DragonFly users List (threaded) for 2007-03
Selecting the Right Network Interface Card to Run VLANs Through
By now, the only NICs that have both hardware support and proper driver
hooks for the 802.1Q VLAN technology in DragonFly are bge(4), em(4),
gx(4), nge(4), re(4), ti(4), and txp(4).
The rest of the ethernet NICs supported by DragonFly can run VLANs using
software emulation in the vlan driver. However, most of them lack the
capability of transmitting and/or receiving oversized frames. Using such
a NIC as a parent interface implies a reduced MTU on the corresponding
vlan 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.
The NICs that support oversized frames are as follows:
dc(4) supports long frames for vlan natively.
de(4) requires defining BIG_PACKET in the
/sys/dev/netif/de/if_de.c source file and rebuilding the
kernel. The hack works only for the 21041, 21140, and
fxp(4) supports long frames for vlan natively.
sis(4) supports long frames for vlan natively.
ste(4) supports long frames for vlan natively.
tl(4) has support for long frames.
tx(4) supports long frames for vlan natively.
xl(4) supports long frames only if the card is built on a newer
chip (Cyclone and above).
Note: Unless marked as having native support for vlan, the above drivers
don't inform the vlan driver about their long frame handling capability.
Just increase the MTU of a vlan interface if it appears to be lower than
1500 bytes after attaching to a parent known to support long frames.
This is from 2001. Is this still appropriate, or should I not think of any HW issues at all? :-)
Gergo Szakal <firstname.lastname@example.org>
University Of Szeged, HU
Faculty Of General Medicine
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