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ovt Bronze

Autonegotiation vs port negotiation

Can anybody explain the difference between Ethernet autonegotiation and "port negotiation" on Catalyst switches (CatOS)? CatOS 6.3 reference manual for 5500 says, that "port negotiation" is only supported on 1000BASE (SX, LX, and ZX) modules, but I see that the command is accepted on WS-X5225R (10/100) also.

"show port negotiation" shows that this feature is enabled on all my 10/100 ports. Autonegotiation is enabled also. Both mechanizms can negotiate duplex. So, the 2nd question is: which one is really used on 10/100 ports to negotiate duplex?

The 3rd question: which mechanizm is used on 1000BaseT links? Autonegotiation? Port negotiation?

What command is used to disable negotiation and set link speed to 1000? "set port speed"? "set port negotiation disable"? Both?

Thank you,

Oleg Tipisov,



Cisco Employee

Re: Autonegotiation vs port negotiation

Unlike autonegotiation with 10/100 Fast Ethernet, Gigabit Ethernet port negotiation does not negotiate port speed. With Gigabit Ethernet ports, port negotiation is used to exchange flow-control parameters, remote fault information, and duplex information (even though Cisco Gigabit Ethernet ports only support full-duplex mode).

Regarding your second question, you cannot issue a sh port negotiation on a 10/100 port. 10/100 ports use autonegotiation. Here is the output when I try it in my lab switch.

swelcor01> (enable) sh port negotiation 4/1

Feature not supported on Port 4/1.

swelcor01> (enable) sh mod 4

Mod Slot Ports Module-Type Model Sub Status

--- ---- ----- ------------------------- ------------------- --- --------

4 4 48 10/100BaseTX Ethernet WS-X6348-RJ-45 yes ok

Mod Module-Name Serial-Num

--- -------------------- -----------

4 SAD04350CUY

Mod MAC-Address(es) Hw Fw Sw

--- -------------------------------------- ------ ---------- -----------------

4 00-01-97-55-0e-70 to 00-01-97-55-0e-9f 1.1 5.4(2) 6.3(3)

Mod Sub-Type Sub-Model Sub-Serial Sub-Hw

--- ----------------------- ------------------- ----------- ------

4 Inline Power Module WS-F6K-VPWR 1.0

Regarding your 3rd question, Port negotiation is not supported on 1000BASE-T Gigabit Ethernet ports. The port is always 1000Mbps and full duplex and cannot negotiate to anything else. If you have a 10/100/1000 ports, they use auto-negotiation

Hope this helps

ovt Bronze

Re: Autonegotiation vs port negotiation

Thank you for the replay.

Here is the output from my lab switch:

Console> (enable) sh mod

Mod Slot Ports Module-Type Model Sub Status

--- ---- ----- ------------------------- ------------------- --- --------

1 1 0 Supervisor III WS-X5530 yes ok

2 2 1 Route Switch WS-X5302 no ok

3 3 24 10/100BaseTX Ethernet WS-X5225R no ok

Mod Module-Name Serial-Num

--- -------------------- --------------------

1 00024705449

2 00023899240

3 00023889665

Mod MAC-Address(es) Hw Fw Sw

--- -------------------------------------- ------ ---------- -----------------

1 00-07-0d-43-7c-00 to 00-07-0d-43-7f-ff 3.5 5.1(2) 6.4(5)

2 00-e0-1e-91-0d-2c to 00-e0-1e-91-0d-2d 7.7 20.21 12.0(7)T,

3 00-03-31-26-62-e8 to 00-03-31-26-62-ff 3.3 4.3(1) 6.4(5)

Mod Sub-Type Sub-Model Sub-Serial Sub-Hw

--- -------- --------- ---------- ------

1 NFFC II WS-F5531A 0024919675 2.2

Console> (enable) sh port neg 3/5

Port Link Negotiation

----- ----------------

3/5 enabled

Console> (enable) set port negotiation 3/5 disable

Port 3/5 negotiation disabled.

Console> (enable)

Console> (enable)

Console> (enable) set port negotiation 3/5 enable

Port 3/5 negotiation enabled.

As you can see port negotiation *IS* supported on 10/100 ports.

Cisco Employee

Re: Autonegotiation vs port negotiation

My bad..I was thinking about CAT6500 line cards as I saw similar post else where.

Certail cards in CAT5k such as WS-X5225R, WS-X5201R, WS-X5234 cards do support port negotiation. I have emailed our documentation folks to inlude this on CCO.

But not all cards support it

10.4-5505a (enable) sh mod 5

Mod Slot Ports Module-Type Model Status

--- ---- ----- ------------------------- ------------------- --------

5 5 12 10/100BaseTX Ethernet WS-X5213A ok

Mod Module-Name Serial-Num

--- ------------------- --------------------

5 00002230862

Mod MAC-Address(es) Hw Fw Sw

--- -------------------------------------- ------ ---------- -----------------

5 00-60-5c-c1-bb-84 to 00-60-5c-c1-bb-8f 1.0 1.4 5.4(4)

10.4-5505a (enable) set port negotiation 5/1 enable

Feature not supported on Port 5/1.

10.4-5505a (enable)