Part 7 – IP version 6

Fundamentals of IPv6



FE00:0:0:1:0:0:0:56 << removing leading zeros
FE00:0:0:1::56 << double colon
FE:0:0:1::56 << wrong
FE00::1::56 << wrong
  • What is the IPv6 prefix value range?
    • 0 – 128
  • How do you calculate the prefix of an IPv6 address?
    • ipv6-prefix.PNG
  • What is the prefix of the following IPv6  address?

    • 2000:1234:5678:9A00:0000:0000:0000:0000/56
  • What is global routing prefix?
    • It’s like an IPv4 network or CIDR address block. This can be assigned to a specific company for example and all IP of that company should begin with this prefix.
  • What IPv6 address types do you know? How do they begin?
    • ipv6-address-types.PNG
  • IPv4 has a subnet and a host field. How does the IPv6 sturcture look like?
    • first global routing prefix, which should be same in an enterprise
    • second is the subnet field
    • in the end is the interface ID, which acts like the host field in IPv4
  • What are Unique Local Unicast Addresses? How can you recognize one?
    • They are similar to IPv4 private addresses. They are not registered with any numbering authority and can be used by multiple organizations.
      They begin with “FD”
  • What is the difference between the global and unique local unicast?
    • Global Unicast: You ask for a prefix.
    • Unique Local Unicast: You create the prefix locally. The prefix is 48 bits long (FD and 40 random bit).
  • Why should or shouldn’t you use a prefix like (company environment): FD00:1:1::/48 ?
    • In case you merge a company with another there is a chance that both use the same “easy to remember” IPv6 Unique Local network. In this case the merge is quite a pain..

Implementing IPv6 Addressing on Routers

  • What is the command to configure an IPv6 address?
    • ipv6 address address/prefix-length
  • What else do you need for IPv6 communication (nothing else configured yet)?
    • Enable IPv6 globally: ipv6 unicast-routing
  • How do you check the IPv6 address of an interface?
    • sho ipv6 interface brief
    • sho ipv6 interface
  • How can you dynamically configure a host via IPv6?
    •  DHCP
    • SLAAC (Stateless Address Auto Configuration(
  • How can you configure predictable IPv6 addresses?
    • static configuration
      ipv6 address address/prefix-length
    • EUI-64 (extended unique identifier)
  • How does EUI-64 work?
    • eui64
  • What is the 5th step in the above example? What are the results of the above examples?
    • EUI64-convert.PNG
  • How do you configure an EUI-64 address?
    • ipv6 address address/prefix-length eui-64
  • What are the 2 options of static IPv6 address configuration?
    • You can configure the whole address statically
    • You can configure the subnet statically and leave the rest for EUI-64.
  • What configuration needed on the interface to learn the IP via DHCP or SLAAC?
    • DHCP: ipv6 address dhcp
    • SLAAC: ipv6 address autoconfig
  • What is a Link-Local address? What is it used for?
    • It is a unicast address which is generated automatically. It will never leave the local data link as the routers do not forward it.
    • Used for some overhead protocols and as for the next-hop address of IPv6 routes.
  •  How are Link-Local addresses generated?
    • First 64bits are always the same (4 variation):
      • FE80::/10
      • FE90::/10
      • FEA0::/10
      • FEB0::/10
    • The remaining 64 bits can be generated differently.. Cisco uses EUI-64
    • Or the remaining 64 bits can be configured manually:
      ipv6 address address link-local
  • What is the difference between Broadcast and Multicast?
    • Broadcast: all devices in the subnet receive the message and they need to decide (CPU) whether they need to reply.
    • Multicast: if a device doesn’t “listen” to a specific multicast address then it will not process the packet at all. This saves CPU!
  • How far can a multicast packet travel?
    • link-local scope multicast: stays in the subnet (as broadcast)
    • organization-local scope: packet can leave the subnet
  • How do you know which multicast group is an interface joined?
    • sho ipv6 interface name
  • What is solicited-node multicast address? How does it work?
    • This packet is sent to all device which unicast address has the same value in the last 6 hex digits.
    • structure:
  • Which IPv6 IPs have the same function as IPv4 and
    •    ::
    • ::1

Implementing IPv6 Addressing on Hosts

  • Note:
  • What functions do the Neighbor Discovery Protocol have?
    • SLAAC: Stateless Address Autoconfiguration learns the first part of its address plus the prefix.
    • Router discovery: learns IPv6 addresses in the subnet
    • Duplicated Address Detection (DAD)
    • Neighbor MAC discovery: NDP replaces IPv4 ARPalso:
    • Router Solicitation (RS): sent to “all IPv6 routers” FF02::2 to identify themselfs (local link only)
    • Router Advertisement (RA): The message lists many facts including link-local IPv6 addresses of the router. It is sent as a reply to RS but also sent periodically without request.
  • How do a router get the MAC address of an IPv6 address (ipv4 arp)?
    • As a part of NDP:
    • Neighbor Solicitation (NS): Asks for the MAC of an IPv6
    • Neighbor Advertisement (NA):  Replies to the NS (unicast) with the MAC
  • What is the “ARP table” called in IPv6?
    • NDP neighbor table
  • How DAD works?
    • The host sends an NS message targeting the address the host wan to use. If no other host replies with NA the IP is free.
  • What is the difference between DHCP ipv4 and Stateful DHCPv6?
    • DHCP v6 doesn’t supply default router information. The host learn the default router via NDP.
  • What is SLAAC and how does it work?
    • Stateless Address Autoconfiguration
    • Alternative of DHCP. The host learns the IPv6 prefix on the link (NDP) then creating it’s own IPv6 address using the learned prefix and EUI-64 or random number. After it has the IP the host also check with DAD whether the IP is in use.
  • What is the one thing that SLAAC cannot provide? What is the solution?
    • DNS server IP
    • Stateless DHCPv6 (providing only DNS IP):



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