WeOS
5.29.0

# Ethernet Port Speed/Duplex Howto

      Host-A                                          Host-B
     .-------.                                       .-------.
     |       |                                       |       |
     |       |                                       |       |
     |   1   |                                       |   1   |
     '---+---'                                       '---+---'
         |                                               |
         +-----------------------------------------------+

## Typical scenarios

### Default settings aim for plug and play

The default settings for speed-duplex aims for plug and play. The examples below describe the behaviour when connecting two WeOS units, but likely they also apply when connecting a WeOS unit with some other unit.

#### Fixed copper ports

Auto-negotiation will result in 1000-full when connecting two Gbit copper ports.

    Host-A:/#> show port
    PORT             LINK     TYPE       SPEED  STATE           OWNER/VLAN
    eth1             Up     1000-T  1000M-Full  Forwarding      vlan U:1
    eth2             Down   1000-T  ----------  No-Link         vlan U:1
    ...
    Host-A:/#>

Auto-negotiation will result in 100-full when connecting two FE ports or a Gbit with an FE port.

    Host-A:/#> show port
    PORT             LINK     TYPE       SPEED  STATE           OWNER/VLAN
    eth1             Up     1000-T   100M-Full  Forwarding      vlan U:1
    eth2             Down   1000-T  ----------  No-Link         vlan U:1
    ...
    Host-A:/#>

#### Fibre SFPs

Auto-negotiation will result in 1000-full when connecting two Gbit Fibre SFPs.

    Host-A:/#> show port
    PORT             LINK     TYPE       SPEED  STATE           OWNER/VLAN
    eth1             Up    1000-LX  1000M-Full  Forwarding      vlan U:1
    eth2             Down   No-SFP  ----------  No-Link         vlan U:1
    ...
    Host-A:/#>

When connecting two FE Fibre SFPs, the link will operate in 100-full (without auto-negotiation).

    Host-A:/#> show port
    PORT             LINK     TYPE       SPEED  STATE           OWNER/VLAN
    eth1             Up     100-FX   100M-Full  Forwarding      vlan U:1
    eth2             Down   No-SFP  ----------  No-Link         vlan U:1
    ...
    Host-A:/#>

If a Gbit and a FE Fibre SFP are connected, the link will not come up.

Note

There are many different types of Gbit and Fibre SFP technologies (multi-mode, single mode, BiDi, etc.), thus it is not only the speed which need to match.

### Configuring auto-negotiation advertisement

Auto-configuration enables the peers to agree on the best common speed/duplex mode. Assume the peer is using auto-negotiation, and you wish to limit the speed to 10 Mbit/s. Then you could set speed-duplex 10-full or speed-duplex 10-half, 10-full. The link will come up in 10-full if the peer supports that mode.

    Host-A:/#> config
    Host-A:/config/#> port eth1
    Host-A:/config/port-eth1/#> auto-negotiate
    Host-A:/config/port-eth1/#> speed-duplex 10-full,10-half
    Host-A:/config/port-eth1/#> leave
    Host-A:/#> show port
    PORT             LINK     TYPE       SPEED  STATE           OWNER/VLAN
    eth1             Up     1000-T    10M-Full  Forwarding      vlan U:1
    eth2             Down   1000-T  ----------  No-Link         vlan U:1
    ...
    Host-A:/#>

When both peers use auto-negotiation, but have no common mode, the link will not come up.

## Trouble-shooting

### Only one peer using auto-negotiation

If one side has auto-negotiation enabled while the peer has not, the link is likely to come up with the right speed, but wrong duplex mode.

Consider the case when A-side uses auto-negotiation, and B is set to 100-full and auto-negotiation disabled: The result will be that A sets its port to 100-half (it can determine the speed, but not the duplex mode, see §28.2.3.1 of 1).). B sets link to 100-full. When reading the RMON counters, A is likely to report lots of late collision errors, while B is likely so report rx checksum errors.

### Mismatching fixed configurations

If A and B both disable auto-configuration, they must set the same speed-duplex mode. If the speeds do not match, the link will not come up. If the speed matches, but not the duplex mode (e.g., 100-full and 100-half), the link will come up but the same kind of error as described in the previous section.

1. IEEE 802.3-2012 Clause 28: “Physical Layer link signalling for Auto-Negotiation on twisted pair” ↩

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