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Questions tagged [gre]

Generic Routing Encapsulation is a tunnelling protocol, used to carry network layer protocols through encapsulation inside others.

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Inner header and Outer header in tunnel packet

What should be at Inner header and Outer header in tunnel packet ? And then we have tunnel IP address(for both router), tunnel source IP address, tunnel destination IP address. In my understanding, ...
jacky chong's user avatar
1 vote
2 answers
284 views

what is the purpose of GRE in UDP encapsulation if its unidirectional

I was going through this feature of GRE called GRE-in-UDP encapsulation. The RFC says it is unidirectional and the tunnel traffic is not expected to be returned back to the UDP source port values used ...
RootPhoenix's user avatar
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BGP: Are Virtual Internet Exchanges more efficient than normal internet transit?

There are a number of virtual internet exchanges that BGP peer over VPN links when local presence is not available. Given the IP encapsulation overhead, and the fact that these routes still cross the ...
KJ7LNW's user avatar
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1 answer
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IPSec over L2GRE scenario

I wanted to know if this is a valid scenario and if it is possible to implement. There is a remote site A. and a Data center site B. Both A and B have a edge router which runs an IPSec tunnel. An ...
RootPhoenix's user avatar
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1 answer
24 views

Which technologies are most relevant for mobile broadband ISP bonding? [closed]

If I have edge router and core router (kind of Hub) and few ISP lines between them what are the most relevant technologies to be used for mobile broadband bonding? Expected result is: if one of ISP ...
baltasvejas's user avatar
1 vote
1 answer
421 views

Multiple GRE tunnels towards single host using anycast IP

I'm trying to build the following network architecture: Where clients try to connect to a backend server (e.g. SSH) by using a Public Anycast IP adddress (1.2.3.4), that routes the client to the ...
John's user avatar
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1 vote
2 answers
187 views

GRE Source IP Spoofing

I've read this blog post, which said that "Unlike some other protocols, the source for GRE packets cannot be faked or spoofed." But why? What is preventing me from setting an arbitrary ...
Gabscap's user avatar
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2 answers
964 views

GRE tunnel bridging and MTU mismatch

Background My workplace has 2 office areas which is only 200 meters away from each other. They have their own local networks, their own Internet connections, with routers configured to fallback to the ...
Livy's user avatar
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2 answers
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Why does IPsec not support Multicast/Broadcast?

Many sources site GRE as supporting broadcast/multicast and IPsec does not. Both GRE and IPsec are merely tunneling protocols. Therefore there is nothing inherent about tunneling protocols which ...
jester's user avatar
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4 votes
1 answer
1k views

Traffic sent to GRE Tunnel fails, but GRE Tunnel is up and OSPF adjacencies are formed

NEW INFO_7-12-21 R1#sho ipv6 rout 2001:db8:B2:200::2:2 Routing entry for 2001:db8:B2:200::2:2/128 Known via "static", distance 1, metric 0 Route count is 1/1, share count 0 Routing ...
Ben's user avatar
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1 answer
253 views

GRE, guarantee 1500 bytes MTU for end hosts

Is it possible to achieve 1500 byte MTU at the end host connections ignoring fragmentation overhead in this simple scenario using GRE. I would like to configure R1 and R2 to do the fragmentation ...
emirjonb's user avatar
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Why does GRE tunnel has lesser TxBS/RxBS than its physical interface?

Given for instance, interface Tunnel200 tunnel destination 110.153.1.1 There's a static route for 110.153.1.1, pointing to physical interface Gi0/0. Gi0/0 is only used for tunnel200. Under show ...
iridescent's user avatar
2 votes
0 answers
161 views

Router on one side of a GRE tunnel not adding OSPF route through the tunnel whilst the router on the other side is

I have configured GRE tunnel between the Dublin and Carlow routers with the following commands: //Carlow int tunnel 0 ip address 172.16.12.1 255.255.255.252 tunnel source s0/0/0 tunnel destination 87....
Anthony's user avatar
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0 answers
93 views

Does multicast over tunnels (e.g., GRE) require IGMP/MLD?

When subscribing to a multicast group on a tunnel device such as a GRE tunnel, are you supposed to participate in IGMP/MLD over that tunnel in order to announce your membership in the multicast group? ...
joshlf's user avatar
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3 votes
1 answer
250 views

What is the purpose of the Set-Link-Info message in PPTP? The RFC seems to contradict itself in regard to this message

A PPTP connection transports payload data by wrapping it into PPP and then sending it over a previously negotiated Enhanced GRE link. As per PPTP RFC, the following holds true: The encapsulated PPP ...
Mecki's user avatar
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1 answer
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GRE Encapsulation

i am learning networks and tunneling and i have problems with understanding some things about GRE. The structure of tunneling below: [Transport Protocol][ensapsulationg protocol(GRE)][encapsulateed ...
violetapple's user avatar
-1 votes
1 answer
224 views

GRE over IPSec Transport vs. Tunnel Mode

I have a misunderstanding, in this article, Figure 4-9, in Transport Mode, first header (IPsec Hdr), is correct? Should not be GRE IP Hdr? https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/...
Lucian's user avatar
  • 29
2 votes
0 answers
2k views

GRE over IPsec problem

I'm trying to build a GRE Tunnel with IPSec encryption between two routers, but I keep getting error message saying "%CRYPTO-4-RECVD_PKT_NOT_IPSEC: Rec'd packet not an IPSEC packet..." Immediately I ...
Lucian's user avatar
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0 votes
1 answer
1k views

qos inside vpn, possible or not ? I read yes and no

I am wondering if possible to do QOS (or similar action) inside vpn tunnel to a cloud server. the goal is to reserved bandwith for voip traffic. I read that you can with GRE and other people said, ...
svi08wi0er92u30r's user avatar
4 votes
1 answer
1k views

How IPsec tunnel mode work without GRE

IPsec tunnel mode encrypt a whole IP packet and sends it as the payload of another IP packet. I have always used GRE as the encapsulation layer when doing IPsec encryption. However, how could I have ...
Nakrule's user avatar
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1 vote
1 answer
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Can a VPN tunnel between routers be built with different tunnel protocol on both ends?

I have two routers and the tunnel between them is up and working well. Router1 has GRE/IP as the protocol on its tunnel interface, and as for Router2 the tunnel interface is working with IPSEC/IP. Can ...
P_K's user avatar
  • 55
1 vote
1 answer
191 views

Gre Tunnel issue

I've encountered an abnormal behavior of my GRE Tunnel between two routers Cisco. When I ping the remote physical IP of the tunnel, I reach it without any loss. But when I ping the remote Tunnel IP, I ...
Mamitiana Ra's user avatar
4 votes
1 answer
1k views

Scaling VXLAN tunnels in openvswitch

As we're creating a cluster of tens of KVM host nodes we've chosen openvswitch as our virtual network infrastructure. So we need to make isolated virtual networks between VMs on demand. I've seen ...
Amir K's user avatar
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4 votes
1 answer
820 views

Use cases for GRE over IPSEC

I'm trying to understand use cases for GRE over IPSEC. In the diagram below, each site uses GRE to encapsulate multicasts associated with OSPF. (There is still a requirement to configure SAs between ...
The_Glidd's user avatar
  • 151
2 votes
1 answer
218 views

Two channels between two switches

Is there a way to provide two physically diverse channels between two switches? I'm using two Cisco Catalysis 3560s, and I want to have two separate channels between them, with different access ...
Matt Hall's user avatar
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4 votes
1 answer
271 views

Encrypt Gre tunnel traffic

I have a gre tunnel between vyatta and juniper srx . I would like to encrypt the gre tunnel traffic if its possible. thanks Pratik
patrick's user avatar
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1 vote
1 answer
47 views

Network Security Tunnel

In the Tunnel Interface, when I edit the tunnel information, it shows: Attributes Values Tunnel Source IF10 Tunnel Destination 1.0.0.1 Tunnel Mode GRE What does IF10 ...
user51909's user avatar
3 votes
2 answers
2k views

GRE-IPsec Tunnel between Cisco Router and a Linux Router

I am trying to create a GRE/IPsec tunnel between Cisco router and a Linux Router. The tunnel is UP and active, but when I do a "show crypto session" on the Cisco router the Active SA's keep on ...
jani's user avatar
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1 vote
2 answers
1k views

TTL, GRE tunnel

I need some advise on the TTL. Currently my application vendor sets TTL to be with value 1 and he should increase it. He is thinking about value of 10, but I'm not sure that this is enough: Assuming ...
user1977050's user avatar
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1 answer
295 views

Is it possible to append custom data to every packet of a request? [closed]

For an end-to-site VPN, i.e. where a device (VPN client) is responsible for encapsulating the GRE packet, is it possible to send some custom data along with the GRE packet beyond just the standard ...
cg14's user avatar
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1 vote
1 answer
1k views

How to use ACL to deny sending packages to the GRE tunnel?

I need to do a small lab. The topology is shown on the image below: What I need to do, is make static routing so all routers can ping each neighbour's physical interface, configure a GRE tunnel ...
Peltatum's user avatar
2 votes
1 answer
436 views

PPP CHAP Authentication password requirement

What is the requirement for CHAP authentication on a PPP interface? I thought both routers had to have the same password defined, such as below. r1> username r2 password demo r2> username r1 ...
dcrearer's user avatar
  • 499
3 votes
2 answers
930 views

OSPF on tunnel interfaces

Can I keep different tunnel interfaces in different OSPF areas. Keep in mind that the physical interface is going to be the same
Fahad's user avatar
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3 votes
3 answers
987 views

Layer 3 tunnel with Dynamic IP address

I want to ask whether it is possible to configure Layer 3 Tunnel with the two end points/interfaces have dynamic IP address? If the interface IP change, the tunnel will have to be re-negotiated, is ...
user34639's user avatar
  • 313
2 votes
1 answer
109 views

Qos implementation

I want to implement Qos on a GRE tunnel and want to give priority to a destination IP 1.1.1.1 of a system from our site using WAN link. I will match the traffic through an ACL in class-map in which ...
Fahad's user avatar
  • 311
1 vote
1 answer
302 views

Secure communication between multiple sites over Internet

Does anyone know what would be the best practice to securely connect 2 or more branches with HQ over the Internet, and to allow communication between all of them (so anyone can contact anyone) if I ...
John's user avatar
  • 812
2 votes
1 answer
1k views

MPLS over GRE tunnel with Linux iproute2 [closed]

I'm trying to encapsulate IP packets in MPLS, transported over a GRE tunnel between two Linux hosts (a and b). a has 10.199.0.1 on GRE tunnel interface foo4, while b has 10.199.0.2 on GRE tunnel ...
KireinaHoro's user avatar
7 votes
2 answers
12k views

What is the difference between L2TP vs GRE

Can anyone clearly explain that what is the difference between L2TP and GRE tunnel? Is L2TPv3 Any different I am trying to understand where these protocol are used and why we use L2TP instead of ...
Terminator's user avatar
3 votes
1 answer
1k views

GRE over IPSec vs L2TP over IPSEC

Every single VPN provider offers L2TP over IPSec. What is the reason GRE over IPSec is never offered ? Is there any downfall ? It seems to be exactly the same.
pHeoz's user avatar
  • 590
2 votes
1 answer
1k views

Different tunnel modes (protected with ipsec)

I’m doing a connection of 2 sites in ipv6 over an ipv4 network. I thought to do a tunnel between this 2 sites and protect it with IPsec. But I saw there are different types of tunnels (by default GRE):...
bd123456's user avatar
3 votes
2 answers
641 views

Site-to-Site VPN tunnel configuration

I remember in uni that we implemented VPN tunnels always on the border routers and then use GRE tunnels to connect between two remote subnets. I was always told that VPN tunnels need to know the ...
Jimmy_A's user avatar
  • 133
2 votes
2 answers
149 views

Cisco IPSec questions on loopback0 and phase 2

ip multicast-routing crypto isakmp policy 2 encr 3des hash md5 authentication pre-share crypto isakmp key 123 address 1.7.129.10 ! crypto ipsec transform-set remotevpn esp-3des esp-md5-hmac ! ...
Thomas G. Lau's user avatar
1 vote
1 answer
984 views

Is a GRE tunnel sensitive to packet loss?

I tested a GRE tunnel on a lousy link, and all traffic seems lagging and slow, but when I switch to a healthy link, everything run smoothly. Is a GRE tunnel, in general, very sensitive to packet loss?...
Thomas G. Lau's user avatar
1 vote
1 answer
1k views

Regarding front door vrf concept

While reading up on front-door vrf concept here, i am just wondering , what if we made the network statements more precise/specific or used different subnets altogether, we would never have our tunnel ...
fsociety's user avatar
  • 905
1 vote
1 answer
413 views

Regarding Gre tunnel encapsulation

Please consider the attached image below: A GRE tunnel is set up between R1 and R4. Tunnel source is R1 interface having the IP address 172.16.0.1/16 Tunnel destination is R4 interface having the IP ...
fsociety's user avatar
  • 905
3 votes
3 answers
1k views

Regarding Multicast over the internet

I was going through the use cases of GRE tunnel and see that it is also used to carry multicast traffic over the internet.I understand that multicast IP belongs to class D address which is a public IP ...
fsociety's user avatar
  • 905
1 vote
0 answers
4k views

Tunnelling difference over VXLAN vs NVGRE vs GENEVE [closed]

Any bullet points that are most imp points when it comes differences between these three tunnellings VXLAN/NVGRE/GENEVE in networks. Found some notes here, anything that you may like to add would be ...
Vasu's user avatar
  • 255
0 votes
1 answer
1k views

More Fragment flag and Frag Offset field after GRE fragmentation

If the length of a packet by attaching GRE-IP header results in bigger size than router MTU, what happen on More Fragment Flag and Frag Offset field of that packet?
kikilinux's user avatar
2 votes
3 answers
6k views

GRE over IPsec between Juniper SRX100 and Fortigate 100D

I need assistance configuring VPN setup between Fortigate and Juniper devices (GRE over IPSec). I have the topology as follows: What I need to do is create a route-based IPSec tunnel between the ...
Alex's user avatar
  • 837
2 votes
2 answers
1k views

Packet flow in GRE Tunnel

In the below image what would be the ip address in the outer ip header when packet goes from R1 to R2. If the ip address in the outer header is 172.16.0.1 , how does it travels the internet as its not ...
Logesh's user avatar
  • 21