Cisco gre tunnel static route

GRE Tunnel Keepalives

We also call this encapsulation. We can tunnel these routing protocols so that the HQ and branch router can exchange routing information. Let me show you a topology that we will use to demonstrate GRE:. Above we have 3 routers connected to each other. Both routers are connected to the Internet, in the middle on top there is an ISP router. We can use this topology to simulate two routers that are connected to the Internet. Let me show you the basic configuration of these routers so that you can recreate it if you want:. They will be unable to reach the networks on each others loopback interfaces however. You can pick any number for the tunnel interface that you like. The default tunneling mode is GRE. There we go…they can ping each other without any issues! Explained As Simple As Possible. Full Access to our Lessons. More Lessons Added Every Week! Tags: GRETunnel. When you use the tunnel source command, you can define an interface or an IP address. When you use the interface, the router will check for the IP address on the interface and use that so the end result is the same. When you use this to tunnel something over the Internet, we typically use the public IP address on the outside interfaces for this. You can use loopbacks as the source addresses if you want redundancy. Once the GRE tunnel is up, it acts like a regular interface. The advantages provided by GRE tunnelling or any kind of network tunnelling is that it allows us to interconnect two remote sites over a third network as if those remote sites are directly connected to each other. You have a subnet of Those two offices will never be able to communicate directly with each other over the Internet, because the Internet uses its own IP address ranges and it does n. Ask a question or join the discussion by visiting our Community Forum. Skip to content Search for: Search. Let me show you a topology that we will use to demonstrate GRE: Above we have 3 routers connected to each other. Tunneling is a concept where we put 'packets into packets' so that they can be transported over certain networks. Normally it w. You may cancel your monthly membership at any time. No Questions Asked! Forum Replies Hi Adam, Did you see this tutorial? This explains exactly how the recursive routing occurs. What would be the difference? Continue reading in our forum. Hi Adrian, When you use the tunnel source command, you can define an interface or an IP address.

GRE Tunnel Configuration with Cisco Packet Tracer


The two RTRs are geographically separated. It is easy to understand and no need for some extra cost of Dynamic routing. It will also help you to maintain a failover case:. RTR2 Configuration:! You are using the public Internet, so just a GRE tunnel is vulnerable. Here is an example of an SVTI:. Here, if we will convert default to floating default route than GRE will go down. Is there any solution without PBR? Yes, he can configure a static route instead of default route but it is not recommended in case of tunnel fail. There have been some interesting and useful responses and I would like to address a few points. The suggestion of configuring the GRE tunnel and running OSPF over the tunnel is nice and would certainly work and achieve the goal of the original poster. But the response suggesting keeping the solution simple and suggesting that OSPF might be overkill has some validity. But if we want to really keep it simple then there is no need for Policy Based Routing. If you simply configure the GRE tunnel, configure a static route for the tunnel destination using the provider address as the next hop, and configure a static default route using the tunnel peer address as the next hop should be all that is required. One factor to consider in this discussion is whether to use a dynamic routing protocol or to use static routing. To provide good advice we need more information about the environment. Dynamic routing is appropriate for environments that need to react to changes in the routing environment and to be able to select alternate paths if the primary path has problems. When there are not alternate paths then dynamic routing has no advantage and static routing is adequate. So which kind of environment is this? There is also a question about using GRE without encryption or using vpn. To provide good advice we need more information about the environment and the requirements. As mentioned in one of the responses sending IP traffic over a simpleGRE tunnel does not provide any protection for the traffic. If the traffic between sites contains sensitive information that needs protection then certainly vpn is the better choice. But if there is not much concern about protecting the content then a simple GRE tunnel is easier and involves less overhead and would seem to achieve the goal stated in the original post. Thanks for your response and here, My question is still open "Yes, he can configure a static route instead of default route but it is not recommended in case of tunnel fail". As per my interest in the design, I will keep internet failover. If my tunnel went down then at least the internet must work. What do you think on this point? And most of the customers I have dealt with feel the same. One of the things I have learned is that it is important to understand what the customer wants and to provide that. One of the things I was saying in my response is that we need to understand the original poster and what is their requirements.

Setting up a GRE Tunnel on a Cisco Router


The Cisco series integrated services fixed-configuration routers support the creation of virtual private networks VPNs. Cisco routers and other broadband devices provide high-performance connections to the Internet, but many applications also require the security of VPN connections which perform a high level of authentication and which encrypt the data between two particular endpoints. Two types of VPNs are supported—site-to-site and remote access. Site-to-site VPNs are used to connect branch offices to corporate offices, for example. Remote access VPNs are used by remote clients to log in to a corporate network. The example in this chapter illustrates the configuration of a site-to-site VPN that uses IPSec and the generic routing encapsulation GRE protocol to secure the connection between the branch office and the corporate network. Figure shows a typical deployment scenario. VPN client—Cisco series integrated services router. LAN interface—Connects to the Internet; with outside interface address of VPN client—Another router, which controls access to the corporate network. LAN interface—Connects to the corporate network, with inside interface address of 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. Traffic forwarded through the GRE tunnel is encapsulated and routed out onto the physical interface of the router. When a GRE interface is used, the Cisco router and the router that controls access to the corporate network can support dynamic IP routing protocols to exchange routing updates over the tunnel, and to enable IP multicast traffic. Note When IP Security IPSec is used with GRE, the access list for encrypting traffic does not list the desired end network and applications, but instead refers to the permitted source and destination of the GRE tunnel in the outbound direction. All packets forwarded to the GRE tunnel are encrypted if no further access control lists ACLs are applied to the tunnel interface. VPN configuration information must be configured on both endpoints; for example, on your Cisco router and at the remote user, or on your Cisco router and on another router. Perform the following tasks to configure this network scenario:. The priority is a number from 1 towith 1 being the highest. Specifies the encryption algorithm used in the IKE policy. Specifies the hash algorithm used in the IKE policy. The example specifies the Message Digest 5 MD5 algorithm. Specifies the authentication method used in the IKE policy. Exits IKE policy configuration mode, and enters global configuration mode. Perform these steps to configure the group policy, beginning in global configuration mode:. Creates an IKE policy group that contains attributes to be downloaded to the remote client. Specifies the IKE pre-shared key for the group policy. Exits IKE group policy configuration mode, and enters global configuration mode. Perform these steps to enable policy lookup through AAA, beginning in global configuration mode:. Specifies AAA authentication of selected users at login, and specifies the method used.

Cisco 1800 Series Integrated Services Routers (Fixed) Software Configuration Guide


GRE is developed by Cisco System. In order to configure the GRE tunnel, you must need connectivity between two remote routers through static Public IP address. GRE usages IP protocol number By default, GRE does not perform any kind of encryption. GRE is initially defined in rfc I have two different routers in two different locations. Router R1 has Public IP R1 and R2 can communicate using their Public IP addresses. We will use another subnet So, configuring the GRE tunnel by checking the connectivity between routers. Just open the console of nay router and ping another end router. First of all, we need to configure the Network Interfaces on both of the Routers. Go to the global configuration mode and enter the following commands:. Now, we will configure the GRE tunnel interface. It is always recommended to provide a different subnet for both the peer ends. On router R1, I configured tunnel interface and IP address Along with the IP address, you also need to configure local and remote public IP addresses as well. Now, we need to configure a static route for the Peer LAN subnet. We need to define the tunnel interface as an exit interface for the destination network. Just, go to router global configuration mode and run the following command. Now, we have finished the configuration between both the GRE Neighbors. Now, we will initiate a ping for the Router R1 and verify our configuration. If your configuration is perfect, you will receive the ping response messages. R1 ping

Generic Routing Encapsulation

This document describes the different conditions that can affect the state of a Generic Routing Encapsulation GRE tunnel interface. GRE tunnels are designed to be completely stateless. This means that each tunnel endpoint does not keep any information about the state or availability of the remote tunnel endpoint. 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. 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. 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. When a tunnel interface is first created and no other configuration is applied to it, the interface is not shut by default:. 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. 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 :. Normally, a P2P GRE Tunnel interface 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. 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 might be configured. This document describes scenarios where other factors might influence the state of the GRE tunnel. 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. 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. Keepalives on the GRE tunnel interface are used in order to solve this issue in the same way keepalives are used on physical interfaces. With this change, the tunnel interface dynamically shuts down if the keepalives fail for a certain period of time. For mGRE tunnel interfaces, since there is no fixed tunnel destination, some of the previous checks for P2P tunnels are not applicable. Here are the reasons an mGRE tunnel's line protocol can be in a down state:. This added an additional check, which keeps such tunnel interfaces in the line protocol down state until the redundancy state changes to ACTIVE. In addition to checking 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 not being active. Skip to content Skip to footer. Available Languages. Updated: August 8, Contents Introduction.

GRE Tunnels and Recursive Routing



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