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Difficulty: MediumFirst Hop Redundancy Protocols (HSRP and VRRP)

A network administrator captures traffic on an Ethernet segment and identifies an ARP reply originating from a virtual default gateway with the MAC address 0000.5E00.01140000.5E00.0114. Which protocol and group number generated this virtual MAC address?

  1. VRRP with group number 20Answer
  2. B
    HSRP version 1 with group number 20
  3. C
    VRRP with group number 14
  4. D
    HSRP version 2 with group number 14

Answer

VRRP with group number 20 is correct because VRRP for IPv4 utilizes the virtual MAC address format 0000.5E00.01XX0000.5E00.01XX, where the last byte 1414 in hexadecimal corresponds to decimal group number 20.
VRRP for IPv4 assigns virtual MAC addresses using the IANA OUI prefix 0000.5E00.01XX0000.5E00.01XX, where XXXX is the group identifier in 2-digit hexadecimal. Converting hexadecimal 1414 to decimal results in group 20.

Step-by-Step Solution

1
Identify the protocol vendor prefix from the virtual MAC address
The MAC address 0000.5E00.01140000.5E00.0114 uses the prefix 0000.5E00.01XX0000.5E00.01XX, which is standard for VRRP IPv4 router redundancy.
VRRP specifies 00−00−5E−00−01−XX00-00-5E-00-01-XX as its standard virtual MAC address block, whereas HSRP v1 uses 00−00−0C−07−AC−XX00-00-0C-07-AC-XX and HSRP v2 uses 00−00−0C−9F−FX−XX00-00-0C-9F-F X-XX.
2
Convert the final byte from hexadecimal to decimal to determine the group number
1416=(1×161)+(4×160)=16+4=2014_{16} = (1 \times 16^1) + (4 \times 16^0) = 16 + 4 = 20
The last byte of the VRRP virtual MAC address encodes the group number in hexadecimal notation.

Key Concept

VRRP and HSRP Virtual MAC Address Formats and Group Encoding
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Topics

First Hop Redundancy Protocols (HSRP and VRRP)

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