Posts Tagged ‘dmvpn’


The recording of last week’s seminar on Introduction to DMVPN for CCIE R&S v5 Candidates is now available to view here.  This is the first of many new free seminars on new topics that have been added to the CCIE R&S version 5 blueprint.  New upcoming sessions will include IPv6 First Hop Security, IPsec LAN-to-LAN tunnels, GET VPN, IGP Convergence & Scalability, and BGP Convergence & Scalability, just to name a few. Feel free to submit requests for additional topics in the comments below.


Good luck in your studies!

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Tomorrow, December 6th 2013, at 10:00 PST (GMT 18:00) I will be running a free live online session on Introduction to DMVPN for CCIE R&S v5 Candidates.  You can sign-up for this seminar here.  Additionally the link to attend is available at the top of the dashboard when you login to the INE Members Site.

This session is the first of many to help candidates transition from the current CCIE R&S v4 Blueprint to the recently announced CCIE R&S v5 Blueprint that goes live on June 4th 2014. We will continue to run additional sessions in the future on new topics that have been added to the CCIE R&S v5 Blueprint, such as IPv6 First Hop Security, IPsec LAN-to-LAN tunnels, GET VPN, IGP Convergence & Scalability, and BGP Convergence & Scalability, just to name a few.  These sessions are not only applicable to CCIE R&S v5 candidates, but also to those pursuing the CCNA, CCNP, or CCIE Security tracks, as well as for everyday engineers looking to apply these technologies in their production environments.

Tomorrow’s session will focus on the theory of what Dynamic Multipoint VPN (DMVPN) is, what problems it was designed to solve, and where it fits in the overall network design as compared to other technologies such as MPLS Virtual Private LAN Service (VPLS) or MPLS Layer 3 VPNs.  The session will also include live implementation examples of DMVPN on the Cisco IOS CLI.  Expect this session to run somewhere around 2 – 3 hours in length.

I hope to see you there!

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In this post we are going to speak mainly of NHRP. The other important part of DMVPN – IPsec – is relatively the same, and did not change with introduction of NHRP Phase 3. To begin with, let’s quickly recall the core features of NHRP Phase 1 & 2. For detailed overview, you may refer to DMVPN Explained

NHRP Phase 1:

No spoke-to-spoke tunnels but spokes dynamically register their NBMA addresses with the hub. Spokes use p2p tunnels and route all traffic across the hub. It is OK to summarize routes on the hub router and limit the amount of routing information received by the spokes.

NHRP Phase 2:

Uses a special CEF “trick” to implement spoke2spoke tunnels. All spokes need to receive full routing information with next-hop unchanged (e.g. using no next-hop-self eigrp or OSPF broadcast network type).

Look at the following topology:

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DMVPN stands for Dynamic Multipoint VPN and it is an effective solution for dynamic secure overlay networks. In short, DMVPN is combination of the following technologies:

1) Multipoint GRE (mGRE)
2) Next-Hop Resolution Protocol (NHRP)
4) Dynamic Routing Protocol (EIGRP, RIP, OSPF, BGP)
3) Dynamic IPsec encryption
5) Cisco Express Forwarding (CEF)

Assuming that reader has a general understanding of what DMVPN is and a solid understanding of IPsec/CEF, we are going to describe the role and function of each component in details. In this post we are going to illustrate two major phases of DMVPN evolution:

1) Phase 1 – Hub and Spoke (mGRE hub, p2p GRE spokes)
2) Phase 2 – Hub and Spoke with Spoke-to-Spoke tunnels (mGRE everywhere)

As for DMVPN Phase 3 – “Scalable Infrastructure”, a separate post is required to cover the subject. This is due to the significant changes made to NHRP resolution logic (NHRP redirects and shortcuts), which are better being illustrated when a reader has good understanding of first two phases. However, some hints about Phase 3 will be also provided in this post.

Note: Before we start, I would like to thank my friend Alexander Kitaev, for taking time to review the post and providing me with useful feedback.

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