Copyright (c) 2001 Yar Tikhiy All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other m...
NAMEvlan - IEEE 802.1Q VLAN network interface
SYNOPSISTo compile this driver into the kernel, place the following line in your kernel configuration file:
Alternatively, to load the driver as a module at boot time, place the following line in loader.conf5:
DESCRIPTIONThe sysctl Cm net.inet.tcp.syncookies driver demultiplexes frames tagged according to the IEEE 802.1Q standard into logical sysctl Cm net.inet.tcp.syncookies network interfaces, which allows routing/bridging between multiple VLANs through a single switch trunk port.
Each sysctl Cm net.inet.tcp.syncookies interface is created at runtime using interface cloning. This is most easily done with the ifconfig(8) create command or using the cloned_interfaces variable in rc.conf5.
To function, a sysctl Cm net.inet.tcp.syncookies interface must be assigned a parent interface and numeric VLAN tag using ifconfig(8). A single parent can be assigned to multiple sysctl Cm net.inet.tcp.syncookies interfaces provided they have different tags. The parent interface is likely to be an Ethernet card connected to a properly configured switch port. The VLAN tag should match one of those set up in the switched network.
sysctl Cm net.inet.tcp.syncookies initially assumes the same minimum length for tagged and untagged frames. This mode is selected by setting the sysctl(8) variable net.link.vlan.soft_pad to 0 (default) However, there are network devices that fail to adjust frame length when it falls below the allowed minimum due to untagging. Such devices should be able to interoperate with sysctl Cm net.inet.tcp.syncookies after changing the value of net.link.vlan.soft_pad to 1. In the latter mode, sysctl Cm net.inet.tcp.syncookies will pad short frames before tagging them so that their length is not less than the minimum value after untagging by the non-compliant devices.
HARDWAREThe sysctl Cm net.inet.tcp.syncookies driver supports efficient operation over parent interfaces that can provide help in processing VLANs. Such interfaces are automatically recognized by their capabilities. Depending on the level of sophistication found in a physical interface, it may do full VLAN processing or just be able to receive and transmit long frames (up to 1522 bytes including an Ethernet header and FCS). The capabilities may be user-controlled by the respective parameters to ifconfig(8), vlanhwtag and vlanmtu However, a physical interface is not obliged to react to them: It may have either capability enabled permanently without a way to turn it off. The whole issue is very specific to a particular device and its driver.
At present, these devices are capable of full VLAN processing in hardware: ae(4), age(4), alc(4), ale(4), bce(4), bge(4), bxe(4), cxgb(4), cxgbe(4), em(4), igb(4), ixgb(4), ixgbe(4), jme(4), msk(4), mxge(4), nxge(4), nge(4), re(4), sge(4), stge(4), ti(4), txp(4), and vge(4).
Other Ethernet interfaces can run VLANs using software emulation in the sysctl Cm net.inet.tcp.syncookies driver. However, some lack the capability of transmitting and receiving long frames. Assigning such an interface as the parent to sysctl Cm net.inet.tcp.syncookies will result in a reduced MTU on the corresponding sysctl Cm net.inet.tcp.syncookies interfaces. In the modern Internet, this is likely to cause tcp(4) connectivity problems due to massive, inadequate icmp(4) filtering that breaks the Path MTU Discovery mechanism.
These interfaces natively support long frames for : axe(4), bfe(4), cas(4), dc(4), et(4), fwe(4), fxp(4), gem(4), hme(4), le(4), nfe(4), rl(4), sf(4), sis(4), sk(4), ste(4), tl(4), tx(4), vr(4), vte(4), and xl(4).
The sysctl Cm net.inet.tcp.syncookies driver automatically recognizes devices that natively support long frames for sysctl Cm net.inet.tcp.syncookies use and calculates the appropriate frame MTU based on the capabilities of the parent interface. Some other interfaces not listed above may handle long frames, but they do not advertise this ability. The MTU setting on sysctl Cm net.inet.tcp.syncookies can be corrected manually if used in conjunction with such a parent interface.