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. Before implementing a GRE tunnel, IP . Both Peers have tunnel protection configured on the tunnel interface. 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. Enter configuration commands, one per line. This is tracked by Cisco bug ID CSCuq31060. I know that I can do a show crypto isakmp sa and it will show the IPSec. A valid tunnel destination is one which is routable. Under normal circumstances, there are only three reasons for a GRE tunnel to be in the up/down state: These three rules (missing, route, interface down, and misrouted tunnel destination) are problems local to the router at the tunnel endpoints and do not cover problems in the intervening network or other features related to the GRE tunnel that can be configured. Thank you all for the possible answers. 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. Name Default RD Protocols Interfaces, CustomerX 6:6 ipv4 Lo1541, CustomerX-Q1541 1541:1541 ipv4 Tu154128, ip address 192.168.212.21 255.255.255.252. These packets illustrate the IP tunneling concepts where GRE is the encapsulation protocol and IP is the transport protocol. RPF packet drops can be observed in the show ip traffic output as follows: As a result, the initiator of the tunnel keepalives will bring down the tunnel due to missed keepalives return packets. "sh crypto isakmp sa" shows the IPSEC tunnel, it doesn't show you the actual data but gives you statistics on traffic transmitted. GRE tunnels are designed to be completely stateless. Generic Routing Encapsulation (GRE) Tunnels can be either imported from the router configuration files, or created from the NorthStar Planner Graphical Interface for what-if studies. Up/up - This implies that the tunnel is fully functional and passes traffic. Method Status YES NVRAM up Protocol up FastEthernet0/1 172.30.1.2 YES NVRAM up up Tunnel0 R1 (config)#exit. Packets from VPN 1 are sourced. We need to specify a source and destination IP address to build the tunnel and we'll use the 192.168.13. Peer B now recieves an encrypted GRE keepalive response whose destination is forwarded to the tunnel interface where it is decrypted. 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. 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 . With this change, the tunnel interface dynamically shuts down if the keepalives fail for a certain period of time. To configure Generic Routing Encapsulation (GRE) over an IPSec tunnel between two routers, perform these steps: 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: interface Tunnel0 Using generic routing encapsulation (GRE) tunnels on Cisco routers can come in handy with Cisco router administration, and configuring GRE tunnels is relatively easy. 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. 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. 11-08-2010 After that, we we will define the Tunnel Source, with IP Address or with Interface name. 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. Configuration interface Tunnel1 description BranchA-vEdge01 In this situation, enabling NAT on the transport interface splits the TLOC between the local router and the data center into two, with one going to the remote router and the other going to the internet. A consequence of this is that the local tunnel endpoint router does not have the ability to bring the line protocol of the GRE Tunnel interface down if the remote end of the tunnel is unreachable. - edited For example, if the tunnel source was changed to. Thank you so much for the information and the explanation. Look for 'NAT' route entry in the RIB. Also there are other applications that trigger when an interface changes state; for example, 'backup 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. 2. If that condition is not true, then the next time Router A attempts to send a keepalive to Router B, the line protocol is brought down. This added an additional check, which keeps such tunnel interfaces in the line protocol down state until the redundancy state changes to ACTIVE. How do I do GRE specifically? 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. Create the tunnel interface and define the local and remote tunnel endpoints. Note: GRE tunnel keepalives are only supported on point-to-point GRE tunnels. The passenger protocol is also IP (although it can be another protocol like Decnet, Internetwork Packet Exchange (IPX), or Appletalk). All traffic exiting from the vEdge router, going either to other overlay network sites or to a public network, passes through this interface. First step is to create our tunnel interface on R1 and R2 : R1(config-if)# ip address 172.16.1.1 255.255.255.0, R1(config-if)# tunnel destination 2.2.2.2, R2(config-if)# ip address 172.16.1.2 255.255.255.0, R2(config-if)# tunnel destination 1.1.1.1. However, it does continue to send keepalive packets. So, this will change the tunnel's status about 30 seconds after a failure. 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. 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. Learn more about how Cisco is using Inclusive Language. It is both administratively up and its protocol is up as well. A setting of 1400 is a common practice and will ensure unnecessary packet fragmentation is kept to a minimum. Yes,you can also use dynamic routing ,Only endpoint should be reachable i.e your source and destination IP. A valid tunnel source consists of any interface that is itself in the up/up state and has an IP address configured on it. 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. Follow the steps below to configure the GRE tunnel on both routers: CLI: Access the Command Line Interface on ER-L using SSH. Administratively down/down - This implies that the interface has been administratively shut down. Because of the tunnel vrf command I had left out. GRE tunnels are designed to be completely stateless. Therefore, if the iVRF and the fVRF do not match then the keepalive reply packet is not forwarded back to the sender. 03-01-2019 With Cisco IOS Software Release 12.2 (8)T, it is possible to configure keepalives on a P2P GRE tunnel interface. The interface that anchors the tunnel source is down. 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. For example, 8.8.8.8 is Google DNS. 4. 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. The information in this document was created from the devices in a specific lab environment. You can track the status of the internet connection with the help of these. Configure nat and tracker on the transport interface. The line protocol on a GRE tunnel interface is up as long as there is a route to the tunnel destination. Keepalives on the GRE tunnel interface are used in order to solve this issue in the same way as keepalives are used on physical interfaces. Now, we will configure the GRE Tunnel on Cisco Router. This document explains what Generic Routing Encapsulation (GRE) keepalives are and how they work. 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. Find answers to your questions by entering keywords or phrases in the Search bar above. 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. Interface ge0/1 faces the local site and is in VPN 1. Keepalives enabled on Peer B cause the tunnel state on Peer B to change to up/down. GRE tunnels are designed to be completely stateless. 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. So Unicast RPF must not be configured in strict or loose mode for GRE tunnel keepalives to work. Sometimes, because of network address translation (NAT), GRE Keepalives can be dropped. This document discusses this issue. A GRE tunnel is a logical interface on a Cisco router that provides a way to encapsulate passenger packets inside a transport protocol. The previous tutorial shown GRE tunnel configuration between Cisco router and Linux Core. interface tunnel-ip Configures an IP-in-IP tunnel interface. OmniSecuR1# configure terminal OmniSecuR1 (config)# interface tunnel 0 OmniSecuR1 (config-if)# ip address . Here, we used Interface name. We are running IPSec inside of a GRE tunnel. Thanks How do I do GRE specifically? 2022 Cisco and/or its affiliates. Step 02: Use following commands to create a tunnel interface, configure an IPv4 Address for the new tunnel interface and to configure a source and destination for the tunnel interface in R2.R2#configure terminal. This is critical on the tunnel endpoint that "reflects" the keepalive back to the requester. When the keepalive request is received it is received in the fVRF and decapsulated. All of the devices used in this document started with a cleared (default) configuration. The question was brought to me as to how to actually show the GRE tunnel itself. In order to better understand how the tunnel keepalive mechanism works, consider this example tunnel topology and configuration: In this scenario, Router A performs these steps: If Router B is unreachable, Router A continues to construct and send keepalive packets as well as normal traffic. The GRE tunnel keepalive mechanism is similar to PPP keepalives in that it gives the ability for one side to originate and receive keepalive packets to and from a remote router even if the remote router does not support GRE keepalives. To direct data traffic from other VPNs to exit from the vEdge router directly to a public network, enable NAT in those VPNs or ensure that those VPNs have a route to VPN 0. This imageexplains how the NAT functionality on the vEdge router splits traffic into two flows (or two tunnels) so that some of it remains within the overlay network and some go directly to the Internet or other public networks. In order to make this interface up/up, a valid tunnel source and tunnel destination must be configured: So far, the tunnel has been configured as a point-to-point (P2P) GRE tunnel, which is the default. Here's my configuration. Step 01: Use following commands to create a tunnel interface, configure an IPv4 Address for the new tunnel interface and to configure a source and destination for the tunnel interface in OmniSecuR1. When you enable NAT, it allows traffic exiting from a vEdge router to pass directly to the Internet rather than being backhauled to a co-location facility that provides NAT services for Internet access. So let's configure the Network Interfaces on Router R1. New here? endpoint-ip or endpoint-dns-name is something on the Internet that can respond to HTTP requests. There are two key differences between when you use a crypto map and when you use tunnel protection: Given the two ways to add encryption to GRE tunnels, there are three distinct ways to set up an encrypted GRE tunnel: The configuration described in Scenarios 1 and 2 are often done in a hub-and-spoke design. Jon 0 Helpful Share Router1 (config-if)#keepalive By default, this keepalive command sends a packet through the tunnel to check its status once every 10 seconds. How to Configure GRE Tunnels on Zscaler (Step-by-Step) 16 Oct, 2020 | 0 Task Configure GRE tunnels on Zscaler router with NAT. Interface ge0/0 faces the transport cloud and is in VPN 0 (the transport VPN). 03:49 PM. Do you need to configure static routes or is dynamic routing (OSPF) sufficient for the tunnel to operate? 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. 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. Configure your router or firewall to allow the GRE tunnel. 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. PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data. This means that each tunnel endpoint does not keep any information about the state or availability of the remote tunnel endpoint. 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. 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. If this tunnel were to be changed to a multipoint GRE (mGRE) tunnel, then all that is required for the tunnel to be in an up state is a valid tunnel source (an mGRE tunnel can have many tunnel destinations, so that cannot be used to control the tunnel interface state): At any point, if the tunnel interface is administratively shut down, the tunnel immediately goes into an administratively down/down state: A P2P GRE Tunnel interface usually comes up as soon as it is configured with a valid tunnel source address or interface which is up and a tunnel destination IP address which is routable as shown in the previous section. The documentation set for this product strives to use bias-free language. In the case, "Tracker Status" will show as "Down". Note: GRE keepalives are not supported together with IPsec tunnel protection under any circumstances. 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. There are several commands used to monitor and troubleshoot GRE tunnels. Packet is forwarded to the tunnel interface. Router B simply decapsulates the keepalive packet and sends it back out the physical interface (S2). In order to better understand how GRE tunnel keepalives work, refer to GRE Tunnel Keepalives. If your network is live, ensure that you understand the potential impact of any command. (access-list permit gre host host ). nice one, simple and clear and easy to understand. Restrictions; Restrictions. This signifies that this is a keepalive packet. 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). 2. Use this section in order to confirm that your configuration works properly. Here are the reasons an mGRE tunnel line protocol can be in a down state: When a tunnel source IP address is configured as a redundancy IP address (for example, a Hot Standby Router Protocol Virtual IP (HSRP VIP) address), then the tunnel interface state tracks the redundancy state. If the Interface State Control feature is enabled for Dynamic Multipoint VPN (DMVPN) and none of the NHSs respond, then the line protocol is put in a down state. Such scenarios would cause data packets that go through the GRE tunnel to be "black holed", even though an alternate route that uses PBR or a floating static route via another interface might be available. Packet is decrypted and decapsulated and then forwarded to the IP destination in clear text. 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. Tunnel keepalives are configurable on multipoint GRE (mGRE) tunnels but have no effect. Peer A has tunnel protection configured on the tunnel interface while Peer B has crypto map configured on the physical interface. - edited Use this section to confirm that your configuration works properly. R2 (config)#interface tunnel 0. In order to see keepalives in action, enable debug tunnel and debug tunnel keepalive. 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. This is true even if the other side of the tunnel has not been configured. After completing step 3, you have the following two types of addresses: Internet-routable public IP addresses, outside the 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. When the software detects that the path to the internet is again functioning, the route to the internet is reinstalled. Since GRE is an encapsulating protocol, we adjust the maximum transfer unit (mtu) to 1400 bytes and maximum segment size (mss) to 1360 bytes. For more information on configuring the GRE tunnel that is used as the destination for the monitor sessions, see the chapter Configuring GRE Tunnels. This document describes how to track transport tunnels' health status in VPN 0. The main drawback of GRE protocol is the lack of built-in security. In Releases 17.2.2 and later, on Network Address Translation (NAT) enabled transport interfaces are used for local internet exit. Ensure that theendpoint-ip or endpoint-dns-name is something on the Internet that can respond to HTTP requests. You will see that the NAT filter is built for, ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------. For mGRE tunnel interfaces, since there is no fixed tunnel destination, some of the previous checks for P2P tunnels are not applicable. Verify the NAT translational filters. 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