Answer to the 2nd IPv6 Addressing Question

By certskills May 22, 2013 09:00

Shortie: Q113-answer

Quick hitter – answer to the 2nd IPv6 addressing question!

The Answer

(Wendell’s note to self: internal question number 113.)

Answer(s): A, C

The Explanation

You need to know a couple of facts to answer this question:

  • The packet that flows through multiple routers, from host A to server S1, needs to use routable IPv6 addresses.
  • The source IPv6 address must be a unicast IPv6 address.
  • Two ranges exist:
    • Unique local – begins FD
    • Global unicast – literally, has many prefixes, but most often begins with hex 2 or 3

Armed with these two facts, a quick scan shows two such IPv6 addresses, at answers A and C.


Answer to the IPv6 Addressing Question
#CCENT and #CCNA Fast Start: Port Security
By certskills May 22, 2013 09:00
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  1. Dirck Copeland July 15, 10:11

    Wendall, I’m looking at the ICND1 100-101 Cert Guide and in the IPv6 part VII page 716 Figure 26-4 shows the IPv6 address in the example 2001:DB8:1111::/48 (with only 3 hex digits in the second group of colon separated values).

    In the rest of the examples on the following pages you show it as 2001:0DB8:1111::/48.

    Is this a valid IPv6 address or just a typo on page 716?

    Reply to this comment
    • CCENTSkills July 15, 17:20

      Hi Dirck,
      Actually, both are correct. The instances with DB8 in the 2nd quarter simply abbreviate by dropping the leading hex 0. In this case, the explanation about figure 26-5 emphasized the prefix length (both in binary and number of hex digits), so to make sure the number of digits was obvious, I showed the unabbreviated numbers. I probably could have followed that same convention in Figure 26-4 as well. Sorry for the misdirection.

      Reply to this comment
      • Dirck Copeland July 16, 10:38

        Thanks Wendall for the clarification. I was thinking about the rules as stated in RFC 4291 section 2.2.2 that talks about the special syntax that allows the zeros to be compressed and replaced by :: but can only occur once in the address. I was not aware of the note in the previous section 2.1.1 that says you can leave off the leading zeros in an individual field and compress the zeros.

        Reply to this comment
  2. adrikayak December 3, 04:10

    Hello Wendell

    Looks like the link to this answer’s question points toward the answer of question 112 instead (

    Reply to this comment
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