Information About Configuring PPPoE over L2TPv3 Tunnels
Overview of PPPoE over L2TPv3 Tunnels
The PPPoE over L2TPv3 feature allows you to establish PPPoE sessions for incoming traffic using Layer 2 Tunneling Protocol Version 3 (L2TPv3) IPv6 tunnels. An L2TPv3 over IPv6 tunnel is a static/stateless P2P overlay tunnel between a physical edge/aggregation router and its peer entity. The peer entity is typically a virtual Broadband Network Gateway (vBNG), Virtual Network Function (VNF). The L2TPv3 tunnel transports ethernet traffic to and from CPEs. Each CPE is connected to an Access Node Optical Line Terminal(OLT)/Digital Subscriber Line Access Multiplexer(DSLAM).
Point-to-Point Protocol over Ethernet (PPPoE)—protocol describing the encapsulation of PPP frames inside ethernet frames and tunneling packets over Digital Subscriber Lines (DSLs) to Internet Service Providers (ISPs).
L2TPv3 Tunnel Interface—logical interface for terminating Broadband Subscriber Layer 2 Ethernet attachment circuits (port/VLAN) from access or edge routers over an IPv6 network with L2TPv3 encapsulation for BNG services. For further information, see IETF RFC8159.
The difference between the situation before and after the introduction of PPPoE sessions for L2TPv3 tunnels is shown in Figures 1 and 2 in: Overview of PPPoE over L2TPv3 Tunnels—Example Topology.
You can use Point-to-Point Protocol over Ethernet (PPPoE) sessions via EoL2TPv3oIPv6 tunnels to deliver the same functions as those described in: How to Enable and Configure PPPoE on Ethernet.
The PPPoE sessions used by this feature have the following key characteristics:
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H-QoS shaper per-session
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In/Out Access Control Lists (ACLs)
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Dual Stack
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Ingress QoS Policing
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Unicast Reverse Path Forwarding (uRPF)
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Lawful Intercept (LI)—both Radius & SNMP-based
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Session termination in VRF
The scope of a vBNG on a static/stateless P2P EoL2TPv3oIPv6 overlay tunnel includes:
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An EoL2TPv3oIPv6 overlay tunnel with and without VLAN tags:
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Plain ethernet traffic OR
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Dot1Q (Single VLAN tagged)
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All applicable features/functionality that are currently supported on physical interfaces for PPPoE sessions:
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PTA (locally terminated) or LAC (forwarded to LNS over L2TPv2oIPv4)
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IPv4 IPoE session (Note: IPv4 only)
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Session authentication/authorization, policy enforcement, accounting and an AAA/RADIUS interface. These all function in the same way as currently supported on physical interfaces for PPPoE sessions
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Only session-level QoS—as currently supported for PPPoE sessions.
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For PPPoE PTA sessions:
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Per-session in and out ACLs
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VRF mapping
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Overview of PPPoE over L2TPv3 Tunnels—Example Topology
The effect of using this feature can be simply shown by looking at example topologies before and after this feature was introduced. Figure 1 shows an example topology using a traditional BNG architecture. This example uses two BNGs for three CPEs. Figure 2 shows an example of the BNG architecture using this feature, which only uses one vBNG for three CPEs.
Benefits of PPPoE over L2TPv3 Tunneling
A benefit of this feature is that a Broadband Network Gateway(BNG) can be placed in each data center, instead of at each point of presence(PoP). An ISP can use L2TPv3 tunneling to send dual-stack PPP packets across its own IPv6 backbone network for a PPP Terminated Aggregation (PTA) session or a L2TP Access Concentrator (LAC) session.
Prerequisites for PPPoE over L2TPv3 Tunnels
Software Prerequisites:
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Currently only supported on a Cisco CSR 1000v VM. This virtual router requires at least 2 CPUs, 8GB RAM or above, and 2 or more (vNIC) interfaces (10Gb).
Restrictions for Configuring PPPoe over L2TPv3 Tunnels
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Q-in-Q tunneling is not supported
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Tunnel H-QoS is not supported
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Access Node Control Protocol (ANCP) is not supported
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IPoE sessions are not supported (only PPPoE sessions are supported)
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Netconf/Yang Model is not supported
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We recommend using a physical interface/subinterface as the tunnel source instead of a loopback interface, to support session-level QoS Queuing or Shaping
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High Availability (HA) is not supported
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This feature does not support any PPPoE feature under the tunnel interface except for PPPoE enable function.
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A VLAN range under the tunnel is not supported
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MIB is not supported
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The size of the secondary local cookie must equal the size of the primary local cookie
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If a PPPoE session is up, the following actions are not allowed:
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Removal of the tunnel mode
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Removal of remote cookies
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Modification or removal of tunnel parameters is not allowed, but removal of local cookies is allowed.
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Scaling of L2P2TPv3 Tunnels
Performance of Cisco CSR 1000v
The scaling and throughput for vBNG on the Cisco CSR 1000v depends upon the compute Node platform and Operating System, including the hypervisor and vRouter. An example specification and the resulting performance, are described below,
Specification—An Intel x86 server platform consisting of a compute node running vBNG instances (Cisco CSR 1000v VMs) with 2 sockets (14 cores per socket), 4 x 10G NICs, a CPU of 2.30 GHz E5-2658 v4/105W 14C/35MB Cache/DDR4 2400MHz. A Linux Ubuntu 14.04 host OS with KVM Hypervisor (QEMU Rx & Tx size=1024) and a vSwitch (DPDK & vhost-user interface to the Cisco CSR 1000v VM). Note: We highly recommend using vCPU pinning for the Cisco CSR 1000v VMs and emulator, because large 1 GB pages are required for Cisco CSR 1000v VMs and the host OS.
Performance—8000 sessions (PPPoE) across 40 static/stateless P2P EoL2TPv3oIPv6 tunnels, with an average of 200 sessions per tunnel, a total throughput (UL + DL) of 4 Gbps. A vNIC with 2 x 10G ports: one port is for DL (to/from Edge/Aggregation router) and another port for UL (to/from core network).
The following table shows the relationship between the number of tunnels and the number of PTA or LAC sessions per tunnel.
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No. of L2TPv3 over IPv6 Tunnels |
PTA sessions per tunnel Single or Dual Stack |
LAC sessions per tunnel Single or Dual Stack |
PTA + LAC Sessions per tunnel Single or Dual Stack |
|---|---|---|---|
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40 |
200 |
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40 |
200 |
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40 |
200 PTA (in 30 tunnels) and 200 LAC (in 10 tunnels) |
Call Flows for PPPoE over L2TPv3oIPv6 Tunnels
The figure below summarizes the call flows for PPPoE over an L2TPv3oIPv6 tunnel. Call flows are also explained here: PPP and L2TP Flow Summary. For Cisco IOS XE Fuji 16.7, PPPoE is supported. (IPoE is not supported.)
NAS-Port-Type Extensions
The following extended NAS-Port-Types are currently defined for a PPPoE service on ethernet and ATM interfaces.
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PPPoA—Radius value 30
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PPPoEoA—Radius value 31
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PPPoEoE—Radius value 3
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PPPoEoVLAN—Radius value 33
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PPPoEoQinQ—Radius value 34
In this feature, PPPoE support is added to the virtual interface (tunnel), which requires a new NAS-Port-Type for the PPPoE service on a virtual interface.
The following extended NAS-Port-Types were introduced for RFC2516, and which support the PPPoE service on virtual interfaces are supported:
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VirtualPPPoEoE (PPP over Ethernet [RFC2516] over Ethernet over tunnel/pseudowire) – Radius Value 44
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VirtualPPPoEoVLAN (PPP over Ethernet [RFC2516] over VLAN tunnel/pseudowire) – Radius Value 45
(The following extended NAS-Port-Type, introduced for RFC2516, is not supported: VirtualPPPoEoQinQ (PPP over Ethernet [RFC2516] over IEEE 802.1QinQ tunnel/pseudowire) – Radius Value 46.)
Network Topology Overview
Figure 3 below is an overview of the network topology. Traffic from CPE1 and CPE2 uses PPPoE sessions and EoL2TPv3oIPv6 tunnels to a vBNG in the data center. For each OLT/VLAN, a static EoL2TPv3oIPv6 tunnel is provisioned between an Edge or Aggregation Router and the vBNG on a Cisco CSR 1000v. The Edge/Agg Router forwards ethernet traffic from CPEs through EoL2TPv3oIPv6 tunnels.
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