IPv6 notes

This topic will be updated with additional notes all the time..

– 128 bit hexadecimal address format.
– 16bit every field.
– 8 fields totally.
– Global Unicast addresses (similar to ipv4 public addresses)
– Link Local addresses (are used only between two connected routers, significant only on the same segment. Are also used for ipv6 routing protocols e.g: OSPFv3, EIGRPv6, RIPng, etc).

IPv6 Packet Header, only 8 fields:
Version: version of IP (6 in this case).
Payload Length: the length of the IP packet excluding the header. (In this field is the Extension Header aswell).
Next Header: this is a value that identifies the header after IPv6 header, can be upper-layer header (TCP, UDP, ICMP etc) or IPv6 Extension Header.
Hop Limit: same as TTL in IPv4.
Source Address: The IP address of the packet originator.
Destination Address: The destination of the packet.
Traffic Class: QoS classification.
Flow Label: QoS classification.

Recommended order of the Extension Headers in the packet:
1. IPv6 main header
2. Hop-by-Hop Options header (if it is present, it Must be the first one following the main header)
3. Destination Options header
4. Routing header
5. Fragment header
6. Authentication header
7. Encapsulating Security Payload header
8. Destination Options header
9. Upper-layer header (ICMPv6, TCP, UDP)


IPv6 address types (using first digits):
1) 00 – Unspecified or loopback, also used as source when no Ipv6 address present.
2) 2 and 3 – Aggregatable global unicast addresses.
3) FE8 – Link Local (Routing protocols use link local addresses).
4) FEC – Site Local (same as IPv4 private range addresses).
5) FF – Multicast.

Well known IPv6 addresses:
FF02::1 – All IPv6 hosts (in IPv4
FF02::2 – All IPv6 routers (in IPv4
FF02::5 – All OSPFv3 routers (in IPv4
FF02::6 – OSPFv3 Designated Routers (in IPv4
FF02::A – EIGRP Routers (in IPv4

– In multipoint non-broadcast interfaces when using IPv6 there is no Proxy ARP like in IPv4, therefore static routing should be configured accordingly (next hop IPv6 address should be configured instead of just the outgoing interface).
– Second solution could be to configure static arp entries (e.g: mac address mapping to specific IPv6 address). Generally this is a Layer 3 to Layer 2 resolution problem.

– If IPv6 is enabled on interface mode only (Ipv6 enable) without the global configuration (ipv6 unicast-routing), the router will enable ipv6 link-local address only, but routing is not possible.

– IPv6 mainly uses access-lists for traffic filtering, and prefix-lists for routing advertisement/updates filtering, but this is user specific preference.

IPv6 address Autoconfiguration:
1) Stateful autoconfiguration – using DHCPv6 an entire /128 IPv6 address is assigned to a host or router.
2) Stateless autoconfiguration – dynamically assigns a host or router a /64 bit prefix and the rest 64bit the host derives using the EUI-64 method.

EUI-64 method:
– Last 64 bits of IPv6 address.
– Mac address of physical link is taken (48 bit) plus 16 bits hexadecimal value (FFFE) is put in the middle of mac address.

Neighbor Discovery Protocol (NDP):
NDP consists of 5 types of ICMPv6 messages:
– Router Advertisement (RA): Router advertises his presence and link prefixes, MTU, hop limits. RA is sent to multicast address FF02::1.
– Router Solicitation (RS): Hosts send queries for the presence of routers on the link. Sent to FF02::2.
– Neighbor Solicitation (NS): Same as ARP request to find out link layer addresses of other nodes in the segment.
– Neighbor Advertisement (NA): Response of NS, and also periodically advertises its link layer address to others. Sent to FF02::1.
– Redirect: Sent by routers to inform nodes of better next-hop routers.

Categories: CCIE Notes

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