A key to the success of MPLS and the L3 MPLS VPN is the use of “tunnels” created by the MPLS labeling. Tunnelling in the service provider cloud has many benefits:

  • Only edge points (ingress and egress) need to understand the meaning of the inner network information (prefixes); core routers simply switch traffic based on labels
  • You can easily re-direct tunnel traffic explicitely
  • Tunnels can be created within tunnels
  • The tunnel is less prone to data spoofing
  • The overhead with MPLS is relatively low (4 bytes per MPLS header)

Examine the Exhibit as we review some of the additional, key components of the L3 MPLS VPN:mpls components

Notice how edge routers are known as Label Edge Routers (LERs) or Provider Edge Routers (PEs). Routers in the core of the provider network are called Label Switching Routers (LSRs) or Provider (P) routers. Label Switched Paths (LSPs) represent the path traffic takes through the provider MPLS network. All of the traffic that is to be forwarded using the same path is known as the Forwarding Equivalence Class (FEC). All of this traffic is forwarded with the same MPLS label. In the simple case of the Routing and Switching CCIE Exam, the FEC typically consists of all packets with a destination address of the BGP next-hop.

Notice how the network is a thing of beauty for the Label Switching Routers (LSRs)/Provider (P)¬†routers, especially when you consider scalability. The service provider can add more customers and introduce many more network prefixes into its infrastructure, but these prefixes only need to exist on Label (Provider)¬†Edge Routers (LERs/PERs). These edge devices are the “workhorses” of the provider network. Notice among many jobs, it is their responsibility to identify the Label Switched Path (LSP) that the packet is destined for.

Customer networks consist of Customer Edge routers (CEs) and Customer (C) routers. These devices need no knowledge whatsoever about MPLS. They can be completely oblivious to the fact they are interacting with a structure that uses MPLS as its basis for forwarding traffic.

In order to master MPLS for the CCIE R&S written and lab exam, this is the first of the terminology we must commit to memory regarding MPLS. Please join me for future posts in this series.

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8 Responses to “MPLS Components”

  1. Sanjeev says:

    Hi Anthony,
    Thank you for the concise explanation. – Sanjeev.

  2. Zabeel Musa says:

    Excellent! Looking forward to the next post.

  3. Dayo says:

    Great post. Pls keep ‘em coming!

  4. Many thanks for sharing the infos, i found it really useful. I am browsing your website from my hotel room

  5. [...] the previous MPLS Components post, we discussed the many benefits that MPLS can bring to the network, and we detailed the [...]

  6. JC G says:

    I have my CCIE RS number since 4 years ago. Now I am interested in voice. 2 questions I have are whether per-call MPLS tunnel is available in today’s IOS mpls implementation. If not, is it necessary to have per-call MPLS tunnel to achieve telco quality and ultimately obsolete ss7? I have seen how mpls tunnels are configured manually, not signaled. If the whole earth obsoletes ss7 and uses mpls te, will the SIP phones initiate RSVP or CUCM or soft switch does that? Thanks. JC

  7. JC G says:

    My third question is whether CUCM-like call managers will be integrated into a cell phone and cell phone companies configures
    the call manager inside the phone and App programmers just program a plain SIP application? Or, SIP will become obsolete once every voice App programmers learns the MPLS-TE tunnel and decides to make his App talks to the MPLS-TE router directly.


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