1. 1. Should we
configure the speed and duplex setting on interface or on port-channel?
Answer: Speed and duplex should be configured on the physical
interfaces.
2. 2. Should the
switchport command be configured on physical interfaces or on port-channel?
Answer: The switchport command should be configured on both the physical interfaces and the port-channel.
In BGP operations, applying a new policy (route-map, prefix-list, filter) traditionally required resetting the BGP session, which causes traffic disruption. To overcome this, soft reset mechanisms were introduced.
Two commonly confused approaches are:
- Soft-Reconfiguration Inbound
- Soft Reset Inbound (Route Refresh – “soft-reconfiguration inbound always”)
Understanding the difference is critical for design efficiency, memory optimization, and operational best practices, especially in large-scale environments like Cisco ACI or data center fabrics.
What is Soft-Reconfiguration Inbound
Soft-reconfiguration inbound is a legacy feature that allows a router to store all received BGP updates before applying inbound policy.
Key Behavior
- Router stores unfiltered BGP routes from the neighbor in memory
- When a policy changes, router re-applies the policy locally
- No need to request routes again from peer
Configuration
router bgp 100
neighbor 10.1.1.1 remote-as 200
neighbor 10.1.1.1 soft-reconfiguration inbound
Pros
- Works even if peer does NOT support route refresh
- Immediate policy re-evaluation without peer interaction
Cons
- High memory consumption (stores full BGP table twice)
- Not scalable for large environments (Internet routes / large DC fabrics)
What is Soft Reset Inbound (Route Refresh / “Always”)
Soft reset inbound using Route Refresh Capability is the modern and preferred method.
When you execute a soft reset, the router requests the neighbor to re-send routing updates, and applies new policy dynamically.
Key Behavior
- No local storage of full routes
- Router requests neighbor: “Send me routes again”
- Policy applied during re-learning process
Configuration (Implicit – modern default)
router bgp 100
neighbor 10.1.1.1 remote-as 200
Most modern devices support route refresh automatically.
Command Usage
clear ip bgp 10.1.1.1 soft in
Optional Keyword (“always”)
clear ip bgp 10.1.1.1 soft in always
This forces refresh even if capability visibility is unclear.
Pros
- No additional memory usage
- Scalable and efficient
- Industry best practice
Cons
- Requires peer support for route refresh
- Slight delay while routes are re-requested
Key Difference: Soft-Reconfiguration Inbound vs Soft Reset Inbound Always
| Feature | Soft-Reconfiguration Inbound | Soft Reset Inbound (Always / Route Refresh) |
|---|---|---|
| Storage | Stores full BGP table locally | No local storage |
| Memory Usage | High | Low |
| Dependency | Independent of peer | Requires route refresh support |
| Performance | Immediate, but heavy | Efficient, slight re-fetch delay |
| Scalability | Poor (not recommended) | Excellent |
| Modern Usage | Deprecated / rare | Preferred approach |
Real-World Example
Scenario
You apply a new inbound route-map on a BGP neighbor.
Using Soft-Reconfiguration Inbound
- Router already has full routing table stored
- Applies new policy instantly
- Uses additional RAM
Using Route Refresh
- Router sends request to neighbor
- Neighbor re-advertises routes
- Policy applied during reprocessing
- No memory overhead
When to Use What
Use Soft-Reconfiguration Inbound Only When:
- Working with very old devices
- Neighbor does NOT support route refresh
- Temporary troubleshooting in constrained scenarios
Use Route Refresh / Soft Reset Always When:
- Modern networks (recommended everywhere)
- Cisco ACI external routing (L3Out BGP)
- Internet edge / DC fabrics
- Large-scale BGP environments
Cisco ACI Perspective
In ACI environments, BGP is widely used for L3Out connectivity.
- ACI uses modern NX-OS capabilities
- Route refresh is supported by default
- Enabling soft-reconfiguration inbound is not recommended
Best practice:
- Avoid unnecessary memory overhead on leaf switches
- Use route refresh for policy changes
Important Interview Question
Q: Why is soft-reconfiguration inbound not recommended in modern networks?
Answer:
Because it consumes significant memory by storing unfiltered BGP routes locally, while route refresh provides the same functionality more efficiently without memory overhead.
Key Takeaways
- Soft-reconfiguration inbound = old, memory heavy method
- Route refresh (soft reset inbound always) = modern, efficient approach
- Always prefer route refresh in production networks
- Avoid enabling soft-reconfiguration unless absolutely necessary
Conclusion
Understanding the difference between soft-reconfiguration inbound and soft reset inbound (route refresh) is essential for designing scalable and efficient BGP networks.
In today’s data center and cloud-driven environments, route refresh is the default and recommended approach, ensuring better performance without unnecessary resource consumption.
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