##
Routing Deep-Dive
All the protocols side by side, plus the static/default route concepts that glue real networks together.
| Protocol | Type | Metric | AD |
|---|
| RIP | Distance-vector | Hop count (max 15) | 120 |
| EIGRP | Advanced DV | Bandwidth + delay | 90 / 170 |
| OSPF | Link-state | Cost = 10⁸ / bw | 110 |
| IS-IS | Link-state | Cost | 115 |
| BGP | Path-vector | AS-path / policy | 20 / 200 |
// route concepts
| Static route | Manually set next-hop / exit interface |
| Default route | 0.0.0.0/0 — gateway of last resort |
| Floating static | High-AD backup to a dynamic route |
| Summarization | Aggregate prefixes to shrink the table |
| Longest prefix match | Most specific route always wins |
// EIGRP
- DUAL algorithm — fast loop-free convergence
- Successor = best path · Feasible successor = backup
- Composite metric from bandwidth + delay
- Multicast 224.0.0.10 · routers share an AS number
// RIP
- RIPv2 is classless, sends mask, multicast 224.0.0.9
- Metric = hop count, 16 = unreachable
- Updates every 30 s · split horizon prevents loops
// fast convergence & resiliency
| BFD | Sub-second failure detection any protocol can subscribe to |
| Graceful Restart / NSF | Keep forwarding while the control plane restarts |
| Fast timers | Lower hello/dead — faster detection, more CPU |
| Summarization | Hide flaps behind a summary — smaller failure domain |
| iSPF / PRC | Partial recompute instead of full SPF (OSPF/IS-IS) |
| LFA / FRR | Pre-computed loop-free backup — instant reroute |