BGP Issue: Use Next-Hop IP
February 23, 2025 - Reading time: 2 minutes
When troubleshooting a BGP session where the session is established but certain routes are missing, one common culprit is an improperly configured static route. Specifically, if a static route points to an interface rather than a next-hop IP address, BGP may not correctly install or advertise those routes.
BGP Issue: Loopback Interface Connectivity
February 23, 2025 - Reading time: 2 minutes
When using loopback interfaces for eBGP peering, it's crucial to understand that by default, eBGP sessions are designed to form only with directly connected neighbors (i.e., within one hop). If you try to peer using a loopback address without additional configuration, the session will remain in the Idle or Active state.
BGP Issue: Layer 3 Connectivity
February 23, 2025 - Reading time: 2 minutes
When dealing with eBGP sessions that remain stuck in the Idle state, it's important to ensure that basic IP connectivity exists between the routers. If Layer 3 connectivity is not established, the eBGP session will never progress beyond Idle.
BGP Issue: Missing Network Statements
February 23, 2025 - Reading time: ~1 minute
When troubleshooting BGP peering issues, it's essential to ensure that the correct network prefixes are being advertised to your BGP neighbors. If you notice an advertised network prefix isn’t visible on the remote router, it often indicates that the appropriate network statements are missing in the BGP configuration.
BGP Issue: AS Number Mismatch
February 23, 2025 - Reading time: 2 minutes
When troubleshooting a BGP session that remains in the Idle or Active state, one of the most common issues is an incorrect configuration of the remote AS (Autonomous System) on one of the routers. In BGP, both peers must have matching AS numbers in their respective remote-as statements for the session to be successfully established.
BGP Verification
February 15, 2025 - Reading time: 3 minutes
In the previous lesson, we established iBGP peering between two routers in the same Autonomous System (AS 2350) and configured network advertisements.
Last Lesson's Summary:
- iBGP Peering Setup – We configured two routers (Router0 & Router1) to form an iBGP relationship.
- Network Advertisements – Router0 advertised 50.50.50.0/24 and 70.70.0.0/16 into BGP.
- Reachability Requirements – iBGP neighbors must be IP reachable before a BGP session can establish.
- Synchronization & Auto-Summary – The configuration assumes that synchronization is disabled and auto-summary is off to ensure proper route advertisement.
We ended the lesson with a challenge to verify iBGP was properly advertising routes and to advertise Loopback1 on both devices.