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. 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 configured on Peer B, the sequence events when a keepalive is generated are as follows: Therefore, even though the Peer A responds to the keepailves and originating router, Peer B receives the responses, it never process them and eventually changes the line protocol of the tunnel interface to down state. 03:49 PM. 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. Here is an example that can be used in order to verify that packets go out to the Internet. 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. Do you need to configure static routes or is dynamic routing (OSPF) sufficient for the tunnel to operate? For more information on configuring the GRE tunnel that is used as the destination for the monitor sessions, see the chapter Configuring GRE Tunnels. Before implementing a GRE tunnel, IP . You can track the status of the internet connection with the help of these. The GRE tunnel will be used to route traffic between the 192.168.1./24 and 172.16.1./24 networks. After that, we we will define the Tunnel Source, with IP Address or with Interface name. Lets us see how to configure and verify the Generic Routing Encapsulation. In order to see keepalives in action, enable debug tunnel and debug tunnel keepalive. 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. 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. To display GRE tunneling Information, use the following commands: show ip interface show ip route show ip interface tunnel show ip tunnel traffic show interface tunnel show statistics tunnel The following shows an example output of the show ip interface command, which includes information about GRE tunnels. If the internet becomes unavailable, traffic is automatically redirected to the non-NATed tunnel on the transport interface. 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. The vEdge router splits its traffic into two flows, which you can think of as two separate tunnels. 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. Enable NAT in the transport VPN (VPN 0) on the WAN-transportfacing interface, which here is ge0/0. These packets illustrate the IP tunneling concepts where GRE is the encapsulation protocol and IP is the transport protocol. The VPN tunnel is created over the Internet public network and encrypted using a number of advanced encryption algorithms to provide confidentiality of the data transmitted between the two sites. This causes 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 is potentially available. 03:34 PM Learn more about how Cisco is using Inclusive Language. In such situations where the GRE packets must be encrypted, there are three possible solutions: 2022 Cisco and/or its affiliates. This document discusses this issue. 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. Now both networks (192.168.1.0/24 and 192.168.2.0/24) are able to freely communicate with each other over the GRE Tunnel . A setting of 1400 is a common practice and will ensure unnecessary packet fragmentation is kept to a minimum. The GRE was developed as the tunneling tool which is meant to carry any of the OSI layer 3 protocol over the IP network. The documentation set for this product strives to use bias-free language. 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. 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. Using generic routing encapsulation (GRE) tunnels on Cisco routers can come in handy with Cisco router administration, and configuring GRE tunnels is relatively easy. 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? Router1# show interface Tunnel5 And the easiest way to determine if a tunnel is operational is simply to use a PING test to either the send ICMP packets through the tunnel or to its destination address: Router1# ping 192.168.66.6 Router1# ping 172.22.1.4 The line protocol on a GRE tunnel interface is up as long as there is a route to the tunnel destination. It is both administratively up and its protocol is up as well. This would have worked if the used Loopback was part of the General/Generic/Unnamed vrf. Since PAN-OS version 9.0 you can configure GRE tunnels on a Palo Alto Networks firewall. This is critical on the tunnel endpoint that "reflects" the keepalive back to the requester. as long as both of them have the route of the addresses used in the tunnel source and destination. There are no specific requirements for this document. Thank you all for the possible answers. 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. 1. 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. This means that each tunnel endpoint does not keep any information about the state or availability of the remote tunnel endpoint. Not sure exactly what you mean. It is then matched against Tunnel 0, becomes decapsulated, and is forwarded to the destination IP which is the tunnel source IP address on Router A. To remove this configuration, use the no prefix of the command. Router1 (config-if)#keepalive By default, this keepalive command sends a packet through the tunnel to check its status once every 10 seconds. ---------------------------------------------------------------------------------------------------------------------------------------------, ------------------------------------------------------------------------------------------------------------------------------------------------------------------, ------------------------------------------------------------------------------------------------------------------------------. For redundancy reasons, Zscaler recommends configuring multiple GRE tunnels to Zscaler. Learn more about how Cisco is using Inclusive Language. Thank you so much for the information and the explanation. Method Status YES NVRAM up Protocol up FastEthernet0/1 172.30.1.2 YES NVRAM up up Tunnel0 The IPsec crypto map is tied to the physical interface and is checked as packets are forwarded out the physical interface. R1 (config)#exit. The information in this document was created from the devices in a specific lab environment. 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 route to the tunnel destination address is through the tunnel itself, which results in recursion. As always, this is done solely through the GUI while you can use some CLI commands to test the tunnel. Tunneling provides a mechanism to transport packets of one protocol within another protocol. 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. Edgar#srint tun1. According this article "GRE Tunnel Keepalives - Cisco" normal keepalive can't be configured on the IPsec tunnel configured with "tunnel protection" command. Command Default None Command Modes XR Config mode Usage Guidelines 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. Cross-check that the default-route from the service-side points to the Transport interface with NAT on. Configure your router or firewall to allow the GRE tunnel. 3. "sh crypto isakmp sa" shows the IPSEC tunnel, it doesn't show you the actual data but gives you statistics on traffic transmitted. For example, 8.8.8.8 is Google DNS. Increments the tunnel keepalive counter by one. Traffic forwarded through the GRE tunnel is encapsulated and routed out onto the physical interface of the router. Upon arrival on Router A, the packet becomes decapsulated and the check of the PT results in 0. 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. 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. With this change, the tunnel interface dynamically shuts down if the keepalives fail for a certain period of time. Sometimes, because of network address translation (NAT), GRE Keepalives can be dropped. PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data. Note: GRE keepalives are not supported together with IPsec tunnel protection under any circumstances. It was so simple and straight forward. After it is done, we will proceed with the configuration. 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. The following are the generic restriction(s): In Releases 17.2.2 and later, on Network Address Translation (NAT) enabled transport interfaces are used for local internet exit. We are running IPSec inside of a GRE tunnel. This signifies that this is a keepalive packet. endpoint-ip or endpoint-dns-name is something on the Internet that can respond to HTTP requests. 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. - edited (Community Manager-Network Infrastructure). 2. This means that each tunnel endpoint does not keep any information about the state or availability of the remote tunnel endpoint. "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. To determine whether the tunnel interface is up or down, use the show ip interface brief command, as shown in Figure 1. However, it does not have to be reachable, which can be seen from this ping test: There is no route, which includes the default route, to the tunnel destination address. 03-01-2019 It processes the GRE keepalive packet just like any other GRE IP data packet. Yes,you can also use dynamic routing ,Only endpoint should be reachable i.e your source and destination IP. Jon 0 Helpful Share This is true even if the other side of the tunnel has not been configured. Up/down - This implies that, even though the tunnel is administratively up, something causes the line protocol on the interface to be down. /24 subnet on the tunnel interface. 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. Go to router global configuration mode and configure the GRE tunnel using the below commands. Interface ge0/1 faces the local site and is in VPN 1. Good overview. 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. This document is not restricted to specific software and hardware versions. Verify the NAT translational filters. Since GRE is a packet tunneling mechanism for tunneling IP inside IP, a GRE IP tunnel packet can be built inside another GRE IP tunnel packet. For example, the case in which the GRE tunneled packets are successfully forwarded, but are lost before they reach the other end of the tunnel. The question was brought to me as to how to actually show the GRE tunnel itself. Router B simply decapsulates the keepalive packet and sends it back out the physical interface (S2). interface tunnel-ip id no interface tunnel-ip id Syntax Description id Specifies the tunnel interface identifier. Interface ge0/0 faces the transport cloud and is in VPN 0 (the transport VPN). I know that I can do a show crypto isakmp sa and it will show the IPSec. Thanks If the software detects that this path is down, it withdraws the route to the internet destination, and traffic destined to the internet is then routed through the data center router. Packets from VPN 1 are sourced. How do I do GRE specifically? You can pick any number for the tunnel interface that you like. This document explains what Generic Routing Encapsulation (GRE) keepalives are and how they work. Packet is decapsulated and then forwarded to the IP destination in clear text. Use this section to confirm that your configuration works properly. Tunnel keepalives are configurable on multipoint GRE (mGRE) tunnels but have no effect. Note: If an inbound Access Control List (ACL) on the GRE tunnel interface is configured, then the GRE tunnel keepalive packet that the opposite device sends must be permitted. New here? 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. nice one, simple and clear and easy to understand. I checked all configs and compared them to another working tunnel, maybe someone has an idea? Peer A has tunnel protection configured on the tunnel interface while Peer B has crypto map configured on the physical interface. This usually happens when the tunnel is misconfigured with a Next Hop Server (NHS) that is its own IP address. Its IP address is 192.23.100.0/24, and it uses the default OMP port number, 12346, for overlay network tunnels. 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 means that a static route or PBR forwarding of packets via the GRE tunnel interface remains in effect even though the GRE tunnel packets do not reach the other end of the tunnel. GRE tunnels are sometimes combined with IPsec because IPsec does not support IP multicast packets. Find answers to your questions by entering keywords or phrases in the Search bar above. 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. A GRE tunnel is a logical interface on a Cisco router that provides a way to encapsulate passenger packets inside a transport protocol. This is true even if you replace iVRF and/or fVRF with "global". 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. 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. You can track the status of the internet connection with the help of these. 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). The previous tutorial shown GRE tunnel configuration between Cisco router and Linux Core. Up/up - This implies that the tunnel is fully functional and passes traffic. This was committed with Cisco bug IDCSCum34057 (initial attempt with Cisco bug IDCSCuj29996and then backed out with Cisco bug IDCSCuj99287). If your network is live, ensure that you understand the potential impact of any command. There are several commands used to monitor and troubleshoot GRE tunnels. 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 use on the Internet, you need addresses that are assigned by an ISP or the registry appropriate to your country (ARIN, RIPE, etc.). The tunnel can become a black-hole for packets directed into the tunnel from the side that did not have keepalives configured. The passenger protocol is also IP (although it can be another protocol like Decnet, Internetwork Packet Exchange (IPX), or Appletalk). 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. Find answers to your questions by entering keywords or phrases in the Search bar above. In order to better understand how GRE tunnel keepalives work, refer to GRE Tunnel Keepalives. Tracker Status should be 'UP' in show interface VPN 0. This is tracked by Cisco bug ID CSCuq31060. The keepalive response that Router B returns to Router A is already inside the Inner IP Header. 2022 Cisco and/or its affiliates. With Cisco IOS Software Release 12.2(8)T, it is possible to configure keepalives on a point-to-point GRE tunnel interface. This is because it is often more important for the spoke to discover that the hub is unreachable and therefore switch to a backup path (Dial Backup for example). 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. Greetings from the clouds. If this situation is true, when the destination sends unicast packets to the source, MR 2 sends them over the tunnel. When you enable transport tunnel tracking, the software periodically probes the path to the internet to determine whether it is up. A valid tunnel source consists of any interface that is itself in the up/up state and has an IP address configured on it. 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. It is an architecture designed to provide the services in order to implement a point-to-point encapsulation scheme. 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. In order to provide users at a local site with direct, secure access to Internet resources, such as websites, you can configure the vEdge router to function as a NAT device, that performs both address and port translation (NAPT). 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 document describes how to track transport tunnels' health status in VPN 0. To verify the state of a GRE tunnel, use the show interface tunnel command. Its IP address is 10.1.12.0/24. 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. GRE tunnels are designed to be completely stateless. 03-04-2019 A consequence of this is that,by default, 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. The GRE will create the private point to point connection as same that of the VPN. 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. The protocol that is carried is called as the passenger protocol, and the protocol that is used for carrying the passenger protocol is called as the transport protocol. How to Configure GRE Tunnels on Zscaler (Step-by-Step) 16 Oct, 2020 | 0 Task Configure GRE tunnels on Zscaler router with NAT. 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. Look for 'NAT' route entry in the RIB. 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. 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. The first step is to configure your firewall device with the appropriate tunnel interfaces. interface tunnel-ip Configures an IP-in-IP tunnel interface. Solution You can look at the attributes for a tunnel with the show interface command. 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. Ensure that theendpoint-ip or endpoint-dns-name is something on the Internet that can respond to HTTP requests. I know that I can show int tunnel0 and it will show me the status of the tunnel interface. Encrypted packet reaches the physical interface. 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. 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. However, when the response is forwarded back out, it is not encrypted since Peer A uses tunnel protection on the tunnel interface. The OCG isn't super helpful on troubleshooting, and I've been looking for documentation as to what kind of requirements you need for connectivity through a GRE tunnel, and all I'm getting is that the tunnel needs IP addresses to anchor each end to. 4. For details on the Interface State Control Feature, see the. 2. Configuration interface Tunnel1 description BranchA-vEdge01 The main drawback of GRE protocol is the lack of built-in security. Both Peers have tunnel protection configured on the tunnel interface. Enter configuration commands, one per line. Afterwards, the GRE tunnel path and details can be viewed, as well as the details and paths of the demands routed over the GRE tunnel. 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. Lastly, we define the Tunnel Destination IP address. 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. Because of the tunnel vrf command I had left out. Create the tunnel interface and define the local and remote tunnel endpoints. 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. "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. But it was another solution. Enter configuration mode. All traffic exiting from the vEdge router, going either to other overlay network sites or to a public network, passes through this interface. 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. Keepalives enabled on Peer B succesfully determine what the tunnel state should be based on the availabilty of the tunnel destination. 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