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Category: DMVPN

Regional Internet Exits in Large DMVPN Deployment

One of my readers wanted to implement a large DMVPN cloud with regional Internet exit points:

We need to deploy a regional Internet exits and I’d like to centralize them.  Each location with a local Internet exit will be in a region and that location will advertise a default-route into the DMVPN domain to only those spokes in that particular region.

He wasn’t particularly happy with the idea of deploying access and core DMVPN clouds:

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DMVPN Split Default Routing

SD-WAN is all the rage these days (at least according to software-defined pundits), but networking engineers still build DMVPN networks, even though they are supposedly impossibly-hard-to-configure Rube Goldberg machinery.

To be honest, DMVPN is not the easiest technology Cisco ever developed, and there are plenty of gotchas, including the problem of default routing in Phase 2/3 DMVPN networks.

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Viptela SEN: Hybrid WAN Connectivity with an SDN Twist

Like many of us Khalid Raza wasted countless hours sitting in meetings discussing hybrid WAN connectivity designs using a random combination of DMVPN, IPsec, PfR, and one or more routing protocols… and decided to try to create a better solution to the problem.

Viptela Secure Extensible Network (SEN) doesn’t try to solve every networking problem ever encountered, which is why it’s simpler to use in the use case it is designed to solve: multi-provider WAN connectivity.

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Is Anyone Using DMVPN-over-IPv6?

One of my readers sent me an interesting challenge: they’re deploying a new DMVPN WAN, and as they cannot expect all locations to have native (non-NAT) IPv4 access, they plan to build the new DMVPN over IPv6. He was wondering whether it would work.

Apart from “you’re definitely going in the right direction” all I could tell him was “looking at the documentation I couldn’t see why it wouldn’t work” Has anyone deployed DMVPN over IPv6 in a production network? Any hiccups? Please share your experience in the comments. Thank you!

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Changes in IBGP Next Hop Processing Drastically Improve BGP-based DMVPN Designs

I always recommended EBGP-based designs for DMVPN networks due to the significant complexity of running IBGP without an underlying IGP. The neighbor next-hop-self all feature introduced in recent Cisco IOS releases has totally changed my perspective – it makes IBGP-over-DMVPN the best design option unless you want to use DMVPN network as a backup for MPLS/VPN network.

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Real Life BGP Route Origination and BGP Next Hop Intricacies

During one of the ExpertExpress engagements I helped a company implement the BGP Everywhere concept, significantly simplifying their routing by replacing unstable route redistribution between BGP and IGP with a single BGP domain running across MPLS/VPN and DMVPN networks.

They had a pretty simple core site network, so we decided to establish an IBGP session between DMVPH hub router and MPLS/VPN CE router (managed by the SP).

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Scaling BGP-Based DMVPN Networks

Cristiano sent me an interesting question:

I saw that to configure BGP as the routing protocol running over DMVPN I have to configure BGP neighbors on the hub site router. Do I really have to configure all the neighbors on the hub site? How many neighbors could I configure? How can I scale that?

According to Cisco Live presentations, BGP-over-DMVPN scales to several thousand spoke sites (per hub router), so you shouldn’t be too worried about the protocol scalability. Configuring all those neighbors is a different issue.

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BGP Routing in DMVPN Networks

Once you decide to use BGP as the routing protocol in your DMVPN network, you face a few more design choices:

  • Should you use IBGP or EBGP?
  • Should you use a unique AS number for every DMVPN site, or the same AS number on all spoke sites?

The BGP Routing in DMVPN Access Networks ExpertExpress case study describes these dilemmas in more details; if you face a similar problem and would like me to review your design, get in touch.

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Combining DMVPN with Existing MPLS/VPN Network

One of the Expert Express sessions focused on an MPLS/VPN-based WAN network using OSPF as the routing protocol. The customer wanted to add DMVPN-based backup links and planned to retain OSPF as the routing protocol. Not surprisingly, the initial design had all sorts of unexpectedly complex kludges (see the case study for more details).

Having a really smart engineer on the other end of the WebEx call, I had to ask a single question: “Why don’t you use BGP everywhere” and after a short pause got back the expected reply “wow ... now it all makes sense.”

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