Configuring IP Tunnels

This chapter contains the following sections:

Information About IP Tunnels

IP tunnels can encapsulate a same-layer or higher-layer protocol and transport the result over IP through a tunnel created between two devices.

IP tunnels consists of the following three main components:

  • Passenger protocol—The protocol that needs to be encapsulated. IPv4 is an example of a passenger protocol.

  • Carrier protocol—The protocol that is used to encapsulate the passenger protocol. Cisco NX-OS supports generic routing encapsulation (GRE), and IP-in-IP encapsulation and decapsulation as carrier protocols.

  • Transport protocol—The protocol that is used to carry the encapsulated protocol. IPv4 is an example of a transport protocol.

An IP tunnel takes a passenger protocol, such as IPv4, and encapsulates that protocol within a carrier protocol, such as GRE. The device then transmits this carrier protocol over a transport protocol, such as IPv4.

You configure a tunnel interface with matching characteristics on each end of the tunnel.

You must enable the tunnel feature before you can configure it.

GRE Tunnels

You can use GRE as the carrier protocol for a variety of passenger protocols. The selection of tunnel interfaces can also be based on the PBR policy.

The figure shows the IP tunnel components for a GRE tunnel. The original passenger protocol packet becomes the GRE payload and the device adds a GRE header to the packet. The device then adds the transport protocol header to the packet and transmits it.

Figure 1. GRE PDU



Point-to-Point IP-in-IP Tunnel Encapsulation and Decapsulation

Point-to-point IP-in-IP encapsulation and decapsulation is a type of tunnel that you can create to send encapsulated packets from a source tunnel interface to a destination tunnel interface. The selection of these tunnel interfaces can also be based on the PBR policy. This type of tunnel will carry both inbound and outbound traffic.

Multi-Point IP-in-IP Tunnel Decapsulation

Multi-point IP-in-IP decapsulate-any is a type of tunnel that you can create to decapsulate packets from any number of IP-in-IP tunnels to one tunnel interface. This tunnel will not carry any outbound traffic. However, any number of remote tunnel endpoints can use a tunnel configured this way as their destination.

Licensing Requirements for IP Tunnels

Product

License Requirement

Cisco NX-OS

IP tunnels require an Enterprise Services license. For a complete explanation of the Cisco NX-OS licensing scheme and how to obtain and apply licenses, see the Cisco NX-OS Licensing Guide.

Prerequisites for IP Tunnels

IP tunnels have the following prerequisites:

  • You must be familiar with TCP/IP fundamentals to configure IP tunnels.

  • You are logged on to the switch.

  • You have installed the Enterprise Services license for Cisco NX-OS.

  • You must enable the tunneling feature in a device before you can configure and enable any IP tunnels.

Guidelines and Limitations for IP Tunnels

IP tunnels have the following configuration guidelines and limitations:

  • Cisco NX-OS software supports the GRE header defined in IETF RFC 2784. Cisco NX-OS software does not support tunnel keys and other options from IETF RFC 1701.

  • The Cisco Nexus device supports the following maximum number tunnels:

    • GRE and IP-in-IP regular tunnels-8 tunnels

    • Multipoint IP-in-IP tunnels-32 tunnels

  • Each tunnel will consume one Equal Cost Multipath (ECMP) adjacency.

  • The Cisco Nexus device does not support the following features:

    • Path maximum transmission unit (MTU) discovery

    • Tunnel interface statistics

    • Access control lists (ACLs)

    • Unicast reverse path forwarding (URPF)

    • Multicast traffic and associated multicast protocols such as Internet Group Management Protocol (IGMP) and Protocol Independent Multicast (PIM)

  • Cisco NX-OS software does not support the Web Cache Control Protocol (WCCP) on tunnel interfaces.

  • Cisco NX-OS software supports only Layer-3 traffic.

  • Cisco NX-OS software supports ECMP across tunnels and ECMP for tunnel destination.

  • IPv6-in-IPv6 tunnels is not supported.

  • Limited control protocols, such as Border Gateway Protocol (BGP), Open Shortest Path First (OSPF), and Enhanced Interior Gateway Routing Protocol (EIGRP), are supported for GRE tunnels.

  • Starting with Release 6.0(2)U5(1), Cisco Nexus 3000 Series switches drop all the packets when the tunnel is not configured. The packets are also dropped when the tunnel is configured but the tunnel interface is not configured or the tunnel interface is in shut down state.

    Point to Point tunnel (Source and Destination) – Cisco Nexus 3000 Series switches decapsulate all IP-in-IP packets destined to it when the command feature tunnel is configured and there is an operational tunnel interface configured with the tunnel source and the destination address that matches the incoming packets' outer source and destination addresses. If there is not a source and destination packet match or if the interface is in shutdown state, the packet is dropped.

    Decapsulate Tunnel (Source only) - Cisco Nexus 3000 Series switches decapsulate all IP-in-IP packets destined to it when the command feature tunnel is configured and there is an operational tunnel interface configured with the tunnel source address that matches the incoming packets' outer destination addresses. If there is not a source packet match or if the interface is in shutdown state, the packet is dropped.

  • Starting with Release 6.0(2)U6(1), Cisco Nexus 3000 Series switches support IPv6 in IPv4 with GRE header only. The new control protocols that are supported on the tunnel are:

    • BGP with v6

    • OSPFv3

    • EIGRP over v6

  • The Cisco Nexus 3000 Series switches ASIC supports the GRE encapsulation and decapsulation in the hardware.

  • On the encapsulation side, the Cisco Nexus 3000 Series switches performs a single lookup in the hardware.

  • Since Cisco Nexus 3000 Series switches perform a single lookup in the hardware, the software has to keep the hardware information up-to-date with any changes related to the second lookup, for example, the tunnel destination adjacency.

  • On the decapsulation side, the Cisco Nexus 3000 Series switches have a separate table to perform the outer IP header lookup and it does not need an ACL for the same.

Default Settings for IP Tunneling

The following table lists the default settings for IP tunnel parameters.

Table 1  Default IP Tunnel Parameters

Parameters

Default

Tunnel feature

Disabled

Configuring IP Tunnels

Enabling Tunneling

Before You Begin

You must enable the tunneling feature before you can configure any IP tunnels.

Procedure
     Command or ActionPurpose
    Step 1switch# configure terminal  

    Enters global configuration mode.

     
    Step 2switch(config)# feature tunnel 

    Enables the tunnel feature on the switch.

     
    Step 3switch(config)# exit 

    Returns to configuration mode.

     
    Step 4switch(config)# show feature 

    Displays the tunnel feature on the switch.

     
    Step 5switch# copy running-config startup-config   (Optional)

    Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

     

    This example shows how to enable the tunnel feature:

    switch# configure terminal
switch(config)# feature tunnel
switch(config)# exit
switch(config)# copy running-config startup-config

    Creating a Tunnel Interface

    You can create a tunnel interface and then configure this logical interface for your IP tunnel. GRE mode is the default tunnel mode.

    Before You Begin

    Both the tunnel source and the tunnel destination must exist within the same virtual routing and forwarding (VRF) instance.

    Ensure that you have enabled the tunneling feature.

    Procedure
       Command or ActionPurpose
      Step 1switch# configure terminal  

      Enters global configuration mode.

       
      Step 2switch(config)# [no] interface tunnel number  

      Creates a new tunnel interface.

       
      Step 3switch(config)# tunnel mode {gre ip | ipip {ip | decapsulate-any}}  

      Sets this tunnel mode to GRE, ipip, or ipip decapsulate-only.

      The gre and ip keywords specify that GRE encapsulation over IP will be used.

      The ipip keyword specifies that IP-in-IP encapsulation will be used. The optional decapsulate-any keyword terminates IP-in-IP tunnels at one tunnel interface. This keyword creates a tunnel that will not carry any outbound traffic. However, remote tunnel endpoints can use a tunnel configured as their destination.

       
      Step 4switch(config)# tunnel source {ip address | interface-name}  

      Configures the source address for this IP tunnel.

       
      Step 5switch(config)# tunnel destination {ip address | host-name}  

      Configures the destination address for this IP tunnel.

       
      Step 6switch(config)# tunnel use-vrf vrf-name   (Optional)

      Uses the configured VRF instance to look up the tunnel IP destination address.

       
      Step 7switch(config)# show interface tunnel number   (Optional)

      Displays the tunnel interface statistics.

       
      Step 8switch# copy running-config startup-config   (Optional)

      Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

       

      This example shows how to create a tunnel interface: 

      switch# configure terminal
switch(config)# interface tunnel 1
switch(config)# tunnel source ethernet 1/2
switch(config)# tunnel destination 192.0.2.1 
switch(config)# copy running-config startup-config

      Configuring a Tunnel Interface Based on Policy Based Routing

      You can create a tunnel interface and then configure this logical interface for your IP tunnel based on the PBR policy.

      Before You Begin

      Ensure that you have enabled the tunneling feature.

      Procedure
         Command or ActionPurpose
        Step 1switch# configure terminal  

        Enters global configuration mode.

         
        Step 2switch(config)# [no] interface tunnel number  

        Creates a new tunnel interface.

         
        Step 3switch(config)# ip address ip address  

        Configures an IP address for this interface.

         
        Step 4switch(config)# route-map map-name  

        Assigns a route map for IPv4 policy-based routing to the interface

         
        Step 5switch(config-route-map)# match ip address access-list-name name  

        Matches an IPv4 address against one or more IP access control lists (ACLs). This command is used for policy-based routing and is ignored by route filtering or redistribution.

         
        Step 6switch(config-route-map)# set ip next-hop address  

        Sets the IPv4 next-hop address for policy-based routing. Tunnel IP addresses can be specified as next-hop addresses to select tunnel interfaces. This command uses the first valid next-hop address if multiple addresses are configured. Use the load-share option to select ECMP across next-hop entries.

         

        This example shows how to configure a tunnel interface that is based on PBR: 

        switch# configure terminal
switch(config)# interface tunnel 1
switch(config)# ip address 1.1.1.1/24
switch(config)# route-map pbr1
switch(config-route-map)# match ip address access-list-name pbr1
switch(config-route-map)# set ip next-hop 1.1.1.1

        Configuring a GRE Tunnel

        You can set a tunnel interface to GRE tunnel mode, ipip mode, or ipip decapsulate-only mode. GRE mode is the default tunnel mode. Starting with Release 6.0(2)U6(1), Cisco Nexus 3000 Series switches support IPv6 in IPv4 with GRE header only.

        Before You Begin

        Ensure that you have enabled the tunneling feature.

        Procedure
           Command or ActionPurpose
          Step 1switch# configure terminal  

          Enters global configuration mode.

           
          Step 2switch(config)# interface tunnel number  

          Enters a tunnel interface configuration mode.

           
          Step 3switch(config-if)# tunnel mode {gre ip | ipip {ip | decapsulate-any}}  

          Sets this tunnel mode to GRE, ipip, or ipip decapsulate-only.

          The gre and ip keywords specify that GRE encapsulation over IP will be used.

          The ipip keyword specifies that IP-in-IP encapsulation will be used. The optional decapsulate-any keyword terminates IP-in-IP tunnels at one tunnel interface. This keyword creates a tunnel that will not carry any outbound traffic. However, remote tunnel endpoints can use a tunnel configured as their destination.

           
          Step 4switch(config-if)# tunnel use-vrf vrf-name  

          Configures tunnel VRF name.

           
          Step 5switch(config-if)# ipv6 address IPv6 address  

          Configures the IPv6 address.

          Note   

          The tunnel source and the destination addresses are still the same (IPv4 address.)

           
          Step 6switch(config-if)# show interface tunnel number   (Optional)

          Displays the tunnel interface statistics.

           
          Step 7switch(config-if)# mtu value  

          Sets the maximum transmission unit (MTU) of IP packets sent on an interface.

           
          Step 8switch(config-if)# copy running-config startup-config   (Optional)

          Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

           

          This example shows how to create the tunnel interface to GRE: 

          switch# configure terminal
switch(config)# interface tunnel 1
switch(config-if)# tunnel mode gre ip
switch(config-if)# tunnel use-vrf red
switch(config-if)# ipv6 address 2:2::2/64
switch(config-if)# copy running-config startup-config

          This example shows how to view the tunnel interface to GRE: 

          switch(config)# show int tunnel 2
Tunnel2 is up
    Internet address(es):
    2.2.2.2/24
    2:2::2/64
    MTU 1476 bytes, BW 9 Kbit
    Transport protocol is in VRF "default"
    Tunnel protocol/transport GRE/IP
    Tunnel source 2.2.3.2, destination 2.2.3.1
    Last clearing of "show interface" counters never
    Tx
    0 packets output, 0 bytes

          This example shows how to create an ipip tunnel: 

          switch# configure terminal
switch(config)# interface tunnel 1
switch(config-if)# tunnel mode ipip
switch(config-if)# mtu 1400
switch(config-if)# copy running-config startup-config
switch(config-if)# no shut

          Assigning VRF Membership to a Tunnel Interface

          You can add a tunnel interface to a VRF.

          Before You Begin

          Ensure that you have enabled the tunneling feature.

          Assign the IP address for a tunnel interface after you have configured the interface for a VRF.

          Procedure
             Command or ActionPurpose
            Step 1switch# configure terminal  

            Enters global configuration mode.

             
            Step 2switch(config)# interface tunnel number 

            Enters interface configuration mode.

             
            Step 3switch(config)# vrf member vrf-name 

            Adds this interface to a VRF.

             
            Step 4switch(config)# ip address ip-prefix/length 

            Configures an IP address for this interface. You must do this step after you assign this interface to a VRF.

             
            Step 5switch(config)# show vrf [vrf-name] interface interface-type number  (Optional)

            Displays VRF information.

             
            Step 6switch(config-if)# copy running-config startup-config   (Optional)

            Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

             

            This example shows how to add a tunnel interface to the VRF:

            switch# configure terminal
switch(config)# interface tunnel 0
switch(config-if)# vrf member RemoteOfficeVRF
switch(config-if)# ip address 209.0.2.1/16
switch(config-if)# copy running-config startup-config

            Verifying the IP Tunnel Configuration

            Use the following commands to verify the configuration:

            Command Purpose

            show interface tunnel number

            Displays the configuration for the tunnel interface (MTU, protocol, transport, and VRF). Displays input and output packets, bytes, and packet rates.

            show interface tunnel number brief

            Displays the operational status, IP address, encapsulation type, and MTU of the tunnel interface.

            show interface tunnel number description

            Displays the configured description of the tunnel interface.

            show interface tunnel number status

            Displays the operational status of the tunnel interface.

            show interface tunnel number status err-disabled

            Displays the error disabled status of the tunnel interface.

            Configuration Examples for IP Tunneling

            This example shows a simple GRE tunnel. Ethernet 1/2 is the tunnel source for router A and the tunnel destination for router B. Ethernet interface 1/3 is the tunnel source for router B and the tunnel destination for router A.

            router A:
feature tunnel
interface tunnel 0
  ip address 209.165.20.2/8
  tunnel source ethernet 1/2
  tunnel destination 192.0.2.2
  tunnel mode gre ip
interface ethernet1/2
  ip address 192.0.2.55/8

router B:
feature tunnel 
interface tunnel 0
  ip address 209.165.20.1/8
  tunnel source ethernet 1/3
  tunnel destination 192.0.2.55
  tunnel mode gre ip
interface ethernet 1/3
ip address 192.0.2.2/8

            Related Documents for IP Tunnels

            Related Topics Document Title

            IP tunnel commands

            Cisco Nexus 3000 Series Interfaces Command Reference

            Standards for IP Tunnels

            No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

            Feature History for Configuring IP Tunnels

            Table 2 Feature History for Configuring IP Tunnels

            Feature Name

            Release

            Feature Information

            Multi-point and Point-to-Point IP-in-IP encapsulation and decapsulation

            6.0(2)U2(1)

            Support for these tunnel modes was added.

            IP tunnels

            5.0(3)U4(1)

            This feature was introduced.