IPsec VTIs allow you to configure a virtual interface to which you can apply features. Features for clear-text packets are configured on the VTI. Features for encrypted packets are applied on the physical outside interface. When IPsec VTIs are used, you can separate the application of features such as Network Address Translation (NAT), ACLs, and QoS and apply them to clear-text, or encrypted text, or both.

There are two types of VTI interfaces: static VTIs (SVTIs) and dynamic VTIs (DVTIs).

SVTI configurations can be used for site-to-site connectivity in which a tunnel provides always-on access between two sites.

Additionally, multiple Cisco IOS software features can be configured directly on the tunnel interface and on the physical egress interface of the tunnel interface. This direct configuration allows users to have solid control on the application of the features in the pre- or post-encryption path.

The figure below illustrates how a SVTI is used.

Figure 1. IPsec SVTI

The IPsec VTI supports native IPsec tunneling and exhibits most of the properties of a physical interface.

DVTIs can provide highly secure and scalable connectivity for remote-access VPNs. The DVTI technology replaces dynamic crypto maps and the dynamic hub-and-spoke method for establishing tunnels.

Note	You can configure DVTIs with IKEv1 or IKEv2. The legacy crypto map based configuration supports DVTIs with IKEv1 only. A DVTI configuration with IKEv2 is supported only in FlexVPN.

DVTIs can be used for both the server and the remote configuration. The tunnels provide an on-demand separate virtual access interface for each VPN session. The configuration of the virtual access interfaces is cloned from a virtual template configuration, which includes the IPsec configuration and any Cisco IOS software feature configured on the virtual template interface, such as QoS, NetFlow, or ACLs.

DVTIs function like any other real interface, so you can apply QoS, firewall, or other security services as soon as the tunnel is active. QoS features can be used to improve the performance of various applications across the network. Any combination of QoS features offered in Cisco IOS software can be used to support voice, video, or data applications.

DVTIs provide efficiency in the use of IP addresses and provide secure connectivity. DVTIs allow dynamically downloadable per-group and per-user policies to be configured on a RADIUS server. The per-group or per-user definition can be created using an extended authentication (Xauth) User or Unity group, or can be derived from a certificate. DVTIs are standards based, so interoperability in a multiple-vendor environment is supported. IPsec DVTIs allow you to create highly secure connectivity for remote access VPNs and can be combined with Cisco Architecture for Voice, Video, and Integrated Data (AVVID) to deliver converged voice, video, and data over IP networks. The DVTI simplifies VPN routing and forwarding- (VRF-) aware IPsec deployment. The VRF is configured on the interface.

A DVTI requires minimal configuration on the router. A single virtual template can be configured and cloned.

The DVTI creates an interface for IPsec sessions and uses the virtual template infrastructure for dynamic instantiation and management of dynamic IPsec VTIs. The virtual template infrastructure is extended to create dynamic virtual-access tunnel interfaces. DVTIs are used in hub-and-spoke configurations. A single DVTI can support several static VTIs.

The figure below illustrates the DVTI authentication path.

Figure 2. Dynamic IPsec VTI

The authentication shown in the figure above follows this path:

1. User 1 calls the router.

2. Router 1 authenticates User 1.

3. IPsec clones the virtual access interface from the virtual template interface.

When an IPsec VTI is configured, encryption occurs in the tunnel. Traffic is encrypted when it is forwarded to the tunnel interface. Traffic forwarding is handled by the IP routing table, and dynamic or static routing can be used to route traffic to the SVTI. DVTI uses reverse route injection to further simplify the routing configurations. Using IP routing to forward the traffic to encryption simplifies the IPsec VPN configuration . The IPsec virtual tunnel also allows you to encrypt multicast traffic with IPsec.

IPsec packet flow into the IPSec tunnel is illustrated in the figure below.

Figure 3. Packet Flow into the IPsec Tunnel

After packets arrive on the inside interface, the forwarding engine switches the packets to the VTI, where they are encrypted. The encrypted packets are handed back to the forwarding engine, where they are switched through the outside interface.

The figure below shows the packet flow out of the IPsec tunnel.

Figure 4. Packet Flow out of the IPsec Tunnel

DVTI supports multiple IPsec SAs. The DVTI can accept multiple IPsec selectors that are proposed by the initiator.

The DVTIs allow per-peer features to be applied on a dedicated interface. You can order features in such way that all features that are applied on the virtual access interfaces are applied before applying crypto. Additionally, all the features that are applied on the physical interfaces are applied after applying crypto. Clean routing is available across all VRFs so that there are no traffic leaks from one VRF to another before encrypting.

Multi-SA VTIs ensure interoperation with third-party devices and provide a flexible, clean, and modular feature-set.

Multi-SA VTIs enable a clean Cisco IOS XE infrastructure, even when the Cisco IOS XE software interoperates with the third-party devices that only implement crypto maps.

VRF and Scalability of Baseline Configuration:

Virtual access instances inherit the Inside-VRF (IVRF) from the template configuration. Users must configure several templates to enforce an appropriate IVRF for each customer. The number of templates must be equal to the number of customers connecting to the headend. Such a configuration is cumbersome and undesirable and also affects performance because each template declaration consumes one Interface Descriptor Block (IDB).

This complication can be avoided by allowing the IKE profile to override the virtual access VRF with the VRF configured on the IKE profile. A better solution is to allow the IKE profile to override the virtual access VRF using AAA, but this method is supported only for IKEv2.

The VRF configured in the ISAKMP profile is applied to the virtual access first. Then the configuration from virtual template is applied to the virtual access. If your virtual template contains ip vrf forwarding command configuration, the VRF from the template overrides the VRF from the ISAKMP profile.

Rules for Initial Configuration of a VRF:

The following rules must be applied during the initial configuration of VRF:

• If you configure IVRF in the IKE profile without configuring it in the virtual template, then you must apply the VRF from the IKE profile on each virtual access derived from this IKE profile.
• If you configure VRF in an IKE profile and virtual template, then the virtual template IVRF gets precedence.

Rules for Changing the VRF:

If you change the VRF configured in an IKE profile, all the IKE SAs, IPsec SAs, and the virtual access identifier derived from this profile will get deleted. The same rule applies when the VRF is configured on the IKE profile for the first time.

IPsec profiles define the policy for DVTIs. The dynamic interface is created at the end of IKE Phase 1 and IKE Phase 1.5. The interface is deleted when the IPsec session to the peer is closed. The IPsec session is closed when both IKE and IPsec SAs to the peer are deleted.

Because VTIs are routable interfaces, routing plays an important role in the encryption process. Traffic is encrypted only if it is forwarded out of the VTI, and traffic arriving on the VTI is decrypted and routed accordingly. VTIs allow you to establish an encryption tunnel using a real interface as the tunnel endpoint. You can route to the interface or apply services such as QoS, firewalls, network address translation (NAT), and NetFlow statistics as you would to any other interface. You can monitor the interface and route to it, and the interface provides benefits similar to other Cisco IOS interface.

The FlexVPN Mixed Mode feature provides support for carrying IPv4 traffic over IPsec IPv6 transport. This is the first phase towards providing dual stack support on the IPsec stack. This implementation does not support using a single IPsec security association (SA) pair for both IPv4 and IPv6 traffic.

This feature is only supported for Remote Access VPN with IKEv2 and Dynamic VTI.

The FlexVPN Mixed Mode feature provides support for carrying IPv6 traffic over IPsec IPv4 transport from Cisco IOS XE Everest 16.4.1.

The IKE Profile Based Tunnel Selection feature uses the Internet Key Exchange (IKE) or Internet Key Exchange version 2 (IKEv2) profile to select a tunnel interface for an IPsec session. Use keywords isakmp-profile or ikev2-profile keyword in the tunnel protection command to specify an IKE profile or IKEv2 profile respectively.

The IKE Profile Based Tunnel Selection feature allows tunnel interfaces to share the tunnel source IP address and IPsec transform set without sharing the IPsec security association databases (SADBs) among tunnel interfaces thereby providing the following benefits:

• Tunnels are secure and there is no traffic leak.
• All tunnel types are supported.
• Seamless migration from IKEv1 to IKEv2 by accommodating configurations from legacy VPN technologies to coexist and share the local address with newer VPN technologies.
• Ability to set up multiple IKE and IPsec tunnels between peers sharing the same local or remote addresses.

IKEv2 profile must be manually applied in the IPsec profile to initiate an ikev2 session. On the responder, a dynamic virtual tunnel interface (DVTI) IKEv2 profile must be manually applied under the IPsec profile for IPsec to accept the incoming connection. For a DVTI responder, IPsec uses the parent IKE profile which is configured under the virtual template for validating the proposal request. By default, IPsec initiates and accepts IKE sessions if no IKE profile is configured on an IPsec profile. You cannot simultaneously configure an IKE profile and an IKEv2 profile on an IPsec profile. If you configure an IKE profile and an IKEv2 profile on an IPsec profile, the IKE profile is overridden by the IKEv2 profile.

When configuring a VPN headend in a multiple vendor scenario, you must be aware of the technical details of the peer or responder. For example, some devices may use IPsec tunnels while others may use generic routing encapsulation (GRE) or IPsec tunnel, and sometimes, a tunnel may be IPv4 or IPv6. In the last case, you must configure an Internet Key Exchange (IKE) profile and a virtual template.

The Tunnel Mode Auto Selection feature eases the configuration and spares you about knowing the responder’s details. This feature automatically applies the tunneling protocol (GRE or IPsec) and transport protocol (IPv4 or IPv6) on the virtual template as soon as the IKE profile creates the virtual access interface. This feature is useful on dual stack hubs aggregating multivendor remote access, such as Cisco AnyConnect VPN Client, Microsoft Windows7 Client, and so on.

Note	The Tunnel Mode Auto Selection feature eases the configuration for a responder only. The tunnel must be statically configured for an initiator.

The IPSec Mixed Mode feature provides support for carrying IPv4 traffic over IPsec IPv6 transport. This is the first phase towards providing dual stack support on the IPsec stack. This implementation does not support using a single IPsec security association (SA) pair for both IPv4 and IPv6 traffic.

This feature is supported for SVTI as well as DVTI and IKEv1 as well as IKEv2.

1.    enable


2.    configure terminal


3.    crypto IPsec profile profile-name


4.    set transform-set transform-set-name [transform-set-name2...transform-set-name6]


5.    exit


6.    interface type number


7.    ip address address mask


8.    tunnel mode ipsec ipv4


9.    tunnel source interface-type interface-number


10.    tunnel destination ip-address


11.    tunnel protection IPsec profile profile-name


12.    end

Device> enable

Device# configure terminal

Device(config)# crypto IPsec profile PROF

Device(ipsec-profile)# set transform-set tset

Device(ipsec-profile)# exit

Device(config)# interface tunnel 0

Device(config-if)# ip address 10.1.1.1 255.255.255.0

Device(config-if)# tunnel mode ipsec ipv4

Device(config-if)# tunnel source loopback 0

Device(config-if)# tunnel destination 172.16.1.1

Device(config-if)# tunnel protection IPsec profile PROF

Device(config-if)# end

1.    router bgp autonomous-system-number


2.    neighbor ip-address remote-as autonomous-system-number


3.    network network-ip-address mask subnet-mask


4.    exit


5.    Enter the following commands on the second router.

6.    router bgp autonomous-system-number


7.    neighbor ip-address remote-as autonomous-system-number


8.    network network-ip-address mask subnet-mask

Device(config)# router bgp 65510

Device(config-router)# neighbor 10.1.1.2 remote-as 65511

Device(config-router)# network 2.2.2.0 mask 255.255.255.0

Device(config-router)# exit

Device(config)# router bgp 65511

Device(config-router)# neighbor 10.1.1.1 remote-as 65510

Device(config-router)# network 1.1.1.0 mask 255.255.255.0

1.    enable


2.    configure terminal


3.    crypto ipsec profile profile-name


4.    set transform-set transform-set-name [transform-set-name2...transform-set-name6]


5.    exit


6.    interface virtual-template number type tunnel


7.    tunnel mode ipsec ipv4


8.    tunnel protection IPsec profile profile-name


9.    exit


10.    crypto isakamp profile profile-name


11.    match identity address ip-address mask


12.    virtual template template-number


13.    end

Device> enable

Device# configure terminal

Device(config)# crypto ipsec profile PROF

Device(ipsec-profile)# set transform-set tset

Device(ipsec-profile)# exit

Device(config)# interface virtual-template 2 type tunnel

Device(config-if)# tunnel mode ipsec ipv4

Device(config-if)# tunnel protection ipsec profile PROF

Device(config-if)# exit

Device(config)# crypto isakamp profile profile1

Device(conf-isa-prof)# match identity address 10.1.1.0 255.255.255.0

Device(config)# virtual-template 1

Device(config)# end

Note	Security threats, as well as the cryptographic technologies to help protect against them, are constantly changing. For more information about the latest Cisco cryptographic recommendations, see the Next Generation Encryption (NGE) white paper.

1.    enable


2.    configure terminal


3.    ip vrf vrf-name


4.    rd route-distinguisher


5.    exit


6.    crypto keyring keyring-name


7.    pre-shared-key address key key


8.    exit


9.    crypto isakmp profile profile-name


10.    keyring keyring-name


11.    match identity address mask


12.    virtual-template template-number


13.    exit


14.    crypto ipsec transform-set transform-set-name transform1 [transform2] [transform3]


15.    exit


16.    crypto ipsec profile name


17.    set security-policy limit maximum-limit


18.    set transform-set transform-set-name [transform-set-name2 .... transform-set-name6]


19.    exit


20.    interface virtual-template number type tunnel


21.    ip vrf forwarding vrf-name


22.    ip unnumbered type number


23.    tunnel mode ipsec ipv4


24.    tunnel protection profile ipsec profile-name


25.    end

Device> enable  

Device# configure terminal

Device(config)# ip vrf VRF-100-1

Device(config-vrf)# rd 100:21

Device(config-vrf)# exit

Device(config)# crypto keyring cisco-100-1

Device(config-keyring)# pre-shared-key address 10.1.1.1 key cisco-100-1

Device(config-keyring)# exit

Device(config)# crypto isakmp profile
cisco-isakmp-profile-100-1

Device(conf-isa-prof)# keyring cisco-100-1

Device(conf-isa-prof)# match identity address 10.1.1.0 255.255.255.0

Device(conf-isa-prof)# virtual-template 101

Device(conf-isa-prof)# exit

Device(config)# crypto ipsec transform-set cisco esp-aes esp-sha-hmac

Device(conf-crypto-trans)# exit

Device(config)# crypto ipsec profile cisco-ipsec-profile-101

Device(ipsec-profile)# set security-policy limit 3

Device(ipsec-profile)# set transform-set cisco

Device(ipsec-profile)# exit

Device(config)# interface virtual-template 101 type tunnel

Device(config-if)# ip vrf forwarding VRF-100-1

Device(config-if)# ip unnumbered GigabitEthernet 0.0

Device(config-if)# tunnel mode ipsec ipv4

Device(config-if)# tunnel protection ipsec profile PROF

Device(config-if)# end

1.    enable


2.    configure terminal


3.    crypto IPsec profile profile-name


4.    set transform-set transform-set-name [transform-set-name2...transform-set-name6]


5.    exit


6.    interface type number


7.    ip address address mask


8.    Do one of the following:

• tunnel mode ipsec ipv4 v6-overlay
• tunnel mode ipsec ipv6 v4-overlay

9.    tunnel source interface-type interface-type


10.    tunnel destination ip-address


11.    tunnel protection IPsec profile profile-name


12.    end

Device> enable

Device# configure terminal

Device(config)# crypto IPsec profile PROF

Device(ipsec-profile)# set transform-set tset

Device(ipsec-profile)# exit

Device(config)# interface tunnel 0

Device(config-if)# ip address 10.1.1.1 255.255.255.0

Device(config-if)# tunnel mode ipsec ipv4 v6-overlay

Device(config-if)# tunnel source loopback 0

Device(config-if)# tunnel destination 172.16.1.1

Device(config-if)# tunnel protection IPsec profile PROF

Device(config-if)# end

1.    enable


2.    configure terminal


3.    crypto ipsec profile profile-name


4.    set mixed mode


5.    set transform-set transform-set-name [transform-set-name2...transform-set-name6]


6.    exit


7.    interface virtual-template number type tunnel


8.    tunnel mode ipsec ipv4


9.    tunnel protection IPsec profile profile-name


10.    exit


11.    crypto isakamp profile profile-name


12.    match identity address ip-address mask


13.    virtual template template-number


14.    end

Device> enable

Device# configure terminal

Device(config)# crypto ipsec profile PROF

Device(config)# set mixed mode

Device(ipsec-profile)# set transform-set tset

Device(ipsec-profile)# exit

Device(config)# interface virtual-template 2 type tunnel

Device(config-if)# tunnel mode ipsec ipv4

Device(config-if)# tunnel protection ipsec profile PROF

Device(config-if)# exit

Device(config)# crypto isakamp profile profile1

Device(conf-isa-prof)# match identity address 10.1.1.0 255.255.255.0

Device(config)# virtual-template 1

Device(config)# end