Gre offers no security so ipsec must be implementedwith gre for encryption of. This post will share how to set up a gre tunnel between cisco and mikrotik routers. Versatile, reliable, flexible and powerful, the cisco switch product line such as the 2960, 3560, 3650, 3850, 4500, 6500, 9400 series etc offer unparalleled performance and features. The gre tunnel is between the west and east routers in ospf area 0. This way we can create a gre tunnel between the two routers, otherwise they dont know how to reach each others ip address. Here is an example of a tunnel set up between two cisco routers.
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 asa as well. However, many routing protocols rely on multicasts. 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 gre semantic scholar. Configuring pointtopoint gre vpn tunnels unprotected. How to configure gre tunnel on cisco ios router tunneling is a concept where we put packets into packets so that they can be transported over certain networks. When the original packet arrives at the router or asa firewall, it will be decrypted and sent to the local network. Tunnel mode is most frequently used in gatewayt ogateway communication or with a virtual private network vpn. Virtual tunnel interface vti a virtual tunnel interface has similar characteristic s to any other interface on the device. Configuring generic routing encapsulationgre tunnel ip. Generic routing encapsulation gre configuration guide.
A gre tunnel is a generic routingencapsulation tunnel. Gre over ip vpn tunnel in packet tracer danscourses. In the example shown in figure 192 on page 193, ip packets from the private. Gre stands for generic routing encapsulation, which is a very simple form of tunneling. Generic routing encapsulation gre is a tunnelling protocol which is used to transport ip packets over a network. Although a cisco switch is a much simpler network device compared with other devices such as. For example, you can also transport multicast traffic and ipv6 through a gre tunnel. On the left side we have the hq router which is our headquarters. Gre tunnel tutorial on cisco devices understand how to configure generic routing encapsulation gre tunnels for your ccna.
Configuring a tunnel with generic routing encapsulation. In my opinion, the cisco switches are the best in the market. Configuring gre tunnel through a cisco asa firewall. Gre generic routing encapsulation is a tunneling protocol that allows us to encapsulate packets into other packets. The goal of the lab is that the two hosts can reach each other via the gre tunnel. Understanding cisco dynamic multipoint vpn dmvpn, mgre. Vpn tunnels allow geographically separate private local area networks to be connected to each other across public wide area networks. Cisco ccna gre tunnel configuration asm, rockville. Some design considerations for these particular ipsec vpns are as follows. How to configure gre tunnel in cisco router ip with ease. Guys, please help me understand the difference between gre and a manually configured tunnel. With gre we can easily create a virtual link between.
In this example, ipsec works in tunnel mode as it encrypts the original packet. Once the gre packet reaches the end of the gre tunnel, the external. Configuring pointtopoint gre vpn tunnels unprotected gre. Cisco eigrp is working by sending multicast traffic. Configuring gre tunnel by r p porwal configuring a gre tunnel. 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. One mgre can handle multiple gre tunnels at the other ends. Gre tunneling over ipsec generic routing encapsulation gre tunnels have been around for quite some time. Next we have to specify the tunnel source and tunnel destination with tunnel source and tunnel destination commands.
In our example, both tunnel interfaces are part of the 172. Then you must configure the tunnel endpoints for the tunnel interface. Ip header information and inserts ipsec fields into the packet. See conventions on page lxvii of preface in the front of this manual for details. There are other gre modes like tunnel mode gre multipoint used in dmvpn mentioned in dmvpn tutorial. Gre is a cisco developed protocol which is one of many tunneling protocols. You will use greipsec with tunnel mode to accomplish this task. The line protocol on a gre tunnel interface is up as long as there is a. 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. Table 192 on page 195 lists the parameter values that will be used in the. The next command tunnel mode gre ip is in fact not necessary as this is the default setting. Make sure multicast traffic is passing through the isp network.
In the event that it is not, treat it like any other. As gre does not have its own mechanism to encrypt traffic it depends on ipsec for getting the encryption job done. Using generic routing encapsulation gre tunnels on cisco routers can come in handy with cisco router administration, and configuring gre tunnels is relatively easy. The below example explain about how to create simple gre tunnels. Gre tunneling to provide traditional pointtopoint functionality. Because you need to totally crosseliminate crypto acls, you can configure a gre tunnel and encrypt all traffic that traverses the tunnel. Gre, based on the example configuration shown in figure 192 on page 193. The problem is that the pat rewrites both ip addresses and tcpudp port numbers to perform n. Gre was first developed by cisco as a means to carry other routed protocols. Let me show you a topology that we will use to demonstrate gre. 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. Developed by cisco systems that can encapsulate a wide variety of network layer protocols inside virtual pointtopoint links over an internet protocol network. You can also test that by using eigrp neighbor command, which allows you to send the routing exchange information.
Communication between the west and east routers and the isp is accomplished using default static routes. 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. An mgre tunnel inherits the concept of a classic gre tunnel but an mgre tunnel does not require a unique tunnel interface for each connection between hub and spoke like traditional gre. After the tunnel interface is configured as shown on the diagram, on each router you should configure a static route towards the subnet where the. While it is a cisco developed protocol, it is also defined in several rfcs 1701, 1702 and 2784.
A gre tunnel is similar to an ipsec tunnel because the original packet is wrapped inside of. Gre datagrams do not have ports and they are inserted directly into ip packets. This demo walks through the purpose and workings of an ipsec vpn tunnel, including implementation and verification of the tunnel. The gre connection endpoints are terminated vi a a virtual tunnel interface vti configured in each device. 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. Gre tunnel cisco to fortigate finally i saw i light in the tunnel. For example, the internet does not route multicast messages. With gre we can easily create a virtual link between routers and allow them to be directly connected, even if they physically arent. So how do we get over this little obstacle, we run a gre tunnel. Generic routing encapsulation gre is a method to tunnel ip packets between two end points. Generic routing encapsulation gre is a tunneling protocol developed by cisco that allows the encapsulation of a wide variety of network layer protocols inside pointtopoint links a gre tunnel is used when packets need to be sent from one network to another over the internet or an insecure network.
The tunnels behave as virtual pointtopoint links that have two endpoints identified by the tunnel source and tunnel destination addresses at each endpoint. Each mode provides strong protection, but using a slightly different solution. Supports a variety of encryption algorithms better suited for wan vpns vs access vpns little interest from microsoft vs l2tp most ipsec implementations support machine vs. The routing tables of two routers show that they are directly connected via gre tunnel. In this configuration tutorial i will show you how to configure a gre tunnel between two cisco ios routers. Open vce files convert vce to pdf exam formatter vce mobile tutorial. I doubt that the gre tunnel through a pat box will work.
A virtual private network vpn provides a secure tunnel across a public and thus, insecure network. Generic routing encapsulation gre is a tunneling protocol that was developed by cisco to encapsulate a wide variety of protocols transported inside a virtual pointtopoint link. Tunnel mode encapsulates the original ip packet inside of an ipsec ip packet. The goal is that pc1 private network be able to ping pc2 another private network, by going via r3 which represent internet. In this lab, you will configure an unencrypted pointtopoint gre vpn tunnel and verify that network traffic is using the tunnel.
Since gre is an encapsulating protocol, we adjust the maximum. Grenumber, gre tunneling protocol and parameters employed in gre verification. For vpn resilience, a spoke must be configured with two gre tunnels, one to the primary hub and the. Configuringgretunnels genericroutingencapsulation gre isatunnelingprotocolthatprovidesasimplegenericapproachto. Difference between gre and manually configured tunnel. In 2008 free ccna workbook originally started as a sharable pdf but quickly evolved into the largest ccna training lab website on the net.
Vpn tunnels are now part of the ccna certification exam. For example, we can encapsulate an ip packet into another ip packet. Configuring a gre tunnel involves creating a tunnel interface, which is a logical interface. Principle of the gre tunnel, encapsulation example. It is used to transport payload of variousprotocols such as ipv4, ipv6 and isis,a linkstate routing protocol. Gre generic routing encapsulation is a simple tunneling technique that can do this for us. Set the source and destination for the endpoints of tunnel 0. Lets us see how to configure and verify the generic routing encapsulation. Therefore, you need to configure a scalable solution that does not require the need for crypto acls. 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. Those interested in configuring a cisco router to perform this can visit firewall.
Later it become industry standard rfc 1701, rfc 2784, rfc 2890. You will also configure the ospf routing protocol inside the gre vpn tunnel. We use the ip addresses on the gre tunnel so we can establish an ospf adjacency between the two routers, the loopbacks are advertised in ospf and learned through the gre tunnel. For tunnel source command, we can either specify the interface for exampel tunnel source e00. Enter your email address to follow this blog and receive notifications of new posts by email. This provides a mechanism for organizations to connect users and offices together, without the high costs of dedicated. For example, if ten sites were fully meshed with gre over ipsec tunnels, it would take. 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. A gre tunnel is established on a router level and differs depending on the hardware type or service you use.
Ipsec over gre configuration and explanation ccie notes. Understanding generic routing encapsulation, configuring generic routing encapsulation tunneling, verifying that generic routing encapsulation tunneling is working correctly. Typically youll be required to set up the tunnel interface ips and provide public ip addresses for both ends of the gre tunnel. Recently i had to configure a router serving as an ipsecgre endpoint. How to configure gre tunnel between cisco and mikrotik routers. Gre is a tunneling protocol that was originally developed by cisco, and it can do a few more things than ipinip tunneling. As opposed to gre over ipsec, which encrypts anything that is encapsulated by gre, ipsec over gre encrypts only the payload and not the routing protocols running over a gre tunnel. Tunnel mode, transport mode tunnel mode original ip header encrypted transport mode original ip header removed. 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. Virtual private networks washington university in st. With gre, a virtual tunnel is created between the two endpoints cisco. This article serves as an introduction to the cisco dynamic multipoint vpn dmvpn service.
Configuration example for gre tunnel ip source and destination vrf membership, on page 3. After all a simple ipsec tunnel will not pass multicast traffic so routing updates will not traverse the tunnel requiring you to either rely on rri reverse route injection or static routes. Learn what dmvpn is, mechanisms used nhrp, mgre, ipsec to achieve its flexibility and data confidentiality, plus the prerequisites for installation and setup. We just want to show you this command and let you know that we are configuring a traditional pointtopoint gre. Tunnel mode is used to keep the original ip header con. The interesting part is that the terminating router is behind a natdevice which changes the outer ipheader of the ipsec tunnel.
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