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

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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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553 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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2k 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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528 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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1answer
795 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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30 views

Load balancing between two (or more) GRE tunnels

I have a hosted service (think zScaler™) that is having me send my traffic to it via GRE tunnels. I am given two appliances and want to load balance my traffic between the two tunnels. I could ...
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50 views

Amazon Linux - iptables NAT rules not matching GRE traffic

I'm trying to prototype something in AWS VPC/EC2, but I can't get my NAT rules to work. I have the following setup (all instances running the Amazon Linux AMI): GRE Tunnel between instances ...
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1answer
114 views

Set up transparent GRE/VPN to redirect all traffic to an External datacenter

I need to setup an existing server with multiple IPs (from OVH) to send all the traffic (through VPN or GRE tunnel) to an external server that has only 1 Public IP. I want to make it like every local ...
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358 views

TLS-intolerant sites suddenly not working

About 2 weeks ago users started reporting that they were unable to access two https-only sites. When I inspected these sites I found they were completely intolerant to TLS. In order to connect, SSL3 ...
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1answer
414 views

GRE Tunnel in CentOS

How to create a GRE Tunnel in CentOS pointing all connections to server A for the server B? I have a public server with DDoS protection and need to use this as a firewall to filter acess to the other ...
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580 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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2k 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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What could cause racoonctl to show a Phase2 count higher than the number of ports racoon is listening on?

In my setup I have some EC2 instances in different regions linked by GRE tunnels, using ISAKMP via racoon. This setup is inherited, so bear with me if I fumble with terminology. Sometimes I get weird ...
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39 views

Ethernet over GRE bridging - Proxmox

I'm trying to install two proxmox on Online.net server's, and I just realized that their RPN feature doesn't work at all like the OVH vRacks. Since I need the different VM's on both hypervisors to be ...
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24 views

Cisco 1941 EIGRP UP DOWN

We have two cisco routers 1841 and 1941. The 1841 keeps generating "holding time expired" and "interface goodbye recieved" about its neighbor the 1941. The VPN IPSec protocol seems to stay up. ...
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28 views

internet access for system over multiple hops of ipsec using GRE and OSPF

I have the following setup: linux client @ 172.16.10.68 linux gateway @ 172.16.10.69, ipsec tunnel to aws box #1, gre tunnel 10.254.0.0/30 aws box #1, ipsec tunnel from linux gw, ipsec tunnel to ...
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40 views

IP Tables forwarding tun0 over gre1 (OpenVPN)

I haven't found a very descriptive thread (and sorry if there is one in existence - in my several hours of searching I've found nothing to my specific situation). My main issue here is getting my ...
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286 views

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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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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408 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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85 views

TCP Out-of-order packets over GRE causing disconnect

I'm experiencing an issue with a small percentage of TCP connections over a GRE tunnel between two servers. The topology is basically Internet <-> GRE Tunnel <-> Backend The GRE tunnel and the ...
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178 views

Strongswan IPsec: routing arbitrary subnets over /32 IPsec endpoints

I have a basic setup between two sites A (FreeBSD, 10.0.0.1/24 nat'd to 1.1.1.1), B (Linux, 2.2.2.2), with only A behind NAT. I've only been able to get it working in tunnel mode. Here's my ...
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49 views

Openbsd set connect on PPTP server behind packet filter

I have firewall on OpenBSD use Packet Filter and behind him MS Windows server with PPTP server. I need allow connect this PPTP server from internet. I set in OpenBSD: net.inet.gre.allow=1 ...
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63 views

GRE Tunnel to Add IPs

Okay, here's the situation: server1 - my "main server" server2 - think of it like a proxy IP1 - main IP of server1 IP2 - main IP of server2 IP3 - additional IP of server2 I have, for years and ...
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181 views

AWS VPC: Windows server 2012 R2 GRE tunneling to Linux based Peer VyOS

I am asking this question after having spent some time googling and trying to work out some issues which I have with a Windows GRE tunnel in our 2nd environment (amazon AWS VPC) to a router in our ...
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40 views

Add FQDN name in gre tunnel in Linux

Since aruba, cisco, etc all support add FQDN as gre tunnel's endpoint, can I do the same thing in linux via iproute2 or something else? Now, when I type a FQDN at ip tunnel, it just says that it's ...
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72 views

Set up a GRE tunnel over multiple communication channels

I am in a situation where I would like to be able to set up a GRE tunnel running seamlessly over GPRS or Wifi in linux 2.6, preferring of course Wifi whenever available. So on one host I have two ...
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240 views

Multicast on mGRE tunnels in Debian not working

I'm trying to setup multipoint GRE tunnels within 4 debian-based servers geographically distributed. Network configured, and hosts can see ping or ssh to each other by local IP. But I cannot get ...
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68 views

GRE Tunnel Collapsing in One Direction

This is a related question to another thread I posted. I'm having an issue where my GRE tunnel is collapsing in one direction, but can be reopened by ping the other server using the GRE Interface. ...
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120 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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307 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 ...