Troubleshoot route maps for any routing protocol (attributes, tagging, filtering)

📘CCNP Enterprise – ENARSI (300-410)

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1️⃣ What Are Route Maps?

A route map is like a set of rules applied to routes. It works with routing protocols (BGP, OSPF, EIGRP, etc.) and allows you to:

• Filter routes: Decide which routes are allowed or denied.
• Modify attributes: Change metrics, tags, or next-hop values.
• Tag routes: Mark routes so that other devices or routing decisions can use them.

Basic Structure of a Route Map

A route map consists of:

route-map <NAME> [permit|deny] <SEQUENCE_NUMBER>
 match <conditions>
 set <actions>

• NAME: Name of the route map.
• permit/deny: Determines if a route meeting the match conditions is permitted (and optionally modified) or denied.
• SEQUENCE_NUMBER: Order in which the route map statements are evaluated.
• match: Conditions used to identify routes (prefix lists, AS paths, metrics, tags, etc.)
• set: Actions to apply to matching routes (set next-hop, set metric, set tag, etc.)

Key idea for exam: Route maps are evaluated top-down, and the first matching sequence stops evaluation for that route.

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2️⃣ Why Troubleshoot Route Maps?

When route maps don’t work as intended, it usually causes:

• Routes not being advertised or received.
• Incorrect route selection.
• Unexpected routing behavior in the network.

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3️⃣ Key Areas to Check When Troubleshooting Route Maps

A. Route Map Sequence and Order

• Problem: Route map statements are processed top-down.
• Tip: If an earlier sequence denies a route, later sequences won’t apply.
• Exam point: Always check sequence numbers; missing or misordered sequences can block expected behavior.

Example:

route-map RM1 permit 10
 match ip address 10
 set metric 50

route-map RM1 permit 20
 match ip address 20
 set metric 100

If a route matches sequence 10, sequence 20 is never checked for that route.

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B. Match Statements

• Match statements define which routes the route map affects.
• Common match conditions:
  • ip address: Match routes using prefix-lists.
  • metric: Match routes based on metrics.
  • tag: Match routes with a specific tag.
  • route-type: Match internal or external routes.

Troubleshooting tip: If your route map isn’t affecting a route, check whether the match criteria actually match the route.

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C. Set Actions

• Set actions define how the route is modified.
• Common set actions:
  • set metric or set metric-type
  • set tag
  • set next-hop
  • set local-preference (BGP-specific)
  • set community (BGP-specific)
• Troubleshooting tip: Verify the set command syntax; invalid values are ignored silently.

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D. Route Tags

• Route tagging is used to identify or mark routes.
• Useful in redistribution, filtering, and controlling routing policies.
• Troubleshooting tip: Check if the tag value is correctly matched in the route map or by other route maps. If tags are missing or incorrect, routing policies won’t work.

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E. Filtering and Denying Routes

• Route maps can deny or permit routes.
• Important exam point:
  • deny: The route is ignored by the routing protocol (not advertised or not redistributed).
  • permit: The route is allowed, and any set actions are applied.
• Troubleshooting tip: A common mistake is denying a route when you meant to modify it. Always double-check the permit/deny logic.

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F. Route Map Logging and Verification Commands

To troubleshoot route maps, Cisco provides several useful commands:

1. Check applied route maps

show run | section route-map

2. Check route map matches

show ip route
show ip bgp

3. Debug commands

debug ip bgp updates
debug ip routing

4. Verify redistribution

show ip route <protocol>
show ip protocols

5. Check route tagging

show ip route tag

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G. Redistribution Context

• Route maps are often applied during redistribution between protocols.
• Example:

router ospf 1
 redistribute bgp 65001 subnets route-map RM-TO-OSPF

• Troubleshooting tip: Ensure that:
  • The route map is applied in the correct direction.
  • Match and set criteria are correct for the redistributed routes.
  • Metrics or tags are consistent.

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4️⃣ Common Route Map Troubleshooting Scenarios

Scenario	Possible Cause	Troubleshooting Step
Route not advertised to another protocol	Deny in route map or mismatch in match statement	Check permit/deny and match conditions
Route has wrong metric	Set metric applied incorrectly or sequence misordered	Verify set commands and sequence numbers
Route is not filtered properly	Tag mismatch or missing match	Check tags and match statements
Route map not applied	Typo or not bound to routing protocol	Verify with show run and correct application

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5️⃣ Practical Tips for Exam

1. Always check top-down evaluation: Sequence numbers matter.
2. Understand permit vs. deny: Deny stops a route; permit allows modifications.
3. Match before set: Only matching routes get modified.
4. Tags are critical for redistribution: Check if tags are applied correctly.
5. Use show commands to verify real routing information after applying a route map.

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✅ Summary

• Route maps = advanced routing filters and modifiers.
• Troubleshooting involves checking:
  • Sequence numbers
  • Match statements
  • Set actions
  • Tags
  • Redistribution applications
• Exam focus: Know how route maps affect routing protocols, how to verify them, and how to fix common issues.

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