Updating the Routing Table in Passive Mode with DUAL

When a path is lost, DUAL first looks in the topology table for a feasible successor. If one is found, the router stays in passive mode (passive, in this sense, means that the router is not actively querying for an alternative path).  Figure 3-5 provides an example network.  Figure 3-5. The Use of Feasible and Advertised Distance—Passive Mode   The following list explains Figure 3-5 with the metrics and actions that EIGRP takes in determining the path..

Cache and Recursive Lookup

You can see from the previous discussion that, although this technique is efficient, it has drawbacks, such as scalability problems. These problems do not affect the enterprise customer because the networks are not changed rapidly and frequently, and because they do not carry very large routing tables. Demand caching is a scalable method for the enterprise environment because packet flow is not very dynamic. Cache deletion frees space in the memory as well.   ISPs..

Variable-Length Subnet Masks

A variable-length subnet mask (VLSM) is designed to allow greater use of IP address space by borrowing bits from the subnet mask and allocating them to host devices. To allow a greater number of devices to connect to the Internet and intranets, the standards bodies of various routing protocols designed an IP routing algorithm to cater to IP networks with a different subnet mask than the default used in classful networks. Note Routing algorithms that support VLSM are as foll..

Using HSRP Preempt

You can ensure that a particular router is always selected as the HSRP active router if it is available. On the router that you wish to make your primary active HSRP router, you need to set a higher priority level and use the standby preempt command: Router1#configure terminal Enter configuration commands, one per line.  End with CNTL/Z. Router1(config)#interface FastEthernet 0/1 Router1(config-if)#standby 1 ip 172.22.1.1   Router1(config-if)#standby 1 pr..

Configuring Multiple DHCP Servers per Subnet

You can configure multiple routers to act as DHCP servers for a single subnet, by ensuring that they don't use the same pool of addresses. Here's Router1: Router1#configure terminal Enter configuration commands, one per line.  End with CNTL/Z. Router1(config)#ip dhcp pool 172.22.1.0/24 Router1(dhcp-config)#network 172.22.1.0 255.255.255.0 Router1(dhcp-config)#default-router 172.22.1.1 Router1(dhcp-config)#domain-name oreilly.com Router1(dhcp-config)#dns-server ..