A Phase 1 transform is a set of security protocols and algorithms used to protect VPN data. During IKE negotiation, the peers must agree on the transform to use. You can define a tunnel so that it offers a peer more than one transform for negotiation. For more information, see Add a Phase 1 Transform. The mode determines the type and number of message exchanges that occur in this phase.
Main Mode. This mode is more secure, and uses three separate message exchanges for a total of six messages. The first two messages negotiate policy, the next two exchange Diffie-Hellman data, and the last two authenticate the Diffie-Hellman exchange. Main Mode supports Diffie-Hellman groups 1, 2, 5, 14, 15, 19, and This mode also allows you to use multiple transforms, as described in Add a Phase 1 Transform.
Aggressive Mode. This mode is faster because it uses only three messages, to exchange data and identify the two VPN endpoints. When you use Aggressive mode, the number of exchanges between two endpoints is fewer than it would be if you used Main Mode, and the exchange relies mainly on the ID types used in the exchange by both appliances. Aggressive Mode does not ensure the identity of the peer. Main Mode ensures the identity of both peers, but can only be used if both sides have a static IP address.
The Firebox attempts Phase 1 exchange with Main Mode. If the negotiation fails, it uses Aggressive Mode. We recommend that you select Dead Peer Detection if both endpoint devices support it.
Settings that are not shared appear in the Gateway Settings tab. Shared settings appear in the Shared Settings tab.
All rights reserved. All other tradenames are the property of their respective owners. Skip To Main Content. Submit Search. IKEv2 requires Fireware v In the IKEv1 Phase 1 settings, you can select one of these modes: Main Mode This mode is more secure, and uses three separate message exchanges for a total of six messages.
Aggressive Mode This mode is faster because it uses only three messages, to exchange data and identify the two VPN endpoints. Do not enable it if the peer is a third-party IPSec gateway endpoint.
Select the Phase 1 Settings tab. From the Version drop-down list, select IKEv1. To set the maximum number of times the Firebox tries to send an IKE keep-alive message before it tries to negotiate Phase 1 again, type the number you want in the Max failures text box. Use the Dead Peer Detection check box to enable or disable traffic-based dead peer detection.
When you enable dead peer detection, the Firebox connects to a peer only if no traffic is received from the peer for a specified length of time and a packet is waiting to be sent to the peer.
This method is more scalable than IKE keep-alive messages.IPsec offers numerous configuration options, affecting the performance and security of IPsec connections. Realistically, for low to moderate bandwidth usage it matters little which options are chosen here as long as DES is not used, and a strong pre-shared key is defined, unless the traffic being protected is so valuable that an adversary with many millions of dollars worth of processing power is willing to devote it to breaking the IPsec encryption.
Even in that case, there is likely an easier and much cheaper way to break into the network and achieve the same end result social engineering, for one. Performance is the most important factor for most, and in cases when that is a concern, more care is needed when crafting a configuration. The settings here control the phase 1 negotiation portion of the tunnel, as described previously.
The Disabled checkbox controls whether or not this tunnel and its associated phase 2 entries are active and used. The differences are discussed in IKE. The Internet Protocol selector sets the protocol for the outside of the tunnel.
That is, the protocol that will be used between the outside peer addresses. For most, this will be IPv4but if both ends are capable of IPv6, that may be used instead. Whichever protocol is chosen here will be used to validate the Remote Gateway and the associated identifiers. In many cases, the Interface option for an IPsec tunnel will be WAN, since the tunnels are connecting to remote sites.
However, there are plenty of exceptions, the most common of which are outlined in the remainder of this section. A static route will automatically be added to ensure that the traffic to the Remote Gateway routes through the appropriate WAN. A gateway group may also be chosen from this list. A gateway group to be used with IPsec must only have one gateway per tier.
When using a gateway group, if the first gateway goes down, the tunnel will move to the next available WAN in the group. When the first WAN comes back up, the tunnel will be rebuilt there again.
When configuring IPsec to add encryption to a wireless network, as described in Additional protection for a wireless networkchoose the OPT interface which corresponds to the wireless card.
When using an external wireless access point, pick the interface which is connected to the wireless access point.
The Remote Gateway is the IPsec peer for this phase 1. This is the endpoint on the other side of the tunnel to which IPsec will negotiate this phase 1.Image Source — www. Network Troubleshooting is an art and site to site vpn Troubleshooting is one of my favorite network job. I believe other networking folks like the same. The first and most important step of troubleshooting is diagnosing the issue, isolate the exact issue without wasting time.
In this article i wanted to describe the steps of Troubleshooting a site-to-site VPN tunnelmost of vpn appliances provide the Plenty of debugging information for engineer to diagnose the issue. The first step to take when Phase-1 of the tunnel not comes up. Make sure your encryption setting, authentication, hashes, and lifetime etc. This could be happening due to the following reason. If receiver has a tunnel group and PSK configured for the initiators peer address, it sends its PSK hash to the initiator.
Once the Phase 1 negotiations have established and you are falling into IPsec phase 2. There are a few different set of things need to be checked. After the above check and validation, Now If you have both phase 1 and phase 2 successful established and vpn tunnel is reported as up. Ensure traffic is passing through the vpn tunnel. Initiates some traffic ICMP Traffic from inside the host or run packet tracer from firewall to originate traffic to bring the phase-2 up and see the Packet encap and Packet decap happing.
These numbers tell us how many packets have traversed the IPSec tunnel and verifies that we are receiving traffic back from the remote end of the VPN tunnel. All of the above steps should resolve vpn tunnel issues that you are experiencing. If the vpn tunnel still not establish and traffic not passingWe recommend to try a different set of encryption settings.
There may be something strange incompatibilities issue encounters with different vendor devices. Also check the latest release notes for firmware version of your VPN appliance. If you have already upgraded any firmware to the latest version. Sometimes it is crazy that vpn tunnel state is going up and down constantly and users getting frustrated due to connection drop with the servers.
About IPSec VPN Negotiations
There are couple of reasons that vpn tunnel is getting dropped and it start all of sudden even you have not made any change in the vpn tunnel. In this case, you need to check following things listed as below Complete the below mentioned steps for the Phase 1 configuration:. Create an access list which defines the traffic to be encrypted and through the tunnel. In this example, the source traffic of interesting subnet would be from the It can contain multiple entries if there are multiple subnets involved between the sites.
Same an identical Transform Set must be created on the remote end as well.I will break down each message below and what it may signify if the VPN is stuck at one of these messages. You can see the status of Phase by looking at the 'show isakmp sa' output. If you have several tunnels then you may want to start the output at your Peer IP 'show isakmp sa begin X. X' where X. X is the Peer IP you are trying to troubleshoot. If you see that you are stuck at this message then this means that the other side is not responding to your requests.
This could be that Remote Peer is blocking UDP portthey are not configured to listen for IKE traffic or you are not able to reach the peer due to routing issues.
Checking with the Remote side to see if they are getting your message 1 is a good first step. This should rarely happen because if Message 2 was sent back to the peer, then the initiating peer should be able to respond with Message 3.
This can happen for a few reasons but the most common is ISP issues. This can be the route back to the initiating peer or UDP could be blocked from the Responding Peer to the Initiating Peer on their edge. Have the Peer with this message check that UDP is allowed from their environment and that they are not having any routing issues back to the Initiating peer.
The initiator here has sent Message 3 which will begin the process of trusting eachothers peer IPs. There is more that goes on here but all you really need to know is that the tunnel-groups need to exist for this phase to complete. If the VPN is at this message, then the other side most likely does not have the Initiators IP configured as a tunnel-group and is dropping the request. The best thing to do here is confirm that the Remote Peer has the right Peer IP configured in the tunnel-group settings.
At this phase, Message 4 was sent back to the Initiator and the Responder is waiting for Message 5.
If this message is present then the Pre-shared keys between the 2 peers do not match or that the Initiator does not have a pre-shared key defined at all. All settings are valid except for Pre-shared keys at this point. You will want to validate that the keys match between both peers and possibly look at special characters or spaces as these can be problematic for some termination devices.
This message indicates that the Pre-shared keys do not match between the peers. The initiator has sent message 5 to the Remote Peer and the Remote peer was not able to validate the Pre-shared key and doesn't respond. The best thing to do here is work with the Remote side to confirm the Pre-shared keys.
When validating the Pre-shared keys, look at special characters or spaces as these can be problematic for some termination devices. If you would like to know more or see more articles on VPNs, please let me know. This site uses Akismet to reduce spam. Learn how your comment data is processed.
A lot of clients will Read more…. This will allow you to narrow Read more….IPSEC 6 packet Exchange Part 2- Sending 1st packet
Toggle Navigation. Categories: ASA. Leave a Reply Cancel reply. Related Posts.To build the VPN tunnel, IPSec peers exchange a series of messages about encryption and authentication, and attempt to agree on many different parameters.
This process is known as VPN negotiations. One device in the negotiation sequence is the initiator and the other device is the responder. The main purpose of Phase 1 is to set up a secure encrypted channel through which the two peers can negotiate Phase 2. When Phase 1 finishes successfully, the peers quickly move on to Phase 2 negotiations. If Phase 1 fails, the devices cannot begin Phase 2. The purpose of Phase 2 negotiations is for the two peers to agree on a set of parameters that define what traffic can go through the VPN, and how to encrypt and authenticate the traffic.
This agreement is called a Security Association. Some of the features described in this section are only available to participants in the WatchGuard Beta program. If a feature described in this section is not available in your version of Fireware, it is a beta-only feature. In Phase 1 negotiations, the two peers exchange credentials. The devices identify each other and negotiate to find a common set of Phase 1 settings to use. This SA is valid for only a certain amount of time.
After the Phase 1 SA expires, if the two peers must complete Phase 2 negotiations again, they must also negotiate Phase 1 again.
IKEv2 Phase 1 (IKE SA) and Phase 2 (Child SA) Message Exchanges
The credentials can be a certificate or a pre-shared key. Both gateway endpoints must use the same credential method. If one peer uses a pre-shared key, the other peer must also use a pre-shared key, and the keys must match. If one peer uses a certificate, the other peer must also use a certificate.
In Fireware v If one peer uses a hex-based pre-shared key, the other peer must use the same hex-based pre-shared key. The VPN configuration on each peer contains the Phase 1 identifier of the local and the remote device, and the configurations must match.
The responder can reject the proposal if it is not configured to use that mode. Aggressive Mode is less secure but faster than Main Mode. When you use Aggressive mode, the number of exchanges between two endpoints is fewer than it would be if you used Main Mode, and the exchange relies mainly on the ID types used in the exchange by both appliances.
Aggressive Mode does not ensure the identity of the peer. Main Mode ensures the identity of both peers, but can only be used if both sides have a static IP address. Transform settings include a set of authentication and encryption parameters, and the maximum amount of time for the Phase 1 SA.
The hardware cryptographic acceleration in those models does not support SHA All other models support SHA The IPSec SA is a set of traffic specifications that tell the device what traffic to send over the VPN, and how to encrypt and authenticate that traffic.Save Digg Del.
Cisco Secure Virtual Private Networks. A security association SA is a relationship between two or more entities that describes how the entities will use security services to communicate securely. The Diffie-Hellman key agreement is always performed in this phase. The sender offers one or more transform sets that are used to specify an allowed combination of transforms with their respective settings. The sender also indicates the data flow to which the transform set is to be applied.
The sender must offer at least one transform set. The receiver then sends back a single transform set, which indicates the mutually agreed-upon transforms and algorithms for this particular IPSec session.
A new Diffie-Hellman agreement may be done in phase 2, or the keys may be derived from the phase 1 shared secret. Figure 1 The function of IKE. Phase 1 consists of main mode or aggressive mode. These modes are described later in this article. Peer authentication occurs during the main mode exchange during IKE phase 1. The IKE protocol is very flexible and supports multiple authentication methods as part of the phase 1 exchange. The two entities must agree on a common authentication protocol through a negotiation process.
Pre-shared keys. A key value entered into each peer manually out of band and used to authenticate the peer. RSA encrypted nonces. Uses RSA encryption to encrypt a nonce value a random number generated by the peer and other values. A common value used by all authentication methods is the peer identity IDwhich helps identify the peer.
Some ID values used are as follows:. See All Related Articles. All rights reserved. Join Sign In. Home Shop By Cert New! Article is provided courtesy of Cisco Press. Date: Feb 22, NOTE A security association SA is a relationship between two or more entities that describes how the entities will use security services to communicate securely.
Pre-Shared Keys Next Section. About Affiliates Cisco Systems, Inc.The Phase 1 configuration mainly defines the ends of the IPsec tunnel.
The remote end is the remote gateway with which the FortiGate unit exchanges IPsec packets.
IOS IPSec and IKE debugs - IKEv1 Main Mode Troubleshooting
The local end is the FortiGate interface that sends and receives IPsec packets. If you want to control how the IKE negotiation is processed when there is no traffic, as well as the length of time the FortiGate unit waits for negotiations to occur, you can use the negotiation-timeout and auto-negotiate commands in the CLI.
For more information, refer to Phase 2 parameters and Phase 2 parameters. You can use the following advanced parameters to select the encryption and authentication algorithms that the FortiGate unit uses to generate keys for the IKE exchange. You can also use the following advanced parameters to ensure the smooth operation of Phase 1 negotiations.
If the FortiGate unit will act as a VPN client, and you are using security certificates for authentication, set the Local ID to the distinguished name DN of the local server certificate that the FortiGate unit will use for authentication purposes. Note that, since FortiOS 5. However, it is also possible to have partial matching of 'user. DN, the first search is done with the whole DN string. The result is that IPsec tunnels do not come up. The solution is IKE fragmentation.
For most configurations, enabling IKE fragmentation allows connections to automatically establish when they otherwise might have failed due to intermediate nodes dropping IKE messages containing large certificates, which typically push the packet size over bytes.
By default, IKE fragmentation is enabled, but upon upgrading, any existing phase1-interface may have have " set fragmentation disable " added in order to preserve the existing behaviour of not supporting fragmentation. After IPsec Phase 1 negotiations end successfully, you begin Phase 2. You can configure the Phase 2 parameters to define the algorithms that the FortiGate unit may use to encrypt and transfer data for the remainder of the session.
During Phase 2, you select specific IPsec security associations needed to implement security services and establish a tunnel. In most cases, you need to configure only basic Phase 2 settings. In Phase 2, the FortiGate unit and the VPN peer or client exchange keys again to establish a secure communication channel between them.
You select the encryption and authentication algorithms needed to generate keys for protecting the implementation details of Security Associations SAs.