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IPv6 Questions

July 20th, 2017 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. 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

  2. Baqah
    March 13th, 2017

    I think the Answer is (B) because when the packet arrives at the inside interface it will be translated from 8080 to 80 and when arrives at the outside interface it will be translated back to 8080 (80 to 8080)… if I am wrong then correct me… thank you

  3. Baqah
    March 13th, 2017

    Note that the configuration description for the static NAT command indicates any packet received in the inside interface with a source address of 172.16.10.8:8080 is translated to 172.16.10.8:80. This also implies that any packet received on the outside interface with a destination address of 172.16.10.8:80 has the destination translated to 172.16.10.8:8080.

    http://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/13772-12.html#

  4. jokie
    August 2nd, 2017
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    November 8th, 2017

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    November 9th, 2017

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    November 21st, 2017

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    November 28th, 2017

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    November 28th, 2017
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    November 29th, 2017

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  15. 1Way
    January 9th, 2018

    Q1 Explanation needs a citation as that is not my understanding of dual stack. My understanding is that dual stack uses both IPv4 and IPv6 on single connection and certainly does not do any IPv4 IPv6 conversion without a suitable tunnelling protocol.

    If the question is ‘Which method allows IPv4 and IPv6 to work together without requiring both to be used for a single connection during the migration process?’ Then the answer should be ‘D’ or possible ‘B’ to a lesser extent.

    Happy to be corrected on this though and welcome others thoughts.

  16. 1WAY
    January 9th, 2018

    Revising my above comment to say only ‘D’ (NAT-PT) is the correct answer as ‘B’ (6to4 tunnelling) requires both tunnel termination end points to support IPv4 and IPv6.

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