Generic Routing Encapsulation (GRE) is a tunneling protocol, developed by Cisco.

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Debian forward through NAT EOIP GRE

eth0 = WAN eth1 = LAN to forward any port through nat I use e.g: iptables -t nat -A PREROUTING -p tcp -d 79.188.31.34 --dport 8291 -j DNAT --to-destination 192.168.0.36:8291 and it works, but ...
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Can different networks connected by MPLS run the same OSPF area? [migrated]

I was wondering if two different OSPF areas connected via an MPLS/GRE tunneled link run OSPF across them? May be keeping the interconnecting MPLS/GRE routers in OSPF backbone area 0?
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Using my IPs on OVH server via GRE

I can't route my IPs into a OVH server, can you help me to find the problem? Mikrotik GRE IP: 192.168.55.10 OVH Server GRE IP: 192.168.55.20 GRE iface name: ali1_fr1-ovz1 IP to route from Mikrotik to ...
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21 views

GRE Routing Troubles

I will try to be concise and fully explain my situation here. I was handed a project after my client had a falling out with a previous developer. We had a defunct copy of his system, and I am trying ...
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62 views

Listening “through” GRE Tunnel

Currently I'm looking to learn about using GRE Tunnels and I have the following scheme: Server1 (200.1.2.3) ----> Server2 (190.1.2.3) Both servers have public IPs Then I've setup a GRE Tunnel with ...
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314 views

WCCP and Squid, and Tunnels

I'm trying to configure WCCP + Squid with the following documentation: http://www.crypt.gen.nz/papers/cisco_squid_wccp.html I have a cisco switch, a test client, and a squid proxy server. I think ...
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62 views

What are pro and cons of gre and vlanx?

I need to connect two openvswitches in order to make a vlan. So, I would simply create trunk ports for certain vlan ids...ok. In order to connect two openvswitch, now, these ports can be either gre ...
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95 views

How is my GRE-Tunneled packet being routed? [closed]

I'm trying to figure out exactly what is happening when I create a GRE tunnel. My network looks like this (-> means directly connected): Computer A (eth0: 10.0.1.1) -> (eth0: 10.0.1.2) Router B ...
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2k views

Transparent Ethernet over GRE not forwarding traffic

I am running on Linux 2.6.30.9 and have been trying to setup a transparent ethernet over GRE tunnel. The network topology used is as follows: I want to bridge PC1 and PC2 using Transparent Ethernet ...
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408 views

IP/GRE compiled in kernel but gre0 interface doesnt exist

Im trying to create IP over GRE tunnel but i get No such device: ip tunnel add gre0 mode gre remote 192.168.152.22 local 192.168.152.21 ttl 255 ioctl: No such device I have compiled GRE support in ...
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228 views

Martian packet errors with physical adapter's IP address on GRE tunnel

I'm very new to the networking world (most of my time is spent as a developer), so I could very well be missing something simple. TL;DR version: I get 'martian packet' errors on response traffic when ...
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308 views

DMVPN and OSPF (two tunnels dynamic routing)

please help me to resolve the problem with routing between dmvpn GRE tunnels. I've got a DMVPN HUB and SPOKE topology. HUB has public ip address in internet. SPOKE has two ISPs for redundancy. I've ...
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191 views

Using public interfaces on a server connected through a GRE tunnel

I'm pretty new to networking so please forgive any terminology mistakes. I have 2 servers connected with a GRE tunnel. Server1 (10.0.0.1) ----> Server2 (10.0.0.2) I want to be able to bind to the ...
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564 views

GRE keepalive with Linux and RouterOS

I have a Linux host and couple of routerboadrs. I created a GRE tunnel, but Linux does not answer keepalive packages. Then router mark gre connection as unreachable, so I cant send to Linux host from ...
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43 views

GRE tunnel / Route traffic based on which domain the user is trying to access

Imagine this kind of setup. 5 servers. 1 server will be the "front-end", all the traffic has to go through it first before going to the 4 other servers. I don't want people to know the IPs of the ...
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2k views

GRE: read from PTY failed error when connecting multiple clients to PPTP

I have just installed a pptp server and now I can make it work. The problem is, it can only be connected to by one client. How do I set it up so that it will allow multiple users? Here is the error ...
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GRE tunnel not allowing Internet

I'm starting with GRE tunneling and I got two machines connected between them-self: tun0 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00 inet ...
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1answer
297 views

How GRE traffic finds way after arrive GRE remote end points (in open vswitch)?

I'm quite new to both network and open vswitch, I'm not sure whether this question is more relevant to open vswitch(ovs) or gre. belows are ovs settint commands. There are two hosts. Each host has ...
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1answer
174 views

GRE tunneling in vmware vsphere guest [closed]

Is it possible to make a GRE tunnel between a dedicated linux machine and a vmware vsphere guest VM (running debian wheezy)?
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141 views

GRE tunnel to a cPanel server shows default cPanel page

I have a DDoS protected VPS from BuyVM and I have a GRE tunnel to my cPanel server. My nameservers are set to the DDoS filtered IP. When I add a account on cPanel with the filtered IP as website IP, ...
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211 views

Ubuntu GRE local ip address, wan ip of router, or ip of ubuntu server

I have an ubuntu server behind a router that I am configuring to have a GRE tunnel to another remote device across the interwebs. in the config, I add the line: pre-up iptunnel add tun1 mode gre ...
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582 views

openvswitch: connecting two virtual private networks on two different machines with gre/ipsec

Here is the setup: We have a hardware (server) that presents a service to the customer (or "outside world", if you so will). Internally, the services and functions are distributed over several virtual ...
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251 views

How to troubleshoot GRE tunnel issues?

I commonly run into issues where a GRE tunnel (CentOS server to server, not router based) works and pings fine from both ends but the IP / Range being tunneled does not function. This almost always ...
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151 views

How to check for GRE Tunnels [closed]

Is there a way to check for GRE Tunnels? I've heard spammers will use GRE tunnels to send mail from a central machine out of another and would like to check for possible GRE tunnels.
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225 views

Why two addresses in configuring a GRE tunnel?

As I can find in this support document, in order to configure a GRE tunnel between two routers R1 and R2, I issue the following sets of commands (mtu and mss omitted), R1 R1(config)# interface ...
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298 views

Redirect SSH traffic through GRE tunnel

I'm trying to redirect all local connections with destination matchs port 22 to specified tunnel using iptables MARK, but, something is going wrong. 1.1.1.1 my public address 2.2.2.2 tunnel public ...
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1k views

How to force certain traffic through GRE tunnel?

Here's what I do. Server (public internet is 222.x.x.x): echo 'net.ipv4.ip_forward=1' >> /etc/sysctl.conf sysctl -p iptunnel add gre1 mode gre local 222.x.x.x remote 115.x.x.x ttl 255 ...
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724 views

Linux/Vyatta failover with GRE and OSPF/BGP

I have strange problem with routing failover in scenario: I'm trying do this failover via ospf or bgp, in both happens the same strange behavior with tunnels: For 192.7.0.0 TUN providing default route ...
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656 views

OpenNHRP configuration without IPsec

I'm attempting to use OpenNHRP on a linux box to connect with a Cisco Router. I want to allow GRE tunnels from the linux box to the Cisco router dynamically, but I'm not implementing DMVPN on the ...
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5k views

PPTP connection fails with errors 800/806

I've got a client (Server 2008 R2) that won't connect to our production environment PPTP VPN server (Server 2003, running RRAS). The server is behind a firewall that has TCP1723 open as well as GRE. ...
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Setting up a GRE tunnel on a Cisco ASA 5505 [duplicate]

Possible Duplicate: Set up a GRE tunnel with Cisco PIX-506 v6.3 I'm trying to establish one half of a GRE tunnel, the other being configured by my service provider. I have a Cisco ASA 5505 ...
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1k views

using a gre tunnel as default route

I have two private networks (A, B) that connects via another company's private network (C). Network A has internet access. I want to make a tunnel between B and A that goes through C. Then network B ...
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341 views

Set up a GRE tunnel with Cisco PIX-506 v6.3

I'm trying to establish one half of a GRE tunnel, the other being configured by my service provider. I have a Cisco PIX-506-E running Firewall version 6.3(5). Provider Router Public IP: 8.8.8.8 My ...
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2k views

Multiple GRE tunnels on the same host, only one routes incoming packets

I'm having a routing problem on CentOS 6.2 (kernel 2.6.32-220) Here's the setup: One host is on my local network. It's talking to two nearly identical hosts at a remote location. The two remote ...
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953 views

What's the difference between GRE and IPIP tunnel?

And which one is better for connecting two linux machines?
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369 views

how to forward all traffic over a GRE over IPsec VPN on cisco routers?

i have 2 cisco ISR 2821 and 2811 and they are connected over a site to site GRE over IPsec vpn. my question is that, how can i forward all traffic or web traffic to the other router? thanks
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297 views

How to forward all GRE traffic to a particular network interface?

I want to forward all GRE traffic (IP protocol 47) coming on eth2 to br0 on my machine. How can I do that?
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287 views

GRE debug: “adding 0 encap bytes”?

What this debug message actually means? Shouldn't encapsulation add 24 extra bytes or not? For what reason encapsulation is not adding bytes to original packet in this debug message? Dec 28 ...
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1k views

GRE Tunnel between Linux server and XP client

I want to set up a simple unencrypted tunnel between a linux-server (running SLES9) and a client (running XP SP3). The reason for this is that there are many network devices in between and the client ...
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755 views

Gre Tunnel Cisco Linux traffic forwarding

I setup a gre tunnel a cisco router and a Linux machine, the tunnel interface in the Linux box named pic. Well i have to forward traffic coming from cisco through the Linux box. the rules i've set in ...
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159 views

GRE Encapsulation and Multicast

How does GRE Encapsulation actually send multicast traffic? My CISCO textbook tells me that the multicast packet is carried inside a unicast packet. My understanding is: Multicast packet, say for ...
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253 views

cannot ping through gre tunnel

This question has been merged I have 4 machines machine 1 have ip address 172.13.0.40/24 machine 2 have two ip address 172.13.0.1/24 and 172.12.0.1/24 machine 3 have two ip address ...
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Is it possible to find out the make/model of the router remotely?

First a little background. My company is renting some servers at the Terremark cloud. As we want to connect our servers to the infrastructure of a mobile carrier in order to restrict our end users to ...
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2answers
3k views

GRE Tunnel over IPsec with Loopback

I'm having a really hard time trying to estabilish a VPN connection using a GRE over IPsec tunnel. The problem is that it involves some sort of "loopback" connection which I don't understand -- let ...
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4k views

Cannot Delete GRE Tunnel

I am configuring a GRE tunnel in Linux 2.6.26 and I've been facing a very strange problem for which I could not find any solution. I have created a GRE tunnel called gre0, but no matter what I do, I ...
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1k views

Routing subnet over GRE tunnel

Im trying to configure a GRE over IPSec connection between two subnets. The IPSec tunnel is opened and now I want to add a GRE tunnel over it: ip tunnel add GRE01 mode gre remote 10.244.0.1 local ...
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3answers
318 views

Does a router have to explicitly support GRE in order to pass those connections?

I have replaced a mess of Cisco routers with a single Dell PowerConnect 6224. These routers serve (and served) public IPs to clients, and just acted as routers to the upstream provider. Prior to the ...
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628 views

How to enable debug logging for GRE?

How to enable debug logging for module ip_gre on linux 2.6?
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643 views

GRE over IPSec behind FW

I have a checkpoint S-Box which is a gateway for network 192.168.0.0/24. Internal IP is 192.168.0.1. On the S-Box configured static VPN tunnel with local IP 10.x.x.x and remote 10.y.y.y. I need to ...
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Multiple GRE NAT router

Does there exist a router that supports multiple GRE connections over NAT? Im currently running pfSense, and it only supports 1 at a time. I understand why, its just a drag as there are multiple ...