This document describes the different conditions that can affect the state of a Generic Routing Encapsulation (GRE) tunnel interface. GRE Tunnel Configuration - Lab Topology. So, I modified the configuration again: interface Tunnel0. The information in this document was created from the devices in a specific lab environment. Find answers to your questions by entering keywords or phrases in the Search bar above. The GRE was developed as the tunneling tool which is meant to carry any of the OSI layer 3 protocol over the IP network. Thank you all for the possible answers. Solution You can look at the attributes for a tunnel with the show interface command. All traffic exiting from the vEdge router, going either to other overlay network sites or to a public network, passes through this interface. Customers Also Viewed These Support Documents. If you use NAT in this way on a vEdge router, you can eliminate traffic "tromboning" and allow for efficient routes, that have shorter distances, between users at the local site and the network-based applications that they use. interface tunnel-ip id no interface tunnel-ip id Syntax Description id Specifies the tunnel interface identifier. At Peer A, the GRE keepalive is received decrypted: Peer B now recieves a GRE keepalive response which is not encrypted on its physical interface, but because of the crypto map configured on the physical interface, it expects an encrypted packet and so drops it. The GRE tunnel interface on the other side, where keepalives are not configured, remains up even if the other side of the tunnel is down. Reset/down - This is usually a transient state when the tunnel is reset by software. When the keepalive request is received it is received in the fVRF and decapsulated. Let's verify that our tunnel is working: interface Tunnel100 ip address 10.1.1.1 255.255.255.252 tunnel source 11.1.1.2 tunnel destination 12.1.1.2 You can choose tunnel interface between 0-2147483647 depends on your router capacity. Tip: In a large hub-and-spoke GRE tunnel network, it might be appropriate to only configure GRE keepalives on the spoke side and not on the hub side. If the keepalives do not come back, the tunnel line protocol stays up as long as the tunnel keepalive counter is less than the number of retries, which in this case is four. This is the destination on the internet to which the router sends probes to determine the status of the transport interface. Packet is decrypted and forwarded to the tunnel interface. This means that the GRE keepalive response packet is not affected by any output features on the tunnel interface, such as 'tunnel protection ', QoS, Virtual Routing and Forwarding (VRF), and so forth. 4. Also there are other applications that trigger when an interface changes state; for example, 'backup interface '. For GRE keepalives, the sender prebuilds the keepalive response packet inside the original keepalive request packet so that the remote end only needs to do standard GRE decapsulation of the outer GRE IP header and then revert the inner IP GRE packet to the sender. Upon arrival on Router A, the packet becomes decapsulated and the check of the PT results in 0. Peer B now recieves an encrypted GRE keepalive response whose destination is forwarded to the tunnel interface where it is decrypted. This would have worked if the used Loopback was part of the General/Generic/Unnamed vrf. In Releases 17.2.2 and later, on Network Address Translation (NAT) enabled transport interfaces are used for local internet exit. The GRE will create the private point to point connection as same that of the VPN. Enter configuration commands, one per line. Packet is decapsulated and then forwarded to the IP destination in clear text. If not, the opposite device's GRE tunnel will be down. The tunnel keepalive counter is then reset to 0 and the packet is discarded. A search of the Cisco web site turned up a result (I can't find it now) that indicated a bug within IOS and suggested the addition of a "tunnel key" statement. This document is not restricted to specific software and hardware versions. As you might know already, GRE tunnel termination is not supported on Cisco ASA firewalls. Configure tracker under the system block. All rights reserved. Because most transport MTUs are 1500 bytes and we have an added overhead because of GRE, we must reduce the MTU to account for the extra overhead. Use this section to confirm that your configuration works properly. interface Tunnel0 description "IPSEC DMVPN MGRE Tunnel Across ENS Network" ip address 172.16.100.1 255.255.255. no ip redirects ip nhrp authentication DMVPN ip nhrp map multicast dynamic ip nhrp network-id 172 ip ospf network broadcast ip ospf priority 2 tunnel source 192.168.100.1 tunnel mode gre multipoint tunnel key 100 A GRE tunnel is a logical interface on a Cisco router that provides a way to encapsulate passenger packets inside a transport protocol. Thank you so much for the information and the explanation. The below diagram shows encapsulation process of GRE packet as it traversers the router and enters the tunnel interface: Configuring a GRE tunnel involves creating a tunnel interface, which is a logical interface. When Unicast RPF is run in strict mode (ip verify unicast source reachable-via rx), the packet must be received on the interface that the router would use in order to forward the return packet. The below example explain about how to create simple GRE tunnels between endpoints and the necessary steps to create and verify the GRE tunnel between the two networks.R1's and R2's Internal subnets(192.168.1.0/24 and 192.168.2.0/24) are communicating with each other using GRE tunnel over internet.Both Tunnel interfaces are part of the 172.16.1.0/24 network. This is true even if you replace iVRF and/or fVRF with "global". :-). Tracking the interface status is useful when you enable NAT on a transport interface in VPN 0 to allow data traffic from the router to exit directly to the internet rather than having to first go to a router in a data center. In such situations where the GRE packets must be encrypted, there are three possible solutions: 2022 Cisco and/or its affiliates. New here? 3. There are four possible states in which a GRE tunnel interface can be: When a tunnel interface is first created and no other configuration is applied to it, the interface is not shut by default: In this state, the interface is always up/down: This is because the interface is administratively enabled, but since it does not have a tunnel source or a tunnel destination, the line protocol is down. Keepalives enabled on Peer B succesfully determine what the tunnel state should be based on the availabilty of the tunnel destination. Note: In the up/down state, the tunnel does not forward or process any data traffic. Note: In general, tunnel keepalives will not work when VRFs are used on the tunnel interface and the fVRF (tunnel vrf ) and iVRF (ip vrf forwarding on tunnel interface) do not match. The big advantage of GRE protocol is that it encapsulates L3 and higher protocols inside the GRE tunnel so routing updates and other multicast traffic can be successfully transferred over the tunnel. Lastly, we define the Tunnel Destination IP address. 2. Follow the steps below to configure the GRE tunnel on both routers: CLI: Access the Command Line Interface on ER-L using SSH. In Releases 17.2.2 and later, on Network Address Translation (NAT) enabled transport interfaces are used for local internet exit. This happens because the routers need to have a good path through the network to carry the tunnel to its destination.Make sure that the routers never get confused and think that the best path to the tunnel destination is through the tunnel itself.you can refer this documents for the same. In Cisco IOS Software Releases 15.4(3)M/15.4(3)S and later, the GRE tunnel line protocol state can follow the IPsecSecurity Association (SA) state, so the line protocol can remain down until the IPsec session is fully established. Before implementing a GRE tunnel, IP . Also, verify that the endpoint IP address is not the same as the Transport interface. Since GRE is an encapsulating protocol, we adjust the maximum transfer unit (mtu) to 1400 bytes and maximum segment size (mss) to 1360 bytes. - edited R2 (config)#interface tunnel 0. For more information on configuring the GRE tunnel that is used as the destination for the monitor sessions, see the chapter Configuring GRE Tunnels. For use on the Internet, you need addresses that are assigned by an ISP or the registry appropriate to your country (ARIN, RIPE, etc.). Interface ge0/0 faces the transport cloud and is in VPN 0 (the transport VPN). We need to specify a source and destination IP address to build the tunnel and we'll use the 192.168.13. Yes,you can also use dynamic routing ,Only endpoint should be reachable i.e your source and destination IP. Thus, Peer B drops the unencrypted keepalive response and does not process it. Using generic routing encapsulation (GRE) tunnels on Cisco routers can come in handy with Cisco router administration, and configuring GRE tunnels is relatively easy. Note: GRE tunnel keepalives are only valid and have an effect on P2P GRE tunnels; they are not valid and do not have any effect on mGRE tunnels. Go to the global configuration mode and enter the following commands: interface FastEthernet0/0 ip address 192.168.1.1 255.255.255. For redundancy reasons, Zscaler recommends configuring multiple GRE tunnels to Zscaler. In this configuration tutorial I will show you how to configure a GRE tunnel between two Cisco IOS routers. All of the devices used in this document started with a cleared (default) configuration. The documentation set for this product strives to use bias-free language. This usually happens when the tunnel is misconfigured with a Next Hop Server (NHS) that is its own IP address. Encrypted packet reaches physicalinterface. Not sure exactly what you mean. This document explains what Generic Routing Encapsulation (GRE) keepalives are and how they work. This output shows the commands you use in order to configure keepalives on GRE tunnels. The basic rules do not cover the case in which the GRE tunneled packets are successfully forwarded, but are lost before they reach the other end of the tunnel. 06-22-2009 The tunnels behave as virtual point-to-point links that have two endpoints identified by the tunnel source and tunnel destination addresses at each endpoint. Configuration interface Tunnel1 description BranchA-vEdge01 The check that MR2 can reach the source over the tunnel is a Reverse Path Forwarding (RPF) check, and the static mroute allows the check to be successful when the interface, on which the multicast packet arrives, is not the . This document describes how to track transport tunnels' health status in VPN 0. Traffic forwarded through the GRE tunnel is encapsulated and routed out onto the physical interface of the router. The vEdge router splits its traffic into two flows, which you can think of as two separate tunnels. It is both administratively up and its protocol is up as well. GRE tunnels are sometimes combined with IPsec because IPsec does not support IP multicast packets. View with Adobe Reader on a variety of devices, View in various apps on iPhone, iPad, Android, Sony Reader, or Windows Phone, View on Kindle device or Kindle app on multiple devices. As always, this is done solely through the GUI while you can use some CLI commands to test the tunnel. Jon 0 Helpful Share Peer B generates a keepalive packet which is GRE encapsulated and then encrypted by the tunnel protection on the tunnel interface and then forwarded to the physical interface. This includes both the data traffic from VPN 1 that is destined for a public network and all control traffic, including the traffic required to establish and maintain DTLS control plane tunnels between the vEdge router and the vSmart controller and between the router and the vBond orchestrator. Use these resources to familiarize yourself with the community: Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type. This allows for the installation of an alternate (floating) static route or for Policy Based Routing (PBR) in order to select an alternate next-hop or interface. Configure Branch vEdges to route all unknown traffic to route using Zscaler Cloud router, this solution should be implemented using service chaining. You will see that the NAT filter is built for, ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------. After completing step 3, you have the following two types of addresses: Internet-routable public IP addresses, outside the GRE tunnels. (Community Manager-Network Infrastructure). Packets from VPN 1 are sourced. R1 (config)#exit. Cross-check that the default-route from the service-side points to the Transport interface with NAT on. This scenario is similar to Scenario 1 in that when Peer A receives the encrypted keepalive, it decrypts and decapsulates it. Router B simply decapsulates the keepalive packet and sends it back out the physical interface (S2). Learn more about how Cisco is using Inclusive Language. This means that each tunnel endpoint does not keep any information about the state or availability of the remote tunnel endpoint. Sending 5, 100-byte ICMP Echos to 172.16.1.2, timeout is 2 seconds: Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms. Here, the vEdge router has two interfaces: In order to configure the vEdge router to act as a NAT device so that some traffic from the router can go directly to a public network, you do three things: When NAT is enabled, all traffic that passes through VPN 0 is NATed. Constructs the inner IP header every five seconds where: the source is set as the local the tunnel destination, which is 192.168.1.2, the destination is set as the local tunnel source, which is 192.168.1.1. This was committed with Cisco bug IDCSCum34057 (initial attempt with Cisco bug IDCSCuj29996and then backed out with Cisco bug IDCSCuj99287). GRE tunnels are designed to be completely stateless. "sh crypto isakmp sa" shows the IPSEC tunnel, it doesn't show you the actual data but gives you statistics on traffic transmitted. description GRE tunnel to other location. Note: GRE keepalives are not supported together with IPsec tunnel protection under any circumstances. The GRE is defined by the RFC 2784. Thanks for this, but i want to ask, in your example, the internet ip addresses used, would one have to get them off an isp or one can just pick up any one? If you the tunnel is up and you are able to ping the tunnel source & destination ips then there is definetly an issue with the routing which is configured for the endpoints, you should check if the routes are configured rightly. To remove this configuration, use the no prefix of the command. It is an architecture designed to provide the services in order to implement a point-to-point encapsulation scheme. ERSPAN involves mirroring traffic through a GRE tunnel to a remote site. You will see that the NAT filter is built for Internet Control Message Protocol (ICMP). PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data. The passenger protocol is also IP (although it can be another protocol like Decnet, Internetwork Packet Exchange (IPX), or Appletalk). 03-01-2019 The second traffic stream, shown in grey, is redirected through the vEdge router's NAT device and then out of the overlay network to a public network. Configure nat and tracker on the transport interface. I know that I can show int tunnel0 and it will show me the status of the tunnel interface. This document describes how to track transport tunnels' health status in VPN 0. 03:49 PM. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. How do I do GRE specifically? Up/up - This implies that the tunnel is fully functional and passes traffic. The main drawback of GRE protocol is the lack of built-in security. A GRE tunnel is a logical interface on a Cisco router that provides a way to encapsulate passenger packets inside a transport protocol. GRE tunnels are typically used to establish a VPN between the Cisco router and a remote device that controls access to a private network, such as a corporate network. Unicast RPF (Unicast Reverse Path Forwarding) is a security feature that helps detect and drop spoofed IP traffic with a validation of the packet source address against the routing table. Tunnel protection is configured on the hub router in order to reduce the size of the configuration and a static crypto map is used on each spoke. These packets illustrate the IP tunneling concepts where GRE is the encapsulation protocol and IP is the transport protocol. You can track the status of the internet connection with the help of these. Normally, a GRE Tunnel interface comes up as soon as it is configured and it stays up as long as there is a valid tunnel source address or interface which is up. It was so simple and straight forward. Tunnel keepalives are configurable on multipoint GRE (mGRE) tunnels but have no effect. vEdge1 router here acts as a NAT device. After it is done, we will proceed with the configuration. The following are the generic restriction(s): Here is an example that can be used in order to verify that packets go out to the Internet. If strict mode or loose mode Unicast RPF is enabled on the tunnel interface of the router that receives the GRE keepalive packets, then the keepalives packets will be dropped by RPF after tunnel decapsulation since the route to the source address of the packet (router's own tunnel source address) is not through the tunnel interface. Then you must configure the tunnel endpoints for the tunnel interface. You can track the status of the internet connection with the help of these. Because of this, dynamic routing protocols cannot run successfully over an IPsec VPN network. 11-08-2010 Site-to-Site IPSec VPN Tunnels are used to allow the secure transmission of data, voice and video between two sites (e.g offices or branches). One traffic flow, shown in green, remains within the overlay network and travels between the two routers in the usual fashion, on the secure IPsec tunnels that form the overlay network. I checked all configs and compared them to another working tunnel, maybe someone has an idea? When the software detects that the path to the internet is again functioning, the route to the internet is reinstalled. /24 subnet on the tunnel interface. Configure your router or firewall to allow the GRE tunnel. In order to better understand how GRE tunnel keepalives work, refer to GRE Tunnel Keepalives. With this change, the tunnel interface dynamically shuts down if the keepalives fail for a certain period of time. 64 bytes from 8.8.8.8: icmp_seq=1 ttl=51 time=0.473 ms, 64 bytes from 8.8.8.8: icmp_seq=2 ttl=51 time=0.617 ms, 64 bytes from 8.8.8.8: icmp_seq=3 ttl=51 time=0.475 ms, 64 bytes from 8.8.8.8: icmp_seq=4 ttl=51 time=0.505 ms, 64 bytes from 8.8.8.8: icmp_seq=5 ttl=51 time=0.477 ms, 5 packets transmitted, 5 received, 0% packet loss, time 3999ms, rtt min/avg/max/mdev = 0.473/0.509/0.617/0.058 ms, Verify the NAT translational filters. Packet is decrypted and decapsulated and then forwarded to the IP destination in clear text. A valid tunnel source consists of any interface that is itself in the up/up state and has an IP address configured on it. "sh int tunnel0" shows you the GRE tunnel, again it doesn't show you actual data but it does show you statistics on traffic transmitted. Look for 'NAT' route entry in the RIB. Sends that packet out of its tunnel interface, which results in the encapsulation of the packet with the outer IP header where: the source is set as the local the tunnel source, which is 192.168.1.1, the destination is set as the local tunnel destination, which is 192.168.1.2. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. This document discusses this issue. There are two different ways that IPsec can encrypt GRE packets: Both methods specify that IPsec encryption is performed after the addition of the GRE encapsulation. Tunnel protection ties the encryption functionality to the GRE tunnel and is checked after the packet is GRE encapsulated but before the packet is handed to the physical interface. R1(config)# ip route 192.168.2.0 255.255.255.0 172.16.1.2, R2(config)# ip route 192.168.1.0 255.255.255.0 172.16.1.1. David Davis has the details . 3. On the reception of a keepalive response, with the implication that the tunnel endpoint is again reachable, the tunnel keepalive counter is reset to 0, and the line protocol on the tunnel comes up. In this scenario, since the GRE keepalives are onfigured on Peer B, the sequence events when a keepalive is generated are as follows: Note: The keepalive response is encrypted. Greetings from the clouds. To check if the tunnel interface is up or down, use the show ip interface brief command as follows: router# show ip interface brief Interface IP-Address FastEthernet0/0 10.0.1.2 OK? Specifically, if the line protocol for an interface is changed to down, then any static routes that point out that interface are removed from the routing table. Sometimes, because of network address translation (NAT), GRE Keepalives can be dropped. Use this section in order to confirm that your configuration works properly. Encrypted packet reaches the physical interface. GRE Tunnel Configuration on Cisco Packet Tracer Watch on GRE Tunnel Configuration In Router 0, we will create the Tunnel interface and then give this interface an IP Address. The ability to mark an interface as down when the remote end of the link is not available is used in order to remove any routes (specifically static routes) in the routing table that use that interface as the outbound interface. 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. If there is no response to three successive polls, the router declares the tunnel interface to be down. 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