How do I test lan cable speed in situ?

I have one leg of my network with switches at each end persistently showing as 100Mb not 1Gb, ie amber lights showing, not green.
As far as I know all the devices on this leg are gigabit devices although there might be a rogue and I am still going through unplugging again after some changes at the weekend. If my device isolation fails I am thinking it could be due to old cat 5 cable.
Does anybody have any ideas how I might test cable throughput for the cables which will be difficult to replace please?

Your description is rather unclear. Do you have 100Mb between two switches or you have 100Mb between switches and each device connected to these switches?

If it is between switches, what is shown for other connected devices (100Mb or 1Gb) on each switch?

And yes, 1Gb requires all 8 wires so any loose wire will cause downgrade to 100Mb (1Gb cards can use any available pair for transmit). Your switch may show information over which wires are not functional (Cisco switches do, at least some of them).

There are cable testers which show all the details about your cable.

Poor man solution is to simply connect two devices directly using this cable, then check established speed and run some benchmarks like iperf.

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Sorry if I was not clear, all the devices, including the switches are gigabit devices and the only indicator lights I have been concerned with are the indicator lights at each switch which are at either end of a wireless bridge.
No suitable cable tester to hand. Will look at the benchmark suggestion. Many thanks for the ideas.

Do you really have 1Gb wireless bridge? What cable are you going to check? Wireless?

Can you log into the network devices?
If yes, are there any counters available in the devices relevant to the throughput information you want to check?

Yes. We have two bridges, both working over quite short distances on 5GHz link within the site. Both are intended to work at 1GB but one has been stubbornly failing and having just upgraded the wifi devices I have been trying to trouble shoot the issue. The cable in question I suspect at present is the cable between PoE injectors and the external wifi devices, sadly the most difficult to change, hence my original question.

Is there a spare Ethernet port on the devices?

  • You may be able to login to the things via that port …

There are Ethernet cable testers available – “newegg” are listing testers priced between about 30 $US and 200 $US – there are testers available from Fluke which are priced here in Germany at between about 800 € and 3,000 € …

Apart from that, take 2 Linux Laptops, one at each end of the cable, generate a large file → “cat” a large file repeatedly to a new large file → iterate that step several times until you have a really large file.

  • Then, transfer that file between the 2 Laptops and monitor the network traffic.

If anyone is wondering how network management looks from a GUI running on a DSL Router, here you are – sorry about the German language but, there are translation tools …

Yes, it looks really nice.

However neither the 7490 nor the 7590 know anything about my (non-AVM) network-switch.

Testing with iperf is straight forward: TCP und UDP Netzwerk Performance mit iperf messen – Thomas-Krenn-Wiki

6700k:~ # iperf3 -c erlangen
Connecting to host erlangen, port 5201
[  5] local 2001:... port 53088 connected to 2001:... port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec  12.8 MBytes   107 Mbits/sec    0    527 KBytes       
[  5]   1.00-2.00   sec  10.8 MBytes  90.7 Mbits/sec    0    667 KBytes       
[  5]   2.00-3.00   sec  11.2 MBytes  94.4 Mbits/sec    0    703 KBytes       
[  5]   3.00-4.00   sec  11.2 MBytes  94.4 Mbits/sec    0    703 KBytes       
[  5]   4.00-5.00   sec  11.2 MBytes  94.4 Mbits/sec    0    703 KBytes       
[  5]   5.00-6.00   sec  10.0 MBytes  83.9 Mbits/sec    0    703 KBytes       
[  5]   6.00-7.00   sec  11.2 MBytes  94.4 Mbits/sec    0    703 KBytes       
[  5]   7.00-8.00   sec  11.2 MBytes  94.4 Mbits/sec    0    703 KBytes       
[  5]   8.00-9.00   sec  11.2 MBytes  94.4 Mbits/sec    0    703 KBytes       
[  5]   9.00-10.00  sec  10.0 MBytes  83.9 Mbits/sec    0    747 KBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec   111 MBytes  93.2 Mbits/sec    0             sender
[  5]   0.00-10.01  sec   108 MBytes  90.7 Mbits/sec                  receiver

iperf Done.
6700k:~ #

H and thanks to all. I should explain that the switches at each end of the link are rather old HP switches. So old, in fact, that they have a lifetime replacement guarantee which I was able to use recently to good effect but only with a replacement by the same device!

One tip:

You can use ethtool to see details of your Ethernet port including the “Link partner advertised link modes” and the actual speed. With this you can see on your PC what the connected device is capable of and what is the outcome of the speed negotiation.

> sudo ethtool -I enp3s0
Settings for enp3s0:
        Supported ports: [ TP    MII ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Half 1000baseT/Full
        Supported pause frame use: Symmetric Receive-only
        Supports auto-negotiation: Yes
        Supported FEC modes: Not reported
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Half 1000baseT/Full
        Advertised pause frame use: Symmetric Receive-only
        Advertised auto-negotiation: Yes
        Advertised FEC modes: Not reported
        Link partner advertised link modes:  10baseT/Half 10baseT/Full
                                             100baseT/Half 100baseT/Full
                                             1000baseT/Half 1000baseT/Full
        Link partner advertised pause frame use: No
        Link partner advertised auto-negotiation: Yes
        Link partner advertised FEC modes: Not reported
        Speed: 1000Mb/s
        Duplex: Full
        Auto-negotiation: on
        master-slave cfg: preferred slave
        master-slave status: master
        Port: Twisted Pair
        PHYAD: 0
        Transceiver: external
        MDI-X: Unknown
        Supports Wake-on: pumbg
        Wake-on: d
        Link detected: yes

And they don’t support SNMP? – <>

Hi and thanks for the thought. Of course the devices support SNMP but I regret I have no knowledge or experience with this. Also the devices are all accessed for management remotely on a management Vlan with several switches in between and I have no idea how to thread my way through the firewalls.

My solution will be to arrange a suitable time to access the end of the cable and pull a new one. Booked for tomorrow morning. Will report results in due course.

Thanks again for the thoughts and help and hope my pragmatic solution works.

The following Network Monitoring tools are available in the openSUSE repositories:

  • Nagios
  • Icinga
  • Zabbix

A comparison of Network Monitoring tools is here: <>

Hi and many thanks for the info.
As I outlined earlier I do not normally have direct access to the devices which were suspect and access through all the firewalls was above my pay grade but I was able to obtain physical access at the weekend.

I have renewed the suspect cat5 cable with new cat 6 cable and also changed the patch leads at the WAN end of the bridge.

I am pleased to report that the link is now running at Gb speeds, all lights green so job done and many thanks meanwhile for the help and advice.