A network engineer is deploying IPv6 across an enterprise branch using the assigned global… — Cisco CCNA

A network engineer is deploying IPv6 across an enterprise branch using the assigned global unicast prefix $2001:\text{db8}:85\text{a}3::/48$ . Interfaces are set to use SLAAC with EUI-64 interface identifier generation. Which two statements correctly describe the prefix subnetting and EUI-64 address generation for this implementation? (Select TWO.)

Subnetting the $2001:\text{db8}:85\text{a}3::/48$ prefix into standard $/64$ subnets yields $65,536$ ( $2^{16}$ ) unique subnets.Answer
A host with MAC address $70:6\text{D}:15:\text{AB}:\text{CD}:\text{EF}$ using EUI-64 auto-configuration generates the interface identifier $726\text{D}:15\text{FF}:\text{FEAB}:\text{CDEF}$ .Answer
C
Subnetting the $/48$ prefix into $/64$ subnets yields $65,534$ usable subnets because the first and last subnets are reserved for network and broadcast identities.
D
Generating an EUI-64 interface ID from a 48-bit MAC address requires inserting the 16-bit hex value $\text{FFFF}$ between the OUI and vendor-assigned serial number.
E
The prefix $2001:\text{db8}:85\text{a}3::/48$ falls within the Unique Local IPv6 address block allocated for non-routable private enterprise networks.

Answer

Subnetting a

/48

prefix into

/64

subnets produces

65,536

unique subnets, and converting the MAC address

70:6\text{D}:15:\text{AB}:\text{CD}:\text{EF}

via EUI-64 produces

726\text{D}:15\text{FF}:\text{FEAB}:\text{CDEF}

Subnetting a

/48

prefix to

/64

provides

16

subnet bits (

64 - 48 = 16

), giving

2^{16} = 65,536

subnets without subtracting any reserved subnets. Additionally, converting the MAC address

70:6\text{D}:15:\text{AB}:\text{CD}:\text{EF}

to EUI-64 splits the address into

706\text{D}:15

and

\text{AB}:\text{CD}:\text{EF}

, inserts

\text{FFFE}

to form

706\text{D}:15\text{FF}:\text{FEAB}:\text{CDEF}

, and flips the 7th bit of

0\text{x}70

(

0111\,0000_2

) to

0\text{x}72

(

0111\,0010_2

), giving

726\text{D}:15\text{FF}:\text{FEAB}:\text{CDEF}

Step-by-Step Solution

Calculate the available subnet bits and total subnets from

/48

/64

Subnet bits =

64 - 48 = 16

. Total subnets =

2^{16} = 65,536

IPv6 does not deduct subnets for network or broadcast designations.

Perform EUI-64 interface ID conversion on MAC address

70:6\text{D}:15:\text{AB}:\text{CD}:\text{EF}

Insert

\text{FFFE}

between

70:6\text{D}:15

and

\text{AB}:\text{CD}:\text{EF}

to get

706\text{D}:15\text{FF}:\text{FEAB}:\text{CDEF}

. Flip the 7th bit of byte

1

(

0\text{x}70 = 0111\,0000_2 \rightarrow 0111\,0010_2 = 0\text{x}72

), yielding

726\text{D}:15\text{FF}:\text{FEAB}:\text{CDEF}

EUI-64 standard requires inserting

\text{FFFE}

in the center of the MAC address and setting the U/L bit to 1 for globally unique scope.

Key Concept

IPv6 Subnetting & EUI-64 Address Generation

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic