Date:	Wed, 25 Apr 2012 13:11:18 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	James Chapman <jchapman@...alix.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] iproute2: add ip-l2tp man page

On Fri, 20 Apr 2012 12:29:43 +0100
James Chapman <jchapman@...alix.com> wrote:

> Add a man page to cover the "ip l2tp" commands. Add a reference to it
> in the main ip page.
> 
> Signed-off-by: James Chapman <jchapman@...alix.com>
> ---
>  man/man8/ip-l2tp.8 |  350 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  man/man8/ip.8      |    3 +-
>  2 files changed, 352 insertions(+), 1 deletions(-)
>  create mode 100644 man/man8/ip-l2tp.8
> 
> diff --git a/man/man8/ip-l2tp.8 b/man/man8/ip-l2tp.8
> new file mode 100644
> index 0000000..c115e7c
> --- /dev/null
> +++ b/man/man8/ip-l2tp.8
> @@ -0,0 +1,350 @@
> +.TH IP\-L2TP 8 "19 Apr 2012" "iproute2" "Linux"
> +.SH "NAME"
> +ip-l2tp - L2TPv3 static unmanaged tunnel configuration
> +.SH "SYNOPSIS"
> +.sp
> +.ad l
> +.in +8
> +.ti -8
> +.B ip
> +.RI "[ " OPTIONS " ]"
> +.B l2tp
> +.RI " { " COMMAND " | "
> +.BR help " }"
> +.sp
> +.ti -8
> +.BR "ip l2tp add tunnel"
> +.br
> +.B remote
> +.RI "[ " ADDR " ]"
> +.B local
> +.RI "[ " ADDR " ]"
> +.br
> +.B tunnel_id
> +.IR ID
> +.B peer_tunnel_id
> +.IR ID
> +.br
> +.RB "[ " encap " { " ip " | " udp " } ]"
> +.br
> +.RB "[ " udp_sport
> +.IR PORT
> +.RB " ] [ " udp_dport
> +.IR PORT
> +.RB " ]"
> +.br
> +.ti -8
> +.BR "ip l2tp add session"
> +.RB "[ " name
> +.IR NAME
> +.RB " ]"
> +.br
> +.B tunnel_id
> +.IR ID
> +.B session_id
> +.IR ID
> +.B peer_session_id
> +.IR ID
> +.br
> +.RB "[ " cookie
> +.IR HEXSTR
> +.RB " ] [ " peer_cookie
> +.IR HEXSTR
> +.RB " ]"
> +.br
> +.RB "[ " offset
> +.IR OFFSET
> +.RB " ] [ " peer_offset
> +.IR OFFSET
> +.RB " ]"
> +.br
> +.ti -8
> +.BR "ip l2tp del tunnel"
> +.B tunnel_id
> +.IR ID
> +.br
> +.ti -8
> +.BR "ip l2tp del session"
> +.B tunnel_id
> +.IR ID
> +.B session_id
> +.IR ID
> +.br
> +.ti -8
> +.BR "ip l2tp show tunnel"
> +.B "[" tunnel_id
> +.IR ID
> +.B "]"
> +.br
> +.ti -8
> +.BR "ip l2tp show session"
> +.B "[" tunnel_id
> +.IR ID
> +.B "] [" session_id
> +.IR ID
> +.B "]"
> +.br
> +.ti -8
> +.IR NAME " := "
> +.IR STRING
> +.ti -8
> +.IR ADDR " := { " IP_ADDRESS " }"
> +.ti -8
> +.IR PORT " := { " NUMBER " }"
> +.ti -8
> +.IR ID " := { " NUMBER " }"
> +.ti -8
> +.ti -8
> +.IR HEXSTR " := { 8 or 16 hex digits (4 / 8 bytes) }"
> +.SH DESCRIPTION
> +The
> +.B ip l2tp
> +commands are used to establish static, or so-called
> +.I unmanaged
> +L2TPv3 ethernet tunnels. For unmanaged tunnels, there is no L2TP
> +control protocol so no userspace daemon is required - tunnels are
> +manually created by issuing commands at a local system and at a remote
> +peer.
> +.PP
> +L2TPv3 is suitable for Layer-2 tunnelling. Static tunnels are useful
> +to establish network links across IP networks when the tunnels are
> +fixed. L2TPv3 tunnels can carry data of more than one session. Each
> +session is identified by a session_id and its parent tunnel's
> +tunnel_id. A tunnel must be created before a session can be created in
> +the tunnel.
> +.PP
> +When creating an L2TP tunnel, the IP address of the remote peer is
> +specified, which can be either an IPv4 or IPv6 address. The local IP
> +address to be used to reach the peer must also be specified. This is
> +the address on which the local system will listen for and accept
> +received L2TP data packets from the peer.
> +.PP
> +L2TPv3 defines two packet encapsulation formats: UDP or IP. UDP
> +encapsulation is most common. IP encapsulation uses a dedicated IP
> +protocol value to carry L2TP data without the overhead of UDP. Use IP
> +encapsulation only when there are no NAT devices or firewalls in the
> +network path.
> +.PP
> +When an L2TPv3 ethernet session is created, a virtual network
> +interface is created for the session, which must then be configured
> +and brought up, just like any other network interface. When data is
> +passed through the interface, it is carried over the L2TP tunnel to
> +the peer. By configuring the system's routing tables or adding the
> +interface to a bridge, the L2TP interface is like a virtual wire
> +(pseudowire) connected to the peer.
> +.PP
> +Establishing an unmanaged L2TPv3 ethernet pseudowire involves manually
> +creating L2TP contexts on the local system and at the peer. Parameters
> +used at each site must correspond or no data will be passed. No
> +consistency checks are possible since there is no control protocol
> +used to establish unmanaged L2TP tunnels. Once the virtual network
> +interface of a given L2TP session is configured and enabled, data can
> +be transmitted, even if the peer isn't yet configured. If the peer
> +isn't configured, the L2TP data packets will be discarded by
> +the peer.
> +.PP
> +To establish an unmanaged L2TP tunnel, use
> +.B l2tp add tunnel
> +and
> +.B l2tp add session
> +commands described in this document. Then configure and enable the
> +tunnel's virtual network interface, as required.
> +.PP
> +Note that unmanaged tunnels carry only ethernet frames. If you need to
> +carry PPP traffic (L2TPv2) or your peer doesn't support unmanaged
> +L2TPv3 tunnels, you will need an L2TP server which implements the L2TP
> +control protocol. The L2TP control protocol allows dynamic L2TP
> +tunnels and sessions to be established and provides for detecting and
> +acting upon network failures.
> +.SS ip l2tp add tunnel - add a new tunnel
> +.TP
> +.BI name " NAME "
> +sets the session network interface name. Default is l2tpethN.
> +.TP
> +.BI tunnel_id " ID"
> +set the tunnel id, which is a 32-bit integer value. Uniquely
> +identifies the tunnel. The value used must match the peer_tunnel_id
> +value being used at the peer.
> +.TP
> +.BI peer_tunnel_id " ID"
> +set the peer tunnel id, which is a 32-bit integer value assigned to
> +the tunnel by the peer. The value used must match the tunnel_id value
> +being used at the peer.
> +.TP
> +.BI remote " ADDR"
> +set the IP address of the remote peer. May be specified as an IPv4
> +address or an IPv6 address.
> +.TP
> +.BI local " ADDR"
> +set the IP address of the local interface to be used for the
> +tunnel. This address must be the address of a local interface. May be
> +specified as an IPv4 address or an IPv6 address.
> +.TP
> +.BI encap " ENCAP"
> +set the encapsulation type of the tunnel.
> +.br
> +Valid values for encapsulation are:
> +.BR udp ", " ip "."
> +.TP
> +.BI udp_sport " PORT"
> +set the UDP source port to be used for the tunnel. Must be present
> +when udp encapsulation is selected. Ignored when ip encapsulation is
> +selected.
> +.TP
> +.BI udp_dport " PORT"
> +set the UDP destination port to be used for the tunnel. Must be
> +present when udp encapsulation is selected. Ignored when ip
> +encapsulation is selected.
> +.SS ip l2tp del tunnel - destroy a tunnel
> +.TP
> +.BI tunnel_id " ID"
> +set the tunnel id of the tunnel to be deleted. All sessions within the
> +tunnel must be deleted first.
> +.SS ip l2tp show tunnel - show information about tunnels
> +.TP
> +.BI tunnel_id " ID"
> +set the tunnel id of the tunnel to be shown. If not specified,
> +information about all tunnels is printed.
> +.SS ip l2tp add session - add a new session to a tunnel
> +.TP
> +.BI name " NAME "
> +sets the session network interface name. Default is l2tpethN.
> +.TP
> +.BI tunnel_id " ID"
> +set the tunnel id, which is a 32-bit integer value. Uniquely
> +identifies the tunnel into which the session will be created. The
> +tunnel must already exist.
> +.TP
> +.BI session_id " ID"
> +set the session id, which is a 32-bit integer value. Uniquely
> +identifies the session being created. The value used must match the
> +peer_session_id value being used at the peer.
> +.TP
> +.BI peer_session_id " ID"
> +set the peer session id, which is a 32-bit integer value assigned to
> +the session by the peer. The value used must match the session_id
> +value being used at the peer.
> +.TP
> +.BI cookie " HEXSTR"
> +sets an optional cookie value to be assigned to the session. This is a
> +4 or 8 byte value, specified as 8 or 16 hex digits,
> +e.g. 014d3636deadbeef. The value must match the peer_cookie value set
> +at the peer. The cookie value is carried in L2TP data packets and is
> +checked for expected value at the peer. Default is to use no cookie.
> +.TP
> +.BI peer_cookie " HEXSTR"
> +sets an optional peer cookie value to be assigned to the session. This
> +is a 4 or 8 byte value, specified as 8 or 16 hex digits,
> +e.g. 014d3636deadbeef. The value must match the cookie value set at
> +the peer. It tells the local system what cookie value to expect to
> +find in received L2TP packets. Default is to use no cookie.
> +.TP
> +.BI offset " OFFSET"
> +sets the byte offset from the L2TP header where user data starts in
> +transmitted L2TP data packets. This is hardly ever used. If set, the
> +value must match the peer_offset value used at the peer. Default is 0.
> +.TP
> +.BI peer_offset " OFFSET"
> +sets the byte offset from the L2TP header where user data starts in
> +received L2TP data packets. This is hardly ever used. If set, the
> +value must match the offset value used at the peer. Default is 0.
> +.SS ip l2tp del session - destroy a session
> +.TP
> +.BI tunnel_id " ID"
> +set the tunnel id in which the session to be deleted is located.
> +.TP
> +.BI session_id " ID"
> +set the session id of the session to be deleted.
> +.SS ip l2tp show session - show information about sessions
> +.TP
> +.BI tunnel_id " ID"
> +set the tunnel id of the session(s) to be shown. If not specified,
> +information about sessions in all tunnels is printed.
> +.TP
> +.BI session_id " ID"
> +set the session id of the session to be shown. If not specified,
> +information about all sessions is printed.
> +.SH EXAMPLES
> +.PP
> +.SS Setup L2TP tunnels and sessions
> +.nf
> +site-A:# ip l2tp add tunnel tunnel_id 3000 peer_tunnel_id 4000 \\
> +           encap udp local 1.2.3.4 remote 5.6.7.8 \\
> +           udp_sport 5000 udp_dport 6000
> +site-A:# ip l2tp add session tunnel_id 3000 session_id 1000 \\
> +           peer_session_id 2000
> +
> +site-B:# ip l2tp add tunnel tunnel_id 4000 peer_tunnel_id 3000 \\
> +           encap udp local 5.6.7.8 remote 1.2.3.4 \\
> +           udp_sport 6000 udp_dport 5000
> +site-B:# ip l2tp add session tunnel_id 4000 session_id 2000 \\
> +           peer_session_id 1000
> +
> +site-A:# ip link set l2tpeth0 up mtu 1488
> +
> +site-B:# ip link set l2tpeth0 up mtu 1488
> +.fi
> +.PP
> +Notice that the IP addresses, UDP ports and tunnel / session ids are
> +matched and reversed at each site.
> +.SS Configure as IP interfaces
> +The two interfaces can be configured with IP addresses if only IP data
> +is to be carried. This is perhaps the simplest configuration.
> +.PP
> +.nf
> +site-A:# ip addr add 10.42.1.1 peer 10.42.1.2 dev l2tpeth0
> +
> +site-B:# ip addr add 10.42.1.2 peer 10.42.1.1 dev l2tpeth0
> +
> +site-A:# ping 10.42.1.2
> +.fi
> +.PP
> +Now the link should be usable. Add static routes as needed to have
> +data sent over the new link.
> +.PP
> +.SS Configure as bridged interfaces
> +To carry non-IP data, the L2TP network interface is added to a bridge
> +instead of being assigned its own IP address, using standard Linux
> +utilities.
> +.PP
> +.nf
> +site-A:# brctl addbr br0
> +site-A:# brctl addif br0 l2tpeth0
> +site-A:# brctl addif br0 eth0
> +site-A:# ip link set br0 up promisc on
> +.fi
> +.PP
> +If you are using VLANs, setup a bridge per VLAN and bridge each VLAN
> +over a separate L2TP session. For example, to bridge VLAN ID 5 on eth1
> +over an L2TP pseudowire:
> +.PP
> +.nf
> +site-A:# brctl addbr brvlan5
> +site-A:# brctl addif brvlan5 l2tpeth0.5
> +site-A:# brctl addif brvlan5 eth1.5
> +site-A:# ip link set brvlan5 up promisc on

The bridge manages promiscuous itself, setting it manually is not required.
If it is required, the the implementation of the device is buggy
and should be fixed.
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