What is a virtual template/access interface?

What is a virtual-template interface?

A virtual-template interface is a logical entity that can be used to apply predefined interface configurations for virtual-access interfaces.

Virtual template interfaces is configured independently of any physical interface and applied dynamically, as needed, to create virtual access interfaces.

What is a virtual-access  interface?

Virtual access interface is a virtual interface that is created, configured dynamically, used, and then freed when no longer needed.The virtual Access interface is not configured manually it gains its configuration via the Virtual Template interface and/or RADIUS and TACAC+ authentication servers.

Applications of virtual-access interfaces:

Applications include but not limited to the following list.

  • VPDN
  • Multilink PPP
  • PPP over ATM
  • PPP over Ethernet
  • PPP over frame-relay

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12 Responses to “What is a virtual template/access interface?”

  1. Hi Wael,

    I have seen configs where the main WAN link say ADSL link ATM0, being bound to Virtual access interface. And also strange thing noticed is that if that Virtual access interface is in up down state, then other remote sites where not able to reach my site irrespective of WAN link staying UP, here I have few queries:

    i) Why do we bound interfaces to Virtual access?

    ii) when does the Virtual access go in UP/DOWN state?

    Hearty request to see answers to my questions … Thanks for sharing your knowledge, Honestly speaking I have improved a lot reading posts here, continue the great work, may Almighty grant you guys a huge success :)

  2. Nice observations Khan, this means they are providing ADSL service using PPPOA.

    Typically virtual templates is used to provide Point to Point connections over different L2 technologies like PPPOA, PPPOE and PPPOFR. You do this when your implementation requires some of the PPP features like authentication of multilink.

    virtual access may go down for any cause affecting any layer of communication between the end points. However, authentication and other PPP are common problems.

    I hope your questions are answered

  3. Yes Thanks a lot :) ….

  4. [...] [...]

  5. Weal,

    your article is great but i want to know what is the difference between creating a MULTILINK interface and bind the physical interfaces to it versus creating a VIRTUAL-TEMPLATE interface with an ip unnumbered to a loopback to it?

    is there difference in the way i should implement those and can you give me an example for each of those?

  6. Hi Sherif,

    Thanks for your comment, The Multilink interface is another kind of logical interface with a single purpose which is to bind multiple PPP links together, the interface will be used as long as there are links up in the bond. The virtual-template for example in the case of PPPOE is used to create interface for each incoming user.

    I hope I have clearly answered your question. Let me know if you are still confused.

  7. Wael,

    thank you for your swift answer but doesn’t the virtual-template interface bind p2p interfaces too?

    what you’re implying is that multilink interface is used when i’m connecting 2 routers with 2 or more serial interfaces and i want to bind them

    but when a router is connected to a DSLAM for example and several different sources are needed to be binded, i use the virtual template

    am i getting this right?

    BTW.. you’re one of my heros :)

  8. Sherif,

    Multilink interfaces are used bond multiple PPP links to be used as a single link, this link will be represented by a virtual access. Multilink must be configured on the two ends of the circuit in order to work and they can be configured by multilink or interfaces or use a virtual-template configuration.

    On the other hand virtual-templates are used to create virtual-access interfaces by cloning the virtual template configuration. For an example of using both, if we are configuring PPPoFR a virtual-template will be needed to create the PPP virtual-access interface dynamically, then if you have multiple PPPoFR that you want to bond together as a single link you will configure a multilink interface to represent the bond.

    If this is still confusing let me know to try to communicate it better.

    BTW: I am very delighted if I am adding value to your life or career and I am very for your nice words :)

    Stay Connected

  9. Thanks for the explanation. This was helpful.

  10. Hamdy Rostom Says:

    Dear Wael,

    thanks for such a topic, but I have a question, when I’m trying to configure virtual-template interface to use it in multilink over ATM, the virtual template is always in state down/down, also the dynamic configured virtual-acess interface is also down/down.why?

    Router#sh run int multilink 10
    Building configuration…

    Current configuration : 135 bytes
    !
    interface Multilink10
    ip address 10.10.10.1 255.255.255.252
    ppp multilink
    ppp multilink group 10
    service-policy input hamdy
    end

    Router#sh run int vir
    Router#sh run int virtual-t
    Router#sh run int virtual-te
    Router#sh run int virtual-template 1
    Building configuration…

    Current configuration : 149 bytes
    !
    interface Virtual-Template1
    no ip address
    ppp multilink
    ppp multilink fragment delay 10
    ppp multilink interleave
    ppp multilink group 10
    end

    Router#
    Router#sh run int atm2/0
    Building configuration…

    Current configuration : 110 bytes
    !
    interface ATM2/0
    no ip address
    no atm ilmi-keepalive
    pvc 17/24
    protocol ppp Virtual-Template1
    !
    end

    Virtual-Access1 unassigned YES unset down down
    Virtual-Template1 unassigned YES manual down down
    Multilink10 10.10.10.1 YES manual down down

  11. tnx for your great and detailed answers. I’m working on PPPoFR and really your posts helped me. and a question: why after configuring PPPoFR, autmatically, 3 virtual accss interfaces are created? these 3 interfaces do what?

  12. abebe getinet Says:

    when we configure VPDN we use virtual-template ip address.my question is how can we use one virtual-template ip address for many point to point connections ?

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