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 connectivity; then check IP connectivity (Layer 3), TCP connections (Layer 4), and finally the BGP configuration in Cisco IOS Software.
The section is arranged to discuss external BGP neighbors' issues, internal BGP neighbors, and then problems that are common in both external and internal BGP neighbor relationships.
The following is the list of problems most commonly seen when forming BGP neighbor relationships.
• Directly connected external BGP neighbors not initializing
• Nondirectly connected external BGP neighbors not initializing
• Internal BGP neighbors not initializing
• BGP neighbors (external and internal) not initializing
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