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12.12.2014
This document provides an example of configuring TACACS+ Authentication and Command Authorization based on AD group membership of a user with Cisco Secure Access Control System (ACS) 5.x and later. The information in this document was created from the devices in a specific lab environment. Refer to the Cisco Technical Tips Conventions for more information on document conventions. Before you begin the configuration of the ACS 5.x for Authentication and Authorization, ACS should have been integrated successfully with Microsoft AD.
In this section, you map two AD groups to two different command sets and two Shell profiles, one with full-access and the other with limited-access on the Cisco IOS devices.
Choose the groups that need to be mapped to the Shell profiles and command sets in the later part of the configuration. Copy AD1:ExternalGroups from Available to Selected section of Customize Conditions and then move Shell Profile and Command Sets from Available to Selected section of Customize Results.
Now choose the newly created full access Shell Profile (Full-Privilege in this example) and click OK. Provide a Name and ensure that the check box next to Permit any command that is not in the table below is checked.
Change the Default Privilege and Maximum Privilege to Static with Values 1 and 15 respectively. Provide a Name and ensure that the checkbox next to Permit any command that is not in the table below is not selected. Similarly add any other commands to be permitted for the users in limited access group with the use of Add.
Complete these steps in order to configure Cisco IOS device and ACS for Authentication and Authorization. The output of the previous command shows that the TACACS server is reachable and the user has been successfully authenticated.
In order to verify authentication and authorization login to the Cisco IOS device through Telnet. IPsec is the next-generation network layer crypto platform for the Cisco security platforms (Cisco IOS® Software, PIX, and so forth). Multivendora€”Since the IPsec framework is standardized, customers are not locked into any specific vendor product. You need to know these terms in order to understand IPsec, and to read the rest of this document. Advanced Encryption Standard (AES)a€”AES was finalized as a Federal Information Processing Standard (FIPS)-approved cryptographic algorithm to be used in order to protect electronic data transmission (FIPS PUB 197). Authentication Header (AH)a€”This is a security protocol that provides authentication and optional replay-detection services.
Certification Authority (CA)a€”This is a third-party entity with the responsibility to issue and revoke certificates. Certificatea€”A cryptographically signed object that contains an identity and a public key associated with this identity.
Classic cryptoa€”This is Cisco proprietary encryption mechanism used in Cisco IOS Software Release 11.2. Certificate Revocation List (CRL)a€”This is a digitally signed message that lists all of the current but revoked certificates listed by a given CA.
Crypto mapa€”This is a Cisco IOS software configuration entity that performs two primary functions. Data integritya€”This is data integrity mechanisms, through the use of secret-key based or public-key based algorithms, that allow the recipient of a piece of protected data in order to verify that the data has not been modified in transit. Data confidentialitya€”This is the method where protected data is manipulated so that no attacker can read it. Data origin authenticationa€”This is a security service where the receiver can verify that protected data might have originated only from the sender. Data Encryption Standard (DES)a€”The DES was published in 1977 by the National Bureau of Standards and is a secret key encryption scheme based on the Lucifer algorithm from IBM. Diffie-Hellmana€”This is a method of the establishment of a shared key over an insecure medium.
DSSa€”A digital signature algorithm designed by The US National Institute of Standards and Technology (NIST) based on public key cryptography.
VIP2-40 in the Cisco 7000 series routers that have the Cisco 7000 series Route Switch Processor (RSP7000) and Cisco 7000 series Chassis Interface (RSP7000CI) cards installed.
IPsec does not use the ESA acceleration, but it does work in a box that has an ESA card on a software-only basis. Encapsulating Security Payload (ESP)a€”A security protocol that provides data confidentiality and protection with optional authentication and replay-detection services.
Hasha€”This is a one way function that takes an input message of arbitrary length and produces a fixed length digest. HMACa€”This is a mechanism for message authentication that uses cryptographic hashes such as SHA and MD5. Internet Key Exchange (IKE)a€”A hybrid protocol that uses part Oakley and part of another protocol suite called SKEME inside the Internet Security Association and Key Management Protocol (ISAKMP) framework. Internet Security Association and Key Management Protocol (ISAKMP)a€”This is a protocol framework that defines the mechanics of the implementation of a key exchange protocol and negotiation of a security policy.
IPsec NAT Transparencya€”The IPsec NAT Transparency feature introduces support for IP Security (IPsec) traffic to travel through Network Address Translation (NAT) or Point Address Translation (PAT) points in the network by addressing many known incompatibilities between NAT and IPsec. Oakleya€”This is a key exchange protocol that defines how to acquire authenticated keying material. Perfect Forward Secrecy (PFS)a€”PFS ensures that a given IPsec SA key was not derived from any other secret, like some other keys.
Replay-detectiona€”This is a security service where the receiver can reject old or duplicate packets in order to defeat replay attacks. RSAa€”This is a public key cryptographic algorithm, named after its inventors, Rivest, Shamir and Adleman, with a variable key length. Security Association (SA)a€”This is an instance of security policy and keying material applied to a data flow. Split Tunnelinga€”This is the process of allowing a remote VPN user in order to access a public network, most commonly the Internet, at the same time that the user is allowed to access resources at the remote office. Transforma€”A transform describes a security protocol (AH or ESP) with its corresponding algorithms.
With the group command, you can declare what size modulus to use for Diffie-Hellman calculation.
Since some RSA keys already exist on this box, it asks if you want to get rid of the keys that exist. Contact the CA administrator because this person wants to confirm the identity of the hose before a certificate is issued.
Whether you use pre-shared keys or configure a CA, once you setup Internet Key Exchange IKE, you still have to setup IPsec.
This command is a very simple ACL that allows the routers to talk to one another, for example, a Telnet from one router to the next.


Packets that are processed by IPsec are slower than packets that are processed through classic crypto. IPsec introduces packet expansion, which is more likely to require fragmentation and the corresponding reassembly of IPsec datagrams. Encrypted packets are probably authenticated, which means that there are two cryptographic operations that are performed for every packet. The authentication algorithms are slow, although work has been done to speed up things as the Diffie-Hellman computations.
In addition, the Diffie-Hellman key exchange used in IKE is an exponentiation of very large numbers (between 768 and 1024 bytes) and can take up to four seconds on a Cisco 2500. For each router, the SA database takes up approximately 300 bytes, plus 120 bytes for every SA therein.
There is a small decrease in performance for non-encrypted packets that go through an interface that does crypto. Use Group 1 for Diffie-Hellman key exchanges within IKE, use MD5 as your hashing algorithm, and use longer lifetimes in order to minimize the impact of the crypto subsystem on the rest of the router.
This command shows the crypto map ToOtherRouter, the ACLs, and the transform proposals applied to this crypto map, the peers, and the key lifetime. Make certain that you have connectivity between the endpoints of the communication before you configure crypto. Make sure that either DNS works on the router, or you have entered the CA hostname, if you use a CA.
IPsec uses IP protocols 50 and 51, and IKE traffic passes on protocol 17, port 500 (UDP 500). For classic crypto users who upgrade to Cisco IOS Software Release 11.3, crypto commands storage methods in the configuration has changed in order to allow for IPsec. If you do a ping test across the encrypted link when you finish your configuration, the negotiation process can take some time, about six seconds on a Cisco 4500, and about 20 seconds on a Cisco 2500, because SAs have not yet been negotiated. If you run into trouble with your negotiation(s) and make configuration changes, use the clear crypto is and clear crypto sa commands in order to flush the databases before you retry.
ACS uses Microsoft Active Directory (AD) as an external identity store to store resources such as users, machines, groups, and attributes. Click Add after typing show in the space provided in the command section and choose Permit in the Grant section so that only the show commands are permitted for the users in the limited access group.
Network Admins group is the group in AD which is mapped to Full-Privilege Shell Profile and Full-Access Command set on the ACS.
Choose AAA Protocol > TACACS+Authorization in order to verify the activities performed by user1 and user2. This document contains basic configurations of Internet Key Exchange (IKE) with pre-shared keys, IKE with a Certification Authority, and IPsec. Originally described in RFCs 1825 through 1829, which are now obsolete, IPsec is currently discussed in a number of documents presented by the IETF IP Security Working Group . When you see acronyms in other portions of this document, refer to this page for definitions.
AES is based on the Rijndael algorithm, which specifies how to use keys with a length of 128, 192, or 256 bits to encrypt blocks with a length of 128, 192, or 256 bits. Authentication establishes the integrity of datastream and ensures that it is not tampered with in transit. Each device that has its own certificate and public key of the CA can authenticate every other device within a given CA domain. This is analogous to a book of stolen charge card numbers that allow stores to reject bad credit cards.
This is commonly provided by data encryption and keys that are only available to the parties involved in the communication.
This service requires a data integrity service plus a key distribution mechanism, where a secret key is shared only between the sender and receiver. Cisco uses both Secure Hash Algorithm (SHA) and Message Digest 5 (MD5) hashes within our implementation of the IPsec framework. IKE is used to establish a shared security policy and authenticated keys for services, such as IPsec, that require keys. ISAKMP is defined in the Internet Security Association and Key Management Protocol (ISAKMP).
Both MD5 and Secure Hash Algorithm (SHA) are variations on MD4, which is designed to strengthen the security of this hashing algorithm.
In other words, if someone breaks a key, PFS ensures that the attacker is not able to derive any other key.
Replay attacks rely on the attacker to send out older or duplicate packets to the receiver and the receiver to think that the bogus traffic is legitimate. The main weakness of RSA is that it is significantly slow to compute compared to popular secret-key algorithms, such as DES. This method of network access enables the user to access remote devices, such as a networked printer and servers at the same time as to access the public network (Internet). Transport Mode encapsulates the upper layer payload, such as Transmission Control Protocol (TCP) or User Datagram Protocol (UDP), of the original IP datagram. Tunnel Mode is used on order to protect datagrams sourced from or destined to non-IPsec systems, such as in a Virtual Private Network (VPN) scenario.
While the IKE configuration is simple and you do not use a CA, it does not scale very well. While the implementation of SHA and MD5 are both mandatory, not all peers can be configured in order to negotiate one or the other. If you do not specify usage-keys at the end of the command, the router generates only one RSA key-pair and uses it for both encryption and digital signatures. This creates a hostname ciscoca-ultra, and tells the router what its IP address is, and the name servers. Once the CA issues the certificate, the status of our certificate changes from pending to available. The first one uses ESP only, the second one uses AH combined with ESP, and the last one uses only AH. Although there is only one peer declared in this crypto map, you can have multiple peers within a given crypto map. Performance of RSA is dependent on the size of the prime number chosen for the RSA key pair. In situations where there are two IPsec SAs, one inbound and one outbound, 540 bytes are required, in most cases. Consequently, these captures can have different IP addresses and reflect slightly different configurations.
This router configuration is used in order to create the debug output listed in the Debug Information section. Tunnel mode is the default and it can be used in transport mode, as well as for its VPN capabilities. Consequently, if classic crypto users ever revert to Cisco IOS Software Release 11.2, these users have to re-enter their crypto configurations.


If your network is live, make sure that you understand the potential impact of any command. If you try to run any command other than the ones mentioned in the Show-Access command set, you should get a Command Authorization Failed error, which shows that the user2 has limited access. Second, it defines the policy for these flows and the crypto peer that traffic needs to go to. Cisco uses DES in classic crypto (40-bit and 56-bit key lengths), IPsec crypto (56-bit key), and on the PIX Firewall (56-bit key). DSS is a component in classic crypto, as well as the Redcreek IPsec card, but not in IPsec implemented in Cisco IOS software. There are no configuration steps for a router that runs Cisco IOS Software Release 12.2(13)T and later. If PFS is not enabled, someone can potentially break the IKE SA secret key, copy all the IPsec protected data, and then use knowledge of the IKE SA secret in order to compromise the IPsec SAs setup by this IKE SA. Replay-detection is done by the use of sequence numbers combined with authentication, and is a standard feature of IPsec. Because SHA produces a 160-bit digest, it is more resistant to brute-force attacks than 128-bit hashes (such as MD5), but it is slower.
An advantage of the use of split tunneling is that it alleviates bottlenecks and conserves bandwidth as Internet traffic does not have to pass through the VPN server. Since IKE negotiates its own policy, it is possible to configure multiple policy statements with different configuration statements, then let the two hosts come to an agreement. When Cisco IOS Software Release 11.3(3) is released, there are only going to be a few CA vendors that ship product.
The dt3-45a(ca-identity)#crypto ca authenticate verisign-ca command instructs the router to fetch the certificate of the CA. First, you have to verify the identity of the CA, then the CA has to verify the identity of the router. In addition, if you do a show crypto ca cert command, you see the CA certificate(s), in addition to your own certificates.
In the event of multipleprotection suites, the policies are presented to the peer in numerical order and the peer negotiates which one to use.
The session key lifetime can be expressed in either kilobytes (after x-amount of traffic, change the key) or seconds, as is shown in these commands. If multiple crypto map entries have the same map-name but a different seq-num, they are part of the same set and are all applied to the interface.
There is no performance impact on packets that traverse the router that avoid an interface that does crypto. Ultimately, it is up to the security policy of the customer in order to determine which features to use and which to leave alone. Another series of show commands is provided in the Debug Information section of this document. This configuration allows a network called X located behind Source Router to talk to a network called Y located behind Peer Router. Refer to the Usage Guidelines for access-list in the PIX command reference for more information. But, this document does help you to understand the tasks and the order in which they are accomplished. You can also see the name classic crypto referred to as Encryption Express or Cisco Encryption Technology (CET) in the marketing literature. Manually enter pre-shared keys into both hosts, by a CA service, or the forthcoming secure DNS (DNSSec) in order to do this. A disadvantage of this method is that it essentially renders the VPN vulnerable to attack as it is accessible through the public, non-secure network. The rsa-encr command configures RSA Encrypted nonces and the rsa-sig command configures RSA Signature. If you ever need to revoke your certificate before it expires, if you renumber the interfaces of your router or if you believe that your certificate is compromised, you need to provide a password to the CA administrator. Consult the Cisco IOS Software documentation for your version of Cisco IOS, or use the Command Lookup Tool (registered customers only) for more information about a particular command.
Both routers have the debug crypto isakmp, debug crypto ipsec, and debug crypto engine commands enabled. With the Diffie-Hellman exchange, the DES key never crosses the network, not even in encrypted form, which is not the case with the RSA encrypt and sign technique.
For example, if you have a pipe that supports ESP between peers, one ESP SA is required for each direction. VeriSign, Entrust, Microsoft and Netscape, and probably a host of others, are working on CA products. Verify the certificate of the CA with the CA administrator in order to ensure authenticity. Transport mode can be used only when the crypto endpoints are also the endpoints of the communication.
This tool allows the user to look up a detailed description or configuration guidelines for a particular command. A potential point of confusion is that the acronyms ISAKMP and IKE are both used in Cisco IOS software in order to refer to the same thing.
SAs are uniquely identified by destination (IPsec endpoint) address, security protocol (AH or ESP), and security parameter index (SPI).
For this reason, you do not want to use group 2 on low-end routers like the Cisco 2500 series or less.
For example, if you configure your policy for rsa-sig and you have no certificate, the router does not negotiate this. Transpot mode can be specified by the mode transport command under the transform-set configuration.
MamaBear is more preferred in this configuration, and then the rest in descending order of preference through to BabyBear. Since this example uses a Cisco 4500, group 2 is used, and make sure the peer is also configured in order to use group 2. Also note that esp-rfc1829 and ah-rfc1828 are based on the original RFCs for this technology and are obsolete transforms included for backwards compatibility.
The match address 101 command means to use access list 101 in order to determine which traffic is relevant.
You can have multiple crypto maps with the same name, which is armadillo, in this example, and different sequence numbers, which is 10, in this example. If you select the default properties, the group 1 lines do not show up when you do a write terminal command. The combination of multiple crypto maps and different sequence numbers allows you to mix and match classic crypto and IPsec.



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