Sunday, January 8, 2012

CCDA 640-864 Official Cert Guide - Chapter 9 Summary






IPv6 Address Representation



IPv4 addresses are represented in dotted-decimal format. This 32-bit address is divided along 8-bit boundaries. Each set of 8 bits is converted to its decimal equivalent and separated by periods.
For IPv6, the 128-bit address is divided along 16-bit boundaries, and each 16-bit block is converted to a 4-digit hexadecimal number and separated by colons. The resulting representation is called colon-hexadecimal.

The following is an IPv6 address in binary form:
0010000111011010000000001101001100000000000000000010111100111011
0000001010101010000000001111111111111110001010001001110001011010

The 128-bit address is divided along 16-bit boundaries, as follows:
0010000111011010   0000000011010011   0000000000000000   0010111100111011
0000001010101010   0000000011111111   1111111000101000   1001110001011010

Each 16-bit block is converted to hexadecimal and delimited with colons. The result is:
21DA:00D3:0000:2F3B:02AA:00FF:FE28:9C5A

IPv6 representation can be further simplified by removing the leading zeros within each 16-bit block. However, each block must have at least a single digit. With leading zero suppression, the address representation becomes:
21DA:D3:0:2F3B:2AA:FF:FE28:9C5A

Compressing zeros

Some types of addresses contain long sequences of zeros. To further simplify the representation of IPv6 addresses, a contiguous sequence of 16-bit blocks set to 0 in the colon-hexadecimal format can be compressed to :: (known as double-colon).
For example, the link-local address of FE80:0:0:0:2AA:FF:FE9A:4CA2 can be compressed to FE80::2AA:FF:FE9A:4CA2. The multicast address of FF02:0:0:0:0:0:0:2 can be compressed to FF02::2. Zero compression can only be used to compress a single contiguous series of 16-bit blocks expressed in colon-hexadecimal notation. You cannot use zero compression to include part of a 16-bit block. For example, you cannot express FF02:30:0:0:0:0:0:5 as FF02:3::5.
To determine how many 0 bits are represented by the ::, you can count the number of blocks in the compressed address, subtract this number from 8, and then multiply the result by 16. For example, in the address FF02::2, there are two blocks (the FF02 block and the 2 block). The number of bits expressed by the :: is 96 (96 = (8 - 2) × 16).
Zero compression can only be used once in a given address. Otherwise, you could not determine the number of 0 bits represented by each instance of a double-colon (::).

IPv4-Compatible IPv6 Addresses

IPv6/IPv4 Address Embedding

IPv6 is backward compatible with IPv4, provided that special techniques are used. For example, to enable communication between "islands" of IPv6 devices connected by IPv4 networks, tunneling may be employed. To support IPv4/IPv6 compatibility, a scheme was developed to allow IPv4 addresses to be embedded within the IPv6 address structure. This method takes regular IPv4 addresses and puts them in a special IPv6 format so they are recognized as being IPv4 addresses by certain IPv6 devices.
Since the IPv6 address space is so much bigger than that of IPv4, embedding the latter within the former is easy; it's like tucking a compact sedan into the hold of a cargo ship. The embedding address space is part of thereserved address block whose addresses begin with eight zero bits, but only a relatively small part of it. Two different embedding formats are used. Both have zeroes for the first 80 bits of the address, and put the embedded IPv4 address into the last 32 bits of the IPv6 address format. They differ on the value of the 16 remaining bits in between (bits 81 to 96, counting from the left):
The two embedding formats are used in order to indicate the capabilities of the device using the embedded address.

IPv4-Compatible IPv6 Addresses
These are special addresses assigned to IPv6-capable devices, such as so-called “dual stack” devices that speak both IPv4 and IPv6. They have all zeroes for the middle 16 bits; thus, they start off with a string of 96 zeroes, followed by the IPv4 address. An example of such an address, shown in Figure 1, would be 0:0:0:0:0:0:101.45.75.219 in mixed notation, or more succinctly, ::101.45.75.219.




Figure 1: IPv4-Compatible Embedded IPv6 Address Representation

IPv4-Mapped IPv6 Addresses
These are regular IPv4 addresses that have been mapped into the IPv6 address space, and are used for devices that are only IPv4-capable. They have a set of 16 ones after the initial string of 80 zeroes, and then the IPv4 address. So, if an IPv4 device has the address 222.1.41.90, such as the one in Figure 2, it would be represented as 0:0:0:0:0:FFFF:222.1.41.90, or ::FFFF:222.1.41.90.



Figure 2: IPv4-Mapped Embedded IPv6 Address Representation

Key Concept: IPv4 address embedding is used to create a relationship between an IPv4 address and an IPv6 address to aid in the transition from IPv4 to IPv6. One type, the IPv4-compatible IPv6 address, is used for devices that are compatible with both IPv4 and IPv6; it begins with 96 zero bits. The other, the IPv4-mapped address, is used for mapping IPv4 devices that are not compatible with IPv6 into the IPv6 address space; it begins with 80 zeroes followed by 16 ones.

Comparing IPv4-Compatible and IPv4-Mapped Embedded IPv6 Addresses
The difference between these two kinds of addresses is subtle, but important. The first 80 bits are always zero, so when this is seen you know it is an embedded IPv4 address of some sort. IPv4-compatible IPv6 addresses are only used for devices that are actually IPv6-aware; the IPv4-compatible address is in addition to its conventional IPv6 address. In contrast, if the "FFFF" is seen for the 16 bits after the initial 80, this designates a conventional IPv4 device whose IPv4 address has been mapped into the IPv6 format. It is not an IPv6-capable device.


::/128 - Unspecified
::1/128 - Loopback
FF00::/8 - Multicast
FE80::/10 - Link-local unicast
FC00::/7 - Unique local unicast
2000::/3 - Global unicast

Global Unicast - like public IP address in IPv4



Multicast - same same, replacing the need of broadcast.



Anycast - finds the nearest IP



Unique local unicast address - like private address (RFC 1918)



Link local unicast address - direct connection without any router. Autoconfiguration of the address, can be few attached to the single interface, routers are not forwarding this IPs.





IPv6 Mechanisms
            ICMPv6
             
            IPv6Neighbor Discovery Protocol
            
            IPv6 Name Resolution
IPv4 uses A record to resolve IP per DNS name, DNS adds a resource record (RR) to support name-to-IPv6-address resolution. New type of record calls AAAA.

Path MTU Discovery
IPv6 does not allow packet segmentation thru the internetwork. Only sending host are allowed to fragment. Maximum MTU is 1280 per RFC 2460.

IPv6 Address-Assignment Strategies
Static or Dynamic:
            Static:
                        Manually
            Dynamic:
                        Stateless autoconfiguration of link-local address (FE80::)
                        Stateless autoconfiguration of globally unique address (
Statefull configuration with DHCPv6

            IPv6 Security
Extension headers carry the IPsec AH and ESP headers. The AH provides authentication and integrity. The ESP header provides confidentiality by encryption a payload.
                       

IPv6 Routing Protocols
            RIPng
            UDP port 521
            Uses multicast group FF02::9

EIGRP for IPv6
            Uses multicast group FF02::A

            OSPFv3
            Uses multicast group FF02::5 for all OSPF routers and FF02::6 for all DR’s.

            IS-IS for IPv6
            (draft)

            MP-BGP for IPv6
            MP_REACH_NLRI
            MP_UNREACH_NLRI
           

IPv4 to IPv6 Transition Mechanisms and Deployment Models

            TransitionMechanisms:
Dual-Stack (IPv4 and IPv6 coexist in host and network)



            Tunneling (IPv6 packets are encapsulated into IPv4 packets)
                        IPv4 compatible
                        6to4
                        6over4
                        ISATAP



            Translation (IPv6 packets are translated to IPv6 packets)     
                        ALG
                        API
                        DSTM – NAT-PT


Summary:


     
            DeploymentModels:
            Dual-Stuck model



            Hybrid model



            Service Block Model



Summary:
IPv6 Deployment Model
Advantages
Disadvantages
Dual-Stack model
Tunneling not required. Better processing performance.
IPv4 & IPv6 independent routing, QoS, security and multicast policies.
Network equipment upgraded
Hybrid model 1
Existing network can be leveraged with no upgrades
IPv6 multicast not supported within ISATAP tunnel.
Terminating ISATAP tunnels in core makes the core appear to be in IPv6 access layer.
Hybrid model 2
IPv4 & IPv6 independent routing, QoS, security and multicast policies.
Many static tunnels which makes it difficult to manage.
Server Block model
Lesser impact on existing network.
Flexible when controlling access to IPv6-enabled applications.
Large amounts of tunneling.
Cost of additional equipment.


IPv6 Comparison with IPv4

Characteristics
IPv6
IPv4
Address length
128 bits
32 bits
Address representation
Hexadecimal
Dotted-decimal
Header length
Fixed (40 bytes)
Variable
Upper-layer protocol
Next header field
Protocol type field
Link address resolution
ND
ARP
Address configuration
Stateless autoconfiguration or Statefull DHCP
Statefull DHCP
Routing protocols
EIGRPv6, OSPFv6, RIPng, ISIS for IPv6
EIGRP, OSPFv2, RIPv2, ISIS
Classification and marking
Traffic Class and Flow label fields, DSCP
IP Precedence bits, ToS, DSCP
Private address
Unique-local address
RFC 1918
Fragmentation
Sending host only
Sending host and intermediate routers
Loopback address
0:0:0:0:0:0:0:1
127.0.0.1
Address scope type
Unicast, anycast, multicast
Unicast, multicast, broadcast

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