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Forum Discussion
emuman100
Mar 01, 2026Aspirant
CM3000 on Xfinity with 1200Mbit, onlt getting around 940Mbit with link aggregation
I just purchased a CM3000 for use with my Xfinity 1200mbit plan. It's currently running firmware 6.01.04. It was set up in link aggregation mode and connected to my router via ethernet ports 1 and 2....
FURRYe38
Mar 02, 2026Guru - Experienced User
Do you get 1200Mbps directly connected behind the CM modem with out the router being connected and LAG disabled on the CM modem?
The CM modem already has a 2.5Gb WAN Port.
If you have a 2.5Gb or higher capable ethernet PC, you should see what your pay for from your ISP from the CM modem.
Brand and model# of the router you have connected to the modem?
Brand and model# of LAN swiches connected to the router?
Model# of Mac you have connected? Supporting of over 1Gb ethernet ports on the Mac?
- emuman100Mar 02, 2026Aspirant
No, I use link aggregation enabled on the CM3000 with LACP active mode on the router. Connection to the Mac is though LAG using the Mac ethernet port and a USB ethernet adapter plugged into a Cisco switch in active LACP mode to another switch, also the same, with a active LACP configuration to the router. So, this should work.
- StephenBMar 03, 2026Guru - Experienced User
emuman100 wrote:
No, I use link aggregation enabled on the CM3000 with LACP active mode on the router. Connection to the Mac is though LAG using the Mac ethernet port and a USB ethernet adapter plugged into a Cisco switch in active LACP mode to another switch, also the same, with a active LACP configuration to the router. So, this should work.
See my reply.
LACP won't deliver more than 1 gbps per dataflow. Each flow is mapped independently by each transmitter on the path to one of the two downstream NICs. That eliminates out-of-order delivery. Speedtest only has one dataflow, so you won't see more than 1 gbps to the mac. LACP active mode doesn't change this behavior.
Generally this works best with a single client when you can use layer 3+4 load balancing on all hops. But I don't see that as an option with the CM3000. Layer 2 load balancing will treat all the traffic going inbound as a single flow, since it only looks at the source and destination MAC addresses when identifying a data flow. That will be mapped onto one NIC by the CM3000, so it is limited to 1 gbps. But even with layer 3+4 load balancing, speedtest still would be treated as one flow, since the packets all have the same IP address and ports.
The easiest way to get full speed is to use multigig ethernet instead of a LAG.
- emuman100Mar 03, 2026Aspirant
The Ookla speedtest, both app and in-browser is multi-connection, so shouldn't this be multiple data flows? I've seen other's Ookla results with link aggregation and it's well over 1000Mbit, so is there something wrong or is the Ookla speedtest not truly multi-connection?
- FURRYe38Mar 03, 2026Guru - Experienced User
As a test, Do you get 1200Mbps directly connected behind the CM modem with out the router being connected and LAG disabled on the CM modem?
If you have a 2.5Gb or higher capable ethernet PC or Ethernet adapters, you should see what your pay for from your ISP from the CM modem with out the switches in line.
This would be first thing to check and test.
emuman100 wrote:
No, I use link aggregation enabled on the CM3000 with LACP active mode on the router. Connection to the Mac is though LAG using the Mac ethernet port and a USB ethernet adapter plugged into a Cisco switch in active LACP mode to another switch, also the same, with a active LACP configuration to the router. So, this should work.