GRE Tunnels for Layer 3 VPNs | Junos OS (2024)

FAQs

Is GRE VPN a layer 3 VPN? ›

Junos OS allows you to configure a generic routing encapsulation (GRE) tunnel between the PE and CE routers for a Layer 3 VPN. The GRE tunnel can have one or more hops.

GRE is an IP encapsulation protocol that is used to transport packets over a network. tunnels are in IPv4 Layer-3 mode. IPv6 encapsulated in IPv4 and IPv4 encapsulated in IPv6 are not supported.

Multicast traffic forwarding – GRE tunnels can be used to forward multicast traffic, whereas a VPN cannot. Because of this, multicast traffic such as advertisem*nts sent by routing protocols can be easily transferred between remote sites when using a GRE tunnel.

Zscaler supports a maximum bandwidth of 1 Gbps for each GRE tunnel if the internal tunnel endpoint IP addresses are not source network address translated (NATed). If the internal tunnel endpoint IP addresses are source NATed, then Zscaler can only support up to 250 Mbps of traffic for each tunnel.

A Layer 3 VPN is composed of a set of customer sites that are connected over a service provider's existing public Internet backbone. A peer-to-peer model is used to connect to the customer sites, where the service providers learn the customer routes on peering with the customers.

Layer 3 VPNs (L3VPNs) are also called VPRNs. The BGP/MPLS VPN, BGP/MPLS VPN with IPsec or GRE tunnels, IPsec VPN, and GRE VPN belong to L3VPNs.

One of the main risks of GRE tunnels is their lack of security and encryption. GRE tunnels do not provide any authentication, confidentiality, or integrity protection for the encapsulated traffic.

The chief disadvantage of GRE is that it is not considered a secure protocol because it doesn't use encryption like the IP Security (IPsec) Encapsulating Security Payload, defined by RFC 2406.

What does GRE tunneling mean? Encapsulating packets within other packets is called "tunneling." GRE tunnels are usually configured between two routers, with each router acting like one end of the tunnel. The routers are set up to send and receive GRE packets directly to each other.

In short (), GRE over IPSec is most useful whenever you need to tunnel dynamic routing protocol traffic across an uncontrolled network securely to provide IP reachability between remote sites.

Why use GRE tunnel over IPSec? ›

IT teams should use IPsec when they require secure IP tunneling. They should use GRE when they require tunneling without privacy and when they need to tunnel multiple protocols or multicast. Teams can combine GRE on top of IPsec when they need GRE's multiprotocol functionality combined with IPsec's data protection.

OpenVPN is the most secure VPN protocol and the safest choice thanks to its near-unbreakable encryption, which keeps users' data private even when using public Wi-Fi. Because it's open source, users can check the source code for vulnerabilities and reassure themselves that there are no weaknesses in its security.

The network connection is done via the GRE protocol (IP protocol number 47. For more information, refer to Wikipedia: List of IP protocol numbers. Since GRE is an IP protocol, it is not based on either TCP or UDP and has no concept of ports. It is an IP protocol by itself.

Here are some of the reasons: You need to encrypt multicast traffic. GRE tunnels can carry multicast packets—just like real network interfaces—as opposed to using IPSec by itself, which can't encrypt multicast traffic. Some examples of multicast traffic are OSPF, EIGRP, and RIPV2.

GRE is best used over a trusted network path because the packets aren't encrypted, but it can be combined with an IPsec tunnel if encryption is required.

IKEv2 stands for Internet Key Exchange Version 2.

It is considered more lightweight and stable than OpenVPN while retaining some customizability. But it is only available over UDP, which is blocked by some firewalls. IKEv2 is one of the newest protocols and has significant strengths, particularly its speed.

Generally speaking, layer 2 VPN bridging is best for extending a LAN across different locations or for applications that need layer 2 features. On the other hand, layer 3 VPN bridging is preferable for connecting networks with different protocols or addresses or for applications that need layer 3 features.

L2TP carries OSI Layer 2 traffic across Layer 3 networks. It achieves this in a three-stage process. Firstly, L2TP must create a connection between the LAC and the LNS. The LNS and LAC serve as endpoints for the point-to-point tunnel, and they must negotiate the relationship between them before transmitting any data.

GRE is a tunneling protocol which is used to transport multicast, broadcast and non-IP packets like IPX etc. IPSec is an encryption protocol. IPSec can only transport unicast packets not multicast & broadcast. Hence we wrap it GRE first and then into IPSec which is called as GRE over IPSec.