On 02/13/2018 01:57 PM, Stephen Morris wrote:
> On 13/2/18 8:51 am, Ed Greshko wrote:
>> On 02/13/18 05:43, Stephen Morris wrote:
>>> I am using a home plug device to get ethernet access across the home
>>> electrical
>>> wires. The home plug device is provide 500 Mb/s, so having seen this
>>> thread I've
>>> checked my ethernet configuration and like Terry is saying my
>>> settings have auto
>>> negotiate unchecked and the link speed is set at 100 Mb/s and Half
>>> Duplex. I have
>>> not explicitly set that configuration but what I don't know, because
>>> I haven't
>>> really taken any notice of it as I only use this connection as a
>>> backup to
>>> wireless, is whether or not those settings have always been there. I
>>> have done any
>>> changes to the configuration since I set it up in F26.
>>
>> One can always use
>>
>> ethtool <devname> to determine what is available and what the
>> current settings are...
>>
>> This is the view from the Fedora side....
>>
>> This is what the Fedora side it telling the outside world what the HW
>> supports
>>
>> Advertised link modes: 10baseT/Half 10baseT/Full
>> 100baseT/Half 100baseT/Full
>> 1000baseT/Half 1000baseT/Full
>>
>> This is what the device that the Fedora system is connected to is
>> saying what it
>> supports.
>>
>>
>> Link partner advertised link modes: 10baseT/Half 10baseT/Full
>> 100baseT/Half 100baseT/Full
>> 1000baseT/Full
>>
>> FWIW, I have never seen an advertised link speed of 500 Mb/s.
>
> I ran the ethtool command and received the following output:
>
> ethtool enp7s0
> Settings for enp7s0:
> Supported ports: [ TP MII ]
> Supported link modes: 10baseT/Half 10baseT/Full
> 100baseT/Half 100baseT/Full
> 1000baseT/Half 1000baseT/Full
> Supported pause frame use: No
> Supports auto-negotiation: Yes
> 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
> Link partner advertised link modes: 10baseT/Half 10baseT/Full
> 100baseT/Half 100baseT/Full
> Link partner advertised pause frame use: Symmetric Receive-only
> Link partner advertised auto-negotiation: Yes
> Speed: 100Mb/s
> Duplex: Full
> Port: MII
> PHYAD: 0
> Transceiver: internal
> Auto-negotiation: on
> Cannot get wake-on-lan settings: Operation not permitted
> Current message level: 0x00000033 (51)
> drv probe ifdown ifup
> Link detected: yes
>
> This surprises me, as this is saying the home plug device is only
> running at 100 Mbps, but it is packaged as 500 Mbps and the device
> itself has 500 Mbps physically stamped on the front of it. I did set the
> manual configuration to 500 Mbps and full duplex, and when I turned on
> auto negotiate and then switched it off, the link speed was reset to 100
> Mbps.
The fact that the link partner advertises 10 and 100baseT, either full
or half duplex indicates that 100baseT/Full is the max it can do (at
least on that port). Typically, a switch won't advertise a higher speed
than it can do. It can, however, connect at a lower speed than it
advertises. In other words, 10Mbps and 100Mbps aren't the _only_ speeds
it can do, but it can't go above 100Mbps on that port.
As an example, I have some HP gear that has a segmentable 10Gbps switch
where I've divvied up its 10Gbps bandwidth into three VLANs, two at
4.5Gbps and one at 1Gbps. Looking at the interfaces of one of the
machines connected to one of the 4.5Gbps VLANs, you find this:
[root@seg3-r0 ~]# ethtool eth2
Settings for eth2:
Supported ports: [ TP ]
Supported link modes: 1000baseT/Full
10000baseT/Full
Supports auto-negotiation: No
Advertised link modes: 1000baseT/Full
10000baseT/Full
Advertised auto-negotiation: No
Speed: 4500Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 1
Transceiver: internal
Auto-negotiation: on
Supports Wake-on: g
Wake-on: g
Link detected: yes
Note that the host can do 1000baseT/Full and 10000baseT/Full. I'm not
sure if the switch advertises (I'm sure it does but the host I'm looking
at is an ancient CentOS 5 machine so its ethtool output may be different
than current versions). That being said, the actual speed of the link
is 4500Mbps (4.5Gbps), which is what I expect over that link. Before you
ask, it's not really twisted pair, it's a backplane...this is all in a
big blade-based system.
On your host, you can try to force a faster speed by doing
ethtool -s enp7s0 speed 500
as root to see if you can get it to go 500Mbps (or "...speed 250" to try
250Mbps). I doubt it'll work, but it's quick and easy to try.
Just because the device is advertised at 500Mbps doesn't mean it can
actually do it and it may be that it's 500Mbps _aggregate_ (i.e. if it
has five ports, each can be set to 100Mbps without contention). If
that's the case, yes the device can do 500Mbps total and they didn't
fib about it, but any _single_ port is limited to 100Mbps.
Now, if the device supports 802.3ad, you could use two NICs on your
host to two ports on the device, set up bonding using mode 4 and get
200Mbps (ok, now I'm just getting crazy!)
----------------------------------------------------------------------
- Rick Stevens, Systems Engineer, AllDigital ri...@alldigital.com -
- AIM/Skype: therps2 ICQ: 22643734 Yahoo: origrps2 -
- -
- Never test for an error condition you don't know how to handle. -
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