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33. IPv6_Part3

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Corrections to Prior Lectures

RFC Requirements for IPv6 Address Representation

  • Leading Zeros: Must be removed.

    • Example: 2001:0db8:0000:0001:0f2a:4fff:fea3:00b1
    • Becomes: 2001:db8:0:1:f2a:4fff:fea3:b1

  • Longest Sequence of All-Zero Quartets: Use :: to shorten.

    • If there is only one all-zero quartet, do not use ::.
    • Example: 2001:0000:0000:0000:0f2a:0000:0000:00b1
    • Becomes: 2001::f2a:0:0:b1

  • Two Equal-Length Choices for ::: Use :: to shorten the leftmost sequence.

    • Example: 2001:0db8:0000:0000:0f2a:0000:0000:00b1
    • Becomes: 2001:db8::f2a:0:0:b1

  • Hexadecimal Characters: Must be written in lowercase.

    • Use a, b, c, d, e, f instead of A, B, C, D, E, F.

IPv6 Header

IPv6 Header

Fixed Header Length

  • The IPv6 header is always 40 bytes.

Header Fields

  • Version (4 bits):

    • Indicates the IP version used.
    • Fixed value: 6 (0b0110) for IPv6.

  • Traffic Class (8 bits):

    • Used for Quality of Service (QoS) to prioritize traffic, such as IP phone calls or live video.

  • Flow Label (20 bits):

    • Identifies specific traffic flows between the source and destination.

  • Payload Length (16 bits):

    • Specifies the length of the payload (Layer 4 segment) in bytes.
    • The IPv6 header itself is not included in this length, as it is always 40 bytes.

  • Next Header (8 bits):

    • Indicates the type of the next header (e.g., TCP or UDP).
    • Equivalent to the IPv4 header’s “Protocol” field.

  • Hop Limit (8 bits):

    • Decrements by 1 each time a router forwards the packet. If it reaches 0, the packet is discarded, similar to the TTL field in IPv4.

  • Source Address (128 bits):

    • The address of the packet’s source.

  • Destination Address (128 bits):

    • The address of the packet’s destination.

Solicited-Node Multicast Address

  • Purpose: An IPv6 solicited-node multicast address is derived from a unicast address.

Generating a Solicited-Node Multicast Address

Solicited-Node Multicast Address Generation

Group Addresses for IPv6 Interface

Group Addresses

Neighbor Discovery Protocol (NDP)

  • Overview: NDP is used with IPv6 to replace ARP from IPv4. It employs ICMPv6 and solicited-node multicast addresses to discover MAC addresses.

Message Types

  • Neighbor Solicitation (NS):

    • ICMPv6 Type 135.

  • Neighbor Advertisement (NA):

    • ICMPv6 Type 136.

NDP Messages Neighbor Discovery Messages

Neighbor Table

Neighbor Table

  • Router Discovery: NDP also enables hosts to discover routers on the local network.

Router Discovery Messages

  • Router Solicitation (RS):

    • ICMPv6 Type 133.
    • Sent to multicast address FF02::2 (All Routers).
    • Requests routers on the local link to identify themselves when an interface is enabled or a host connects to the network.

  • Router Advertisement (RA):

    • ICMPv6 Type 134.
    • Sent to multicast address FF02::1 (All Nodes).
    • Announcements from routers about their presence and other link information.
    • Sent in response to RS messages and periodically.

Router Discovery Messages

Stateless Address Auto-Configuration (SLAAC)

  • Definition: SLAAC allows hosts to automatically configure their IPv6 addresses using RS/RA messages.

  • Commands:

    • Manual prefix entry: ipv6 address prefix/prefix-length eui-64.
    • Auto-configured prefix: ipv6 address autoconfig, where the device uses NDP to determine the local prefix.

  • Interface ID Generation: Can be done using EUI-64 or randomly generated, depending on the device.

SLAAC

Duplicate Address Detection (DAD)

  • Purpose: DAD ensures that an IPv6 address is unique on the local link.

  • Process:

    • Performed when an interface is initialized or an IPv6 address is configured.
    • Uses NS and NA messages:
      • The host sends an NS to its own address.
      • If no reply is received, the address is unique.
      • If a reply is received, another device is using the same address.

IPv6 Static Routing

  • Routing Basics:

    • IPv6 routing operates similarly to IPv4 but with separate processes and tables.
    • IPv4 routing is enabled by default; IPv6 routing is disabled by default and must be enabled with ipv6 unicast-routing.

  • Automatic Routes:

    • Connected Network Route: Added automatically for each connected network.
    • Local Host Route: Added automatically for each address configured on the router.
    • Link-Local addresses are not included in the routing table.

Static Routing Static Routing Example Routing Table

Static Route Types

  • Directly Attached:
    • Only the exit interface is specified.
    • Command: ipv6 route destination/prefix-length exit-interface.
    • Example: ipv6 route 2001:db8:0:3::/64 g0/0.

  • Recursive:

    • Only the next-hop address is specified.
    • Command: ipv6 route destination/prefix-length next-hop.
    • Example: ipv6 route 2001:db8:0:3::/64 2001:db8:0:12::2.

  • Fully Specified:

    • Both exit interface and next-hop address are specified.
    • Command: ipv6 route destination/prefix-length exit-interface next-hop.
    • Example: ipv6 route 2001:db8:0:3::/64 g0/0 2001:db8:0:12::2.

Recursive Routes Example

  • Network Route:

    • Command: ipv6 route 2001:db8:0::/64 2001:db8:0:12::2.
    • Routes to R3/PC2 network via R2’s G0/0 interface.

  • Host Route:

    • Command: ipv6 route 2001:db8:0:1::100/128 2001:db8:0:12::1.
    • Command: ipv6 route 2001:db8:0:3::100/128 2001:db8:0:23::2.
    • Routes to specific hosts PC1 and PC2 via next-hop addresses of R1 and R3 G0/0 interfaces.

  • Default Route:

    • Command: ipv6 route ::/0 2001:db8:0:23::1.
    • Equivalent to 0.0.0.0/0 in IPv4.

Floating Static Routes

  • Configuration: Requires increasing the Administrative Distance (AD) above the current IGP AD value.

Link-Local Next Hops

  • Note: When using link-local next hops, specify the interface name, similar to a fully specified static route.

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