[c-nsp] connection speed at physical layer

[John Gill]

I see - thanks for the clarification.

The command on most of our switches to determine what speeds we can 
support is:

show interface capabilities (nxos/ios)
show port capabilities (catos)

Chances are, your friend was using a 10/100/1000 port - but some 
interfaces are strictly 1000 (usually gbic/sfp interfaces though) and in 
that case no link should be observed.

Regards,
John Gill
cisco


On 7/21/11 3:48 PM, Martin T wrote:
> Hi John,
> I determine it with:
>
> ethtool -s eth0 advertise 0x02
>
> For example "0x04" would be 100BASE-TX/Half or "0x20" would be
> 1000BASE-T/Full. "ethtool eth0" gives:
>
> root at martin-ThinkPad-T60:/home/martin# ethtool eth0
> Settings for eth0:
> 	Supported ports: [ TP ]
> 	Supported link modes:   10baseT/Half 10baseT/Full
> 	                        100baseT/Half 100baseT/Full
> 	                        1000baseT/Full
> 	Supports auto-negotiation: Yes
> 	Advertised link modes:  10baseT/Full
> 	Advertised pause frame use: No
> 	Advertised auto-negotiation: Yes
> 	Speed: 10Mb/s
> 	Duplex: Full
> 	Port: Twisted Pair
> 	PHYAD: 1
> 	Transceiver: internal
> 	Auto-negotiation: on
> 	MDI-X: off
> 	Supports Wake-on: pumbag
> 	Wake-on: g
> 	Current message level: 0x00000001 (1)
> 	Link detected: yes
> root at martin-ThinkPad-T60:/home/martin#
>
> As you can see, after executing "ethtool -s eth0 advertise 0x02", the
> only link mode I advertise, is "10baseT/Full". It's same as for
> example on Cisco 4500 platform many line cards with GI ports support
> "speed auto 100" or "speed auto 10" which means that they advertise
> themselves as 100BASE-TX or 10BASE-T ports.
>
>
> The reason I asked this question at first place, was that I heard a
> story from a friend of mine, that if you connect for example FE port
> and GI port like this:
>
> Cisco2950[Fa0/1]<->  [Gi0/11]Cisco2960
>
> ..using "speed auto" and "duplex auto" on both Fa0/1 and Gi0/11 port
> the link will of course come up at 100BASE-TX/Full mode, but actually
> GI interface will send electrical signals 10 times faster than FE port
> sends towards GI port and this fills inbound buffers of FE port
> faster. However, now it's sorted out, that it was a myth :)
>
> regards,
> martin
>
>
> 2011/7/21 John Gill<johgill at cisco.com>:
>> Hi Martin,
>> I am not sure how you determine you only advertise 10/full, but speed
>> detection is not hard, but rather duplex is where it's more necessary.
>>
>> The interface on the switch is able to operate in 10 or 100 at the phy, in
>> this case it knows it can understand the 10Mb/s signaling coming from the
>> T60, so it steps down and that is the only way link is established.  I have
>> not heard of two phy's operating at different speeds on the same link.
>>
>> John Gill
>> cisco
>>
>>
>> On 7/21/11 7:42 AM, Martin T wrote:
>>>
>>> Martin,
>>> I'm running GNU/Linux(Debian). I set this manually for testing
>>> purposes. In other words eth0 interface is configured to allow
>>> autonegotiation, but advertises only 10BASE-T/Full.
>>>
>>> So it's clear, that if GE interface is configured to 10BASE-T mode, it
>>> will send traffic on physical layer at max 10Mbps. Or for example if
>>> FE interface is set to 10BASE-T mode, it will not send electrical
>>> signals at rate of 100Mbps, but instead 10 times slower?
>>>
>>>
>>> regards,
>>> martin
>>>
>>>
>>> 2011/7/21 Martin Barry<marty at supine.com>:
>>>>
>>>> $quoted_author = "Martin T" ;
>>>>>
>>>>> This might be a bit stupid question, but I have following topology:
>>>>>
>>>>> IBM_T60[eth0]<->    [Fa0/2]WS-C2950C-24
>>>>>
>>>>> eth0 port is an "Intel Corporation 82573L" GE port and Fa0/2 port in
>>>>> WS-C2950C-24 switch is of course FE port. I have enabled
>>>>> autonegotiation on eth0 port, but it advertises only 10BASE-T/Full
>>>>> mode, so switch port, which is configured to "speed auto" and "duplex
>>>>> auto", is up with following settings:
>>>>>
>>>>> Fa0/2     ->    T60             connected    1          a-full   a-10
>>>>> 10/100BaseTX
>>>>
>>>> What operating system are you running on the T60? You need to figure out
>>>> why
>>>> it's not offering the full range of speeds during auto-negotiation.
>>>>
>>>>
>>>>> Am I correct, that actual signalling on physical layer is 10BASE-T? Or
>>>>> is eth0 port actually sending at 1Gbps(1000BASE-T signalling) rate and
>>>>> Fa0/2(100BASE-TX signalling) is sending at 100Mbps rate on physical
>>>>> layer?
>>>>
>>>> Your first instinct is correct, both sides with be operating at 10/full
>>>> rather than the 100/full which you would obviously prefer.
>>>>
>>>> cheers
>>>> Marty
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