no information about nonrouters, with no MAC address info
d. IPv6 routers, with no information about nonrouters, with MAC address info
A.
The show ipv6 neighbors command lists all IPv6 addresses of neighbors (both routers and hosts), plus their matching MAC addresses. It does not note which are routers, leaving that information for the show ipv6 routers command.
