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Jonathan Brewer Technical Director Araneo Wireless Solutions www.araneo.net.nz 23-03-2006 Layer 3 Tunnels for Broadband Delivery
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2 Layer 3 Tunnels for Broadband Delivery – Outline What's the Point? Open-Access Networks Why Segregate Traffic? Sub-Layer 3 Traffic Segregation (VLAN & MPLS) Point-to-Point Protocol (PPP) Generic Routing Encapsulation (GRE) Point-to-Point Tunneling Protocol (PPTP) Point-to-Point Protocol over Ethernet (PPPoE) IP in IP Tunneling (IPIP) Layer 2 Tunneling Protocol (L2TP) Next Steps – L2TPv3 References
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3 What's the Point of this Talk? Layer 3 Tunnels are useful for delivery of broadband Private Layer 2 services are expensive IP Services are cheap and reliable enough They're not without their quirks and issues I'll show how we use these services day to day
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4 Open-Access Networks A physical access network shared by multiple operators Any user can select any service provider Any service provider can deliver services
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5 Homogeneous Open-Access Network Ethernet Based Metropolitan Area Network
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6 Heterogeneous Open-Access Network Multi-Modal Wide Area Network
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7 Why Segregate Traffic? Gain Simple Traffic Engineering P-P circuits are easy to rate-limit Reduce Network Complexity Avoid using an IGP Avoid ugly source routing Add Security to End Users No proxy-arp related outages :-) Increase Safety to Network / Network Operator Hide internal router addresses Provide a seamless end-user experience End user doesn't see what goes on behind the curtain
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8 Sub-Layer 3 Traffic Segregation VLAN – 802.1Q Bridged Ethernet Segments Frames with a VLAN id for traffic segregation Inexpensive and standards based Difficult over Heterogeneous Networks MPLS – Multi-Protocol Label Switching Any protocol (though in practice mostly IP) Designed for creating virtual circuits over packet nets Expensive to buy, implement, maintain Different implementations from each vendor
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9 Point-to-Point Protocol (PPP) (RFC 1661) Can encapsulate many layer 3 protocols Link Control Protocol manages up/down/maintain Authentication can happen before network brought up PAP, CHAP, MSCHAPv1, MSCHAPv2 Used for virtually all dial-up Internet connections Used over L3 in some tunnel technologies
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10 Generic Routing Encapsulation (GRE) (RFC 1701/2) Put any Layer 3 packet inside another Layer 3 packet Packets are IP Protocol 47 Completely Stateless Reduces packet size in most cases (24 byte overhead)
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11 Point-to-Point Tunneling Protocol (PPTP) (RFC 2637) GRE + PPP = PPTP GRE Session managed on TCP port 1723 Cisco-developed protocol licensed to Microsoft Popular because included in MS Windows Uses established PPP authentication infrastructure MPPE Encryption Optional (Typical)
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12 PPTP Example – CafeNET VPN Access CafeNET = CityLink owned WiFi access network Typical user experience is a captive portal + pay per mb ISPs can have tunnels allowed to particular addresses User first receives a CafeNET IP address via DHCP On PPTP establishment, user receives an ISP address VPN can then be used to deliver ISP service End user is routed a /32 on the ISP network
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13 PPP over Ethernet (PPPoE) (RFC 2516) Not a Layer 3 tunnel, but worth mentioning Encapsulation of PPP inside of Ethernet Allows PPP to run directly over Ethernet links Requires a bridged Ethernet topology Not going to do this on top of cheap IP services Popular with DSL and Wireless broadband services
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14 IP in IP Tunneling Encapsulates an IP packet inside of another IP packet Used to simplify complex routing problems Easy way of creating a non-secure VPN Overhead of 20 bytes (did you know Halliburton has their own /8?)
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15 Layer 2 Tunneling Protocol (L2TP) (RFC 2661) PPP over UDP/IP (Port 1701) PPP can carry any protocol L2TP frequently carries IP traffic over IP networks When run over IP, can be encrypted via IPSEC Used extensively in New Zealand (UBS)
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16 L2TP & IPIP Example – Araneo Access Network Ten ISPs offering broadband services Eight Commodity IP network connections
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17 Next Steps for Tunneling – L2TPv3 Standardized Frame Relay, ATM, Ethernet over IP Even 802.1Q VLANs can be encapsulated with L2TPv3 Seen as robust and a pragmatic challenger to MPLS How about Frame over 802.11?
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18 References PPP http://www.ietf.org/rfc/rfc1661.txt GRE http://www.ietf.org/rfc/rfc1701.txt IPIP http://www.ietf.org/rfc/rfc2003.txt PPPoE http://www.ietf.org/rfc/rfc2516.txt PPTP http://www.ietf.org/rfc/rfc2637.txt L2TP http://www.ietf.org/rfc/rfc2661.txt MPLS http://www.ietf.org/rfc/rfc3031.txt L2TPv3 http://www.ietf.org/rfc/rfc3931.txt
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