Blognational

VPN tunnels are used to connect physically isolated networks that are more often than not separated by nonsecure internetworks. To protect these connections, we employ the IP Security (IPSec) protocol to make secure the transmission of data, voice, and video between sites. These secure tunnels over the Internet public network are encrypted using a number of advanced algorithms to provide confidentiality of data that is transmitted between multiple sites. This chapter explores how to configure routers to create a permanent secure site-to-site VPN tunnel.

Configuring Cisco Easy VPN With IPSec Dynamic Virtual Tunnel ..

Encryption will be provided by IPSec in concert with VPN tunnels. The Internet Security Association and Key Management Protocol (ISAKMP) and IPSec are essential to building and encrypting VPN tunnels. Waves nx crack windows. ISAKMP, also called IKE (Internet Key Exchange), is the negotiation protocol that allows hosts to agree on how to build an IPSec security association.

ISAKMP negotiation consists of two phases:

• Phase 1 creates the first tunnel, which protects later ISAKMP negotiation messages.

• Phase 2 creates the tunnel that protects data.

IPSec then encrypts exchanged data by employing encryption algorithms that result in authentication, encryption, and critical anti-replay services.

Lab 13-1: Basic Site-to-Site IPSec VPN

Figure 13-1Configuring Basic Site-to-Site IPSec VPN (Main Mode)

Figure 13-1 illustrates the topology that will be used in the following lab.

I'm struggeling with some dVTI Issue on a Cisco ASR1000 box. Here is my configuration for the hub site: crypto keyring FOO-KEYRING pre-shared-key hostname r2-foo key iawg8b32hah! Crypto isakmp policy 104 encr aes 256 authentication pre-share group 5 lifetime 7200 crypto isakmp keepalive 10 crypto isakmp profile FOO-IKEPROFILE keyring FOO-KEYRING match identity user-fqdn r2-foo virtual. In a FlexVPN Hub and Spoke design spoke routers are configured with a normal static VTI with the tunnel destination of the Hub’s IP address, the Hub however is configured with a Dynamic VTI. The DVTI on the Hub router is not configured with a static mapping to the peer’s IP address. The configuration of this tunnel interface is similar to a GRE tunnel interface and is well understood. – Dynamic VTI (DVTI) on headend crypto systems, and static VTI on the branches.

Task 1

Configure a basic site-to-site IPSec VPN to protect traffic between IP addresses 1.1.1.1 and 2.2.2.2 using the policy shown in Table 13-1.

Table 13-1 Policy Guidelines for Configuring Task 1

Reachability to the loopback0 interfaces is provided in the initial configuration.

ISAKMP, originally defined in RFC 7296, covers the following:

• Procedures to authenticate a communicating peer

• How to create and manage security associations (SAs)

• Key-generation techniques

• Threat mitigation, such as denial-of-service (DoS) and replay attacks

IKE does not specify any details of key management or key exchange, and it’s not bound to any key-generation techniques. Inside IKE, Cisco uses OAKLEY for the key exchange protocol.

OAKLEY enables you to choose between different well-known Diffie-Hellman (DH) groups. RFC 2412 describes the OAKLEY protocol and covers DH groups 1 through 5. Of these groups, Cisco supports DH groups 1, 2, and 5. RFC 3526 describes DH group 5 and groups 14 through 18. Cisco supports DH groups 5, 14, 15, and 16. RFC 5114 covers DH groups 19 through 26. Of these DH groups, Cisco supports 19, 20, 21, and 24. The following is a list of the DH groups supported by Cisco:

• 1: Diffie-Hellman group 1 (768 bit)

• 2: Diffie-Hellman group 2 (1024 bit)

• 5: Diffie-Hellman group 5 (1536 bit)

• 14: Diffie-Hellman group 14 (2048 bit)

• 15: Diffie-Hellman group 15 (3072 bit)

• 16: Diffie-Hellman group 16 (4096 bit)

• 19: Diffie-Hellman group 19 (256-bit ECP)

• 20: Diffie-Hellman group 20 (384-bit ECP)

• 21: Diffie-Hellman group 21 (521-bit ECP)

• 24: Diffie-Hellman group 24 (2048 bit, 256-bit subgroup)

ISAKMP and OAKLEY create an authenticated, secure tunnel between two entities, and then negotiate the SA for IPSec. Both peers must authenticate each other and establish a shared key.

Three authentication methods are available: RSA signatures (PKI), RSA encrypted pseudorandom numbers (nonces), and preshared keys (PSK). The DH protocol is used to agree on a common session key.

IPSec uses a different shared key from ISAKMP and OAKLEY. The IPSec shared key can be derived by using DH again to ensure Perfect Forward Secrecy (PFS) or by refreshing the shared secret derived from the original DH exchange.

IKE is a hybrid protocol that establishes a shared security policy and authenticated keys for services that require keys, such as IPSec. Before an IPSec tunnel is established, each device must be able to identify its peer. ISAKMP and IKE are both used interchangeably; however, these two items are somewhat different. IKE was originally defined by RFC 2409. IKE version 2 is currently described by RFC 7296.

• IKE Phase 1: The two ISAKMP peers establish a secure and an authenticated channel. This channel is known as the ISAKMP SA. There are two modes defined by ISAKMP: Main Mode and Aggressive Mode.

• IKE Phase 2: SAs are negotiated on behalf of services such as IPSec that need keying material. This phase is called Quick Mode.

To configure IKE Phase 1, you need to configure ISAKMP policies. It is possible to configure multiple policies with different configuration statements and then let the two hosts negotiate the policies. The first matched policy on the responder will be used.

Let’s start configuring Phase 1 on both routers:

The IP address of a loopback interface can be used when there are multiple paths to reach the peer’s IP address:

To configure the Phase 2, we need to define the transform-set, which specifies the hashing, the security protocol, and the encryption used for Phase 2:

Next, we need to define the crypto ACL/proxy ID, which defines the interesting traffic:

In the last step, a crypto map is configured to specify the peer, crypto ACL, and the transform set. There are three choices when configuring the following crypto map:

• IPSec-ISAKMP: This is the best option. It states that we are using ISAKMP to encrypt and decrypt the key.

• IPSec-manual: This is the worst choice. It means that the key needs to be entered manually. (Can you imagine entering a 512-bit key manually?)

• GDOI: This choice is used for GETVPN configuration. It stands for group domain of interpretation.

You should see the following console message:

The final step applies the crypto map to the interface facing the other peer:

You should see the following console message:

Let’s verify the configuration before testing:

Now we can test the configuration:

The first ICMP packet triggers the ISAKMP process, as this is our interesting traffic matching the configured crypto ACL.

Before we actually start sending IKE packets to the peer, the router first checks whether there is a local SA (security association) matching that traffic. This check is against the IPSec SA and not an IKE SA.

We can see the outbound and remote IP addresses, port number, local proxy, and remote proxy. The protocol used is ESP, and the transform-set is the default mode of tunnel.

The following highlighted line specifies that no SA was found. The router first tried to find an IPSec SA matching the outgoing connection, but it failed to find one.

IKE Phase 1 (Main Mode) Message 1

By default, IKE Main Mode is used, so we should expect six packets for Phase 1. The following highlighted message states that the Aggressive Mode cannot start. However, this does not mean that we are experiencing errors; it just means that Aggressive Mode is not configured on the local router.

The router checks for the configured ISAKMP policy and sees that pre-shared key (PSK) authentication is configured. It has to check whether there is a key for the configured peer as well. After that, the first IKE packet is sent out to the peer’s IP address on port UDP 500.

The packet contains locally configured ISAKMP policies to be negotiated by the peer. The pre-shared key for the remote peer is found, which means that ISAKMP is going to use it to authenticate the peer. This will happen in the last stage of IKE Phase 1.

The router initiating the IKE exchange is called the initiator, and the router responding to IKE request is called the responder. The initiator (R1) has sent the ISAKMP policy along with vendor-specific IDs that are part of the IKE packet payload. MM_NO_STATE indicates that ISAKMP SA has been created, but nothing else has happened yet.

IKE Phase 1 (Main Mode) Message 2

It looks like everything is going smoothly. We received a response packet from the peer. However, this is one area where things can typically go wrong.

The received packet contains the SA chosen by the peer and some other useful information, such as vendor IDs. Those vendor-specific payloads are used to discover network address translation (NAT) along the path and to maintain keepalives. The router matches the ISAKMP policy from the packet to one that’s locally configured. If there is a match, the tunnel-establishment process continues. If the policy configured on both routers is not the same, the crosscheck process fails and the tunnel is down.

The router is processing ISAKMP parameters that have been sent as the reply. The vendor IDs are processed to determine whether the peer supports the NAT-Traversal, Dead Peer Detection feature. ISAKMP policy is checked against policies defined locally. The atts are acceptable message indicates that the ISAKMP policy matches with remote peer:

The lifetime timer has been started. Note that default value is used (86,400 seconds). This is the lifetime for ISAKMP SA. Note that IPSec SAs have their own lifetime parameters, which may be defined as number of seconds or kilobytes of transmitted traffic.

IKE Phase 1 (Main Mode) Message 3

The third message is sent out containing key-exchange (KE) information for the Diffie-Hellman (DH) secure key-exchange process:

IKE Phase 1 (Main Mode) Message 4

The fourth message has been received from the peer. This message contains the KE payload, and based on that information, both peers can generate a common session key to be used in securing further communication. The pre-shared key configured locally for the peer is used in this calculation.

After receiving this message, peers can determine whether there is NAT along the path.

IKE Phase 1 (Main Mode) Message 5

The fifth message is used for sending out authentication information to the peer. This information is transmitted under the protection of the common shared secret.

MM_KEY_EXCH indicates that the peers have exchanged Diffie-Hellman public keys and have generated a shared secret. The ISAKMP SA remains unauthenticated. Note that the process of authentication has just been started.

IKE Phase 1 (Main Mode) Message 6

The peer identity is verified by the local router and the SA is established. This message finishes ISAKMP Main Mode (Phase I), and the status is changed to IKE_P1_COMPLETE.

IKE Phase 2 (Quick Mode) Message 1

Now it’s time for Phase 2, which is Quick Mode (QM). The router sends out the packet containing local proxy IDs (network/host addresses to be protected by the IPSec tunnel) and the security policy defined by the transform set.

Dvi Configurations

The state of IKE is QM_IDLE. This indicates that the ISAKMP SA is idle. It remains authenticated with its peer and may be used for subsequent Quick Mode exchanges. It is in a quiescent state.

Dvti Configuration - Image Results

The routers are negotiating the parameters for the IPSec tunnel that will be used for traffic transmission. These parameters are defined by the crypto ipsec transform-set command.

Note that lifetime values of the IPSec SA are visible at this moment. You are able to set this both globally and in the crypto map entry. The attr are acceptable message indicates that the IPSec parameters defined as the IPSec transform-set match on both sides.

The local and remote proxies are defined. This indicates the sources and destinations set in crypto ACL, which defines the interesting traffic for the IPSec tunnel. Remember that it is enough when only one entry is mirrored. If not, you may get the following entry in the debug output: PSEC(initialize_sas): invalid proxy IDs.

The IPSec SAs have been created and inserted into the router’s security associations database (SADB). SAs are distinguished by Security Parameter Index (SPI) values, which are also used to differentiate many tunnels terminated on the same router. Note that two SPI values are generated for one tunnel: one SPI for the inbound SA and one SPI for the outbound SA.

The SPI value is inserted in the ESP header of the packet leaving the router. At the other side of the tunnel, the SPI value inserted into the ESP header enables the router to reach parameters and keys that have been dynamically agreed upon during IKE negotiations, or session key refreshment in case of lifetime timeout.

Task 2

Erase the startup configuration of the routers and reload them before proceeding to the next lab.