Customer-owned DOCSIS 3.1 modem capped at 200 Mbps on a 1 Gig plan

Figured out. Issue was related to prior pfSense QoS setting to fix Buffer Bloat. I have asked Gemini to summarize the issue and fix:

Technical Summary: Throughput Bottleneck Resolved

Subject: Resolution of 400 Mbps Speed Cap – Configuration Conflict on CPE

Issue Description: Following a hardware upgrade to a Hitron CODA56 (DOCSIS 3.1) and a transition to the Xfinity Gigabit Extra tier, the connection was consistently capped at approximately 400–420 Mbps Download and 40 Mbps Upload. Diagnostics were performed to determine if the bottleneck was physical (layer 1/2), ISP-provisioning related, or internal routing overhead.

Diagnostic Steps Taken:

1. Interface Verification: Verified the WAN interface (Intel igb0) was negotiating at 1000baseT <full-duplex> with 0 input errors and 0 drops (netstat -i -d), ruling out physical cable or port negotiation issues between the 2.5G modem port and the 1G router port.

2. Provisioning Check: Confirmed with Xfinity support that the correct Next-Gen Gigabit bootfile (d11_m_coda56_gennxgig_c01.cm) was pushed and active.

3. Service Overhead: Temporarily disabled multiple OpenVPN instances to rule out CPU "context switching" bottlenecks on the router's i3 processor.

4. QoS/Traffic Shaper Audit: Identified an active FQ_CoDEL Limiter within the pfSense firewall.

Root Cause: The bottleneck was a legacy Traffic Shaper (Limiter) configuration. The router was configured with a "Download Pipe" hard-coded to 500 Mbps and an "Upload Pipe" of 20 Mbps. These settings were originally implemented to mitigate "Bufferbloat" on a previous, slower service tier. Due to the computational overhead of the CoDel algorithm on a single CPU core, the 500 Mbps logical limit resulted in an effective real-world throughput of ~400 Mbps.

Resolution: The Download Limiter was updated to 950 Mbps (to match the physical overhead of the 1G Ethernet handoff) and the Upload Limiter was increased to 100 Mbps. Immediately following these changes, the system achieved a sustained throughput of 940+ Mbps Download and 115+ Mbps Upload, confirming that the Xfinity "Mid-Split" provisioning and the Hitron hardware are performing at peak specifications.