doc: mention vlan matching in ip/ip6/inet families

It only works if vlan_reorder is turned off to disable the vlan tag
removal.

Signed-off-by: Florian Westphal <fw@strlen.de>

1 files changed, 8 insertions, 0 deletions

diff --git a/doc/payload-expression.txt b/doc/payload-expression.txt
index 106ff74c..113f5bfc 100644
--- a/doc/payload-expression.txt
+++ b/doc/payload-expression.txt
@@ -23,6 +23,14 @@ VLAN HEADER EXPRESSION
 [verse]
 *vlan* {*id* | *dei* | *pcp* | *type*}
 
+The vlan expression is used to match on the vlan header fields.
+This expression will not work in the *ip*, *ip6* and *inet* families,
+unless the vlan interface is configured with the *reorder_hdr off* setting.
+The default is *reorder_hdr on* which will automatically remove the vlan tag
+from the packet. See ip-link(8) for more information.
+For these families its easier to match the vlan interface name
+instead, using the *meta iif* or *meta iifname* expression.
+
 .VLAN header expression
 [options="header"]
 |==================