Additional Commands for IKE

The following paragraphs provide some additional commands for 1KB configuration. The command group 2 configures the IKE transform set for Diffie-Hellinan group 2 (1024-bit numbers). The default is group 1 (768-bit numbers). Group 2 provides greater security but takes longer to compute (the computational time can make a difference on routers with smaller RTA(config) crypto isakmp policy 10 RTA(config-isakmp) group 2 The command crypto isakmp identity hostname applies to IKJ2 with pre-shared keys...

Advanced Security Services Part I IPsec

The Internet provides a wealth of services for any organization that chooses to connect to it. No longer are organizations confined to the connectivity and information available in their private networks. Instead, a huge infrastructure and vast repositories of data can be tapped into simply by connecting to a local service provider. In a sense, the Internet becomes an extension, a very large extension, of the private network. On the other hand, the Internet is a very public place. Data...

Anti Replay

Anti-replay provides the assurance that past transactions cannot be replayed by an attacker. In spite of taking the precautions mentioned earlier (encryption, hashing, digital signatures, and certificates), an attacker might simply try to record and replay a transaction and not bother with subverting the security defenses. IKE provides anti-replay security for IPsec by using sequence numbers combined with authentication. With anti-replay, senders and rcccivcrs can detect and reject data that is...

Associations

A security association (SA) is a logical connection that protects data flowing from one peer to another by using a transform set. Security associations are like logical tunnels between peers Traffic entering an SA is protected and transported to the other side (the other peer). SAs are unidirectional an SA protects data flowing in one direction only. Therefore, for secure bidirectional communication between peers, a pair of SAs is required. IPsec maintains many pieces of data needed to support...

Authentication Header and Encapsulating Security Payload

IPsec defines two security protocols called Authentication Header (AH) (RFC 2402) and Encapsulating Security Payload (ESP) (RFC 2406). Bach protocol defines its own format for the IPsec header that follows the IP header of an IPsec packet (see Figures 7-2 and 7-3). Both protocols use the concept of an SA therefore, SAs can be either AH SAs or liSP SAs (an SA cannot be both an AH and ESP SA). Additionally, both AH and ESP upporT transport and tunnel mode. NOTE A device might send a transform set...

Check Configurations and Show Commands

Examine the configuration of each peer (issue the show running-contig command) and double-check the following IKE SA transform sets (policies) agree on both peers including the lifetime parameter. IKE pre-shared keys, public keys, or certificates are correct. Crypto maps on both routers share a common IPsec transform set. Crypto access lists on both routers are mirror images of each other and are included in the crypto maps. Crypto maps are configured with the peer's correct and reachable IP...

Confidentiality Encryption

Confidentiality provides privacy for the data being exchanged only the intended recipient can easily read the data. This is achieved through encryption algorithms that scramble plaintext data into an unintelligible form called ciphertext. As part of the scrambling process, an encryption algorithm requires a key (or more than one key in the case of public key cryptography). The key is nothing more than a string of bits usually written in ASCII or hexadecimal notation. For example, the key...

Configuring and Applying Crypto Maps

After configuring crypto access lists and transform sets, you can add them to a crypto map. Consider the network in Figure 7-12 with two routers that peer over an untrustcd network. Assume that IKJi, crypto access lists, and transform sets are configured and a crypto map is now needed. Figure 7-12 A Network with a Basic Crypto Map Configuration Figure 7-12 A Network with a Basic Crypto Map Configuration In the preceding diagram, Router A's serial interface to the untrusted network is...

Configuring Crypto Access Lists

As mentioned previously, crypto access lists define the scope or set of packets that need protection of an IPsec SA. You configure crypto access lists no differently than regular extended access lists. However, crypto access lists have a different purpose and meaning than regular extended aeeess lists. The following list describes the unique characteristics of crypto access lists Unlike regular access lists, crypto access lists do not specify the traffic to filter on an interface, but rather...

Configuring IKE

Cisco's implementation of IKE supports three authentication methods. They are Pre-shared keys Two peers are configured with a predetermined shared key. Peers are authenticated if they both possess the same key. This is a simple configuration, does not use public key cryptography or digital certificates, and might be suitable for small networks. RSA encryption RSA encryption uses public key cryptography to authenticate peers but does not use digital certificates (does not provide...

Configuring IPsec

After IKE is configured, the next step is to configure policies called crypto maps that tell a router how to build IPsec SAs within the IKE SA. Crypto Map Configuration Overview Configuring Crypto Access Lists Crypto Access Lists An Example Configuring IPsec Transform Sets Configuring and Applying Crypto Maps Configuring IPsec SA Lifetimes Configuring Perfect Forward Secrecy Configuring Dynamic Crypto Maps Validating IPsec Configuration A crypto map defines the IPsec policies on a router. These...

Configuring IPsec Transform Sets

A transform set (also called a transform proposal) defines the security protocols and algorithms that protect traffic for a given IPsec SA. Before two devices can establish an IPsec SA, they must negotiate and agree on a common transform set. To configure a transform set, use the crypto ipsec transform-set global configuration command RTA(config) crypto ipsec transform-set TRANS-ESP esp-des esp-md5-hmac The command crypto ipsec transform-set TRANS-ESP esp-des esp-md5-hmac creates a transform...

Configuring Perfect Forward Secrecy

The following commands configure a crypto map entry for PFS RTA(config) crypto map MAP-TO NY 20 ipsec-isakmp RTA(config-crypto-map) set pfs groupl The command set pfs groupl tells the router to use PFS on all IPsec SAs creatcd with this entry. By default, PFS is off. The keyword groupl specifies Diffie-Hellman group 1 (768-bit numbers). The other option, group2, specifies Diffie-Hellman group 2 (1024-bit numbers). Group 2 provides greater security but requires more time to compute. See Internet...

Crypto Maps

An interface can have only one crypto map. Use multiple entries within a crypto map to assign different policies for different types of traffic. Figure 7-9 is a conceptual view of a crypto map. Figure 7-9 Conceptual View of a Crypto Map Applied to Router A's Serial I Interface Access list 101 Transform set TRANS-ESP Peer 192.168.1.2 Access list 102 Transform set TRANS-AH Peer 192.168.1.2 Access list 101 Transform set TRANS-ESP Peer 192.168.1.2 Access list 102 Transform set TRANS-AH Peer...

Hashing Algorithms Examples with Message Digest

To illustrate the security provided by cryptographic hashing algorithms, consider the hash values computed by a popular algorithm, Message Digest 5 (MD5), in the following examples. NOTE Another popular hashing_algorithm used_with IPsec is Secure Hash Algorithmic A-1), which was designed by the National Institute of Standards and Technology (N1ST), a division of the U.S. Department of Commerce, and the National Security Agency (NSA), the official security organization of the U.S. government....

Integrity

Integrity (also called data integrity) provides a guarantee that data has not been altered in transit. Two parties that are communicating over an untrusted network must be able to verify that the data received is exactly the same as the data originally sent. Integrity is achieved through cryptographic hashing algorithms that calculate a unique value when given a piecc of data or message as input. The unique value (called a hash value or message authentication code) is like a fingerprint. Given...

Psec Enables Virtual Private Networks

The IPsec standard is an architecture for transporting data securely on an untrusted network, using encryption and other services. Although IPsec can be used on any IP network, its most popular use by far is for building virtual private networks (VPNs) over the public Internet .RFC 2401 defines the general architecture of IPsec, and RFCs 2402 through 2412 define specific technologies within the IPsec framework. A VPN is a network service over a public infrastructure (like the Internet or other...

Of IPsecs Layer 3 Service

IPsec works at the IP layer (Layer 3) and integrates with your existing IP network. You might, for example, replace a costly leased line connection between two international offices with an intranet VPN that connects the offices through an Internet Service Provider (ISP). The rest of your network can be left unchanged. The IP layer approach gives IPsec advantages over more traditional security strategies such as link-layer and application-layer encryption. The following are some key IPsec...

Origin Authentication

Origin authentication provides the assurance that the person you are communicating with is who he or she claims to be. Consider again Rob and Alice An attacker could masquerade as Bob and attempt to communicate with Alice. If Alice has no means of authenticating Bob, Alice might then communicate with the attacker, thinking she's communicating with Bob. Alice needs a way to know for certain that a message claiming to be from Bob was indeed sent by Bob. Digital signatures and digital certificates...

V

In Figure 7-1, the routers apply IPsec services (encryption, authentication, and so on) to traffic that is exchanged between the two sites. Because IPsec is an IP layer function, no modification is required for the Internet (it simply forwards IP packets) or to the clients and servers at each site. Because it is a trusted network, the traffic on the LAN within each site is not protected, but data exchanged between the sites is protected to maintain privacy over the Internet. Finally, rules are...

Validating IKE Configuration

To view the IKE transform sets (policies) and verify IKE configuration, issue the show crypto isakmp policy command. The following is an example output TA sh cry isakmp pol Protection suite of priority 7 encryption algorithm hash algorithm authentication method Diffie-Hellman group lifetime Protection suite of priority 9 encryption algorithm hash algorithm authentication method Diffie-Hellman group lifetime Protection suite of priority 10 encryption algorithm hash algorithm authentication...

VJfternet Key Exchange

The Internet Key Exchange (IKE) protocol (RFC 2409) is a management protocol used in conjunction with IPsec and is based on three key management protocols Internet Security Association and Key Management Protocol (ISAKMP) (RFC 2408), Oakley (RFC 2412), and SKEME (simply called A Versatile Secure Key Exchange Mechanism for Internet in a paper by Hugo Krawczyk). IKE is an important protocol that provides IPsec with the following services Establishes IPsec SAs dynamically as they are needed....

When Are SAs Established

The following list describes the logic of a router as it pertains to the setup of IPsec and IKE SAs When a packet requiring IPsec needs to be transmitted, the router checks for an existing IPsec S A suitable for protecting the packet. An SA is suitable if its source and destination criteria (as defined by a crypto access list rule) match the packet. If a suitable IPsec SA exists, the packet is sent using the transform set and peer parameters associated with the SA. If a suitable IPsec S A does...

Crypto Access Lists An Example

Consider the scenario depicted in Figure 7-10 with two routers that must peer across an untrusted network and provide IPsec services on behalf of devices located in multiple subnets. Figure 7-10 Scenario for Configuring Crypto Access Lists Figure 7-10 Scenario for Configuring Crypto Access Lists Suppose all subnets have a 16 mask and you are given the following requirements Traffic between subnets 172.17.0.0 and 10.1.0.0 requires EPsec. Traffic between subnets 172.17.0.0 and 10.2.0.0 requires...

Transport and Tunnel Modes

IPsec defines two kinds of SAs transport and tunnel mode SAs. A transport mode SA is an association between two hosts. In transport mode, the IP pay load is protected by IPsec and the original IP header isjeft intact. Additionally, an IPsec header is inserted after the IP header. This is illustrated in Figure 7-2. Transport mode protects traffic between two IPscc hosts (between a PC and a server, for example) and does not afford any traffic flow confidentiality. That is, the volume of traffic...

J All of the Pieces Together A Comprehensive Example with IPsec and IKE

The sections up to this point have covered the building blocks of IPsec, but how do all of these technologies work together The following sequence between Alice and Bob incorporates the concepts covered in the preceding sections and describes how IPscc's cryptographic techniques can achieve secure communication over an untrusted network. in this example, assume that no prior communication has occurred between Alice and Bob. To make the example more concrete, further assume that Alice needs to...

Basic IPsec Security Concepts and Cryptography

IPsec is a fairly large collection of technologies that encompasses network and security protocols, cryptographic algorithms, and recommendations. IPsec is an architecture for building secure communications over untrusted networks and provides the security services listed in the following sections. These services are confidentiality, integrity, origin authentication, and anti-replay. The following sections cover these services and introduce basic security and cryptographic principles as they...

Configuring IKE with Pre Shared Keys

Authentication with pre-shared keys is the simplest implementation of IKE and-might be suitable for small networks (10 routers and fewer, perhaps). As mentioned previously, this configuration does not have the scaling advantages of public key cryptography and digital certificates. Instead, two peers arc manually configured with the same key (a shared key). How the keys are determined and programmed into the routers is the responsibility of the router administrators. When a pre-shared key needs...

Validating IPsec Configuration

The following enable mode commands are useful for validating the IPsec configuration show crypto isakmp policy returns the router's active IKE transform sets (policies) in order of priority. show crypto isakmp sa displays the status of the router's IKE SAs. A state of QM_IDLE means the IKE SA is up and functioning properly. Recall that both IKE and IPsec SAs are built only when they are needed and are triggered by traffic that matches a crypto map. show crypto map displays the crypto maps...

Enable Debugging and Clearing Existing SAs

To get more detailed information and observe IKE and IPsec negotiations, enable debugging with these commands RTA debug crypto isakmp RTAtfdebug crypto ipsec With debugging enabled, the router displays the status of IKE and IPsec events in detail. See the following section Messages for IKE Negotiation and CA Servers. To debug CA events, issue these additional commands RTA debug crypto pki messages RTAtfdebug crypto pki transactions To observe IKE negotiation, you might want to clear any...

Configuring IPsec SA Lifetimes

The following commands modify the lifetimes associated with IPsec SAs RTA(config) crypto map MAP-TO NY 20 ipsec-isakmp RTA(config crypto-map) set security-association lifetime seconds 2700 RTA(config-crypto-map) set security association lifetime kilobytes 2000000 The command set security-association lifetime seconds 2700 sets the lifetime of IPsec SAs created by this crypto map entry to 2700 seconds (45 minutes). The default is 3600 seconds (60 minutes). The command set security-association...

Tunnel Endpoint Discovery

Tunnel Endpoint Discovery (TED) is a Cisco feature that improves the scalability and availability of IPsec VPNs by extending the capabilities of dynamic crypto maps. As mentioned in the preceding section, Configuring Dynamic Crypto Maps, dynamic crypto maps greatly reduce your work by eliminating the configuration of specific IPsec peers. However, dynamic crypto maps (by default) are only receivers of IKE negotiation requests. That is, unlike regular crypto maps, they cannot initiate outbound...

Configuring IKE with RSA Signatures and Digital Certificates

IKE authentication with digital certificates uses RSA digital signatures and provides scalability for larger networks. As mentioned previously, digital certificates provide nonrepudiation through the service of a CA. Your organization might administer a CA server and act as the CA for all of the devices and people that belong to your organization. Also, you might be the CA for third parties (suppliers, partners, customers) that do business with your organization. With digital certificate...

Transform Sets

A transform set is a list of IPsec protocols and cryptographic algorithms that a peer can accept. Because IPsec allows for the use of different protocols and algorithms, a peer needs to declare and negotiate with other peers what it can support. Peers communicate the protocols and algorithms they support by exchanging transform sets. For two peers to communicate successfully, they must share a common transform set. If they do not, their attempt to establish a peering will fail and they will not...