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Chapter 7 IP Addressing (3. IPv6 Addresses (IPv6 is designed to be the…

- - - - IPv4 address is a hierarchical address that is made up of a network portion and a host portion
        
        The bits within the network portion of the address must be identical for all devices that reside in the same network.
        The bits within the host portion of the address must be unique to identify a specific host within a network.
        
        Subnet mask- Used to identify the network/host portion of the IPv4 address
        
        To identify the network and host portions of an IPv4 address, the subnet mask is compared to the IPv4 address bit for bit, from left to right. The 1s in the subnet mask identify the network portion while the 0s identify the host portion. Note that the subnet mask does not actually contain the network or host portion of an IPv4 address, it just tells the computer where to look for these portions in a given IPv4 address.
        The actual process used to identify the network portion and host portion is called ANDing.
        
        an alternate shorthand method of identifying a subnet mask called the prefix length (e.g. /24).
      - Network, Host, and Broadcast Addresses
        
        Network address: Address and subnet mask refer to a network. (192.168.0.0/24)
        
        Host addresses: Unique IP addresses assigned to host and devices. (192.168.0.1 to 192.168.0.254)
        
        Broadcast address: The host portion is all in 1s. (192.168.0.255
      - IPv4 Communication
        
        A host successfully connected to a network can communicate with other devices in one of three ways:
        
        Unicast - The process of sending a packet from one host to an individual host.
        
        Broadcast - The process of sending a packet from one host to all hosts in the network.
        
        Broadcast may be directed or limited
        
        A directed broadcast is sent to all hosts on a specific network. For example, a host on the 172.16.4.0/24 network sends a packet to 172.16.4.255.
        
        A limited broadcast is sent to 255.255.255.255. By default, routers do not forward broadcasts.
        
        Multicast - The process of sending a packet from one host to a selected group of hosts, possibly in different networks.
        
        Class D (224-239) is reserved for multicas
        
        A typical use of reserved local network multicast address is in routing protocols using multicast transmission to exchange routing information.
        
        For instance, 224.0.0.9 is the multicast address used by Routing Information Protocol (RIP) version 2 to communicate with other RIPv2 routers.
        
        Hosts that receive particular multicast data are called multicast clients.
      - Public and Private IPv4 Addresses
        
        Public IPv4 addresses are addresses which are globally routed between ISP (Internet Service Provider) routers.
        
        There are blocks of addresses called private addresses that are used by most organizations to assign IPv4 addresses to internal hosts ( RFC 1918).
        
        Specifically, the private address blocks are:
        
        10.0.0.0 /8 or 10.0.0.0 to 10.255.255.255
        
        172.16.0.0 /12 or 172.16.0.0 to 172.31.255.255
        
        192.168.0.0 /16 or 192.168.0.0 to 192.168.255.255
        
        It is important to know that private addresses within these address blocks are not allowed on the Internet and must be filtered (discarded) by Internet routers.
        
        Network Address Translation (NAT) is used to translate between private IPv4 and public IPv4 addresses.
      - Special User IPv4 Addresses
        
        There are also special addresses that can be assigned to hosts, but with restrictions on how those hosts can interact within the network.
        
        Loopback addresses (127.0.0.0 /8 or 127.0.0.1 to 127.255.255.254) – More commonly identified as only 127.0.0.1, these are special addresses used by a host to direct traffic to itself
        
        Link-Local addresses (169.254.0.0 /16 or 169.254.0.1 to 169.254.255.254) – More commonly known as the Automatic Private IP Addressing (APIPA) addresses, they are used by a Windows DHCP client to self-configure in the event that there are no DHCP servers available.Useful in a peer-to-peer connection.
        
        TEST-NET addresses (192.0.2.0/24 or 192.0.2.0 to 192.0.2.255) – These addresses are set aside for teaching and learning purposes and can be used in documentation and network examples.
        
        There are also Experimental Addresses in the block 240.0.0.0 to 255.255.255.254 that are reserved for future use
      - Legacy Classful Addressing
        
        In 1981, Internet IPv4 addresses were assigned using classful addressing as defined in RFC 790, Assigned Numbers. Customers were allocated a network address based on one of three classes
        
        Class A (0.0.0.0/8 to 127.0.0.0/8) – Designed to support extremely large networks with more than 16 million host addresses. It used a fixed /8 prefix with the first octet to indicate the network address and the remaining three octets for host addresses. All class A addresses required that the most significant bit of the high-order octet be a zero creating a total of 128 possible class A networks. Figure 1 summarizes the class A.
        
        Class B (128.0.0.0 /16 – 191.255.0.0 /16) – Designed to support the needs of moderate to large size networks with up to approximately 65,000 host addresses. It used a fixed /16 prefix with the two high-order octets to indicate the network address and the remaining two octets for host addresses. The most significant two bits of the high-order octet must be 10 creating over 16,000 networks. Figure 2 summarizes the class B.
        
        Class C (192.0.0.0 /24 – 223.255.255.0 /24) – Designed to support small networks with a maximum of 254 hosts. It used a fixed /24 prefix with the first three octets to indicate the network and the remaining octet for the host addresses. The most significant three bits of the high-order octet must be 110 creating over 2 million possible networks. Figure 3 summarizes the class C.
        
        There is also a Class D multicast block consisting of 224.0.0.0 to 239.0.0.0 and a Class E experimental address block consisting of 240.0.0.0 – 255.0.0.0.
      - Classless Addressing
        
        The system in use today is referred to as classless addressing. The formal name is Classless Inter-Domain Routing (CIDR, pronounced “cider”)
      - Assignment of IP Addresses
        
        Both IPv4 and IPv6 addresses are managed by the Internet Assigned Numbers Authority (IANA) (http://www.iana.org).
        
        The IANA manages and allocates blocks of IP addresses to the Regional Internet Registries (RIRs)
        
        RIRs are responsible for allocating IP addresses to ISPs who in turn provide IPv4 address blocks to organizations and smaller ISPs. Organizations can get their addresses directly from an RIR subject to the policies of that RIR.
- - - - Tunneling – tunneling is a method of transporting an IPv6 packet over an IPv4 network. The IPv6 packet is encapsulated inside an IPv4 packet, similar to other types of data.
      - Translation – Network Address Translation 64 (NAT64) allows IPv6-enabled devices to communicate with IPv4-enabled devices using a translation technique similar to NAT for IPv4. An IPv6 packet is translated to an IPv4 packet and vice versa.
      - Dual Stack – dual stack allows IPv4 and IPv6 to coexist on the same network segment. Dual stack devices run both IPv4 and IPv6 protocol stacks simultaneously.
    - - IPv6 addresses are 128 bits in length and written as a string of hexadecimal values
        
        Every 4 bits is represented by a single hexadecimal digit; for a total of 32 hexadecimal values
        
        Rules
        
        Omit Leading 0s
        01AB can be represented as 1AB
        09F0 can be represented as 9F0
        0A00 can be represented as A00
        00AB can be represented as AB
        
        Omit All 0 Segments
        
        The second rule to help reduce the notation of IPv6 addresses is that a double colon (::) can replace any single, contiguous string of one or more 16-bit segments (hextets) consisting of all 0s.
        
        The double colon (::) can only be used once within an address
    - - Unicast - An IPv6 unicast address uniquely identifies an interface on an IPv6-enabled device. A source IPv6 address must be a unicast address.
        
        Global unicast: this is similar to a public IPv4 address. These are globally unique, Internet routable addresses. Global unicast addresses can be configured statically or assigned dynamically.
        
        Structure of an IPv6 Global Unicast Address (GUA)
        
        Currently, only global unicast addresses with the first three bits of 0010 or 2000::/3 are being assigned. In other words, the first hexadecimal digit of a GUA address will begin with a 2 or a 3.
        
        A global unicast address has three parts:
        
        Global routing prefix
        
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        Subnet ID
        
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        Interface ID
        
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        The 2001:0DB8::/32 address has been reserved for documentation purposes, including use in examples.
        
        Unlike IPv4, in IPv6, the all-0s and all-1s host addresses can be assigned to a device. The all-1s address can be used due to the fact that broadcast addresses are not used within IPv6. The all-0s address can also be used, but is reserved as a Subnet-Router anycast address, and should be assigned only to routers.
        
        Configuration of a Global Unicast Address
        
        Static
        
        R1(config)# int g0/0
        R1(config-if)# ipv6 address ipv6_adres/prefix
        R1(config-if)# no shutdown
        
        automatically
        
        There are two ways in which a device can obtain an IPv6 global unicast address automatically:
        
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        2000::/3
        
        Link-local address enables a device to communicate with other IPv6-enabled devices on the same link and only on that link (subnet). With IPv6, the term link refers to a subnet. Link-local addresses are confined to a single link. Their uniqueness must only be confirmed on that link because they are not routable beyond the link. In other words, routers will not forward packets with a link-local source or destination address.
        
        The global unicast address is not a requirement. However, every IPv6-enabled network interface is required to have a link-local address.
        
        If a link-local address is not configured manually on an interface, the device will automatically create its own without communicating with a DHCP server. IPv6-enabled hosts create an IPv6 link-local address even if the device has not been assigned a global unicast IPv6 address. This allows IPv6-enabled devices to communicate with other IPv6-enabled devices on the same subnet. This includes communication with the default gateway (router).
        
        Dynamic Link-Local Addresses
        
        All IPv6 devices must have an IPv6 link-local address.
        
        Operating systems will typically use the same method for both a SLAAC created global unicast address and a dynamically assigned link-local address
        
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        Static Link-Local Addresses
        
        Typically, it is only necessary to create recognizable link-local addresses on routers. This is beneficial because router link-local addresses are used as default gateway addresses and in routing advertisement messages.
        
        Link-local addresses can be configured manually using the same interface command used to create IPv6 global unicast addresses but with the additional link-local parameter. When an address begins with this hextet within the range of FE80 to FEBF, the link-local parameter must follow the address.
        
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        IPv6 link-local addresses are in the FE80::/10 range. The /10 indicates that the first 10 bits are 1111 1110 10xx xxxx.
        
        Another type of unicast address is the unique local unicast address. IPv6 unique local addresses have some similarity to RFC 1918 private addresses for IPv4, but there are significant differences. Unique local addresses are used for local addressing within a site or between a limited number of sites. These addresses should not be routable in the global IPv6 and should not be translated to a global IPv6 address. Unique local addresses are in the range of FC00::/7 to FDFF::/7.
        
        Unique local addresses can be used for devices that will never need or have access from another network.
        
        FC00::/7
        
        Loopback ::1/128
        
        Unspecified address ::/128
      - Multicast
        
        IPv6 multicast addresses are similar to IPv4 multicast addresses. Recall that a multicast address is used to send a single packet to one or more destinations (multicast group).
        
        There are two types of IPv6 multicast addresses
        
        Assigned multicast
        
        Addresses that are reserved for predefined groups of devices.
        
        Two common IPv6 assigned multicast groups include:
        
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        Solicited node multicast
        
        IPv6-enabled devices send ICMPv6 Router Solicitation (RS) messages to the all-routers multicast address. The RS message requests an RA message from the IPv6 router to assist the device in its address configuration
        
        It is similar to the all-nodes multicast address.
        A solicited-node multicast address is mapped to a special Ethernet multicast address.
        This allows the Ethernet NIC to filter the frame by examining the destination MAC address without sending it to the IPv6 process to see if the device is the intended target of the IPv6 packet.
        
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        FF02::1:FFAE:F85F
        
        IPv6 multicast addresses have the prefix FF00::/8.
        
        Multicast addresses can only be destination addresses and not source addresses.
      - Anycast
        
        An IPv6 anycast address is any IPv6 unicast address that can be assigned to multiple devices. A packet sent to an anycast address is routed to the nearest device having that address. Anycast addresses are beyond the scope of this course.
      - Unlike IPv4, IPv6 does not have a broadcast address. However, there is an IPv6 all-nodes multicast address that essentially gives the same result.
    - - IPv6 uses the prefix length to represent the prefix portion of the address. IPv6 does not use the dotted-decimal subnet mask notation. The prefix length is used to indicate the network portion of an IPv6 address using the IPv6 address/prefix length.
      - The prefix length can range from 0 to 128. A typical IPv6 prefix length for LANs and most other types of networks is /64
    - - Although IP is only a best-effort protocol, the TCP/IP suite does provide for messages to be sent in the event of certain errors.
        
        These messages are sent using the services of ICMP
        
        The purpose of these messages is to provide feedback about issues related to the processing of IP packets under certain conditions, not to make IP reliable
        
        ICMP messages common to both ICMPv4 and ICMPv6 include:
        
        Host Confirmation
        
        An ICMP Echo Message can be used to determine if a host is operational. The local host sends an ICMP Echo Request to a host. If the host is available, the destination host responds with an Echo Reply.
        
        Destination or Service Unreachable
        
        When a host or gateway receives a packet that it cannot deliver, it can use an ICMP Destination Unreachable message to notify the source that the destination or service is unreachable. The message will include a code that indicates why the packet could not be delivered.
        
        Time Exceeded
        
        An ICMPv4 Time Exceeded message is used by a router to indicate that a packet cannot be forwarded because the Time to Live (TTL) field of the packet was decremented to 0. If a router receives a packet and decrements the TTL field in the IPv4 packet to zero, it discards the packet and sends a Time Exceeded message to the source host.
        ICMPv6 also sends a Time Exceeded message if the router cannot forward an IPv6 packet because the packet has expired. IPv6 does not have a TTL field; it uses the hop limit field to determine if the packet has expired.
        
        ICMPv6 Router Solicitation and Router Advertisement Messages
        
        ICMPv6 includes four new protocols as part of the Neighbor Discovery Protocol (ND or NDP)
        
        Messaging between an IPv6 router and an IPv6 device:
        
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        Messaging between IPv6 devices:
        
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        Neighbor Solicitation and Neighbor Advertisement messages are used for Address resolution and Duplicate Address Detection (DAD).
        
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        ICMP messages are not required and are often not allowed within a network for security reasons.
      - Traceroute – Testing the Path
        
        Traceroute (tracert) is a utility that generates a list of hops that were successfully reached along the path. This list can provide important verification and troubleshooting information. If the data reaches the destination, then the trace lists the interface of every router in the path between the hosts. If the data fails at some hop along the way, the address of the last router that responded to the trace can provide an indication of where the problem or security restrictions are found.
        
        Round Trip Time (RTT)
        
        Using traceroute provides round trip time for each hop along the path and indicates if a hop fails to respond. The round trip time is the time a packet takes to reach the remote host and for the response from the host to return. An asterisk (*) is used to indicate a lost or unreplied packet.
        
        This information can be used to locate a problematic router in the path. If the display shows high response times or data losses from a particular hop, this is an indication that the resources of the router or its connections may be stressed.
        
        IPv4 TTL and IPv6 Hop Limit
        
        Traceroute makes use of a function of the TTL field in IPv4 and the Hop Limit field in IPv6 in the Layer 3 headers, along with the ICMP time exceeded message.
        
        The first sequence of messages sent from traceroute will have a TTL field value of 1. This causes the TTL to time out the IPv4 packet at the first router. This router then responds with an ICMPv4 message. Traceroute now has the address of the first hop.
        
        Traceroute then progressively increments the TTL field (2, 3, 4...) for each sequence of messages. This provides the trace with the address of each hop as the packets timeout further down the path. The TTL field continues to be increased until the destination is reached, or it is incremented to a predefined maximum.