Transcript l2tp overview

L2TP OVERVIEW
18-May-05
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Agenda
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VPN
Tunneling
PPTP
L2F
LT2P
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VPN
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Virtual Private Network is a private
network that uses a public network
(usually the Internet) to connect remote
sites or users together. Instead of using
a dedicated connection such as leased
line, a VPN uses “virtual” connections
routed though the internet.
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Tunneling
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Tunneling is the transmission of data
intended for use only within a private,
usually corporate network through a
public network in such a way that the
routing nodes in the public network are
unaware that the transmission is part of
a private network.
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Tunneling illustrated
Step 2
Original IP
packet
encapsulated
in another IP
packet
Original IP
packet
Router A
Workstation
X
Original IP
packet dest Y
New IP
Packet
Tunnel
Tunnel
Router B
Step 1.
Step 3
Original, unroutable
IP Packet sent to router
Original packet
extracted, sent
to destination
Original IP
packet dest Y
Workstation
Y
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Types of Tunneling
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Two basic types of tunnels
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Voluntary tunnels
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Tunneling initiated by the end-user
(Requires client software on remote computer)
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Compulsory tunnels
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Tunnel is created by NAS or router
(Tunneling support required on NAS or Router)
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Voluntary Tunnels
PPTP Virtual Interface
PPP access protocol
Dial IP Access
Client Host
Serial Interface
Dial Access
Server
Dial Access Provider
PPTP Access
Server
VPN Service
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Voluntary Tunnels (Cont.)
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Will work with any network device
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But user must have a tunneling client compatible with
tunnel server
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Tunneling transparent to leaf and intermediate devices
PPTP, L2TP, L2F, IPSEC, IP-IP, etc.
Simultaneous access to Intranet (via tunnel) and
Internet possible
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Employees can use personal accounts for corporate access
Remote office applications
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Dial-up VPN’s for low traffic volumes
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Compulsory Tunnels
PPP access protocol
V.x modem protocol
L2TP
Dial Access
Server
Client Host
L2TP Access
Server
Non-routed
forwarding path
Dial Access Provider
Internet or VPN Service
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Compulsory Tunnels (Cont.)
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Will work with any client
But NAS must support same tunnel method
But… Tunneling transparent to intermediate routers
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Network access controlled by tunnel server
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User traffic can only travel through tunnel
Internet access possible
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Must be by pre-defined facilities
Greater control
Can be monitored
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Compulsory Tunnels (Cont.)
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Static Tunnels
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Realm-based tunnels
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All calls from a given NAS/Router tunneled to a
given server
Each tunnel based on information in NAI
(I.e. user@realm)
User-based tunnels
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Calls tunneled based on userID data stored in
authentication system
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PPTP
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Point-to-point tunneling protocol
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PPTP (Cont.)
PPP access by remote computers to a private
network through the Internet
1.
Remote user dials in to the local ISP network
access server using PPP.
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PPTP (Cont.)
2.
The PAC establishes a control channel (TCP)
across the PPP connection and through the internet
to the PNS attached to the home network.
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PPTP (Cont.)
3.
Parameters for the PPTP channel are negotiated
over the control channel, and the PPTP tunnel is
established.
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PPTP (Cont.)
4.
A second PPP connection is made from the
remote user, through the PPTP tunnel between the
PAC and the PNS, and into the private networks NAS.
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PPTP (Cont.)
5.
IP datagrams or any other protocol’s datagrams
are sent inside the PPP frames
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L2F
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Layer 2 Forwarding
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L2F
Tunnel is constructed from the service provider.
1.
Remote user dials in to the local ISP network
access server using PPP/SLIP.
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L2F (Cont.)
2.
L2F builds a tunnel from the NAS to the private network.
Uses packet-oriented protocol that provides end-to-end
connectivity, such as UDP, frame relay, etc. as the
encapsulating protocol.
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L2F (Cont.)
3. L2F establishes PPP connection between NAS and
home gateway.
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L2F (Cont.)
4. IP packets are sent over the PPP.
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L2TP
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Layer 2 Tunneling protocol
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L2TP
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