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Deploying IPv6 in WAN/Branch Networks

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Apr 13, 2011.

Chapter Description

This chapter provides and overview of WAN/branch deployment and also covers WAN/branch IPv6 deployment considerations, WAN/branch deployment over native IPv6, and includes an example of WAN/branch implementation.

This chapter covers the following subjects:

WAN/branch deployment overview: This section describes the single-tier, dual-tier, and multitier branch deployment models.

General WAN/branch IPv6 deployment considerations: Details on generic IPv6 considerations that apply to any of the WAN/branch deployment models are presented.

WAN/branch implementation example: Detailed configuration information is provided for a WAN/branch design that combines elements of the single-tier, dual-tier, and multitier profiles.

WAN/branch deployment over native IPv6: Configuration details are shown for branch-to-WAN head-end deployments, where the Internet Protocol used between sites is IPv6 instead of IPv6-over-IPv4 shown in other examples.

This chapter focuses on providing you with various options for connecting branch offices to the regional or headquarters site using IPv6. As has been discussed in other chapters, there are times when IPv6 needs to be encapsulated into IPv4 to traverse the WAN transport. This happens most often because of the lack of native IPv6 support by the WAN provider and not by lacking features or capabilities of the networking gear. There are a wide variety of deployment options in WAN/branch scenarios that can provide you with a way to provide IPv6 connectivity to branch users and access applications and services located at the main site and beyond.

Native IPv6 deployment is also discussed in this chapter. When port-to-port IPv6 access is available by the WAN service provider, the dependency for encapsulating IPv6 into IPv4 IPsec or SSL is no longer present. IPv6 over IPsec can be deployed today between Cisco IOS branch routers and the WAN head-end routers.

WAN/Branch Deployment Overview

The following sections provide a high-level overview of the three most commonly deployed Cisco branch profiles and the associated WAN head-end. These sections provide a basic understanding of how IPv6 can be integrated into the following branch profiles:

  • Single-tier profile
  • Dual-tier profile
  • Multitier profile

Single-Tier Profile

The single-tier branch profile is a fully integrated design and based on the Cisco Dynamic Multipoint Virtual Private Network (DMVPN) solution. The requirements for LAN and WAN connectivity and security are met by a single Integrated Services Router (ISR). More information about the Cisco ISR platform can be found in the references section of this chapter. Figure 8-1 shows a high-level view of the single-tier branch profile.

Figure 8-1

Figure 8-1 Single-Tier Profile Overview

The single-tier uses a single ISR and is used to provide WAN connectivity through a T1/E1 line to an Internet service provider (ISP). This T1/E1 is used as the primary link to the headquarters (HQ) site. For WAN redundancy, a backup connection is made through asymmetric digital subscriber line (ADSL). There are many alternatives that can be used in this design, such as a different WAN media type and VPN type.

IPv4 and IPv6 connectivity to the HQ site is provided by IPv4 IPsec using DMVPN technologies (DMVPN supports both IPv4 and IPv6-over-IPv4 IPsec). DMVPN works by encapsulating both IPv4 and IPv6 traffic into a generic routing encapsulation (GRE) tunnel, encrypted by IPv4 IPsec and forwarded between sites. The DMVPN tunnels traverse the T1 link as the primary path and establish backup tunnels over the ADSL link.

All traffic leaving the branch traverses the VPN connections to the HQ, including the Internet-bound traffic. Generally, Cisco does not recommend the use of split tunneling at the branch site. If the customer requires split tunneling (that is, Internet traffic leaves the branch directly while corporate-bound traffic traverses the VPN connection), Cisco recommends a careful analysis and testing of the routing and the security implications of such a deployment.

LAN connectivity is provided by an integrated switch module (EtherSwitch Service Module). Dual-stack (running both an IPv4 TCP/IP stack and IPv6 TCP/IP stack) is used on the VLAN interfaces at the branch.

In addition to all the security policies in place at the HQ, local security for both IPv4 and IPv6 is provided by a common set of infrastructure security features and configurations. Additionally, an integrated firewall such as the Cisco IOS Firewall or the Cisco IOS Zone-based Firewall is used. Quality of service (QoS) for IPv4 and IPv6 is integrated into a single policy.

The obvious disadvantage of the single-tier profile is the lack of router and switch redundancy. There is redundancy for the link to the Internet and the VPN connections to HQ. However, because there is a single integrated switch and single router, if either component fails, the site is completely disconnected from HQ. The dual-tier or multitier profile is the solution for customers requiring additional redundancy for the network components (switches, routers, firewalls, and HQ connections).

Dual-Tier Profile

The dual-tier profile separates the routing and switching roles in the branch and provides device and link redundancy for the branch routers.

Figure 8-2 shows a high-level view of the dual-tier profile.

Figure 8-2

Figure 8-2 Dual-Tier Profile Overview

There are three primary differences between the single-tier and dual-tier profile:

  • Redundancy
  • Scalability
  • WAN transport


The dual-tier separates the LAN (switch) and WAN (router) components to offer fault tolerance. A single switch or multiple switches can be used to provide LAN access in the branch. There are two WAN routers redundantly connected to the Frame Relay cloud (or other WAN/VPN type), in addition to being redundantly connected to the LAN switch.


The dual-tier scales better because the single-tier is pretty much an "everything but the kitchen sink" approach. In other words, every network role required in the branch is performed by the ISR. This is great for cost and manageability but can limit availability and scalability. The larger the branch and the more services enabled on the ISR, the higher the risk gets for overextending the performance capabilities of the ISR. This can be alleviated by using a more powerful ISR model, but this does not help with the fault-tolerance requirement. If additional LAN switches are needed at the branch, the Catalyst switches can be used together using the Cisco StackWise technology.

WAN Transport

The WAN connections in the dual-tier model can use Frame Relay, point-to-point IPsec VPN, DMVPN, Multiprotocol Label Switching (MPLS), or whatever WAN type is available. IPv6 is fully supported over Frame Relay in Cisco IOS, and therefore there is no need to run tunnels of any kind between the branch and HQ. This is a great advantage for deployment and management because dual-stack is used all the way from the hosts in the branch LAN across the WAN and into the HQ network. This greatly eases the operational aspects of deploying IPv6 in the branch because no special tunnel considerations (such as availability, security, QoS, and multicast) need to be made.

Security for the dual-tier profile is the same as for the single-tier with the exception that both routers in the dual-tier provide security services.

Multitier Profile

The goal of the multitier profile is complete separation of roles and to offer device and link redundancy at each tier or layer in the branch network. Basically, the multitier is a combination of the single-tier and dual-tier with an additional focus on availability, scalability, and more robust firewall services. The multitier, for the most part, looks like a small campus deployment, and both very often use the same or similar products, design concepts, and configurations. The differences between a small campus and the multitier are more around the presence of the firewall and WAN routers in the multitier example.

Figure 8-3 shows a high-level view of the multitier profile.

Figure 8-3

Figure 8-3 Multitier Profile Overview

Figure 8-3 shows how the tiers or roles are distributed. Several changes are evident with the multitier versus the dual-tier:

  • Firewall tier: Firewall services are now separated from the WAN routers. The Cisco ASA 5500 series is shown here and is providing stateful firewall services for both IPv4 and IPv6. The second ASA (the bottom ASA in Figure 8-3) is in stateful failover mode. In a stateful failover configuration, the ASA is operating in an active/standby (shown in Figure 8-3) or active/active mode.
  • Access tier: The access tier is used for internal service and VLAN termination for the LAN tier. The access tier is like a campus distribution layer in many ways.
  • LAN tier: The LAN tier is the same as with the dual-tier LAN switch. There are just more of them to account for the larger-scale requirements that are most likely found in a larger branch.
2. General WAN/Branch IPv6 Deployment Considerations | Next Section

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