This section describes the two types of IPv6 unicast addresses: global aggregatable and link-local. Note Older specifications mentioned two other types of IPv6 unicast addresses which have now been deprecated, in RFC 4291, IP Version 6 Addressing Architecture. These addresses are mentioned here for your information only. IPv4-compatible IPv6 addresses were made by concatenating 0::/96 and the IPv4 address. For instance, the IPv4 address 192.168.9.5 became 0..
IP forwarding, or IP routing, is simply the process of receiving an IP packet, making a decision of where to send the packet next, and then forwarding the packet. The forwarding process needs to be relatively simple, or at least streamlined, for a router to forward large volumes of packets. Ignoring the details of several Cisco optimizations to the forwarding process for a moment, the internal forwarding logic in a router works basically as shown in Figure 7-1. Figure 7-1 F..
When a device realizes that a packet cannot be delivered to its destination, the device sends an ICMP Unreachable message. To help determine the root cause of why the packet cannot be delivered, the ICMP Unreachable message includes one of five code field values to convey the reason for the failure. For instance, in Figure 5-1, assume that Fred is trying to connect to the web server, called Web. Table 5-3, following the figure, lists the key ICMP Unreachable message codes, al..
The link-state request packet, OSPF packet type 3, is sent in response to a router during the database exchange process. This request is sent when a router detects that it is missing parts of the database or when the router has a copy of LSA older than the one it received during the database exchange process. Figure 9-5 shows fields in the link-state request packet. The request packet contains each LSA specified by its LS type, link-state ID, and advertising router. This uniq..
Gateway Load Balancing Protocol
You should now know how both HSRP and VRRP can effectively provide a redundant gateway (virtual router) address. You can accomplish load balancing by configuring only multiple HSRP/VRRP groups to have multiple virtual router addresses. More manual configuration is needed so that the client machines are divided among the virtual routers. Each group of clients must point to the appropriate virtual router. This makes load balancing somewhat labor-intensive, having a more or less..
