📘 CCNA 200-301 v1.1
3.1 Interpret the components of routing table
3.1.d Next hop
In networking, routers use a routing table to decide where to send packets next.
Each routing table entry tells the router:
- Which destination network can be reached,
- How to reach it (the next hop or exit interface),
- And what route type it is (e.g., static, dynamic, connected, etc.).
The “Next Hop” is a key field in the routing table that tells the router where to send the packet next on its way to the destination.
🧩 What is the “Next Hop”?
The Next Hop is the IP address of the next router that the current router should forward the packet to in order to reach the final destination network.
Think of it as:
“Who should I give this packet to next so it gets closer to the destination?”
🔹 Example in an IT environment
Let’s say we have three routers in a network:
PC ---- Router A ---- Router B ---- Router C ---- Destination Network
- The PC sends data to a remote server connected to Router C.
- Router A checks its routing table. It sees:
Destination: 192.168.50.0/24 Next Hop: 10.0.0.2 - The Next Hop (10.0.0.2) is Router B’s IP address on the network shared with Router A.
So Router A doesn’t send the packet directly to the destination network (192.168.50.0/24) — it sends it to Router B (Next Hop), which knows what to do next.
🧠 Why the Next Hop is Important
- It tells the router which neighboring device to forward packets to.
- Without a valid next hop, the router cannot forward the packet.
- It allows multi-router paths across large networks (like the internet).
- It’s used in both static and dynamic routing.
⚙️ How the Next Hop Appears in a Routing Table
Here’s how a Cisco router shows a typical routing table entry (using the show ip route command):
R1# show ip route
S 192.168.50.0/24 [1/0] via 10.0.0.2, GigabitEthernet0/0
Let’s break it down:
| Field | Meaning |
|---|---|
| S | Route source (Static route) |
| 192.168.50.0/24 | Destination network |
| [1/0] | Administrative Distance (1) / Metric (0) |
| via 10.0.0.2 | Next Hop IP address (Router B) |
| GigabitEthernet0/0 | Exit interface used to reach the next hop |
👉 The Next Hop (10.0.0.2) is crucial here. It tells Router A which IP address (neighbor router) will handle the packet next.
🗺️ Types of Next-Hop Information in a Routing Table
Depending on how a route is learned, the next-hop information might appear differently:
| Route Type | Example | Description |
|---|---|---|
| Connected route | C 10.0.0.0/24 is directly connected, GigabitEthernet0/0 | No next hop needed — the destination is directly attached. |
| Static route | S 192.168.50.0/24 [1/0] via 10.0.0.2 | The next hop is manually set by the admin. |
| Dynamic route (e.g., OSPF, EIGRP) | O 192.168.60.0/24 [110/20] via 10.0.0.2, 00:00:12, GigabitEthernet0/1 | Learned automatically through routing protocols — next hop provided by the neighbor router. |
| Default route | S* 0.0.0.0/0 [1/0] via 10.0.0.1 | Used when no specific route matches; next hop is where all “unknown” traffic goes. |
🔄 Next Hop vs Exit Interface
| Term | Meaning | Example |
|---|---|---|
| Next Hop | The IP address of the next router in the path | via 10.0.0.2 |
| Exit Interface | The local interface used to reach that next hop | GigabitEthernet0/0 |
Sometimes both are shown in the routing table, depending on the routing method.
✅ Directly connected next hop:
If the next hop is on a directly connected network, the router can resolve the next-hop IP address to a MAC address using ARP (Address Resolution Protocol) and send the frame out of the correct interface.
🧮 How the Router Uses the Next Hop
When a packet arrives:
- The router checks the destination IP address in the packet.
- It searches the routing table for the best match (longest prefix match).
- It finds the entry — which includes a next hop and exit interface.
- The router forwards the packet to that next-hop IP address through the specified interface.
- The process repeats on the next router until the destination network is reached.
⚠️ Common Issues with Next Hop
| Problem | Cause | Result |
|---|---|---|
| Invalid next-hop IP | Admin typed wrong IP in a static route | Packet gets dropped (no route found). |
| Next hop not reachable | Link down or neighbor router offline | Route becomes inactive. |
| No ARP resolution | Router can’t find MAC address for next-hop IP | Packet can’t be sent — router keeps retrying. |
🧾 In Short (Exam Summary)
| Concept | Description |
|---|---|
| Definition | The IP address of the next router that should receive the packet to reach the destination. |
| Purpose | Guides the router on where to send packets next. |
| Used In | Static and dynamic routing. |
| Displayed As | “via <IP address>” in the routing table. |
| Difference from Exit Interface | Next hop = neighbor router’s IP; Exit interface = your router’s local port used to send it. |
| Importance | Without next-hop info, the router can’t forward packets to other networks. |
✅ Key Command for CCNA:
show ip route
This command displays:
- Destination networks
- Next-hop addresses
- Administrative distances and metrics
- Exit interfaces
- Route sources (C, S, O, D, etc.)
