## IPv6 Header  * The IPv6 header has a fixed size of 40 bytes compared to the IPv4 header (20 - 60 bytes). * **Version**: * 4 bits in length. * Indicates the version of IP that is used. * Fixed value of 6 (0b0110) to indicate IPv6. * **Traffic Class**: * 8 bits in length. * Used for QoS (Quality of Service) to indicate high-priority traffic. * For example, IP phone traffic, live video calls, etc, will have a Traffic Class value which gives them priority over other traffic. * **Flow Label**: * 20 bits in length. * Used to identify specific traffic 'flows' (communication between a specific source and destination). * **Payload Length**: * 16 bits in length. * Indicates the length of the payload (the encapsulated 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 in length. * Indicates the type of the 'next header' (header of the encapsulated segment). For example, TCP or UDP. * Same function as the IPv4 header's 'Protocol' field. * **Hop Limit**: * 8 bits in length. * The value in this field is decremented by 1 by each router that forwards it. If it reaches 0, the packet is discarded. * Same function as the IPv4 header's TTL field. * **Source/Destination Address**: * 128 bits each. * These fields contain the IPv6 addresses of the packet's source and the packet's intended destination. ## Solicited-Node Multicast Address * An IPv6 solicited-node multicast address is calculated from a unicast address. * The address begins with a fixed prefix. Then, add the last 6 hex digits of the unicast address for which this solicited-node address is being generated from. * `ff02:0000:0000:0000:0000:0001:ff` + Last 6 hex digits of unicast address ### Solicited-Node Multicast Address Example 1 * Unicast address: * `2001:0db8:0000:0001:0f2a:4fff:fea3:00b1` * Solicited-Node Multicast Address: * `ff02:0000:0000:0000:0000:0001:ffa3:00b1` * `ff02::1:ffa3:b1` ### Solicited-Node Multicast Address Example 2 * Unicast Address: * `2001:db8:0:1:489:4eda:073a:12b8` * Solicited-Node Multicast Address: * `ff02::1:ff3a:12b8` ## 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-node multicast addresses to learn the MAC address of other hosts. * Two message types are used: * Neighbor Solicitation (NS): ICMPv6 Type 135. * ARP in IPv4 uses broadcast messages for ARP requests. * Solicited-node multicast messages are much more efficient, being addresses to a specific host, unlike a broadcast which is for all hosts. * Neighbor Advertisement (NA): ICMPv6 Type 136. * 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 (local network) 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). All hosts on the local link (local network) receive this message. * The router announces its presence, as well as other information about the link (local network). * These messages are sent in response to RS messages. * They are also sent periodically, even if the router hasn't received a RS. ### Neighbor Solicitation (NS)  ### Neighbor Advertisement (NA)  ### IPv6 Neighbor Table IPv6 doesn't use ARP, therefore there isn't an ARP table. Instead, the devices will keep an IPv6 neighbor table.  * IPv6 Address: * Lists neighbor global unicast addresses and their link-local address as well. The link-local address is learned automatically. * Age: * Indicates how long ago traffic was received from these addresses (in minutes). * Link-layer Address: * Shows the device's MAC address. * Interface: * Shows the interface this entry was learned on. * State: * Do research on it if you want (not needed for CCNA). ### Duplicate Address Detection * Duplicate Address Detection (DAD), which is another function of NDP, 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 perform DAD. * DAD uses two messages: NS and NA. * The host will send an NS to the solicited-node multicast address joined based on the configured IPv6 address on the interface. * If it doesn't get a reply, it knows the address is unique. * If it gets a reply (a NA message), it means another host on the network is already using the address. ## SLAAC * Stands for **Stateless Address Auto-configuration** and it is an IPv6 address configuration mechanism. * SLAAC is a standard function of IPv6 and end hots like PCs can do this too, not just routers. Although hosts don't use Cisco IOS commands. * Hosts use the RS/RA messages to learn the IPv6 prefix of the local link (ie. `2001:db8::/64`), and then automatically generate an IPv6 address. * Using the `ipv6 addres autoconfig` command, you don't need to enter the network prefix and interface identifier. The device uses NDP to learn the prefix used on the local link (local network). * The device will use EUI-64 to generate the interface ID, or it will be randomly generated (depending on the device/maker). In this example below, R1 is connected to R2. R1 is configured with an IPv6 address, but R2 doesn't have one yet. The command `ipv6 address autoconfig` is used on R2's G0/0 interface to automatically assign it an IPv6 address.  ## IPv6 Static Routing * IPv6 routing works the same as IPv4 routing. However, the two processes (IPv4 routing, IPv6 routing) are separate on the router, each with their own separate routing table. * Display IPv6 routing table: `show ipv6 route`. * IPv4 routing is enabled by default. * IPv6 routing is disabled by default, and must be enabled with `ipv6 unicast-routing`. * If IPv6 routing is disabled, the router will be able to send and receive IPv6 traffic, but will not route IPv6 traffic (will not forward it between networks). ### IPv6 Routing Table * 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.  ### Configure Static Route **Command** :`ipv6 route destination/prefix-length {next-hop | exit-interface [next-hop]} [ad]` * **Directly attached** static route: only the exit interface is specified. * In IPv6, you can't use directly attached static routes for Ethernet interfaces (it works for serial interfaces though). * The route will be part of the router's routing table, but it won't forward any traffic if it's an Ethernet interface. * **Recursive** static route: Only the next hop is specified. * **Fully Specified** static route: Both the exit interface and next hop are specified. #### Link-Local Next-Hops When using a Link-Local address as the next hop, a *fully specified* route is required, otherwise it won't work. The router isn't able to figure out, on its own, which interface that next-hop address is connected to. * Link-local addresses are not added to the routing table! ### IPv6 Static Route Types **Network route**: a route to a specific subnet. * `R1(config)#ipv6 route 2001:db8:0:3::/64 2001:db8:0:12::2` **Host Route**: a route to a single specific host. * `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` * Since there are probably plenty of other PCs in the these networks, we wouldn't normally use host routes in a situation like this. It's best to just configure two network routes on R2. **Default Route**: * `R3(config)#ipv6 route ::/0 2001:db8:0:23::1` **Floating Static Route**: By raising the AD (administrative distance), we can make static backup routes, called **floating static routes**. * Always set the AD to higher than the main route. * If the main route to the destination was learned via OSPF, for example, you'll need to set the static route's AD to higher than 110, because OSPF's AD is 110.