datapath: Fix handling of 802.1Q and SNAP headers.
The kernel and user datapaths have code that assumes that 802.1Q headers
are used only inside Ethernet II frames, not inside SNAP-encapsulated
frames. But the kernel and user flow_extract() implementations would
interpret 802.1Q headers inside SNAP headers as being valid VLANs. This
would cause packet corruption if any VLAN-related actions were to be taken,
so change the two flow_extract() implementations only to accept 802.1Q as
an Ethernet II frame type, not as a SNAP-encoded frame type.
802.1Q-2005 says that this is correct anyhow:
Where the ISS instance used to transmit and receive tagged frames is
provided by a media access control method that can support Ethernet
Type encoding directly (e.g., is an IEEE 802.3 or IEEE 802.11 MAC) or
is media access method independent (e.g., 6.6), the TPID is Ethernet
Type encoded, i.e., is two octets in length and comprises solely the
assigned Ethernet Type value.
Where the ISS instance is provided by a media access method that
cannot directly support Ethernet Type encoding (e.g., is an IEEE
802.5 or FDDI MAC), the TPID is encoded according to the rule for
a Subnetwork Access Protocol (Clause 10 of IEEE Std 802) that
encapsulates Ethernet frames over LLC, and comprises the SNAP
header (AA-AA-03) followed by the SNAP PID (00-00-00) followed by
the two octets of the assigned Ethernet Type value.
All of the media that OVS handles supports Ethernet Type fields, so to me
that means that we don't have to handle 802.1Q-inside-SNAP.
On the other hand, we *do* have to handle SNAP-inside-802.1Q, because this
is actually allowed by the standards. So this commit also adds that
support.
I verified that, with this change, both SNAP and Ethernet packets are
properly recognized both with and without 802.1Q encapsulation.
I was a bit surprised to find out that Linux does not accept
SNAP-encapsulated IP frames on Ethernet.
Here's a summary of how frames are handled before and after this commit:
Common cases
------------
Ethernet
+------------+
1. |dst|src|TYPE|
+------------+
Ethernet LLC SNAP
+------------+ +--------+ +-----------+
2. |dst|src| len| |aa|aa|03| |000000|TYPE|
+------------+ +--------+ +-----------+
Ethernet 802.1Q
+------------+ +---------+
3. |dst|src|8100| |VLAN|TYPE|
+------------+ +---------+
Ethernet 802.1Q LLC SNAP
+------------+ +---------+ +--------+ +-----------+
4. |dst|src|8100| |VLAN| LEN| |aa|aa|03| |000000|TYPE|
+------------+ +---------+ +--------+ +-----------+
Unusual cases
-------------
Ethernet LLC SNAP 802.1Q
+------------+ +--------+ +-----------+ +---------+
5. |dst|src| len| |aa|aa|03| |000000|8100| |VLAN|TYPE|
+------------+ +--------+ +-----------+ +---------+
Ethernet LLC
+------------+ +--------+
6. |dst|src| len| |xx|xx|xx|
+------------+ +--------+
Ethernet LLC SNAP
+------------+ +--------+ +-----------+
7. |dst|src| len| |aa|aa|03| |xxxxxx|xxxx|
+------------+ +--------+ +-----------+
Ethernet 802.1Q LLC
+------------+ +---------+ +--------+
8. |dst|src|8100| |VLAN| LEN| |xx|xx|xx|
+------------+ +---------+ +--------+
Ethernet 802.1Q LLC SNAP
+------------+ +---------+ +--------+ +-----------+
9. |dst|src|8100| |VLAN| LEN| |aa|aa|03| |xxxxxx|xxxx|
+------------+ +---------+ +--------+ +-----------+
Behavior
--------
--------------- --------------- -------------------------------------
Before After
this commit this commit
dl_type dl_vlan dl_type dl_vlan Notes
------- ------- ------- ------- -------------------------------------
1. TYPE ffff TYPE ffff no change
2. TYPE ffff TYPE ffff no change
3. TYPE VLAN TYPE VLAN no change
4. LEN VLAN TYPE VLAN proposal fixes behavior
5. TYPE VLAN 8100 ffff 802.1Q says this is invalid framing
6. 05ff ffff 05ff ffff no change
7. 05ff ffff 05ff ffff no change
8. LEN VLAN 05ff VLAN proposal fixes behavior
9. LEN VLAN 05ff VLAN proposal fixes behavior
Signed-off-by: Ben Pfaff <blp@nicira.com>
projects / openvswitch / commit