cisco 300-180 dumps

cisco 300-180 dumps.At the distribution layer of each switching block, two routing devices can be placed to give endpoints redundant egress away from their VLANs. However, this may not provide a true fault-tolerant solution, especially in the following cases: the endpoint does not support the use of a router discovery protocol to learn about the routers available; the endpoint cannot be configured to use multiple default gateway addresses.Chapter 18 Basic Routing 477Problems with Proxy ARPSome endpoints use proxy ARP to learn the IP address of the default gateway; in this case, the endpoint dynamically learns the IP address and MAC address of the default gateway and sends all of its inter-VLAN traffic to that routing device. Initially, the end device does not know how to get to the destination device and therefore generates an ARP request to learn the MAC address of the destination device. Obviously, if the destination device is not in the current VLAN, there will be no answer, so the endpoint considers the destination device unreachable. However, the Cisco router can act as a proxy and respond to the ARP request by sending its MAC address to the endpoint, so that the endpoint can send traffic off the subnet through the router. It appears to the endpoint that it is sending traffic directly to the destination device, but the traffic is actually relayed by the router. On a Cisco IOS device with routing enabled, the default will be to enable proxy ARP on the routing interface oHowever, a failure of the default gateway will cause problems. When the default gateway fails, the endpoint still sends its traffic to it, and that traffic will be discarded. The client may perform ARP after a long time to verify that the default gateway is still in place; at that point it will find that the default gateway has failed and that another routing device is available to act as a proxy. However, in most ARP implementations, the endpoint continues to use the MAC address of the faulty default gateway until it reboots.Problems with the ICMP Router Discovery ProtocolThe ICMP Router Discovery Protocol (IRDP) is not a routing protocol like OSPF and RIP, but rather an ICMP extension that allows an endpoint to automatically discover the default gateway in the VLAN to which it belongs. 1RDP is defined in RFC1256. In this environment, the routing device periodically generates special multicast packets to inform the client of their presence. The delivery interval is typically 5.10 minutes; the learned information is typically retained at the client for a maximum of 30 minutes one-by-one if no new IRDP message is ever received from the announcing routing device. This multicast packet contains the address and lifecycle value of the routing device.In the event of a failure of the primary default gateway, the endpoint can use IRDP to dynamically discover other routing devices. However, this can take up to 30 minutes, depending on the lifecycle values in the multicast packets sent by the routing device. Also, even if IRDP is used on the access layer devices, most endpoint IP stacks do not support IRDPoProblems with routing protocolsTo overcome the two aforementioned problems, routing protocols can be run on endpoints - if they support such functionality. Most terminals only support the IP routing protocols RIP or OSPF; by using RIP or OSPF, the terminal is able to determine which Layer 3 routing device to use to get to other subnets. However, the problem with RIP is that convergence is very slow: when the primary routing device fails, it takes 180 seconds to select a replacement routing device. For TCP sessions, this results in a timeout. Given this and the various other overheads associated with RIP, even if endpoints and other network devices support routing protocols such as RIP, this solution is not well suited.