The MPLS-OPS Archive

["Sonali Francis" <Sonali.Francis@lntinfotech.com>]

Here are some ideas on Layer 2 and Layer 3 VPN:

The Layer 2 VPN is mainly based on overlay model where PE maps maps
incoming Layer 2 traffic onto the appropriate point-to-point tunnel. Simple
point-to-point tunnels are established on an provider's network to handle
various forms of Layer 2 traffic (Ethernet, frame relay, ATM, TDM, and
PPP/HDLC). From the peering aspect, CE router is peer to CE router; PE is
not a peer to the CE and does not maintain separate routing tables. No L3
processing of the customer packet takes place in PE.

The Advantages are
1. Advantageous where direct interoperability with existing Layer 2 VPN
deployments is important.
2. Layer 2's MPLS "overlay" model is  more attractive for carriers with
existing Layer 2 VPN

Disadvantages are
1. Scaling problem: Lack the scope of routed networks, limiting a Layer 2
implementation to the confines of the transport medium

The Layer 3 VPN is based on Peer-to-peer Model. In case of Layer 3 MPLS
VPN, it is implemented by using two-level label stack.  The ingress PE
router pushes both a Next-Hop BGP header (for the private network) and a
Next-Hop Interior Gateway Protocol (IGP) header (for the shared
infrastructure) onto the packet. After reaching the egress PE router via
one or more MPLS Label Switched Paths (LSPs), the PE pops the MPLS headers
and delivers a normal IP packet to the customer.
In this case CE routers peers with PE routers.

The advantages are
1.Ubiquity of IP networks over multiple transport networks.
2. Multiple customers having IP running over different data link layer can
form a VPN.
3.Dynamic VPNs by virtue of strong automatic route discovery.
4. Economical for ISPs that already use BGP extensively and have already
deployed high-end IP/MPLS routing equipment at the edge.
But Disadvantage is this is more complex and expensive

http://lambdanet.net/userfiles/france/download/white_paper/Keep_it_Simple_with_BGP_MPLS_VPN_LambdaNet.pdf

      is quite informative. But it is to be noted that Layer 2 or layer 3
VPN can exist in non-MPLS domain too.

Please correct me if I am wrong....

Regards,
Sonali



                                                                                                           
                      Alexandre Carlos                                                                     
                      de Oliveira              To:       <mpls-ops@mplsrc.com>                             
                      <alexandre@redes.        cc:                                                         
                      unb.br>                  Subject:  [MPLS-OPS]: MPLS L2 VPN end L3 VPN                
                                                                                                           
                      26/03/2003 11:16                                                                     
                      PM                                                                                   
                                                                                                           
                                                                                                           




Can some one tell me whats the difference between L2 VPN and L3 VPN?

Alex


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