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IPv6_Part3.md

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33. IPv6 : PART 3

CORRECTION TO PRIOR LECTURES:

RFC Requirements for IPv6 Address Representation

  • Leading 0s MUST be removed
    • This - 2001 : 0db8 : 0000 : 0001 : 0f2a : 4fff : fea3 : 00b1
    • Becomes - 2001 : db8 : 0 : 1 : f2a : 4fff : fea3 : b1
  • :: MUST be used to shorten the longest string of all-0 quartets
    • If there is only ONE all-0 quartet, don’t use ‘::’
    • This - 2001 : 0000 : 0000 : 0000 : 0f2a : 0000 : 0000 : 00b1
    • Becomes - 2001 :: f2a : 0 : 0 : b1
  • If there are two equal-length choices for the :: , use :: to the shorten the one on the LEFT
    • This - 2001 : 0db8 : 0000 : 0000 : 0f2a : 0000 : 0000 : 00b1
    • Becomes - 2001 : db8 :: f2a : 0 : 0 : b1
  • Hexadecimal characters ‘a’, ‘b’, ‘c’, ‘d’, ‘e’, and ‘f’ MUST be written using lower-case, NOT upper case A B C D E F

IPv6 HEADER

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Length is ALWAYS 40 bytes (Fixed Header)

Version (4 bits)

  • Indicates version of IP used
  • Fixed value of ‘6’ (0b0110) to indicate IPv6

Traffic Class (8 bits)

  • Used for QoS (Quality of Service) to indicate high-priority traffic
  • Example: IP phone traffic, live video calls, etc.

Flow Label (20 bits)

  • Identifies specific traffic “flows” (communication between Source and Destination)

Payload Length (16 bits)

  • Indicates the LENGTH of the PAYLOAD (the encapsulation LAYER 4 SEGMENT) in bytes
  • The length of the IPv6 header, itself, isn’t included, because it’s ALWAYS 40 bytes

Next Header (8 bits)

  • Indicates the TYPE of the ‘next header’ (header of the encapsulated SEGMENT)
    • Example: TCP or UDP
  • Same function as the IPv4 header’s ‘Protocol’ field

Hop Limit (8 bits)

  • Value in this field decrements by 1 every time a ROUTER forwards it. If it reaches ‘0’, the PACKET is discarded (similar to IPv4 TTL field )

Source Address (128 bits)

  • Packet’s SOURCE address

Destination Address (128 bits)

  • Packet’s DESTINATION address

SOLICITED-NODE MULTICAST ADDRESS

  • An IPv6 SOLICITED-NODE Multicast Address is calculated from a UNICAST ADDRESS

How to generate a SOLICITED-NODE Multicast Address

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Note the automatically joined group addresses for this IPv6 Interface

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NEIGHBOR DISCOVERY PROTOCOL (NDP)

  • NEIGHBOR DISCOVERY PROTOCOL (NDP) is a PROTOCOL used with IPv6

  • It has various functions and one of those functions is to replace ARP, which is no longer used in IPv6

  • The ARP-like function of NDP uses ICMPv6 and SOLICITED-MODE Multicast Addresses to learn the MAC ADDRESS of other HOSTS (ARP in IPv4 uses Broadcast Messages)

  • TWO MESSAGES types are used:

      1. NEIGHBOR SOLICITATION (NS)
      • ICMPv6 Type 135
      1. NEIGHBOR ADVERTISEMENT (NA)
      • ICMPv6 Type 136

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IPv6 NEIGHBOR TABLE

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  • Another function of NDP allows HOSTS to automatically discover ROUTERS on the LOCAL NETWORK

  • TWO MESSAGES are used for this process:

    • ROUTER SOLICITATION (RS)

      • ICMPv6 Type 133
      • Sent to Multicast Address FF02::2 (All Routers)
      • Asks ALL ROUTERS on the Local Link to identify themselves
      • Sent when an INTERFACE is enabled / HOST is connected to the NETWORK

    • ROUTER ADVERTISEMENT (RA)

      • ICMPv6 Type 134
      • Sent to Multicast Address FF02::1 (All Nodes)
      • The ROUTER announces its presence, as well as other information about the link
      • These messages are sent in response to RS messages
      • They are also sent periodically, even if the ROUTER hasn’t received an RS

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SLAAC

  • Stands for STATELESS ADDRESS AUTO-CONFIGURATION
  • HOSTS use the RS / RA messages to learn the IPv6 Prefix of the LOCAL LINK (ie: 2000:db8:: /64) and then automatically generate an IPv6 Address
  • Using the ipv6 address prefix / prefix-length eui-64 command, you need to manually enter the prefix
  • Using the ipv6 address autoconfig command, you DON’T need to enter the prefix. The device uses NDP to learn the prefix used on the local link
  • The device will use EUI-64 to generate the INTERFACE ID or it will be randomly generated (depending on the device / maker)

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DUPLICATE ADDRESS DETECTION (DAD)

  • One final point about NDP!
  • Duplicate Address Detection (DAD) allows HOSTS to check if other devices on the Local Link are using the same IPv6 Address
  • Any time an IPv6-enabled interface initializes (no shutdown command) or an IPv6 ADDRESS is configured on an INTERFACE (by any method: manual, SLAAC, etc.) it performs DAD
  • DAD uses TWO MESSAGES you learned earlier : NS and NA
  • The HOST will send an NS to its own IPv6 ADDRESS.
    • If it doesn’t get a reply, it KNOWS the ADDRESS is unique
    • If it DOES get a reply, it means ANOTHER HOST on the NETWORK is already using that ADDRESS

IPv6 STATIC ROUTING

  • IPv6 ROUTING works the same as IPv4 ROUTING
  • However, the TWO processes are separate on the ROUTER, and the TWO routing tables are separate, as well.
  • IPv4 ROUTING is enabled BY DEFAULT
  • IPv6 ROUTING is disabled BY DEFAULT
    • MUST BE ENABLED with the ipv6 unicast-routing command
  • If IPv6 ROUTING is disabled, the ROUTER will be able to SEND and RECEIVE IPv6 traffic, but will not route IPv6 traffic (ie: will NOT FORWARD it between NETWORKS)

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  • A CONNECTED NETWORK ROUTE is automatically added for EACH CONNECTED NETWORK
  • A LOCAL HOST ROUTE is automatically added for each ADDRESS configured on the ROUTER
  • Routes for Link-Local ADDRESSES are not added to the ROUTING TABLE

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Everything is configured similar to normal static routes in IPv4

[AD] = Administrative Distance. You NEED this value in order to configure a STATIC ROUTE

DIRECTLY ATTACHED Static Route:

  • Only the EXIT INTERFACE is specified
  • ipv6 route destination / prefix-length exit-interface
  • Example : ~~R1(config)# ipv6 route 2001:db8:0:3:: /64 g0/0~~
💡 In IPv6, you CANNOT use DIRECTLY ATTACHED Static Routes if the INTERFACE is an ETHERNET INTERFACE

RECURSIVE Static Route:

  • Only the Next-Hop is specified
  • ipv6 route destination / prefix-length next-hop
  • Example: R1(config)# ipv6 route 2001:db8:0:3::/64 2001:db8:0:12::2

FULLY SPECIFIED Static Route:

  • Both the Exit Interface and Next Hop are specified
  • ipv6 route destination / prefix-length exit-interface next-hop
  • Example: R1(config)# ipv6 route 2001:db8:0:3::/64 g0/0 2001:db8:0:12::2

(NOTE THAT THESE ROUTES ARE ALL RECURSIVE : They specify the Next-Hop)

NETWORK ROUTE:

R1(config)# ipv6 route 2001:db8:0::/64 2001:db8:0:12::2

This is a route to R3/PC2 NETWORK via R2’s G0/0 INTERFACE

(We did this in Day 32’s Lab)

HOST ROUTE:

R2(config)# ipv6 route 2001:db8:0:1::100/128 2001:db8:0:12::1

R2(config)# ipv6 route 2001:db8:0:3::100/128 2001:db8:0:23::2

This is a route from R2 to PC1 and PC2 using the “next hop” ADDRESSES of R1 and R3 G0/0 INTERFACES

Note the /128 prefix. This is how SPECIFIC IPv6 ADDRESSES are written

DEFAULT ROUTE:

R3(config)# ipv6 route ::/0 2001:db8:0:23::1

::/0 is the IPv6 equivalent of 0.0.0.0/0 in IPv4

FLOATING STATIC ROUTES:

  • Require you to increase the [AD] number HIGHER than the currently used NETWORK IGP AD value

LINK-LOCAL NEXT HOPS:

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You HAVE to specify the INTERFACE name when using Link-Local Next-Hops

This is EXACTLY like a FULLY-SPECIFIED STATIC ROUTE