2960C performance

[Marcel Tempelman]

Hello all,

one of our customers uses the 2960c at a lot of locations but at one location we see some strange behavior when it comes to performance.The location has this setup:

887VA DSL router for E-VPN connectivity

2 2960C switches

1800 access points

30/3 VDSL E-VPN connection

300/40 Docsis Internet connection

The DSL is for corporate use, the other connection is for clients (this is a healthcare customer).

The location has an Internet connection with a Docsis modem. The connection is +/- 300/40 Mbps. For a part of the network the Docsis modem is also DHCP-server and router.. The Docsis modem is directly connected to Gi0/2 on the 2960C. This port is configured as an access port.

If we test the internet connection, connected to one of the fast ethernet interfaces on the 2960C, the download speed tops at 40-41 Mbps. It does not matter if one client of several clients are using this switch. The upload speed during tests is conform what the ISP allows. If I move the link to the Docsis modem to a fast ethernet interface, the results are even more dramatic because then the download speed drops to 10 Mbps. If I change the vlan to break out via the E-VPN the download speed goes to 30 Mbps. One should be able to expect near 100 Mbps performance.

so in summary:

laptop -> fast ethernet

docsis modem -> gigabit

download max 40 Mbps

laptop -> fast ethernet

docsis modem -> fast ethernet

download max 10 Mbps

laptop -> fast ethernet

internet via E-VPN (881 is connected to a gig interface)

download max 30 Mbps

A client directly connected to the Docsis modem gets the full monty when it comes to performance.

To rule out any interop issues I placed a 891 router between the Docsis modem and the 2960c (knowing that it will not give us max speed) and the results stayed the same. Directly connected to the 891 gave me 120 Mbps down (routed but also when using the switch only).

The portconfig for the tested ports are:

switchport mode access

switchport access vlan 34

spanning-tree portfast

The switces were originally running a late 12.2.55 version. I upgraded them to 15.2(6)E and downgraded one of the two switches (there are 2 at this location) to 15.2(2)E7. This made no difference.

There are two other locations with a similar setup. One site shows the same behavior, the other does not (a speedtest on an iPhone gave 80Mbps down). The main difference is the two slow site use a Connect Box docsis modem and the other uses an older Cisco Docsis modem. My first thought was interop issue but the test with the 891 router ruled that out.

CPU and memory use were always low during the tests.

I am a bit lost where to look for a solution. The customer already tested with a few el cheapo switches and the performance was good on those so that also bugs us.

Any ideas ?

With kind regards,

Marcel Tempelman.

[Joseph W. Doherty · Accepted solution]

Switch to DOCSIS is gig? Client to switch is FE? If so, 2960 (and 3560/3750) switches, often have insufficient buffers for the speed slow down (especially if QoS is enabled and running with defaults). Any drops show on switch ports?

Have you tried DOCSIS and client at gig?

Am I reading correctly, you did try DOCSIS and client at FE? If so, that too was slow? For that, perhaps the DOCSIS cannot sufficient queue packets. You might client<>DOCSIS at both FE and gig and see how they compare.

[Marcel Tempelman]

Hello Joseph,

the DOCSIS modem is connected to the gig port om the 2960c and QoS is enabled. I see drops on the fast ethernet ports. I haven's tried the client on the other gig port.

A colleague of mine tested with a 2960c and a ASA5505 in front of the DOCSIS and he was able to reach 70-80 Mbps (conform max perf of the 5505). He has a Ubee DOCSIS modem which is a different one. A test with a Cisco DOCSIS modem on another location gave also better results.

Your analysis seems the right one to me. I overestimated the switch performance probably, so we might want to go for the CX of another Gig model.

[Marcel Tempelman]

Just did a test with a Ubee DOCSIS modem and a 2960c and a simple speedtest gave me 90-95 Mbps with and without QoS enabled. Gig-Gig gave me 116 Mbps (connection is limited to 150 Mbps).

Fa-Fa set the limit around 65 Mbps. So it seems the DOCSIS plays a crucial role in this.

[Marcel Tempelman]

Iperf3 test between 2 laptops

Gig(C)-Gig(S)

[SUM]   0.00-10.00  sec  1.10 GBytes   942 Mbits/sec                  sender
[SUM]   0.00-10.00  sec  1.10 GBytes   942 Mbits/sec                  receiver

Gig(C) - 100M(S)

60:  [SUM]   0.00-10.00  sec   114 MBytes  95.4 Mbits/sec                  sender
60:  [SUM]   0.00-10.00  sec   113 MBytes  95.0 Mbits/sec                  receiver

I think I'll give the 2960c the benefit of the doubt :-)