IKEv1 versus IKEv2

Let me start writing this blog starting with what IPsec VPN really is ?




One day  our boss comes and tell us that he wants full data network connectivity between his Head office and newly open branch. So what can we do ? So the one answer would simply be , we could easily leverage the internet and create a logical link between the two Sites ( HO and the branch office). The challenging part would be security as there would be lot of illegitimate people trying to get the data sent from one site to the other. This is where IPsec VPN (Site to Site Tunnel)  comes in the picture.

IPsec VPN primarily does 2 thing

1. Encryption : uses encryption algorithm such as AES, DES, 3DES for protecting the data .
2. Data Integrity : makes sure that  bits has not  been manipulated in  between.

There are other things as well like Authentication , Hashing,  Replay Protection  that IPsec VPN does but Encryption and Data Integrity is the main thing.

IPsec can establish the VPN in one of the two ways : via Internet Key Exchange ( IKE) or via manual key exchange. IKE is much more preferred when compared to manual key exchange . IKE negotiates VPN between two endpoints in much more secure way as compared to manual key exchange. There are mainly two version of IKE(Internet Key Exchange) which is IKEv1 and the other one is IKEv2.

IKE Version is not to be confused with the different phase of IKE negotiation which will be briefly talking about later in this blog.

IKEv1 versus IKEv2

So why was IKEv2 introduced in the presence of IKEv1 ? Basically writing down,  IKEv2 has much more streamlined negotiation process which provides better security . IKEv1 are also much more prone to DoS attacks, an attacker can attack IKEv1 gateway by spoofing the IKE packet and consuming resources without having a good way to validate whether the packet is authentic or not . IKEv2 builds upon a cookie negotiation to ensure that peer is a valid peer.

The negotiation part in IKEv1 is also very rigid and would fail because of a lack of exact match . IKEv2 provides flexibility in terms of negotiations to allows gateway to purpose certain attributes.

Moreover speaking about IKEv1 and IKEv2 , IKEv1 has two phases IKE Phase I and IKE Phase II. The main aim of Phase I is to establish IKE SA for Phase II is establish IPSEC SA for data transmission. IKE Phase I uses two modes

1. Main Mode : widely used and also provides more security with total of 6 ISAKMP message to establish IKE SA.

2. Aggressive Mode : uses 3 ISAKMP message to establish IKE SA but is less secured .

IKE Phase II only has one mode i.e Quick Mode .

Technically IKEv2 doesnt have any phases like there is in IKEv1 for  establishing  the SA but rather there are total of 4 exchanges in request/respsone format . Out of 4 exchanges the most important is the first two one.

1. IKE-SA-INIT : negotiates security attributes such as Diffie-Hellman group, parameters used to establish the IPSEC tunnel.

2. IKE-AUTH : peer at this stage authenticates their identities. IPSEC tunnel is already establish at this stage.

So with all the benefits why are people still not using IKEv2 ? If you can use IKEv2 it is a much much easier and efficient way for communicating between two end points. IKEv2 has not been as much popular as IKEv1 so either you will be needing access to both the sides or you might be forced to use IKEv1.

This blog is getting too long for basic introduction of IPSEC VPN as well as comparing IKEv1 adn IKEv2 . In my next blog I will be talking more about IPSEC VPN and the protocols used to transfer data between the logical tunnels.