1

I am new to VPN technology and trying to connect and get the bigger picture after going through lot of online documents. Here are my confusions:

  1. Differences between L2 VPN and L3 VPN. It would be better to understand from the packet structure point of view.

  2. What exactly is EVPN? Why it came into existence?

  3. EVPN along with MPLS is used to provide L2 VPN or L3 VPN or both?

  4. How is DCI achieved with all these technologies?

Sorry if the questions are too many. I would be glad if someone can clarify my doubts.

Thanks.

  • Do you understand the network layers, what they are, why we have them, and what they do? That is Networking 101, and understanding that will make the answer to your first question obvious. – Ron Maupin Jul 21 '18 at 18:10
  • Yes, I understand OSI layers. If I go with that, I understand that - - L2 VPN is extending the L2 network over a public network. - L3 VPN is extending the L3 network ( I am not sure what this means) Am I correct? Partially? – Saurabh Suman Jul 21 '18 at 18:17
  • L2 VPN is a layer-2 (bridged) tunnel, and L3 VPN is a layer-3 (routed) tunnel. – Ron Maupin Jul 21 '18 at 18:20
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer. – Ron Maupin Dec 25 '18 at 9:07
4

This is a very broad question and you need to do some more background reading, but quick answers to your questions:

L2 MPLS VPN – forwards based on the L2 address of the L2 PDU. The L2 PDU is encapsulated in the transport protocol (MPLS). The VPN can provide point-to-point (AToM) or LAN type multipoint service (VPLS). Something to remember about these types of VPN is that L2 forwarding information is learned though the data plane (for VPLS), similar to standard switch MAC learning. The control plane does not get involved in distributing L2 forwarding information. This means traffic from unknown MAC addresses is initially flooded, until return traffic is received across the pseudowire and the destination MAC is learned. Point-to-point L2 VPNs don't need to learn MAC information as they just forward out of the other port/pseudowire (they only have two interfaces per device).

L3 MPLS VPN – forwards based on the L3 address of the L3 PDU. The L3 PDU is encapsulated in the transport protocol (MPLS). With MPLS VPN, MP-BGP is used to distribute L3 forwarding information between sites for routes within the VPN.

EVPN – Another form of multipoint L2 VPN (LAN type service). Can use MPLS or VXLAN for transport. The important part that EVPN adds to L2 VPN is the distribution of L2 forwarding information between sites (through MP-BGP with new EVPN address family). It doesn’t have to rely on data plane learning, so can cut down on flooding between sites. In addition, the EVPN address family can also transport L2 to L3 address mappings, allowing sites to synchronise L2 to L3 mapping (ARP), cutting down on ARP broadcast.

DCI – You can use L2 VPN (AToM for two sites, VPLS for two or more sites) or EVPN to achieve DCI as you need to interconnect the sites at L2. EVPN is more efficient and reduces the amount of L2 flooding and ARP traffic between sites, so if your hardware supports it, it may be the better choice.

  • Regarding L2 VPN: When you say L2 PDU is encapsulated, what will be the destination mac address of the frame coming from CE side? – Saurabh Suman Jul 21 '18 at 18:41
  • If a frame is coming from the CE device to the PE device, the PE device will usually encapsulate the entire L2 frame and transport it over the SP network and forward out the egress PE router towards the egress CE router. The frame header will not be altered so it will have the same destination MAC. There are also outer Ethernet headers used by the SP during transport, but they are irrelevant from the customer side. – Karl Billington Jul 21 '18 at 18:47
  • ok. Thanks a lot for the precise answer. It helped a lot to clear some of the things. – Saurabh Suman Jul 21 '18 at 18:49

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