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9 votes
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What is the difference between L2TP vs GRE

L2tp and GRE are totally diffrent protocols GRE is a simple IP packet encapsulation protocol. a GRE tunnel is used when packets need to be sent from one network to another, without being parsed or ...
Mr.lock's user avatar
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5 votes
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Use cases for GRE over IPSEC

Running multicast or multicast based routing protocols does not necessarily require GRE-over-IPsec. "Tunnel based" or "route based" VPN (tunnel mode ipsec ipv4 a.k.a. IPsec Virtual Tunnel Interfaces ...
Marc 'netztier' Luethi's user avatar
5 votes
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How IPsec tunnel mode work without GRE

So what's the difference between GRE+IPsec and IPsec only? In GRE+IPsec the original IP packet is encapsulated in a GRE tunnel packet. The GRE packet is then encapsulated in the IPSec packet. The ...
Ron Trunk's user avatar
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4 votes
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Regarding Multicast over the internet

Why is multicast not supported over the internet ? There is only one multicast range. Sharing that range across the Internet would mandate an address allocation scheme akin to public unicast ...
Zac67's user avatar
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4 votes

OSPF on tunnel interfaces

Yes, what's important to the router is layer 3 interfaces. You can think of a layer 3 interface as a logical construct, which can be be tied to a VLAN, physical or tunnel interface.
JFL's user avatar
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4 votes
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Scaling VXLAN tunnels in openvswitch

You could solve this by running VXLAN on the hypervisor using software like FRR. That would imply that you run a full mesh BGP setup between your hypervisors, or use route reflectors. Then, you can ...
Teun Vink's user avatar
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4 votes

GRE, guarantee 1500 bytes MTU for end hosts

When there's additional overhead eating into the MTU size, there are three basic approaches: increase outer MTU/frame size, decrease inner MTU, or live with fragmentation. Routers may fragment (for ...
Zac67's user avatar
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3 votes
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Regarding front door vrf concept

You have to at least create static host routes pointing to the endpoint IPs of your tunnel to make sure they remain established. Front door vrf is handy if your endpoint is using a dynamic IP address,...
John K.'s user avatar
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3 votes

Regarding Multicast over the internet

The multicast use case for the GRE tunnel is typically to allow the routers on either side of the link to run a routing protocol between each other. Say you've got an office in Boston with 10 IP ...
Sheep's user avatar
  • 31
3 votes

Regarding Multicast over the internet

A1: Because normally you need to run PIM protocol in order to achieve end-to-end connectivity for multicast network. PIM doesn't normally run between ISP boundaries. It would be pretty complicated and ...
ar_'s user avatar
  • 1,133
3 votes

Splitting Data and Voice by creating GRE tunnel for Data, using overhead for Voice

Do not create GRE tunnels - this will appear to your L3 network as two distinct paths to the same site, meaning you'll end up with extra routing complexity you don't need. GRE will also add overhead ...
Benjamin Dale's user avatar
3 votes
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Why source and destination addresses should match in GRE tunnel?

One simple explanation is that R3 needs to determine which tunnel the packet came from. It's often that there may be more than one tunnel terminating on the same interface on R3. EDIT: More ...
Ron Trunk's user avatar
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3 votes
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Gre Tunnel issue

There is not a lot to go on in your output there, but try removing qos pre-classify from the tunnel interface - it may be that you have misconfigured qos settings causing traffic to be dropped.
Benjamin Dale's user avatar
3 votes
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qos inside vpn, possible or not ? I read yes and no

Possible? Generally, yes. However, you need to consider the tunnel outside as well. How effective QoS works depends on a large number of parameters only some of which you have control over. QoS ...
Zac67's user avatar
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3 votes

GRE over IPSec Transport vs. Tunnel Mode

No, it should not be GRE. In both cases as shown (IPSec tunnel mode and transport mode), it's always IPsec encrypting GRE (and whatever it may contain). Therefore, the outermost header has to be ...
Marc 'netztier' Luethi's user avatar
2 votes

Packet flow in GRE Tunnel

While Configuring GRE tunnel you may have specify source and destination address. That Source and destination IP are 1.1.1.10 and 2.2.2.10. These IPs will be routed in the internet and helps to bring ...
Saurav_Shaw's user avatar
2 votes

Packet flow in GRE Tunnel

In the outer IP header, it would definitely be 1.1.1.10 / 2.2.2.10, as this is what is used to route the packet to the tunnel endpoint. Note that you may not even need IP addresses on the tunnel ...
jcaron's user avatar
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2 votes
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Why specify the source tunnel address?

Often, you may want to use a loopback, since it will never go down, as the source because you may have a backup path to the other end. It is not always the right thing to do to use the exit interface ...
Ron Maupin's user avatar
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2 votes
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Two GRE tunnels in one subnet

A 'normal' GRE tunnel is a used as a point-to-point connection. A /30 (or even /31) would be a better use of your subnet space. There also exist multipoint GRE tunnels, such as DMVPN. Here you can ...
JelmerS's user avatar
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2 votes

Splitting Data and Voice by creating GRE tunnel for Data, using overhead for Voice

First, if the three sites connect to the data center over WAN circuits with any appreciable latency, layer-2 connections are not a very good idea. Layer-2 must send all the broadcasts across the layer-...
Ron Maupin's user avatar
  • 98.8k
2 votes

Support GRE tunneling router or firewall

Although GRE is developed by Cisco, it doesn't mean that other vendors don't support it. It's became kinda standard in the industry and I have not seen any single vendor who doesn't support it, ...
Mo Moghaddas's user avatar
2 votes
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Regarding Gre tunnel encapsulation

Q1: Inner Source: 1.1.1.1 Inner Dest: 4.4.4.4 Outer source: 172.16.0.1 Outer Dest: 192.16.0.2 Q2: The source address is the tunnel source, 172.16.0.1 (for R1-R4 traffic). The inner and outer ...
Ron Trunk's user avatar
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2 votes

Qos implementation

Unless you have a specific agreement with your ISP and the whole path is under the control of you and your ISP, no there's no QoS on the Internet. All Internet router will simply ignore all QoS ...
JFL's user avatar
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2 votes
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How to use ACL to deny sending packages to the GRE tunnel?

On R0 you need to deny ip 172.16.0.0/24 172.17.0.0/24 for the appropriate port/VLAN and vice versa on R1 deny ip 172.17.0.0/24 172.16.0.0/24 Make sure you put a 9999 permit ip any any (or ...
Zac67's user avatar
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2 votes
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Two channels between two switches

Depending on your actual goal, there are several possibilities. Load balancing your flows 'at will' requires them to be split across different VLANs or very delicate fine tuning. VLANs with spanning ...
Zac67's user avatar
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2 votes
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Why does GRE tunnel has lesser TxBS/RxBS than its physical interface?

(from comment) The overhead is only visible (and countable) outside the tunnel. Roughly you should see (outer packet header + GRE header) * number of packets more traffic on the outside (physical) ...
Zac67's user avatar
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2 votes
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Traffic sent to GRE Tunnel fails, but GRE Tunnel is up and OSPF adjacencies are formed

It turns out the Palo Alto tunnel inspection policy was the root of the issue. Once I disabled the policy in each firewall, I was able to ping through the tunnel. I used traceroute to verify from ...
Ben's user avatar
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2 votes
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Why does IPsec not support Multicast/Broadcast?

GRE and IPsec aren't one-to-many technologies. Thus multicast/broadcast doesn't have much meaning. That said, there are ways to push multicast across either system -- both sender and receiver -- but ...
Ricky's user avatar
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2 votes

GRE tunnel bridging and MTU mismatch

Moving to using jumbo frames on the 'WAN' link between the networks (where you are using GRE for some unexplained reason) would also work since there would no longer be an issue with the frame size ...
FrameHowitzer's user avatar

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