cisco ccna book pdf

cisco ccna book pdf.Exam Points Be sure to know the differences between anycast, multicast, and unicast IPv6 addresses o IPv6 does not support broadcast addresses.The IETF defines support for many data link layer types, but Cisco only supports Ethernet, Point-to-Point Protocol (PPP), Advanced Data Link Control (HDLC), Asynchronous Transfer Mode (ATM) using PVCs, and Frame Relay using PVCs. The next few subsections discuss these address types in more depth.Chapter 23 IPv6 613Anycast.One of the problems with IPv4 addressing is the use of broadcasts: every device in the segment must handle them even if the broadcast was not sent to it. IPv4 makes extensive use of broadcasts to discover devices in the segment (such as ARP) and to obtain addressing information (such as Dynamic Host Configuration Protocol (DHCP)) O There are no broadcast addresses in IPv6; instead, there are anycast and multicast addresses.Exam Essentials An anycast address allows a device to communicate with the nearest device represented by that address. An anycast address is derived from the global address space and is assigned to multiple devices.An anycast address represents one or more interfaces. Note that the term device is not used here because devices may have multiple interfaces. Sometimes, the term node is used to denote a device's interface. Basically, an anycast address is a hybrid of a unicast address and a multicast address. With a unicast address, packets are sent to one device; with a multicast address, packets are sent to all members of a multicast group; and with an anycast address, packets are sent to one of a group of devices configured with that multicast address. By default, packets sent to an anycast address are forwarded to the nearest interface (node), with the meaning of nearest depending on the routing process used to route the packet to its destination. With this in mind, the anycast address is often referred to as the nearest address. Interestingly, an anycast address is derived from the IPv6 global unicast address space, so it is not possible to distinguish whether the address in a packet is a unicast or an anycast address. Since the same anycast address can be configured on multiple devices, anycast addresses are commonly used to implement load balancing, sending traffic (e.g., Web content) to two different target devices.Anycast addresses and their applications are still in their infancy, and some issues have been identified that can arise when using them. Until administrators learn more about how anycast addresses work through practice and the industry agrees on how to solve these problems, they should follow these guidelines: do not assign anycast addresses to hosts, but only to routers; do not use anycast addresses as packet source addresses. Probably the most common use of anycast addresses is for default gateways. Instead of implementing Hot Standby Router Protocol (HSRP) or Virtual Router Redundancy Protocol (VRRP), you can configure the same anycast address and a locally unique global unicast address on both routing devices, and then set the default gateway address to that anycast address on all devices in the VLAN.MulticastAn IPv6 multicast address functions similarly to an IPv4 multicast address: it represents a group of devices that want to receive a specific amount of traffic. Figure 23.1 shows an IPv6 multicast address. The first 8 bits are set to FF, and the next 4 bits are the lifetime of the address: 0 for permanent, 1 for temporary. The next 4 bits indicate the range of the multicast address (how far packets can travel using it): 1 for node, 2 for link, 5 for site, 8 for organization, and E for global (the entire Internet). o For example, the multicast address FF02::/16 is the permanent link address, while the multicast address is FF15::/16 the temporary site address. FF02::l indicates all IPv6 devices (similar to IPv4 broadcast addresses),FF02::2 indicates all routers in an IPv6 segment or VLAN.