Troubleshooting BGP Neighbor Relationships This section discusses the most common issues in forming a neighbor relationship between two BGP-speaking routers. BGP speakers exchange routing information only after they successfully become neighbors with each other. Troubleshooting neighbor relationship issues should follow the OSI reference model. First, you should check Layer 2 … [Read more...]
Understanding Border Gateway Protocol Version 4 (BGP-4)
Understanding Border Gateway Protocol Version 4 (BGP-4) BGP-4 Protocol Specification and Functionality RFC 1771 defines the current Border Gateway Protocol 4 (BGP-4) implementation. BGP relies on a reliable transport mechanism to establish its connection and for exchanging information between BGP peers. BGP uses TCP port 179 for this purpose and benefits from the TCP protocol … [Read more...]
Troubleshooting PIM
Troubleshooting PIM Troubleshooting IGMP Joins As discussed in Chapter 12, "Understanding Protocol Independent Multicast (PIM)," IGMP joins are a line of communication between the multicast receiver (host) and the router. IGMP joins are used by the multicast receiver to inform the multicast router that hosts on the local segment are interested in certain multicast groups; … [Read more...]
Understanding Protocol Independent Multicast (PIM)
Understanding Protocol Independent Multicast (PIM) Fundamentals of IGMP Version 1, IGMP Version 2, and Reverse Path Forwarding Before diving into the intricacies of the PIM protocol, you need to understand the concept behind the Internet Group Management Protocol (IGMP) and reverse path forwarding (RPF). IGMP is the protocol that functions between the host, also called the … [Read more...]
Troubleshooting IS-IS
Troubleshooting IS-IS Troubleshooting IS-IS Adjacency Problems IS-IS adjacency-related problems normally are caused by link failures and configuration errors. On Cisco routers, link failures easily can be identified by inspection of a show interface command output. Also, because IS-IS routing is not required to establish IP connectivity to directly attached routers, it is … [Read more...]
Troubleshooting SPF Calculation and Route Flapping
Troubleshooting SPF Calculation and Route Flapping This section explains the most common reasons behind route flapping in OSPF and SPF calculation. Whenever there is a change in topology, OSPF runs the SPF algorithm to compute the shortest path first tree again. Unstable links existing within the OSPF network could cause constant SPF calculation. This section discusses the … [Read more...]
Troubleshooting Dial-on-Demand Routing Issues in OSPF
Troubleshooting Dial-on-Demand Routing Issues in OSPF This section discusses the issues related to DDR. When OSPF is configured over a DDR link, be sure to suppress OSPF Hellos because OSPF sends Hellos over point-to-point links every 10 seconds. The most common issues related to OSPF over DDR links are as follows: Problem: OSPF Hellos are bringing up the link … [Read more...]
Troubleshooting Redistribution Problems in OSPF
Troubleshooting Redistribution Problems in OSPF This section describes problems related to redistribution in OSPF. When a router in OSPF does the redistribution, it becomes an ASBR. The routes that are redistributed into OSPF could be directly connected routes, static routes, or dynamically learned routes from another routing protocol or another OSPF process. The following … [Read more...]