Re: [libvirt] Exact meaning of "nativeMode" attribute in vlan tags
To clarify the behaviour of open vswitch:
With either of the native modes selected, a packet that comes in to the switch without a
vlan header will be placed in the native vlan and the header added before the packet is
forwarded.
With nativeMode='tagged', a packet in the native vlan will be sent out of the
switch with its vlan header intact. With nativeMode='untagged' a packet in the
native vlan will be sent out of the switch with the vlan header removed.
In case it helps, here is the open vswitch doc for the vlan settings:
Bridge ports support the following types of VLAN configuration:
trunk A trunk port carries packets on one or more specified VLANs
specified in the trunks column (often, on every VLAN). A
packet that ingresses on a trunk port is in the VLAN specified in its
802.1Q header, or VLAN 0 if the packet has no
802.1Q header. A packet that egresses through a trunk port will have
an 802.1Q header if it has a nonzero VLAN ID.
Any packet that ingresses on a trunk port tagged with a VLAN that the
port does not trunk is dropped.
access An access port carries packets on exactly one VLAN specified in
the tag column. Packets egressing on an access port
have no 802.1Q header.
Any packet with an 802.1Q header with a nonzero VLAN ID that
ingresses on an access port is dropped, regardless of
whether the VLAN ID in the header is the access port’s VLAN ID.
native-tagged
A native-tagged port resembles a trunk port, with the exception that
a packet without an 802.1Q header that ingresses on
a native-tagged port is in the ‘‘native VLAN’’ (specified in the tag
column).
native-untagged
A native-untagged port resembles a native-tagged port, with the
exception that a packet that egresses on a native-
untagged port in the native VLAN will not have an 802.1Q header.
________________________________________
From: sendmail [justsendmailnothingelse(a)gmail.com] on behalf of Laine Stump
[laine(a)laine.org]
Sent: 22 February 2015 19:31
To: Libvirt
Cc: Robson, James
Subject: Exact meaning of "nativeMode" attribute in vlan tags
You'd think that I would know this, since I'm the person who reviewed
jrobson's patch adding support for the nativeMode attribute to the vlan
tag element. But you'd be wrong. Here is what the config looks like:
<vlan trunk='yes'>
<tag id='42' nativeMode='untagged'/>
<tag id='47'/>
</vlan>
I understand that trunk='yes' means that packets with any of the tags
listed in a <tag> subelement can be sent out this port (and the tag will
*not* be removed), and likewise packets arriving into the bridge from
the port are allowed to have any of the listed tags (and, again, no tag
will be removed). But what exactly do nativeMode='untagged' and
nativeMode='tagged' mean?
As I understand it, (nativeMode='untagged'|nativeMode='tagged') means
that packets (arriving from|sent to) the port (without a tag/with that
tag) will be (tagged|untagged). Can someone who fully understands this
please select A or B for each of the 4 parenthesized items (in as many
permutations as make sense).
I guess that in one of the modes, untagged packets going in one
direction or the other will be tagged, and vice versa, I just don't know
which direction does which, and for which mode, and don't want to guess.
(I'm asking this because I want to implement identical functionality for
standard Linux host bridges - I want to make sure there are no surprises
for people switching between OVS and Linux host bridge implementations).
To report this email as SPAM, please forward it to spam(a)websense.com