man: ip-link: document MACVLAN/MACVTAP interface types

Signed-off-by: Phil Sutter <phil@nwl.cc>

man/man8/ip-link.8.in

@@ -768,6 +768,56 @@ the following additional arguments are supported:
 
 .in -8
 
+.TP
+MACVLAN and MACVTAP Type Support
+For a link of type
+.I MACVLAN
+or
+.I MACVTAP
+the following additional arguments are supported:
+
+.BI "ip link add link " DEVICE " name " NAME
+.BR type " { " macvlan " | " macvtap " } "
+.BR mode " { " private " | " vepa " | " bridge " | " passthru
+.BR " [ " nopromisc " ] } "
+
+.in +8
+.sp
+.BR type " { " macvlan " | " macvtap " } "
+- specifies the link type to use.
+.BR macvlan " creates just a virtual interface, while "
+.BR macvtap " in addition creates a character device "
+.BR /dev/tapX " to be used just like a " tuntap " device."
+
+.B mode private
+- Do not allow communication between
+.B macvlan
+instances on the same physical interface, even if the external switch supports
+hairpin mode.
+
+.B mode vepa
+- Virtual Ethernet Port Aggregator mode. Data from one
+.B macvlan
+instance to the other on the same physical interface is transmitted over the
+physical interface. Either the attached switch needs to support hairpin mode,
+or there must be a TCP/IP router forwarding the packets in order to allow
+communication. This is the default mode.
+
+.B mode bridge
+- In bridge mode, all endpoints are directly connected to each other,
+communication is not redirected through the physical interface's peer.
+
+.BR mode " " passthru " [ " nopromisc " ] "
+- This mode gives more power to a single endpoint, usually in
+.BR macvtap " mode. It is not allowed for more than one endpoint on the same "
+physical interface. All traffic will be forwarded to this endpoint, allowing
+virtio guests to change MAC address or set promiscuous mode in order to bridge
+the interface or create vlan interfaces on top of it. By default, this mode
+forces the underlying interface into promiscuous mode. Passing the
+.BR nopromisc " flag prevents this, so the promisc flag may be controlled "
+using standard tools.
+.in -8
+
 .SS ip link delete - delete virtual link
 
 .TP