auto negotiataion on utp cable

[sarahr202]

Hi everybody.

Let say we have a switch1 with a port 10/100/1000-T. Let say we have another switch2  with a port 1000-T.

Will switch2's port 1000-T be capable of running auto-negotiation protocol considering that it supports only one speed ?

Does  any body know a good link showing the actual contents of messages being exchanged during auto-negotiation between two hosts ?

thanks and have a great weekend.

[nkarpysh]

Hello,

Usually built-in Gigabit Ethernet ports are capable of negotiation, but in cases like modular SFP or GBIC types, they do not negotiate. Line protocol will be down for a Gigabit Ethernet port when connected to a Fast Ethernet port.

There is good doc about negotiation:

http://www.cisco.com/en/US/tech/tk389/tk214/technologies_tech_note09186a0080094781.shtml

Hope this helps,

Nik

[sarahr202]

Thanks Nik.

1000BASE-X includes 1000base-sx.1000base-lx and 1000 base-cx

My question is :

Are these above technologies implemented as fixed ports too?

"Usually built-in Gigabit Ethernet ports are capable of negotiation, but  in cases like modular SFP or GBIC types, they do not negotiate"

Below is excerpt from my book:

Auto-Negotiation for 1000BASE-X Interfaces

Auto-Negotiation is a mandatory  function for 1000BASE-X interfaces. These include the

1000BASE-SX and 1000BASE-LX fiber optic interfaces and the 1000BASE-CX copper interface.

It is physically impossible for incompatible types (for example, 1000BASE-SX and 1000BASE-LX,

or 1000BASE-LX and 1000BASE-CX) to communicate across a link, so the technology type is not

negotiable. The capabilities that are negotiated include

•Full–duplex or half-duplex capabilities.

•Flow control capability (for a full–duplex link). As was the case for twisted-pair cabling, 2 bits are

used to describe whether the system can send and/or receive PAUSE messages.

These Auto-Negotiation messages optionally also can describe remote fault conditions or include

vendor- or product-specific data.

thanks and  have a great weekend

[nkarpysh · Accepted solution]

Hey,

Thing is that this statement:

"Usually built-in Gigabit Ethernet ports are capable of negotiation, but  in cases like modular SFP or GBIC types, they do not negotiate"

is related only to speed negotiation for SFP/GBIC ports. Copper ports still send the speed negotiation parameters even whn if can't go lower than 1000 - just as they need clean clock source with a partner (but this may vary from platform to platform - 4500 really does it).

As for the SFP/GBIC ports - they do not do speed negotiation but can do Duples and flow control negotiation and that is configured with

•Cisco IOS Software command:

negotiation auto/no negotiation auto

Check this document as well - it has some additional details.

http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a00800a7af0.shtml#addl_ts

Hope this helps,

Nik

[sarahr202]

Thanks Nik.

What about gbic/sfp for copper ? is speed negotiation parameter sent on such gbic/sfp ?

thanks and have a great weekend

[nkarpysh]

Hello,

As far as I see Copper SFP can negotiate speed:

"You cannot configure speed on SFP module ports, but you can configure speed to not negotiate (nonegotiate) if connected to a device that does not support autonegotiation. However, when a 1000BASE-T SFP module is in the SFP module port, you can configure speed as 10, 100, or 1000 Mbps, or auto."

http://www.cisco.com/en/US/products/hw/modules/ps4999/products_tech_note09186a00807a30d6.shtml#config

Though I guess this can be very specific to each platform/SFP used.

Nik

[Leo Laohoo · Accepted solution]

However, when a 1000BASE-T SFP module is in the SFP module port, you can configure speed as 10, 100, or 1000 Mbps, or auto."

As long as the SFP port does not belong to a 6500 line card or an ASR. 

[nkarpysh]

Agree,

Thats why I wrote

Though I guess this can be very specific to each platform/SFP used.

Similar for NEXUS as many LC are just 10G fixed speed though there are some where it can be chnaged between 1/100/1000. So it really depends.

Nik