9
votes
Accepted
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 ...
- 1,723
5
votes
Accepted
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 ...
- 8,826
5
votes
Accepted
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 ...
- 67.1k
4
votes
Accepted
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 ...
- 82.7k
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.
- 19.5k
4
votes
Accepted
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 ...
- 17.1k
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 ...
- 82.7k
3
votes
Accepted
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,...
- 969
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 ...
- 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 ...
- 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 ...
- 9,421
3
votes
Accepted
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 ...
- 67.1k
3
votes
Accepted
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.
- 9,421
3
votes
Accepted
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 ...
- 82.7k
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 ...
- 8,826
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 ...
- 66
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 ...
- 733
2
votes
Accepted
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 ...
- 98.8k
2
votes
Accepted
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 ...
- 1,383
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-...
- 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, ...
- 132
2
votes
Accepted
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 ...
- 67.1k
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 ...
- 19.5k
2
votes
Accepted
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 ...
- 82.7k
2
votes
Accepted
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 ...
- 82.7k
2
votes
Accepted
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) ...
- 82.7k
2
votes
Accepted
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 ...
- 157
2
votes
Accepted
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 ...
- 31.8k
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 ...
- 2,070
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