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. 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 The GRE is defined by the RFC 2784. Configure your router or firewall to allow the GRE tunnel. Tip: The problem with the configuration of keepalives only on one side of the tunnel is that only the router that has keepalives configured marks its tunnel interface as down if the keepalive timer expires. 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. 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. A GRE tunnel is a logical interface on a Cisco router that provides a way to encapsulate passenger packets inside a transport protocol. In order to see keepalives in action, enable debug tunnel and debug tunnel keepalive. 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. Also, verify that the endpoint IP address is not the same as the Transport interface. This added an additional check, which keeps such tunnel interfaces in the line protocol down state until the redundancy state changes to ACTIVE. All rights reserved. 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. Do you need to configure static routes or is dynamic routing (OSPF) sufficient for the tunnel to operate? So let's configure the Network Interfaces on Router R1. This document discusses this issue. Note: GRE tunnel keepalives are only supported on point-to-point GRE tunnels. Also there are other applications that trigger when an interface changes state; for example, 'backup interface '. Method Status YES NVRAM up Protocol up FastEthernet0/1 172.30.1.2 YES NVRAM up up Tunnel0 All rights reserved. This is true even if the other side of the tunnel has not been configured. Its IP address is 10.1.12.0/24. As you might know already, GRE tunnel termination is not supported on Cisco ASA firewalls. The IPsec crypto map is tied to the physical interface and is checked as packets are forwarded out the physical interface. Edgar#srint tun1. If the internet becomes unavailable, traffic is automatically redirected to the non-NATed tunnel on the transport 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. Note: GRE keepalives are not supported together with IPsec tunnel protection under any circumstances. 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. Use this section to confirm that your configuration works properly. Find answers to your questions by entering keywords or phrases in the Search bar above. Direct traffic to existing locally via VPN 0. Create the tunnel interface and define the local and remote tunnel endpoints. interface tunnel-ip Configures an IP-in-IP tunnel interface. A valid tunnel source consists of any interface that is itself in the up/up state and has an IP address configured on it. Jon 0 Helpful Share Here's my configuration. Keepalives enabled on Peer B succesfully determine what the tunnel state should be based on the availabilty of the tunnel destination. 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. When you enable transport tunnel tracking, the software periodically probes the path to the internet to determine whether it is up. 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. PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data. interface tunnel-ip id no interface tunnel-ip id Syntax Description id Specifies the tunnel interface identifier. The previous tutorial shown GRE tunnel configuration between Cisco router and Linux Core. Another attribute of GRE tunnel keepalives is that the keepalive timers on each side are independent and do not have to match, similar to PPP keepalives. 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. Peer B now recieves an encrypted GRE keepalive response whose destination is forwarded to the tunnel interface where it is decrypted. 2020-07-21 Network, Palo Alto Networks Cisco Router, GRE, Palo Alto Networks, Static Route Johannes Weber. Click Save and activate the change. I checked all configs and compared them to another working tunnel, maybe someone has an idea? 2. 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. The interface that anchors the tunnel source is down. 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. 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 line protocol on a GRE tunnel interface is up as long as there is a route to the tunnel destination. 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. It is an architecture designed to provide the services in order to implement a point-to-point encapsulation scheme. 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. This is the destination on the internet to which the router sends probes to determine the status of the transport interface. With Cisco IOS Software Release 12.2 (8)T, it is possible to configure keepalives on a P2P GRE tunnel interface. GRE tunnels are designed to be completely stateless. With Cisco IOS Software Release 12.2(8)T, it is possible to configure keepalives on a point-to-point GRE tunnel 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. 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 . 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. as long as both of them have the route of the addresses used in the tunnel source and destination. 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. - edited According this article "GRE Tunnel Keepalives - Cisco" normal keepalive can't be configured on the IPsec tunnel configured with "tunnel protection" command. Cross-check that the default-route from the service-side points to the Transport interface with NAT on. 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). GRE Tunnel Configuration - Lab Topology. Workstations on either network will still not be able to reach the other side unless a routing is configure on each router.Here We will configure static route on both router. Configuration interface Tunnel1 description BranchA-vEdge01 The documentation set for this product strives to use bias-free language. Follow the steps below to configure the GRE tunnel on both routers: CLI: Access the Command Line Interface on ER-L using SSH. Here is an example that can be used in order to verify that packets go out to the Internet. If this situation is true, when the destination sends unicast packets to the source, MR 2 sends them over the tunnel. New here? If your network is live, ensure that you understand the potential impact of any command. When the software detects that the path to the internet is again functioning, the route to the internet is reinstalled. 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. OmniSecuR1# configure terminal OmniSecuR1 (config)# interface tunnel 0 OmniSecuR1 (config-if)# ip address . Up/down - This implies that, even though the tunnel is administratively up, something causes the line protocol on the interface to be down. 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. For use on the Internet, you need addresses that are assigned by an ISP or the registry appropriate to your country (ARIN, RIPE, etc.). A GRE tunnel is a logical interface on a Cisco router that provides a way to encapsulate passenger packets inside a transport protocol. For example, 8.8.8.8 is Google DNS. If the internet becomes unavailable, traffic is automatically redirected to the non-NATed tunnel on the transport interface. Since GRE tunnels do support IP multicast, a dynamic routing protocol can be run over a GRE tunnel. "sh crypto isakmp sa" shows the IPSEC tunnel, it doesn't show you the actual data but gives you statistics on traffic transmitted. When the keepalive request is received it is received in the fVRF and decapsulated. This document describes how to track transport tunnels' health status in VPN 0. Peer A has tunnel protection configured on the tunnel interface while Peer B has crypto map configured on the physical interface. 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. 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. 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. This usually happens when the tunnel is misconfigured with a Next Hop Server (NHS) that is its own IP address. Not sure exactly what you mean. Learn more about how Cisco is using Inclusive Language. 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. With the assumption that there is a way to reach the far end tunnel endpoint and the tunnel line protocol is not down due to other reasons, the packet arrives on Router B. Before implementing a GRE tunnel, IP . 1. A valid tunnel destination is one which is routable. So Unicast RPF must not be configured in strict or loose mode for GRE tunnel keepalives to work. 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 . 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. If there is no response to three successive polls, the router declares the tunnel interface to be down. Peer A has crypto map configured on the physical interface while Peer B has tunnel protection configured on the tunnel interface. You are unable to see the GRE packets via TCP Dump, as the packets are generated by the fast path. 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. 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. Enable NAT in the transport VPN (VPN 0) on the WAN-transportfacing interface, which here is ge0/0. Consider each of these scenarios with GRE keepalives enabled on Peer B(spoke) and where tunnel mode is used for encryption. The main drawback of GRE protocol is the lack of built-in security. How do I do GRE specifically? The question was brought to me as to how to actually show the GRE tunnel itself. After that, we we will define the Tunnel Source, with IP Address or with Interface name. Interface ge0/0 faces the transport cloud and is in VPN 0 (the transport VPN). Both Peers have tunnel protection configured on the tunnel interface. 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. Learn more about how Cisco is using Inclusive Language. Go to router global configuration mode and configure the GRE tunnel using the below commands. 03:49 PM. 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. This is true even if you replace iVRF and/or fVRF with "global". There are no specific requirements for this document. So, this will change the tunnel's status about 30 seconds after a failure. (access-list permit gre host host ). This means that each tunnel endpoint does not keep any information about the state or availability of the remote tunnel endpoint. You will see that the NAT filter is built for, ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------. The tunnel can become a black-hole for packets directed into the tunnel from the side that did not have keepalives configured. David Davis has the details . How do I do GRE specifically? Packets from VPN 1 are sourced. 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. Not sure exactly what you mean. This mechanism causes the keepalive response to forward out the physical interface rather than the tunnel interface. Restrictions; Restrictions. 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 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. Without the normal "keepalive" command, what can be implemented so a router can detect and bring down the the IPsec tunnel interface if the connection was actually down? It processes the GRE keepalive packet just like any other GRE IP data packet. /24 subnet on the tunnel interface. Sometimes, because of network address translation (NAT), GRE Keepalives can be dropped. 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. This would have worked if the used Loopback was part of the General/Generic/Unnamed vrf. For more information about Unicast RPF, refer to Understanding Unicast Reverse Path Forwarding. Tunneling provides a mechanism to transport packets of one protocol within another protocol. (Community Manager-Network Infrastructure). 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. 10:24 AM. In Releases 17.2.2 and later, on Network Address Translation (NAT) enabled transport interfaces are used for local internet exit. 03-04-2019 06-22-2009 4. To determine whether the tunnel interface is up or down, use the show ip interface brief command, as shown in Figure 1. Tunnel keepalives are configurable on multipoint GRE (mGRE) tunnels but have no effect. 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. In this configuration tutorial I will show you how to configure a GRE tunnel between two Cisco IOS routers. Packet is decrypted and decapsulated and then forwarded to the IP destination in clear text. End with CNTL/Z. This was committed with Cisco bug IDCSCum34057 (initial attempt with Cisco bug IDCSCuj29996and then backed out with Cisco bug IDCSCuj99287). This signifies that this is a keepalive packet. 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. Thanks Note: In the up/down state, the tunnel does not forward or process any data traffic. Traffic forwarded through the GRE tunnel is encapsulated and routed out onto the physical interface of the router. For details on the Interface State Control Feature, see the. 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. With this change, the tunnel interface dynamically shuts down if the keepalives fail for a certain period of time. GRE tunnels are designed to be completely stateless. For example, if the tunnel source was changed to. These packets illustrate the IP tunneling concepts where GRE is the encapsulation protocol and IP is the transport protocol. So, I modified the configuration again: interface Tunnel0. We are running IPSec inside of a GRE tunnel. I know that I can show int tunnel0 and it will show me the status of the tunnel interface. 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. After it is done, we will proceed with the configuration. Thank you all for the possible answers. Because of this, dynamic routing protocols cannot run successfully over an IPsec VPN network. Tracker Status should be 'UP' in show interface VPN 0. We need to specify a source and destination IP address to build the tunnel and we'll use the 192.168.13. If there is an issue, configure an Access Control List (ACL or access-list) to see if the GRE (47) packets are going out/in. Use this section in order to confirm that your configuration works properly. Now, we will configure the GRE Tunnel on Cisco Router. Direct traffic to existing locally via VPN 0. 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. 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. 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. Keepalives on the GRE tunnel interface are used in order to solve this issue in the same way keepalives are used on physical interfaces. 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. Ensure that theendpoint-ip or endpoint-dns-name is something on the Internet that can respond to HTTP requests. In order to better understand how GRE tunnel keepalives work, refer to GRE Tunnel Keepalives. 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. 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. Verify the NAT translational filters. ---------------------------------------------------------------------------------------------------------------------------------------------, ------------------------------------------------------------------------------------------------------------------------------------------------------------------, ------------------------------------------------------------------------------------------------------------------------------. 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. - edited Enter configuration mode. 03:34 PM vEdge1 router here acts as a NAT device. 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. :-). 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. The tunnel keepalive counter is then reset to 0 and the packet is discarded. 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). Therefore, if the iVRF and the fVRF do not match then the keepalive reply packet is not forwarded back to the sender. Lastly, we define the Tunnel Destination IP address. GRE tunnels are designed to be completely stateless. 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 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 following are the generic restriction(s): The documentation set for this product strives to use bias-free language. Configure tracker under the system block. R2 (config)#interface tunnel 0. Thank you so much for the information and the explanation. 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. How to configure GRE Tunnel on Cisco Routers Configuring the Router Interfaces First of all, we need to configure the Network Interfaces on both of the Routers. For mGRE tunnel interfaces, since there is no fixed tunnel destination, some of the previous checks for P2P tunnels are not applicable. 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. Administratively down/down - This implies that the interface has been administratively shut down. The documentation set for this product strives to use bias-free language. 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. This document describes how to track transport tunnels' health status in VPN 0. You can track the status of the internet connection with the help of these. 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. With this change, the tunnel interface dynamically shuts down if the keepalives fail for a certain period of time. Thus, Peer B drops the unencrypted keepalive response and does not process it. 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. Find answers to your questions by entering keywords or phrases in the Search bar above. 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. 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. 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 is not restricted to specific software and hardware versions. Lets us see how to configure and verify the Generic Routing Encapsulation. The GRE tunnel will be used to route traffic between the 192.168.1./24 and 172.16.1./24 networks. The first step is to configure your firewall device with the appropriate tunnel interfaces. 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, The tunnel source interface is in a down state, DMVPN Tunnel Health Monitoring and Recovery Configuration Guide, RFC 1701, Generic Router Encapsulation (GRE), RFC 2890, Key and Sequence Number Extensions to GRE, Generic Routing Encapsulation (GRE) Tunnel Keepalive, Technical Support & Documentation - Cisco Systems. The GRE IP unicast packets that result can be encrypted by IPsec. I know that I can do a show crypto isakmp sa and it will show the IPSec. How to Configure GRE Tunnels on Zscaler (Step-by-Step) 16 Oct, 2020 | 0 Task Configure GRE tunnels on Zscaler router with NAT. 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 document describes scenarios where other factors can influence the state of the GRE tunnel. ERSPAN involves mirroring traffic through a GRE tunnel to a remote site. 3. In the case, "Tracker Status" will show as "Down". 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. If not, the opposite device's GRE tunnel will be down. 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. The GRE was developed as the tunneling tool which is meant to carry any of the OSI layer 3 protocol over the IP network. 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. Look for 'NAT' route entry in the RIB. 2022 Cisco and/or its affiliates. With Cisco IOS Software Release 12.2(8)T, it is possible to configure keepalives on a P2P GRE tunnel interface. Before GRE keepalives were implemented, there were only ways to determine local issues on the router and no way to determine problems in the intervening network. Yes,you can also use dynamic routing ,Only endpoint should be reachable i.e your source and destination IP. It's almost exactly per OCG p.54. 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. Using generic routing encapsulation (GRE) tunnels on Cisco routers can come in handy with Cisco router administration, and configuring GRE tunnels is relatively easy. Then you must configure the tunnel endpoints for the tunnel interface. R1 (config)#exit. For redundancy reasons, Zscaler recommends configuring multiple GRE tunnels to Zscaler. 02:51 PM 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. For more information on how other forms of keepalives work, refer to Overview of Keepalive Mechanisms on Cisco IOS. Solution You can look at the attributes for a tunnel with the show interface command. description GRE tunnel to other location. 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. Up/up - This implies that the tunnel is fully functional and passes traffic. "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. 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. Upon arrival on Router A, the packet becomes decapsulated and the check of the PT results in 0. 2. 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. This output shows the commands you use in order to configure keepalives on GRE tunnels. 03-01-2019 Since GRE is an encapsulating protocol, we adjust the maximum transfer unit (mtu) to 1400 bytes and maximum segment size (mss) to 1360 bytes. It is both administratively up and its protocol is up as well. This document explains what Generic Routing Encapsulation (GRE) keepalives are and how they work. In order to better understand how GRE tunnel keepalives work, refer to GRE Tunnel Keepalives. The route to the tunnel destination address is through the tunnel itself, which results in recursion. 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. 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). 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. It was so simple and straight forward. Its IP address is 192.23.100.0/24, and it uses the default OMP port number, 12346, for overlay network tunnels. After completing step 3, you have the following two types of addresses: Internet-routable public IP addresses, outside the GRE tunnels. 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. Greetings from the clouds. Go to the global configuration mode and enter the following commands: interface FastEthernet0/0 ip address 192.168.1.1 255.255.255. 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. All traffic exiting from the vEdge router, going either to other overlay network sites or to a public network, passes through this interface. 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. You can track the status of the internet connection with the help of these. The vEdge router splits its traffic into two flows, which you can think of as two separate tunnels. Packet is decrypted and forwarded to the tunnel interface. In Releases 17.2.2 and later, on Network Address Translation (NAT) enabled transport interfaces are used for local internet exit. 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. 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. 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. For more information on configuring the GRE tunnel that is used as the destination for the monitor sessions, see the chapter Configuring GRE Tunnels. You will see that the NAT filter is built for Internet Control Message Protocol (ICMP). 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. 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. 3. Reset/down - This is usually a transient state when the tunnel is reset by software. Customers Also Viewed These Support Documents. 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. Router1 (config-if)#keepalive By default, this keepalive command sends a packet through the tunnel to check its status once every 10 seconds. 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. 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. Customers Also Viewed These Support Documents. However, when the response is forwarded back out, it is not encrypted since Peer A uses tunnel protection on the tunnel interface. Configure nat and tracker on the transport interface. Here, we used Interface name. 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. Packet is decapsulated and then forwarded to the IP destination in clear text. 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. 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. 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? Before we begin with the tunnel configuration, we need to make sure no ACL is blocking GRE protocol (47) from the Incapsula Public IP to the Customer Public IP. Let's verify that our tunnel is working: But it was another solution. After configuring tunnel,two tunnel endpoints can see each other can verify using an icmp echo from one end. You can pick any number for the tunnel interface that you like. Here is an example of a keepalive packet that originates from Router A and is destined for Router B. This is critical on the tunnel endpoint that "reflects" the keepalive back to the requester. Router B simply decapsulates the keepalive packet and sends it back out the physical interface (S2). 11-08-2010 Because of the tunnel vrf command I had left out. To verify the state of a GRE tunnel, use the show interface tunnel command. 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. endpoint-dns-name is theDNS name of the endpoint of the tunnel interface. 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. 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. "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. 4. configure 2. Encrypted packet reaches the physical interface. In this example, a misconfigured ipc zone default configuration causes redundancy to be in the NEGOTIATION state and keeps such tunnel interfaces in a down state: In addition to the reasons previously outlined, the tunnel line state evaluation for the tunnel down reason can be seen with the show tunnel interface tunnel x hidden command as shown here: Note: There is an open enhancement to make the tunnel down reason more explicit in order to indicate that it is due to the redundancy state because it is notactive. You can track the status of the internet connection with the help of these. With this change, the tunnel interface dynamically shuts down if the keepalives fail for a certain period of time. The GRE will create the private point to point connection as same that of the VPN. Peer B generates a keepalive packet which is GRE encapsulated and then forwarded to the phyiscal interface where it is encrypted and sent on to the tunnel destination, Peer A. ip address 192.168.254.1 255.255.255.252. ip mtu 1400. This scenario is similar to Scenario 1 in that when Peer A receives the encrypted keepalive, it decrypts and decapsulates it. 1. 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. Learn more about how Cisco is using Inclusive Language. 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. Dynamic routing and tunnels combination can be a dangerous.You need to be careful when using a dynamic routing protocol bcoz it cause a GRE tunnel to avoid the recursive routing error message, which brings down the tunnel. 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. Range is from 0 to 131070. endpoint-ip or endpoint-dns-name is something on the Internet that can respond to HTTP requests. The keepalive response that Router B returns to Router A is already inside the Inner IP Header. This document describes the different conditions that can affect the state of a Generic Routing Encapsulation (GRE) tunnel 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. 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. All of the devices used in this document started with a cleared (default) configuration. 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. 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? This means that each tunnel endpoint does not keep any information about the state or availability of the remote tunnel endpoint. It is an architecture designed to provide the services in order to implement a point-to-point encapsulation scheme. However, it does continue to send keepalive packets. Good overview. New here? This is tracked by Cisco bug ID CSCuq31060. There are several commands used to monitor and troubleshoot GRE tunnels. Palo Alto GRE Tunnel. The passenger protocol is also IP (although it can be another protocol like Decnet, Internetwork Packet Exchange (IPX), or Appletalk). Increments the tunnel keepalive counter by one. 2022 Cisco and/or its affiliates. Packet is forwarded to the tunnel interface. GRE tunnels are sometimes combined with IPsec because IPsec does not support IP multicast packets. In such situations where the GRE packets must be encrypted, there are three possible solutions: 2022 Cisco and/or its affiliates. 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. "sh crypto isakmp sa" shows the IPSEC tunnel, it doesn't show you the actual data but gives you statistics on traffic transmitted. As always, this is done solely through the GUI while you can use some CLI commands to test the tunnel. Command Default None Command Modes XR Config mode Usage Guidelines 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. To configure the tunnel source and destination, issue the tunnel source {ip-address | interface-type} and tunnel destination {host-name | ip-address} commands under the interface configuration mode for the tunnel. 1. 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. 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. Configure Branch vEdges to route all unknown traffic to route using Zscaler Cloud router, this solution should be implemented using service chaining. The information in this document was created from the devices in a specific lab environment. Interface ge0/1 faces the local site and is in VPN 1. Close. 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. All rights reserved. To remove this configuration, use the no prefix of the command. This reveals the pre-made keepalive reply, which then needs to be forwarded back to the sender, BUT that forwarding is in the context of the iVRF on the tunnel interface. Encrypted packet reaches physicalinterface. 2. Keepalives enabled on Peer B cause the tunnel state on Peer B to change to up/down. 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. Since PAN-OS version 9.0 you can configure GRE tunnels on a Palo Alto Networks firewall. 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. The tunnel destination IP address must also be routable. nice one, simple and clear and easy to understand. 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. In Releases 17.2.2 and later, on Network Address Translation (NAT) enabled transport interfaces are used for local internet exit. A setting of 1400 is a common practice and will ensure unnecessary packet fragmentation is kept to a minimum. 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, GRE Keepalives and Unicast Reverse Path Forwarding, Problems with Keepalives When You Combine IPsec and GRE, Overview of Keepalive Mechanisms on Cisco IOS, Understanding Unicast Reverse Path Forwarding, RFC 1701, Generic Router Encapsulation (GRE), RFC 2890, Key and Sequence Number Extensions to GRE, Generic Routing Encapsulation (GRE) Tunnel Keepalive. 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