Generic routing encapsulation gre is a tunneling protocol that. Recently i had to configure a router serving as an ipsec gre endpoint. When additional keywords are not used, manual ipv6 tunnels are configured. Acl blocking traffic on interface between r2 and r3. Generic routing encapsulation gre is one of the available tunneling mechanisms which uses ip as the transport protocol and can be used for carrying many different passenger protocols.
Ipsec gre tunnels are gre tunnels that are encapsulated inside of an ipsec payload and sent across a public network. Generic routing encapsulation gre is a tunneling protocol developed by cisco systems that. Cli commands for configuring gre tunnel interfaces on the cisco ncs 5500 series routers. The multiprotocol functionality of gre can be used in conjunction with the security functionality of ipsec. The tunnels behave as virtual pointtopoint links that have two endpoints identified by the tunnel source and tunnel destination addresses at each endpoint. Generic routing encapsulation gre is a tunneling protocol that can encapsulate a variety of network layer protocols. Troubleshooting commands certain show commands are supported by the output interpreter tool registered customers only, which allows you to view an analysis of show command output. Specify how often the gre interface sends keepalive packets on the gre tunnel. Using generic routing encapsulation gre tunnels on cisco routers can come in handy with cisco router administration, and configuring gre tunnels is relatively easy. Gre tunneling occurs before ipsec security functions are applied to a packet. Gre tunnel tutorial on cisco devices understand how to configure generic routing encapsulation gre tunnels for your ccna. Gre is a tunneling protocol that was originally developed by cisco, and it can do a few more things than ipinip tunneling. In this article, well take you through the steps to configure a gre tunnel on a cisco router.
Gre tunneling over ipsec generic routing encapsulation gre tunnels have been around for quite some time. Cisco sdwan documentation is now accessible via the cisco product support portal. Configuring gre tunnel through a cisco asa firewall in this configuration tutorial i will show you how to configure a gre tunnel between two cisco ios routers. When using gre over the public internet, security is a concern and therefore you would want to encrypt the traffic, this is where ipsec comes in. Some network administrators tried to reduce the administrative overhead in the core. The gre tunnel is between the west and east routers in ospf area 0. This lesson discusses the theory behind a generic routing encapsulation gre tunnel and describes how a gre tunnel can be combined with an ipsec tunnel to add security. Generic routing encapsulation or gre for short, is a tunneling protocol developed by cisco systems that can encapsulate a wide variety of network layer protocols inside virtual pointtopoint links over an internet protocol network. Cisco ccna gre tunnel configuration asm, rockville. The gre tunnel does not authenticate or encrypt traffic. Routing configuration guide, cisco ios xe everest 16.
Generic routing encapsulation on the cisco cmts cisco. Another two routers couldnt establish adjacency because. Create a tunnel interface the ip address of tunnel interface on both routers must be in the same subnet, and configure a tunnel source and tunnel destination under tunnel interface configuration, as shown. For example, we can encapsulate an ip packet into another ip packet. Gre multilink sim troubleshooting gre tunnel ccna 200. We previously wrote about how to set up a generic routing encapsulation gre tunnel for incapsula ip protection on an ubuntu aws client. There are four possible states in which a gre tunnel interface can be. Contents 6 pointtopoint gre over ipsec design guide ol902301 sizing the branch sites 510 tunnel aggregation and load distribution 511 network layout 511 appendix a scalability test bed configuration files a1 cisco 7200vxr headend configuration a1 cisco catalyst 6500sup2vpnsm headend configuration a2 cisco 7600sup720vpn spa headend configuration p2p gre. The definitive design and deployment guide for secure virtual private networks learn about ipsec protocols and cisco ios ipsec packet processing understand the differences between ipsec tunnel mode and transport mode evaluate the ipsec features that improve vpn scalability and fault tolerance, such as dead peer detection and control plane keepalives overcome the.
The ethernet over gre tunnels feature allows customers to leverage. This tutorial is designed to help prepare you for the cisco ccna certification exam. Eompls over gre helps you to create the gre tunnel as. Configuration example page 4 generic routing encapsulation gre configurable tunnel destination ipv4 address configurable tunnel destination using hostname configurable checksum insertion and checking disabled by default configurable ttl value for insertion into the outer header configurable dscp value for insertion into the outer header copied from the inner. Let me show you a topology that we will use to demonstrate gre. Setting a gre tunnel between devices is pretty straight forward. On the left side we have the hq router which is our headquarters. Tunnel source select the tunnel source wan1, wan2, usb1, or usb2. Gre keepalive display information about the keepalive packets transmitted and received on gre tunnels that originate on the local router on vedge routers only. One of the routers is located behind a cisco asa 5500 firewall, so i will show you also how to pass gre traffic through a cisco.
Wan connections and technologies explained configuring singlehomed external bgp for the ccna cloud services and easy virtual network for the ccna snmp v1, v2c and v3 on cisco devices explained. For our gre tunnel configuration example, we will use the below topology and the given ip addresses. Download cisco 300 206 senss exam dumps updated practice exam pdf questions. Contents 6 pointtopoint gre over ipsec design guide ol902301 sizing the branch sites 510 tunnel aggregation and load distribution 511 network layout 511 appendix a scalability test bed configuration files a1 cisco 7200vxr headend configuration a1 cisco catalyst 6500sup2vpnsm headend configuration a2 cisco 7600sup720vpn spa headend configuration p2p gre on sup720 a6. That was the reason why the pptp tunnels, quite popular for windows vpn networking, also did not work from behind a pat device because the pptp also uses gre in a slightly modified way as far as i know. Feature history for configuring link bundling on cisco ios xr software contents. How to configure gre tunnels for the mcn site optional. Gre tunneling is accomplished through tunnel endpoints that encapsulate or deencapsulate traffic. In this lab, you will configure an unencrypted pointtopoint gre vpn tunnel and verify that network traffic is using the tunnel. For gre tunnel information interface name enter the name of the interface to connect to tunnel.
This feature is a tunneling protocol that enables the encapsulation of a wide variety of protocol packet types inside ip tunnels, creating a virtual pointtopoint link to cisco routers at remote points over an ip internetwork. Ipsec tunnel between the cisco asr series aggregation services routers and the cpe devices. Two routers couldnt establish adjacency because of acl. The routing tables of two routers show that they are directly connected via gre tunnel. Cisco configuring a gre tunnel over ipsec with ospf. Create a generic routing encapsulation gre tunnel to connect two endpoints in a pointto. This video will help in configuring secure connection between two routers with the help of gre tunnel. How to configure gre over an ipsec tunnel on routers cisco. Gre generic routing encapsulation is a simple tunneling technique that can do this for us. Gre tunnels are links between two points, with a separate tunnel for each link.
Implementing generic routing encapsulation generic routing encapsulation gre is a tunneling protocol developed by cisco systems that encapsulates a wide variety of network layer protocols inside virtual pointtopoint links over an internet protocol internetwork. In this confgiuration example, we will see how to configure cisco gre generic routing encapsulation tunnel with packet tracer. If you do not want to configure this site as a gre tunnel termination node, you can skip this step, and proceed to the section, configuring the wan links for the mcn site. Generic routing encapsulation gre is a tunneling protocol that can encapsulate a wide variety of network layer protocols inside virtual pointtopoint links over an internet protocol network.
To locate and download mibs for selected platforms, cisco software. We can use gre to create tunnels between routers, the tunnels are established with public ip addresses and the ip packets we encapsulate use private ip addresses. You will also configure the ospf routing protocol inside the gre vpn tunnel. Generic routing encapsulation gre provides a private, secure path for transporting packets through an otherwise public network by encapsulating or tunneling the packets. When a service, such as a firewall, is available on a device that supports only gre tunnels, you can configure a gre tunnel on the vedge router to connect to the remote device by configuring a logical gre interface. Gre tunnel configuration examples wiki knowledge base. Before issuing debug commands, please see important information on debug commands. Gre tunnel interface states and what impacts them cisco. Create a generic routing encapsulation gre tunnel to connect two endpoints in a pointtopoint, logical link. There may be different faults in this sim so please notice the following faults. The gre tunnel interfaces act as a logical interface that performs gre encapsulation or decapsulation. Gre tunnel configuration ccnp best cisco ccna ccnp and.
Configuring a tunnel with generic routing encapsulation. I covered gre tunnels a few posts back now there are a few ways we can do this, the first is to run the gre tunnel over the ipsec tunnel, in this case the tunnel destination is at the other end of the ipsec tunnel and is matched by the acl of the ipsec tunnel to ensure the traffic between the tunnel endpoints are encrypted. The following switches support the ipv4 forwarding of. The device at one end of a vpn tunnel takes an ip packet, encrypts it making it unreadable, and then sends the encrypted packet after encapsulating it in a new ip header. The goal is that pc1 private network be able to ping pc2 another private network, by going via r3 which represent internet. At the minimum, you need only to configure the source, the destination of the tunnel and the ip address. However, gre tunnels are not as secure as a tunnel established using ipsec.
This document describes the generic routing encapsulation gre feature. To configure generic routing encapsulation gre over an ipsec tunnel between two routers, perform these steps. When the sending router decides to send a packet into the gre tunnel, it will wrap the whole packet into another ip packet with two headers. Interface and hardware component configuration guide, cisco ios xe release 3s. Security for vpns with ipsec configuration guide, cisco ios release 15s. Because gre tunnels are stateless, sending of keepalive packets is the only way to determine whether the remote end of the tunnel is up. Use the vpninterface gre template for all vedge cloud and vedge router devices. The sdwan gre tunnels settings enable you to configure sdwan appliances to terminate gre tunnels on the lan. Configuring gre tunnel through a cisco asa firewall.
We will repeat this test after configuring the gre tunnel. For example, you can also transport multicast traffic and ipv6 through a gre tunnel. Gre generic routing encapsulation is a tunneling protocol that allows us to encapsulate packets into other packets. You are familiar with the fundamental operation of a virtual private network vpn, and the concept of tunneling by now. Configuring greclns ctunnels to carry ipv4 and ipv6 packets. Gre is a tunneling protocol developed by cisco that encapsulates a wide variety. Gre generic routing encapsulation is a tunneling protocol developed by cisco systems that can encapsulate a wide variety of network layer. You can also use a firewall filter to deencapsulate gre traffic on. Configuringgretunnels genericroutingencapsulation gre isatunnelingprotocolthatprovidesasimplegenericapproachto. The tunnel source, on the local router, must be pointed to as the tunnel destination, on the remote router. To locate and download mibs for selected platforms. This additional configuration overhead does not scale well with a large number of ipsec tunnels. The interesting part is that the terminating router is behind a natdevice which changes the outer ipheader of the ipsec tunnel. As you can see, the gre tunnel configuration required for ccna exam is pretty straightforward.