Resource Allocation and Failures

Week 7: Read Chapter 19: Troubleshooting Management Protocols and Tools

Week 7 Review Lecture 1:

Week 7 Discussion (20 Points): “Resource Allocation and Failures” Please respond to the following:

Imagine that you have been contracted as a network consultant for a mid-sized company. You have observed a router that is slow to respond to commands issued on the console; in addition, it is not sending routing protocol packets to other routers. Analyze the potential causes of these symptoms and suggest one (1) way in which you would troubleshoot the router in order to restore baseline operations.

Discuss the most common causes for router memory failure and recommend both preventative strategies and early actions that your organization can take in order to prevent router memory failure from occurring. Provide a rationale to support your response.

Response:

If I were contracted as a network consultant for a mid-sized company and I observed a router that needed troubleshooting, to analyze potential causes of the symptoms and restore baseline operations I would first verify the problem. If the router was slow to respond to commands issued or “hang” on the console, I would first verify cable connectivity and then verify that the power supply is plugged in or on. I would then verify the router LED status by examining the routers lights. If all LEDs are down, it is most likely an issue with the power supply of the router. A quick solution would be to simply replace the power supply, but further analysis would suggest I test the questionable power supply on a known good unit, otherwise simply rebooting the router may resolve the immediate issue. If traffic still flows through the router I would disconnect all network interfaces and see if the router responds. If the router’s lights don’t indicate an issue I would examine another possible cause of the hang which would be memory allocation failure. Either the router has used all available memory, or the memory has been fragmented into such small pieces that the router cannot find a usable available block. If the console does not respond because the router CPU utilization is high, it is important to find and correct the cause of the high CPU utilization. In most cases it is important to collect the output from show interfaces, show interfaces stat, and possibly show processes to further diagnose the problem. To fix the problem, I would reduce the amount of switched IP traffic. If the router was not sending routing protocol packets to other routers I would troubleshoot for misconfigurations, lack of system resources, or physical connectivity problems. Networks directly connected to a router are automatically installed into the routing table and are marked as connected, once the IP addresses are configured under the interfaces. Routers can route packets between these connected networks without a routing protocol or static routes. Routers can route packets between these connected networks; therefore, configuring a routing protocol is not required. To verify basic IP connectivity to a network, I would issue the ping command in the user EXEC or privileged EXEC mode. Basic IP connectivity can also be tested, and the path to the destination determined by issuing the traceroute command in the user EXEC or privileged EXEC mode. If these tests fail, I would verify that the destination device is assigned an IP address and that it is correct. I would also, check the connectivity to the local gateway, and confirm that subnet and mask information matches. I would then examine the possibility of duplicate IP addresses. If the problem is not resolved, I would examine Layer 1 and Layer 2 while making sure cables are properly connected and verify hardware is operational. If the physical layer is found to be in order, I would check if sufficient router resources are available and verify that memory and CPU utilization are not overstretched. I would also check that an Access Control List (ACL) is not dropping packets and that Network Address Translation (NAT) is configured properly. The last resort would be to verify if the upper layer protocols need to be examined for issues such as authentication problems, version mismatches and software incompatibility.

The most common causes for router memory failure are memory leak and running out of memory. Memory leak is caused by a Cisco IOS bug where the bug causes one process to consume an excessive amount of memory until all memory is utilized. Routers can run out of memory due to the processes and configurations on the device that are not associated with a bug. Border Gateway Protocol (BGP) holding a large amount of memory because of the number of routes that it takes would be an example. This issue of the router running out of memory can be corrected by altering the router’s configuration to achieve optimal routing and reduce memory consumption. A feasible preventative strategy and early action that an organization can take to possibly prevent router memory failure from occurring would be to identify how much memory should be allocated and how much free memory is available early and on a routine basis.