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IPv6 Questions

August 10th, 2015 in ROUTE 300-101 Go to comments

Question 1

Explanation

Dual-stack method is the most common technique which only requires edge routers to run both IPv4 and IPv6 while the inside routers only run IPv4. At the edge network, IPv4 packets are converted to IPv6 packets before sending out.

6to4 tunnel is a technique which relies on reserved address space 2002::/16 (you must remember this range). These tunnels determine the appropriate destination address by combining the IPv6 prefix with the globally unique destination 6to4 border router’s IPv4 address, beginning with the 2002::/16 prefix, in this format:

2002:border-router-IPv4-address::/48

For example, if the border-router-IPv4-address is 64.101.64.1, the tunnel interface will have an IPv6 prefix of 2002:4065:4001:1::/64, where 4065:4001 is the hexadecimal equivalent of 64.101.64.1. This technique allows IPv6 sites to communicate with each other over the IPv4 network without explicit tunnel setup but we have to implement it on all routers on the path.

NAT-PT provides IPv4/IPv6 protocol translation. It resides within an IP router, situated at the boundary of an IPv4 network and an IPv6 network. By installing NAT-PT between an IPv4 and IPv6 network, all IPv4 users are given access to the IPv6 network without modification in the local IPv4-hosts (and vice versa). Equally, all hosts on the IPv6 network are given access to the IPv4 hosts without modification to the local IPv6-hosts. This is accomplished with a pool of IPv4 addresses for assignment to IPv6 nodes on a dynamic basis as sessions are initiated across IPv4-IPv6 boundaries.

Question 2

Explanation

Overlay tunneling encapsulates IPv6 packets in IPv4 packets for delivery across an IPv4 infrastructure (a core network or the Internet). By using overlay tunnels, you can communicate with isolated IPv6 networks without upgrading the IPv4 infrastructure between them. Overlay tunnels can be configured between border routers or between a border router and a host; however, both tunnel endpoints must support both the IPv4 and IPv6 protocol stacks.

IPv6_tunneling.jpg

Reference: http://www.cisco.com/c/en/us/td/docs/ios/ipv6/configuration/guide/12_4t/ipv6_12_4t_book/ip6-tunnel.html

Question 3

Explanation

In Stateless Configuration mode, hosts will listen for Router Advertisements (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

Question 4

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.

In this question, the MAC address C601.420F.0007 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 5

Question 6

Explanation

NPTv6 stands for Network Prefix Translation. It’s a form of NAT for IPv6 and it supports one-to-one translation between inside and outside addresses

Question 7

Explanation

The command “ipv6 flowset” allows the device to track destinations to which the device has sent packets that are 1280 bytes or larger.

Question 8

Explanation

NAT64 is used to make IPv4-only servers available to IPv6 clients.

Note:
NAT44 – NAT from IPv4 to IPv4
NAT66 – NAT from IPv6 to IPv6
NAT46 – NAT from IPv4 to IPv6
NAT64 – NAT from IPv6 to IPv4

Question 9

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.

Question 10

Explanation

IPv6 allows devices to configure their own IP addresses and other parameters automatically without the need for a DHCP server. This method is called “IPv6 Stateless Address Autoconfiguration” (which contrasts to the server-based method using DHCPv6, called “stateful”). In Stateless Autoconfiguration method, a host sends a router solicitation to request a prefix. The router then replies with a router advertisement (RA) message which contains the prefix of the link. Host will use this prefix and its MAC address to create its own unique IPv6 address.

Note:
+ RA messages are sent periodically and in response to device solicitation messages
+ In the absence of a router, a host can generate only link-local addresses. Link-local addresses are only sufficient for allowing communication among nodes that are attached to the same link

Comments
  1. Dereje
    February 27th, 2015

    Q4.Which IPv6 addresses should the engineer add to the documentation?

    A. 2001:DB8:0:1:C601:42FF:FE0F:7
    B. 2001:DB8:0:1:FFFF:C601:420F:7
    C. 2001:DB8:0:1:FE80:C601:420F:7
    D. 2001:DB8:0:1:C601:42FE:800F:7

    Universal/Local bit (“U/L” bit) in the 7th position of the first octet.has not been changed
    mac address C601.420F.0007
    subnet 2001:DB8:0:1::/64

    the answer has to be 2001:DB8:0:1:C601:42FF:FE0F:7
    10101000
    so 2001:DB8:0:1:C801:42FF:FE0F:7

  2. Duro
    February 28th, 2015

    Q4.Which IPv6 addresses should the engineer add to the documentation?

    A. 2001:DB8:0:1:C601:42FF:FE0F:7
    B. 2001:DB8:0:1:FFFF:C601:420F:7
    C. 2001:DB8:0:1:FE80:C601:420F:7
    D. 2001:DB8:0:1:C601:42FE:800F:7

    C601, in 6 we have the 7th bit. 6 in bit is equal 0110. The third bit (1) became 0 so we have in bit 0100 that’s in hex 4.
    Should be?
    2001:DB8:0:1:C401:42FF:FE0F:7

  3. Duro
    March 4th, 2015

    look
    but Theortically says the 7th bit turned in to 1. not 0.
    we don’t need to set this bit to 1 because it is already 1. it is rule. sorry my first comment is incorrect. but the question and the answer on this site are correct.

  4. Jamanu
    March 4th, 2015

    the curricula says that we must flip the 7th bit, i understand that we change the 0 to 1 and the 1 to 0.

  5. Jamanu
    March 4th, 2015

    I’d found this: “Globally unique addresses assigned by the IEEE originally have this bit set to zero, indicating global uniqueness” then we ever change the 0 to 1

  6. NIko
    March 19th, 2015

    This is the correct answer, in all the courses says that you have to invert the 7 bit.
    It doesnt says that set to 1 if the bit is 0. I have check this on all the books, INE and CBT material.

    Q4.Which IPv6 addresses should the engineer add to the documentation?
    A. 2001:DB8:0:1:C601:42FF:FE0F:7
    B. 2001:DB8:0:1:FFFF:C601:420F:7
    C. 2001:DB8:0:1:FE80:C601:420F:7
    D. 2001:DB8:0:1:C601:42FE:800F:7
    C601, in 6 we have the 7th bit. 6 in bit is equal 0110. The third bit (1) became 0 so we have in bit 0100 that’s in hex 4.
    Should be
    2001:DB8:0:1:C401:42FF:FE0F:7

  7. Nitish
    March 19th, 2015

    So wats the final sol to this????

  8. Run
    March 26th, 2015

    Actually the correct answer on Q4 is A, that is already 1 so we don’t need to flip/inverse it.

    From Jamanu:
    I’d found this: “Globally unique addresses assigned by the IEEE originally have this bit set to zero, indicating global uniqueness” then we ever change the 0 to 1

    Think about this:
    1 – Universally Unique in Ethernet MAC
    0 – Locally Unique addresses in Ethernet MAC

    So think about it, the address given is Global Unicast address so that the 7th bit should be 1.

  9. Fateh
    March 29th, 2015

    I have tried this mac address on an interface using the “mac-address” command … i then assigned IPV6 address using EUI-64. and the answer was: 2001:DB8:0:1:C401:42FF:FE0F:7

  10. John Rambo
    April 5th, 2015

    @fateh, you are right, you should invert the 7 bit no matter is if its 1 or 0 , just need to flip, the correct answer is 2001:DB8:0:1:C401:42FF:FE0F:7

    Unfortunately neither of the answers are correct, but the best answer of all its the one that includes FFFE in the middle of the IPv6 Address. Remember that this exams choose the “best of all the answers”.

  11. Anonymous
    April 15th, 2015

    q1, because of “without requiring both to be used for a single connection”, i feel “d” is better answer than “a”?

  12. Prezes
    April 26th, 2015

    @Anonymous, I think in the same way. QC Dual-stack means an interface has two addresses, Ip and Ipv6. NAT-PT can translate and forward different protocols on the egde of Enterprise or Company.

    Can someone confirm Q1 genuine answer? “A” or “D”?

  13. BOSS
    May 15th, 2015

    My two cents for Q4 – It should be the 7th bit should be flipped from 1 to 0. This was my understanding per my studies. So I went ahead and tested this on GNS3. Overall, the IPv6 ends up like “2001:DB8:0:1:C401:42FF:FE0F:7”

    Unless someone has a pretty good explanation on this, I am always flipping that 7th bit for IPv6 autoconfig via EUI-64.

    See output below:

    R7(config-if)#do sh int fa0/1
    FastEthernet0/1 is administratively down, line protocol is down
    Hardware is Gt96k FE, address is c601.420f.0007 (bia c207.48ea.0001)

    R7(config-if)#do sh ipv6 int fa0/1
    FastEthernet0/1 is administratively down, line protocol is down
    IPv6 is enabled, link-local address is FE80::C401:42FF:FE0F:7 [TEN]
    Global unicast address(es):
    2001:DB8:0:1:C401:42FF:FE0F:7, subnet is 2001:DB8:0:1::/64 [EUI/TEN]
    Joined group address(es):
    FF02::1
    FF02::1:FF0F:7
    MTU is 1500 bytes
    ICMP error messages limited to one every 100 milliseconds
    ICMP redirects are enabled
    ND DAD is enabled, number of DAD attempts: 1
    ND reachable time is 30000 milliseconds

  14. Richard
    May 17th, 2015

    Boss,

    You’re right! the 7th bit should flip from 1 if 0 and 1. But in real word, the first 8 bits are always zero.

    per RFC4291 2.5.1, The use of the universal/local bit in the Modified EUI-64 format identifier is to allow development of future technology that can take advantage of interface identifiers with universal scope, this may change in the future as the technology evolves.

  15. SzymonS89
    July 14th, 2015

    I have also always been under the impression that the 7th bit needs to be flipped no matter what it is. It’s a bit weird to not see the correct answer as one of the answers

  16. digitaltut
    July 24th, 2015

    @all: Because of copyrighted issue, we had to remove all the questions and answers. We can only keep the explanations. You can download all the questions and answers at: http://www.digitaltut.com/route-questions-and-answers

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    August 8th, 2015

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    December 6th, 2015

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  22. Sharing_IS_Caring
    March 17th, 2016

    Guys,
    I don’t know if this is clear for everyone or still needs some explanation. (A is the correct answer!)

    There are two different kinds of IPv6 addresses: global address & link-local address. You can configure them both manually, but if you only configure global address, then link-local will be generated automatically.

    How?
    Link-local auto-configuration mechanism will add FE80 at the beginning and FFFE at the middle of the MAC-address of the interface, while flipping the 7th bit ( either 1 to 0 or 0 to 1).

    Examples:

    If mac-address is: C601.420F.0007
    C6=1100 0110
    Link-local auto-configuration address will flip the 7th bit= 110001(1)0 = 11000100 = C4
    So the link-local address is : FE80::C401:42FF:FE0F:7

    If mac-address is: C401.420F.0007
    C4=1100 0100
    Link-local auto-configuration address will flip the 7th bit= 110001(0)0 = 11000110 = C6
    So the link-local address is : FE80::C601:42FF:FE0F:7

    Router simulation:
    R1(config-if)#mac-address C601.420F.0007
    R1(config-if)#ipv6 address 2001:DB8:0:1:C601:42FF:FE0F:7/64
    R1(config-if)#no shut
    R1(config-if)#end
    R1#sh ipv int br
    Ethernet0/0 [up/up]
    FE80::C401:42FF:FE0F:7 <<<<<<<<<<< link-local address is automatically generated
    2001:DB8:0:1:C601:42FF:FE0F:7
    !
    R1(config-if)#mac-address C401.420F.0007
    R1(config-if)#ipv6 address 2001:DB8:0:1:C401:42FF:FE0F:7/64
    R1(config-if)#do sh ipv int br
    Ethernet0/0 [up/up]
    FE80::C601:42FF:FE0F:7 <<<<<<<<<<< link-local address is automatically generated
    2001:DB8:0:1:C401:42FF:FE0F:7

    Good luck!

  23. Iordan144
    July 30th, 2016

    Q6 I was wrong. E is correct since it is IPv6 to IPv6, not IPv6 to IPv4.

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    October 4th, 2016

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  36. phillip
    January 17th, 2017

    Please correct answer reply..
    1. The enterprise network WAN link has been receiving several denial of service attacks from both
    IPv4 and IPv6 sources. Which three elements can you use to identify an IPv6 packet via its
    header, in order to filter future attacks? (Choose three.)
    A. Traffic Class
    B. Source address
    C. Flow Label
    D. Hop Limit
    E. Destination Address
    F. Fragment Offset
    Correct Answer: A,C,D –It is correct or any more
    2. Which three IP SLA performance metrics can you use to monitor enterprise-class networks?
    (Choosethree.)
    A. Delay
    B. Reliability
    C. Packet loss
    D. Traps
    E. Connectivity
    Correct Answer: A,C,E–Pls say to correct answer
    3. Refer to the following configuration command.
    Router(config)# ip nat inside source static tcp 172.16.10.8 8080 172.16.10.8 80
    Which statement about the command is true ?
    A. Any packet that is received in the inside interface with a source IP port address of
    172.16.10.8:80 is translated to 172.16.10.8:8080.
    B. Any packet that is received in the inside interface with a source IP port address of
    172.16.10.8:8080 is transtated to 172.16.10.8:80.
    C. The router accepts only a TCP connection from port 8080 and port 80 on IP address
    172.16.10.8.
    D. Any packet that is received in the inside interface with a source IP address of 172.16.10.8 is
    redirected to port 8080 or port 80.
    Correct Answer: A—Pls correct answer say to me .., anybody
    reply
    phillip January 17th, 2017
    Please give me a answer in the following IPv6 Question .
    Which two statements are true about 6to4 tunnels? (Choose two.)
    A. In a 6to4 tunnel, the first two bytes of the IPv6 address will be 0?002 and the next four bytes will be the hexadecimal equivalent of the IPv4 address.
    B. In a 6to4 tunnel, the first two bytes of the IPv6 address will be locally derived and the next two bytes will be the hexadecimal equivalent of the IPv4 address.
    C. In a 6to4 tunnel, the IPv4 address 192.168.99.1 would be converted to the 2002:c0a8:6301::/48 IPv6 address.
    D. In a 6to4 tunnel, the IPv4 address 192.168.99.1 would be converted to the 2002:c0a8:6301::/16 IPv6 address.
    E. In a 6to4 tunnel, the IPv4 address 192.168.99.1 would be converted to the 2002:1315:4463:1::/64 IPv6 address.
    Anonymous August 11th, 2016

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