Observing Performance Issues After Migration From F5 to Avi

Products

• VMware Avi Load Balancer

Issue/Introduction

Users experienced degraded download throughput when accessing services fronted by Avi load balancers following migration from F5.

Example impact observed:

• Slow download speeds

• Inconsistent throughput

• No issues observed with uploads

Cause

Packet captures indicated:

• Network drops and out-of-order packet delivery, leading to congestion buildup on the Service Engine (SE).

• F5 uses a proprietary TCP algorithm (“Woodside”) that recovers more aggressively from packet loss.

• Avi, using a standards-based TCP stack, entered congestion recovery more conservatively under the same network conditions.

This increased Avi’s sensitivity to underlying network issues, resulting in reduced download throughput until TCP tuning was applied.

Resolution

Avi TCP profile parameters were adjusted to improve resilience against packet drops and reordering.

Updated TCP Profile Settings

Frontend TCP Profile (Edit VS > Network Profile)

• Receive Window: 2048 KB

• Reorder Threshold: 16

• Auto Window Growth: Disabled

Backend TCP Profile (Edit VS > Advance > Server Network Profile)

• Receive Window: 1024 KB

• Reorder Threshold: 16

• Auto Window Growth: Disabled
  
  
  

Refer this doc for more details:

https://techdocs.broadcom.com/us/en/vmware-security-load-balancing/avi-load-balancer/avi-load-balancer/30-1/vmware-avi-load-balancer-configuration-guide/load-balancing-overview/tcp-or-udp-profile/tcp-proxy.html

 

Note: Reorder Threshold and Auto Window Growth needs to be changed via CLI.

[admin:]: > configure networkprofile <name of network profile>
[admin:]: networkprofile> profile tcp_proxy_profile
[admin:]: networkprofile:profile:tcp_proxy_profile> no auto_window_growth
[admin:]: networkprofile:profile:tcp_proxy_profile> reorder_threshold 16
[admin:]: networkprofile:profile:tcp_proxy_profile> save
[admin:]: networkprofile> save

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Results After Tuning

Platform	Observed Download Throughput
Avi	~3–3.5 MBps (consistent)
F5	~1 MBps (average)

Additional observations:

• Upload performance was unaffected both before and after tuning.

• No defects were identified on Avi; the behaviour was driven by upstream network conditions plus algorithm differences.
  
  

If you are unsure about applying the above TCP profile changes or require guidance tailored to your environment, please contact Avi Support for assistance.

Additional Information

The performance issue stemmed from network-level packet behaviour rather than Avi functionality. After applying optimized TCP parameters, Avi provided significantly better download performance than the previous F5 deployment. This configuration can be recommended for similar environments where packet drop or reordering is expected.