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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.
After provisioning, I'm only getting around 940Mbit in Ookla speedtests. My Mac and switches are all connected via two ethernet ports in LACP active mode back to my router. I should be getting ~1300Mbit in speedtests.
My upload speeds are around 20-30Mbit when they should be ~40Mbit.
Is this related to firmware 6.01.04? Has anyone had similar experiences? As you can guess, Xfinity support is zero help. I read posts that earlier versions of firmware were better or worked.
Thanks.
8 Replies
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?
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.
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.
After provisioning, I'm only getting around 940Mbit in Ookla speedtests. My Mac and switches are all connected via two ethernet ports in LACP active mode back to my router. I should be getting ~1300Mbit in speedtests.
A common misconception here on LACP. Each dataflow is mapped to a single NIC - which means that it is limited to 1 gpbs. You only get more throughput when you have multiple flows - for instance, downloading from multiple clients simultaneously. Also, the decision on how to map each flow is made by the sending device. So the router is deciding how to map the download flows to the switch, and the switch decides how to map the download flows to the Macs (perhaps differently).
FWIW, LACP (and static LAG) perform best when set up as a trunk between switches/routers which carry a lot of data flows. Results are often disappointing on home networks, because they generally don't have enough simultaneous flows to get good load balancing.
940 mbps is a reasonable measurement for a 1 gigabit ethernet connection.
My upload speeds are around 20-30Mbit when they should be ~40Mbit.
Are you ever seeing faster speeds? I'd expect something between 35 and 40 mbps. If not, you might want to contact Xfinity.
