English
Menu

Network Design and Operations

An interface with MAC address 00-1A-2B-3C-4D-5E creates an address with SLAAC from the prefix 2001:db8:1:1::/64 and an interface ID in the EUI-64 format. Which address results?

  1. A2001:db8:1:1:21a:2bff:fe3c:4d5e
  2. B2001:db8:1:1:1a:2bff:fe3c:4d5e
  3. C2001:db8:1:1:21a:2bfe:ff3c:4d5e
Show answer and explanation

Answer: A. 2001:db8:1:1:21a:2bff:fe3c:4d5e

In the EUI-64 format, the 48-bit MAC address is split into its upper 24 bits and lower 24 bits, and FF-FE is inserted between them to make 64 bits. Inserting it between 00-1A-2B and 3C-4D-5E gives 00-1A-2B-FF-FE-3C-4D-5E. In addition, the second-lowest bit of the first byte (the U/L bit) is inverted, so 00 becomes 02, giving 02-1A-2B-FF-FE-3C-4D-5E. Grouping this into 16-bit pieces and dropping leading zeros in each gives 21a:2bff:fe3c:4d5e, and with the prefix the address is 2001:db8:1:1:21a:2bff:fe3c:4d5e. Because an address that reveals the MAC address makes the host easier to track, most current operating systems use interface IDs based on random values.

  • A. Correct. FF-FE is inserted and the U/L bit is inverted.
  • B. This is the value without inverting the U/L bit. The leading 00 becomes 02.
  • C. This inserts FE-FF instead. The bytes inserted are FF-FE, in that order.
Practice this topic Back to topic

Related calculators

IP address and subnet calculatorFind the network and broadcast addresses, host range and host count from an IP address and a prefix or mask, with a binary view and subnet splittingDijkstra's algorithm calculatorCompute shortest paths and distances from a list of weighted edges, and follow each step of finalizing vertices in a table and a diagram

Books on Network Design and Operations Ad

As an Amazon Associate I earn from qualifying purchases.

More Network Design and Operations questions

  1. Two sites that run only IPv6 are to be connected through a network that runs only IPv4, and the traffic between the sites should remain IPv6 packets. Which method is appropriate?
  2. In traceroute, what value is the TTL in the IP header set to in the packet sent to make the fourth router from the source return an ICMP Time Exceeded message?
  3. Running traceroute from a host to web server 198.51.100.80 showed, on lines 1 to 5, 192.168.1.1, 10.0.0.1, "* * *" (no response), 203.0.113.1 and 198.51.100.80, in that order, and the web server could be used without problems. Which is the most appropriate interpretation of line 3?
  4. In IPv4, a packet with a total length of 4000 bytes (a 20-byte header and 3980 bytes of data) is split up (fragmented) on a link with an MTU of 1500 bytes. The fragments also have 20-byte headers, and fragmentation is allowed. What is the value of the fragment offset field in the last fragment?
  5. A host communicates with a distant web server through a site-to-site VPN tunnel. TCP connections can be established and small pages load, but large file downloads stall partway. The MTU inside the tunnel is 1400 bytes, and the server sends 1500-byte packets with fragmentation prohibited (the DF bit set to 1). The firewall in front of the server is also set to discard all ICMP. Which is the most likely cause?

Comparisons in this topic