NAME¶

addEthCaps - Show / manipulate Additional Ethernet Capabilities TLV

SYNOPSIS¶

lldptool -t -i ethx -V addEthCaps [-c CONFIG_ARG ...]

CONFIG_ARG := { enableTx | addFragSize }

lldptool -T -i ethx -V addEthCaps CONFIG_ARG=value ...

CONFIG_ARG :=

enableTx = {yes|no} |

addFragSize = {0|1|2|3}

DESCRIPTION¶

The Additional Ethernet Capabilities (addEthCaps) TLV allows neighbour systems to automatically discover the Frame Preemption capability and enable their MAC Merge layers to make use of it.

ARGUMENTS¶

enableTx

Enables the addEthCaps TLV to be transmitted

addFragSize

Sets the additional fragment size to be advertised. This informs the link partner what is the minimum size of non-final fragments that it should transmit. An addFragSize of 0 corresponds to a minimum fragment size of 60 octets, 1 corresponds to 124 octets, 2 to 188 octets, and 3 to 252 octets.

THEORY OF OPERATION¶

If transmission of the Additional Ethernet Capabilities TLV is enabled, the application queries the kernel for MAC Merge layer support, and if successful, it advertises "Frame Preemption Capability Supported". If the link partner advertises the "Frame Preemption Capability Supported" too, the application unconditionally enables the pMAC (to allow receiving preemptible and/or verification frames from the link partner) and transmission through the MAC Merge layer. The latter operation causes the "Frame Preemption Capability Enabled" to also be advertised in subsequent TLVs.

Since the application automatically enables the Frame Preemption capability, without any coordination with the link partner, it may be possible for the link partner to not enable reception on its pMAC, and thus, all preemptible frames transmitted by this device would be dropped as error frames.

To avoid this, the application also requests the kernel to enable TX verification, which starts a handshake of SMD-V and SMD-R frames outside the LLDP protocol. If the verification process succeeds (link partner responds to a SMD-V frame), the MAC Merge layer also becomes active, and the application will advertise "Frame Preemption Capability Active" in subsequent TLVs.

Which packets are transmitted as preemptible and which are transmitted as express (based on their user priority) is outside of the scope of this application (and of the LLDP protocol).

EXAMPLE & USAGE¶

Enable the transmission of the Additional Ethernet Capabilities TLV for interface eth0:

lldptool -T -i eth0 -V addEthCaps enableTx=yes

Configure the minimum fragment size for interface eth0 to receive fragments no smaller than 252 octets:

lldptool -T -i eth0 -V addEthCaps addFragSize=3

Display the additional fragment size advertised by eth0:

lldptool -t -i eth0 -V addEthCaps -c addFragSize

Display last transmitted Additional Ethernet Capabilities TLV

lldptool -t -i eth0 -V addEthCaps

NOTES¶

The Additional Ethernet Capabilities TLV requires kernel support for the ETHTOOL_MSG_MM_GET and ETHTOOL_MSG_MM_SET netlink commands, which first appeared in Linux kernel v6.3.

SEE ALSO¶

lldptool(8), lldpad(8), ethtool(8),

AUTHOR¶

This man page was written by Vladimir Oltean <vladimir.oltean@nxp.com>.