Changes between Version 2 and Version 3 of ethernet

Timestamp:

07/17/2025 09:34:34 PM (3 months ago)

Author:

Tim Harvey

Comment:

moved ethtool details from ventana/ethernet here and removed deprecated mii-tool details

ethernet

@@ -67 +67 @@
 Also see the Venice Ethernet page: [wiki:venice/ethernet]
 
+
+[=#ethtool]
+== ethtool
+{{{ethtool}}} is the standard Linux tool used to talk to the Ethernet PHY.
+
+
+Examples:
+ * show PHY details about an interface:
+{{{
+#!bash
+# ethtool eth0
+Settings for eth0:
+        Supported ports: [ TP MII ]
+        Supported link modes:   10baseT/Half 10baseT/Full
+                                100baseT/Half 100baseT/Full
+                                1000baseT/Full
+        Supported pause frame use: Symmetric
+        Supports auto-negotiation: Yes
+        Advertised link modes:  10baseT/Half 10baseT/Full
+                                100baseT/Half 100baseT/Full
+                                1000baseT/Full
+        Advertised pause frame use: Symmetric
+        Advertised auto-negotiation: Yes
+        Link partner advertised link modes:  10baseT/Half 10baseT/Full
+                                             100baseT/Half 100baseT/Full
+                                             1000baseT/Full
+        Link partner advertised pause frame use: Symmetric Receive-only
+        Link partner advertised auto-negotiation: Yes
+        Speed: 1000Mb/s
+        Duplex: Full
+        Port: MII
+        PHYAD: 0
+        Transceiver: external
+        Auto-negotiation: on
+        Supports Wake-on: d
+        Wake-on: d
+        Link detected: yes
+}}}
+
+
+[=#speed]
+=== Setting the Ethernet Port Speed
+When using a 4-wire (2-pair) cable suitable for 100BASE-T on a Gigabit interface depending on the PHY and the link partner you may need to force the speed to 100Mbps.
+
+For customers who would like to force a specific speed, you can use the following:
+
+Examples:
+ * force 100mbps speed
+{{{#!bash
+# ifconfig eth0 down
+[  261.516832] libphy: 2188000.ethernet:00 - Link is Down
+# ethtool -s eth0 autoneg off speed 100
+# ifconfig eth0 up
+[  265.516787] libphy: 2188000.ethernet:00 - Link is Up - 100/Full
+}}}
+
+[=#duplex]
+=== Duplex
+Most Ethernet NICs can be configured to be either full or half duplex. For information on what this means, please see [https://en.wikipedia.org/wiki/Duplex_%28telecommunications%29 this page].
+
+You can use {{{ethtool}}} to configure duplex:
+{{{#!bash
+# ifconfig eth0 down
+[  261.516832] libphy: 2188000.ethernet:00 - Link is Down
+# ethtool -s eth0 autoneg off duplex half
+# ethtool eth0 | grep Duplex
+        Duplex: Half
+}}}
+
+[=#flowcontrol]
+=== Ethernet PAUSE frames for flow control (802.3x)
+The IEEE 802.3x standard introduced Ethernet PAUSE frames which can be used at the MAC level as a mechanism of flow-control much like that used in UARTs. A transmitter can send a PAUSE frame to a receiver to tell them to stop sending for a specified period of time if they can't keep up with the data flow.
+
+This is typically only used if one end of the transmission can't keep up with the line-speed of the medium (ie a board supporting GigE that can't keep up with 1gbps).
+
+Because the Fast Ethernet Controller (FEC) integrated into the IMX6 can't perform at 1000mbps the use of PAUSE frames may be desirable in certain cases.
+
+Ethernet PAUSE frames are not supported across all the various Gateworks products (in some cases the hardware can't support it, in others the drivers may not support it):
+ * IMX6 FEC: (used as eth0 on GW51xx/GW52xx/GW53xx/GW54xx/GW55x) supports PAUSE frames (yet tx/rx must be set the same)
+ * Intel i210: (used on GW5520 and GW16083) supports symmetric PAUSE frames with independent control
+ * Marvell SKY2: (used as eth1 on GW54xx/GW53xx) supports PAUSE frames but no auto-negotiation
+
+Use {{{ethtool}}} to configure:
+{{{#!bash
+# Show pause-frame status
+root@OpenWrt:/# ethtool --show-pause eth0
+Pause parameters for eth0:
+Autonegotiate:  on
+RX:             off
+TX:             off
+RX negotiated:  on
+TX negotiated:  on
+
+# Disable pause frame support
+root@OpenWrt:/# ethtool --pause eth0 autoneg off rx off tx off
+rx unmodified, ignoring
+tx unmodified, ignoring
+root@OpenWrt:/# [   92.519412] libphy: 2188000.ethernet:00 - Link is Up - 1000/Full
+
+# Enable pause frame
+root@OpenWrt:/# ethtool --pause eth0 autoneg on # enable pause frame autoneg
+root@OpenWrt:/# [  137.518636] libphy: 2188000.ethernet:00 - Link is Up - 1000/Full
+}}}
+
+Notes:
+ * Note that FEC tx/rx pause frame support must be the same (you can't enable tx and disable rx for example)
+ * If PAUSE frames are supported by the NIC/driver their default configuration is auto-negotiated.
+ * If autonegotiation of PAUSE frames is enabled from a disabled state the link will go down and come back up
+
+
+See also:
+ * https://en.wikipedia.org/wiki/Ethernet_flow_control
+