Cisco CCNP BSCI Exam Tutorial Introduction To Policy Routing
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Cisco CCNP BSCI Exam: A Guide to Policy Routing
Overview
Understanding policy routing is essential for passing the Cisco Certified Network Professional (CCNP) BSCI exam. But what exactly is policy routing? In this guide, we'll cover the basics, helping you grasp this crucial concept with insights from Chris Bryant, CCIE
12933.
What is Policy Routing?
Policy-based routing refers to using route maps to determine the path a packet takes to reach its destination. As you advance in your CCNP studies or pursue further certifications, such as the Cisco Quality of Service, you’ll notice how traffic can be marked for differentiated service levels. This involves placing various traffic classes in different router queues, allowing higher-priority transmission for certain data.
Key Principles of Policy Routing
- Path Determination: Policy routing influences the path a packet takes, not its final destination.
- Traffic Forwarding: It can forward traffic based on source or destination IP addresses via an extended Access Control List (ACL).
- Configuration Levels: Policy routing can be set at an interface level or globally.
Interface-Level Policy Routing
When applied to an interface, policy routing affects only the packets arriving there:
```plaintext
R2(config)
int s0
R2(config-if)ip policy route-map CHANGE_NEXT_HOP
```Global Policy Routing
Applying it globally impacts packets generated on the router, unlike those received on all interfaces.
Verification
Whether implemented at the interface or globally, use the command `show ip policy` to ensure the correct route maps are applied where needed.
```plaintext
R2
show ip policy
Interface Route maplocal CHANGE_NEXT_HOP
Serial0 CHANGE_NEXT_HOP
```
The Golden Rule
If a packet doesn’t match any route map criteria or matches a line with an explicit deny statement, it is processed normally. To prevent routing packets that don't meet any criteria, use the `set` command to send them to the null0 interface as the final step in the route map.
Route Map Examples
Consider this scenario involving route maps:
```plaintext
R2(config)
access-list 29 permit host 20.1.1.1
R2(config)access-list 30 permit host 20.2.2.2
R2(config)route-map EXAMPLE permit 10
R2(config-route-map)match ip address 29
R2(config-route-map)set ip next-hop 40.1.1.1
```- A packet from 20.1.1.1 matches the first route map line, setting its next-hop IP to 40.1.1.1.
- A packet from 20.2.2.2 matches the next line but returns to normal routing due to no specific action.
- Traffic that doesn’t match is routed normally.
To block traffic from certain sources, use multiple match statements and direct them to null0:
```plaintext
R2(config)
route-map EXAMPLE permit 30
R2(config-route-map)match ip address 31
R2(config-route-map)match ip address 32
R2(config-route-map)set interface null0
```This will discard traffic matching ACLs 31 or 32, while any unmatched traffic proceeds normally.
Conclusion
Mastering policy routing is crucial for the BSCI exam and CCNP certification. It not only boosts your credentials but also enhances your employability. Ensure you get hands-on practice in a CCNA/CCNP lab or through a rack rental to complement your theoretical knowledge. With practice, you'll become proficient in writing and applying policy routing quickly.
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You can find the original non-AI version of this article here: Cisco CCNP BSCI Exam Tutorial Introduction To Policy Routing.
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