Routing

BGP Graceful Restart (GR) is one of those features you turn on everywhere because the vendor datasheet says it improves availability — and then you spend the next year debugging weird convergence behavior because of it. Let me break down what GR actually does, and more importantly, when it helps versus when it makes things worse. The Problem It Solves When a BGP speaker restarts (software upgrade, process crash, failover), it tears down all its sessions. Every peer withdraws the routes it learned from that speaker, and the network reconverges. This takes time — seconds to minutes, depending on your topology. ...

OSPF link-state advertisements are the currency of the protocol. Understanding which LSA type carries what information — and who generates it — is essential for troubleshooting convergence issues. Quick Reference Type Name Originated By Scope 1 Router LSA Every router Single area 2 Network LSA DR on broadcast segment Single area 3 Summary LSA ABR Area → backbone 4 ASBR Summary ABR Area → backbone 5 AS External ASBR Entire OSPF domain 7 NSSA External ASBR in NSSA Single NSSA area Type 1 — Router LSA Every OSPF router originates one Type 1 LSA per area it belongs to. It describes: ...