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This module describes how to configure basic IP Security (IPsec) VPNs. IPsec is a framework of open standards developed by the Internet Engineering Task Force (IETF). It provides security for transmission of sensitive information over unprotected networks such as the Internet. IPsec acts at the network layer, protecting and authenticating IP packets between participating IPsec devices ("peers"), such as Cisco routers.
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
You must configure Internet Key Exchange (IKE) as described in the module "Configuring Internet Key Exchange Security for IPsec VPNs."
Even if you decide to not use IKE, you must disable it as described in the module "Configuring Internet Key Exchange for IPsec VPNs."
IKE uses UDP port 500. The IPsec Encapsulating Security Payload (ESP) and Authentication Header (AH) protocols use protocol numbers 50 and 51. Ensure that your access lists are configured so that protocol 50, 51, and User Datagram Protocol (UDP) port 500 traffic is not blocked at interfaces used by IPsec. In some cases, you might need to add a statement to your access lists to explicitly permit this traffic.
At this time, IPsec can be applied to unicast IP datagrams only. Because the IPsec Working Group has not yet addressed the issue of group key distribution, IPsec does not currently work with multicasts or broadcast IP datagrams.
If you use Network Address Translation (NAT), you should configure static NAT translations so that IPsec works properly. In general, NAT translation should occur before the router performs IPsec encapsulation; in other words, IPsec should be working with global addresses.
Cisco IOS XE IPsec supports nested tunnels that terminate on the same router. Double encryption of locally generated IKE packets and IPsec packets is supported only when a static virtual tunnel interface (sVTI) is configured. Double encryption is not supported on later releases.
Cisco IOS XE does not support IPv4 options; hence, the crypto engine drops IPv4 packets that contain IPv4 options.
Cisco IOS XE does not support access control lists (ACLs) that have discontiguous masks in IPsec.
Cisco implements the following standards with this feature:
Note |
The term IPsec is sometimes used to describe the entire protocol of IPsec data services and IKE security protocols and is also sometimes used to describe only the data services. |
The component technologies implemented for IPsec include:
Cisco IOS XE also implements Triple DES (168-bit) encryption, depending on the software versions available for a specific platform. Triple DES (3DES) is a strong form of encryption that allows sensitive information to be transmitted over untrusted networks. It enables customers to utilize network layer encryption.
Note |
Cisco IOS XE images with strong encryption (including, but not limited to, 56-bit data encryption feature sets) are subject to United States government export controls, and have a limited distribution. Images to be installed outside the United States require an export license. Customer orders might be denied or subject to delay due to United States government regulations. Contact your sales representative or distributor for more information or e-mail export@cisco.com. |
IPsec as implemented in the Cisco IOS XE software supports the following additional standards:
Table 1 | Supported Switching Paths for IPsec |
Switching Paths |
Examples |
---|---|
Process switching |
interface fastethernet0/0/1 no ip route-cache |
Fast switching |
interface fastethernet0/0/1 ip route-cache ! Ensure that you will not hit flow switching. no ip route-cache flow ! Disable CEF for the interface, which supercedes global CEF. no ip route-cache cef |
Cisco Express Forwarding (CEF) |
ip cef interface fastethernet0/0/1 ip route-cache ! Ensure that you will not hit flow switching. no ip route-cache flow |
Fast-flow switching |
interface fastethernet0/0/1 ip route-cache ! Enable flow switching p route-cache flow ! Disable CEF for the interface. no ip route-cache cef |
CEF-flow switching |
! Enable global CEF. ip cef interface fastethernet0/0/1 ip route-cache ip route-cache flow ! Enable CEF for the interface ip route-cache cef |
IPsec works with the following serial encapsulations: High-Level Data-Links Control (HDLC), PPP, and Frame Relay.
IPsec also works with the Generic Routing Encapsulation (GRE) and IPinIP Layer 3 protocols. Other Layer 3 tunneling protocols may not be supported for use with IPsec.
Because the IPsec Working Group has not yet addressed the issue of group key distribution, IPsec currently cannot be used to protect group traffic (such as broadcast or multicast traffic).
IPsec provides the following network security services. (In general, local security policy dictates the use of one or more of these services.)
IPsec provides secure tunnels between two peers, such as two routers. You define which packets are considered sensitive and should be sent through these secure tunnels, and you define the parameters that should be used to protect these sensitive packets, by specifying characteristics of these tunnels. Then, when the IPsec peer recognizes such a sensitive packet, the peer sets up the appropriate secure tunnel and sends the packet through the tunnel to the remote peer. (The use of the term tunnel in this chapter does not refer to using IPsec in tunnel mode.)
More accurately, these tunnels are sets of security associations (SAs) that are established between two IPsec peers. The SAs define which protocols and algorithms should be applied to sensitive packets and specify the keying material to be used by the two peers. SAs are unidirectional and are established per security protocol (AH or ESP).
With IPsec, you define what traffic should be protected between two IPsec peers by configuring access lists and applying these access lists to interfaces by way of crypto map sets. Therefore, traffic may be selected on the basis of source and destination address, and optionally Layer 4 protocol, and port. (The access lists used for IPsec are used only to determine which traffic should be protected by IPsec, and not which traffic should be blocked or permitted through the interface. Separate access lists define blocking and permitting at the interface.)
A crypto map set can contain multiple entries, each with a different access list. The crypto map entries are searched in order--the router attempts to match the packet to the access list specified in that entry.
When a packet matches a permit entry in a particular access list, and the corresponding crypto map entry is tagged as cisco, connections are established, if necessary. If the crypto map entry is tagged as ipsec-isakmp, IPsec is triggered. If no SA exists that IPsec can use to protect this traffic to the peer, IPsec uses IKE to negotiate with the remote peer to set up the necessary IPsec SAs on behalf of the data flow. The negotiation uses information specified in the crypto map entry as well as the data flow information from the specific access list entry. (The behavior is different for dynamic crypto map entries. See the "t_Creating_Dynamic_Crypto_Maps_1064598.xml#task_1064598" section later in this module.)
If the crypto map entry is tagged as ipsec-manual, IPsec is triggered. If no SA exists that IPsec can use to protect this traffic to the peer, the traffic is dropped. In this case, the SAs are installed via the configuration, without the intervention of IKE. If the SAs did not exist, IPsec did not have all of the necessary pieces configured.
Once established, the set of SAs (outbound, to the peer) is then applied to the triggering packet and to subsequent applicable packets as those packets exit the router. "Applicable" packets are packets that match the same access list criteria that the original packet matched. For example, all applicable packets could be encrypted before being forwarded to the remote peer. The corresponding inbound SAs are used when processing the incoming traffic from that peer.
Multiple IPsec tunnels can exist between two peers to secure different data streams, with each tunnel using a separate set of SAs. For example, some data streams might be authenticated only while other data streams must both be encrypted and authenticated.
Access lists associated with IPsec crypto map entries also represent which traffic the router requires to be protected by IPsec. Inbound traffic is processed against the crypto map entries--if an unprotected packet matches a permit entry in a particular access list associated with an IPsec crypto map entry, that packet is dropped because it was not sent as an IPsec-protected packet.
Crypto map entries also include transform sets. A transform set is an acceptable combination of security protocols, algorithms, and other settings to apply to IPsec protected traffic. During the IPsec SA negotiation, the peers agree to use a particular transform set when protecting a particular data flow.
You can nest IPsec traffic to a series of IPsec peers. For example, in order for traffic to traverse multiple firewalls (these firewalls have a policy of not letting through traffic that they have not authenticated), the router must establish IPsec tunnels with each firewall in turn. The "nearer" firewall becomes the "outer" IPsec peer.
In the example shown in the figure below, Router A encapsulates the traffic destined for Router C in IPsec (Router C is the inner IPsec peer). However, before Router A can send this traffic, it must first reencapsulate this traffic in IPsec in order to send it to Router B (Router B is the "outer" IPsec peer).
Figure 1 | Nesting Example of IPsec Peers |
It is possible for the traffic between the "outer" peers to have one kind of protection (such as data authentication) and for traffic between the "inner" peers to have different protection (such as both data authentication and encryption).
Crypto access lists are used to define which IP traffic is protected by crypto and which traffic is not protected by crypto. (These access lists are not the same as regular access lists, which determine what traffic to forward or block at an interface.) For example, access lists can be created to protect all IP traffic between Subnet A and Subnet Y or Telnet traffic between Host A and Host B.
The access lists themselves are not specific to IPsec. It is the crypto map entry referencing the specific access list that defines whether IPsec processing is applied to the traffic matching a permit in the access list.
Crypto access lists associated with IPsec crypto map entries have the following primary functions:
If you want certain traffic to receive one combination of IPsec protection (for example, authentication only) and other traffic to receive a different combination of IPsec protection (for example, both authentication and encryption), you need to create two different crypto access lists to define the two different types of traffic. These different access lists are then used in different crypto map entries which specify different IPsec policies.
Crypto protection can be permitted or denied for certain IP traffic in a crypto access list as follows:
Note |
IP traffic is not protected by crypto if it is refused protection in all of the crypto map entries for an interface. |
After the corresponding crypto map entry is defined and the crypto map set is applied to the interface, the defined crypto access list is applied to an interface. Different access lists must be used in different entries of the same crypto map set. However, both inbound and outbound traffic is evaluated against the same "outbound" IPsec access list. Therefore, the access list's criteria is applied in the forward direction to traffic exiting your router and in the reverse direction to traffic entering your router.
In the figure below, IPsec protection is applied to traffic between Host 10.0.0.1 and Host 192.168.0.2 as the data exits Router A's S0 interface en route to Host 192.168.0.2. For traffic from Host 10.0.0.1 to Host 192.168.0.2, the access list entry on Router A is evaluated as follows:
source = host 10.0.0.1 dest = host 192.168.0.2
For traffic from Host 192.168.0.2 to Host 10.0.0.1, that same access list entry on Router A is evaluated as follows:
source = host 192.168.0.2 dest = host 10.0.0.1
Figure 2 | How Crypto Access Lists Are Applied for Processing IPsec |
If you configure multiple statements for a given crypto access list that is used for IPsec, in general the first permit statement that is matched is the statement used to determine the scope of the IPsec SA. That is, the IPsec SA is set up to protect traffic that meets the criteria of the matched statement only. Later, if traffic matches a different permit statement of the crypto access list, a new, separate IPsec SA is negotiated to protect traffic matching the newly matched access list statement.
Any unprotected inbound traffic that matches a permit entry in the crypto access list for a crypto map entry flagged as IPsec is dropped, because this traffic was expected to be protected by IPsec.
Note |
If you view your router's access lists by using a command such as show ip access-lists, all extended IP access lists are shown in the command output. This display output includes extended IP access lists that are used for traffic filtering purposes and those that are used for crypto. The show command output does not differentiate between the different uses of the extended access lists. |
The following example shows that if overlapping networks are used, then the most specific networks are defined in crypto sequence numbers before less specific networks are defined. In this example, the more specific network is covered by the crypto map sequence number 10, followed by the less specific network in the crypto map, which is sequence number 20.
crypto map mymap 10 ipsec-isakmp set peer 192.168.1.1 set transform-set test match address 101 crypto map mymap 20 ipsec-isakmp set peer 192.168.1.2 set transform-set test match address 102 access-list 101 permit ip 10.1.1.0 0.0.0.255 172.16.1.0 0.0.0.255 access-list 102 permit ip 10.0.0.0 0.255.255.255 172.16.0.0 0.15.255.255
The following example shows how having the deny keyword in one crypto map sequence number and having the permit keyword for the same subnet and IP range in another crypto map sequence number is not supported.
crypto map mymap 10 ipsec-isakmp set peer 192.168.1.1 set transform-set test match address 101 crypto map mymap 20 ipsec-isakmp set peer 192.168.1.2 set transform-set test match address 102 access-list 101 deny ip 10.1.1.0 0.0.0.255 172.16.1.0 0.0.0.255 access-list 101 permit ip 10.0.0.0 0.255.255.255 172.16.0.0 0.15.255.255 access-list 102 permit ip 10.1.1.0 0.0.0.255 172.16.1.0 0.0.0.255
Cisco recommends that for every crypto access list specified for a static crypto map entry that you define at the local peer, you define a "mirror image" crypto access list at the remote peer. This ensures that traffic that has IPsec protection applied locally can be processed correctly at the remote peer. (The crypto map entries themselves must also support common transforms and must refer to the other system as a peer.)
The figure below shows some sample scenarios when you have mirror image access lists and when you do not have mirror image access lists.
Figure 3 | Mirror Image vs. Nonmirror Image Crypto Access Lists (for IPsec) |
As the figure above indicates, IPsec SAs can be established as expected whenever the two peers' crypto access lists are mirror images of each other. However, an IPsec SA can be established only some of the time when the access lists are not mirror images of each other. This can happen in the case where an entry in one peer's access list is a subset of an entry in the other peer's access list, such as shown in Cases 3 and 4 of the figure. IPsec SA establishment is critical to IPsec--without SAs, IPsec does not work, causing any packets matching the crypto access list criteria to be silently dropped instead of being forwarded with IPsec.
In the figure above, an SA cannot be established in Case 4. This is because SAs are always requested according to the crypto access lists at the initiating packet's end. In Case 4, Router N requests that all traffic between Subnet X and Subnet Y be protected, but this is a superset of the specific flows permitted by the crypto access list at Router M. Therefore, the request is not permitted. Case 3 works because Router M's request is a subset of the specific flows permitted by the crypto access list at Router N.
Because of the complexities introduced when crypto access lists are not configured as mirror images at peer IPsec devices, Cisco strongly encourages you to use mirror image crypto access lists.
When you create crypto access lists, using the any keyword could cause problems. Cisco discourages the use of the any keyword to specify source or destination addresses.
The any keyword in a permit statement is discouraged when you have multicast traffic flowing through the IPsec interface; the any keyword can cause multicast traffic to fail.
The permit any any statement is strongly discouraged, because this causes all outbound traffic to be protected (and all protected traffic sent to the peer specified in the corresponding crypto map entry) and requires protection for all inbound traffic. Then, all inbound packets that lack IPsec protection are silently dropped, including packets for routing protocols, Network Time Protocol (NTP), echo, echo response, and so on.
You need to be sure you define which packets to protect. If you must use the any keyword in a permit statement, you must preface that statement with a series of deny statements to filter out any traffic (that would otherwise fall within that permit statement) that you do not want to be protected.
Also, use of the any keyword in access control lists (ACLs) with reverse route injection (RRI) is not supported. (For more information about RRI, see the section "Creating Crypto Map Sets.")
A transform set represents a certain combination of security protocols and algorithms. During the IPsec SA negotiation, the peers agree to use a particular transform set for protecting a particular data flow.
You can specify multiple transform sets, and then specify one or more of these transform sets in a crypto map entry. The transform set defined in the crypto map entry is used in the IPsec SA negotiation to protect the data flows specified by that crypto map entry's access list.
During IPsec security association negotiations with IKE, the peers search for a transform set that is the same at both peers. When such a transform set is found, it is selected and is applied to the protected traffic as part of both peers' IPsec SAs. (With manually established SAs, there is no negotiation with the peer, so both sides must specify the same transform set.)
If you change a transform set definition, the change is only applied to crypto map entries that reference the transform set. The change is not applied to existing security associations, but is used in subsequent negotiations to establish new SAs. If you want the new settings to take effect sooner, you can clear all or part of the SA database by using the clear crypto sa command.
The table below shows allowed transform combinations.
Table 2 | Allowed Transform Combinations |
Transform Type |
Transform |
Description |
---|---|---|
AH Transform |
ah-md5-hmac
ah-sha-hmac |
AH with the MD5 (a Hash-based Message Authentication Code [HMAC] variant) authentication algorithm
AH with the SHA (an HMAC variant) authentication algorithm |
ESP Encryption Transform
|
esp-aes esp-aes 192 esp-aes 256 esp-des esp-3des esp-null
|
ESP with the 128-bit AES encryption algorithm ESP with the 192-bit AES encryption algorithm ESP with the 256-bit AES encryption algorithm
ESP with the 56-bit DES encryption algorithm ESP with the 168-bit DES encryption algorithm (3DES or Triple DES) Null encryption algorithm |
ESP Authentication Transform |
esp-md5-hmac
esp-sha-hmac |
ESP with the MD5 (HMAC variant) authentication algorithm
ESP with the SHA (HMAC variant) authentication algorithm |
Before you create crypto map entries, you should determine which type of crypto map--static, dynamic, or manual--best addresses the needs of your network.
Crypto map entries created for IPsec pull together the various parts used to set up IPsec SAs, including:
Crypto map entries with the same crypto map name (but different map sequence numbers) are grouped into a crypto map set. Later, you apply these crypto map sets to interfaces; then, all IP traffic passing through the interface is evaluated against the applied crypto map set. If a crypto map entry sees outbound IP traffic that should be protected and the crypto map specifies the use of IKE, an SA is negotiated with the remote peer according to the parameters included in the crypto map entry; otherwise, if the crypto map entry specifies the use of manual SAs, an SA should have already been established via configuration. (If a dynamic crypto map entry sees outbound traffic that should be protected and no security association exists, the packet is dropped.)
The policy described in the crypto map entries is used during the negotiation of SAs. If the local router initiates the negotiation, it uses the policy specified in the static crypto map entries to create the offer to be sent to the specified IPsec peer. If the IPsec peer initiates the negotiation, the local router checks the policy from the static crypto map entries, and any referenced dynamic crypto map entries to decide whether to accept or reject the peer's request (offer).
For IPsec to succeed between two IPsec peers, both peers' crypto map entries must contain compatible configuration statements.
When two peers try to establish an SA, they must each have at least one crypto map entry that is compatible with one of the other peer's crypto map entries. For two crypto map entries to be compatible, they must at least meet the following criteria:
You can define multiple remote peers using crypto maps to allow for load sharing. Load sharing is useful because if one peer fails, there continues to be a protected path. The peer that packets are actually sent to is determined by the last peer that the router heard from (received either traffic or a negotiation request from) for a given data flow. If the attempt fails with the first peer, IKE tries the next peer on the crypto map list.
If you are not sure how to configure each crypto map parameter to guarantee compatibility with other peers, you might consider configuring dynamic crypto maps as described in the section "Creating Dynamic Crypto Maps." Dynamic crypto maps are useful when the establishment of the IPsec tunnels is initiated by the remote peer (such as in the case of an IPsec router fronting a server). They are not useful if the establishment of the IPsec tunnels is locally initiated, because the dynamic crypto maps are policy templates, not complete statements of policy. (Although the access lists in any referenced dynamic crypto map entry are used for crypto packet filtering.)
You can apply only one crypto map set to a single interface. The crypto map set can include a combination of IPsec/IKE and IPsec/manual entries. Multiple interfaces can share the same crypto map set if you want to apply the same policy to multiple interfaces.
If you create more than one crypto map entry for a given interface, use the seq-num argument of each map entry to rank the map entries: the lower the seq-num argument, the higher the priority. At the interface that has the crypto map set, traffic is evaluated against higher priority map entries first.
You must create multiple crypto map entries for a given interface if any of the following conditions exist:
If you are not using IKE to establish a particular set of security associations, and want to specify multiple access list entries, you must create separate access lists (one per permit entry) and specify a separate crypto map entry for each access list.
Dynamic crypto maps can ease IPsec configuration and are recommended for use with networks where the peers are not always predetermined.
Note |
Dynamic crypto maps are only available for use by IKE. |
A dynamic crypto map entry is essentially a static crypto map entry without all the parameters configured. It acts as a policy template where the missing parameters are later dynamically configured (as the result of an IPsec negotiation) to match a remote peer's requirements. This allows remote peers to exchange IPsec traffic with the router even if the router does not have a crypto map entry specifically configured to meet all of the remote peer's requirements.
Dynamic crypto maps are not used by the router to initiate new IPsec security associations with remote peers. Dynamic crypto maps are used when a remote peer tries to initiate an IPsec security association with the router. Dynamic crypto maps are also used in evaluating traffic.
A dynamic crypto map set is included by reference as part of a crypto map set. Any crypto map entries that reference dynamic crypto map sets should be the lowest priority crypto map entries in the crypto map set (that is, have the highest sequence numbers) so that the other crypto map entries are evaluated first; that way, the dynamic crypto map set is examined only when the other (static) map entries are not successfully matched.
If the router accepts the peer's request, at the point that it installs the new IPsec security associations it also installs a temporary crypto map entry. This entry is filled in with the results of the negotiation. At this point, the router performs normal processing, using this temporary crypto map entry as a normal entry, even requesting new security associations if the current ones are expiring (based upon the policy specified in the temporary crypto map entry). Once the flow expires (that is, all of the corresponding security associations expire), the temporary crypto map entry is then removed.
For both static and dynamic crypto maps, if unprotected inbound traffic matches a permit statement in an access list, and the corresponding crypto map entry is tagged as "IPsec," then the traffic is dropped because it is not IPsec-protected. (This is because the security policy as specified by the crypto map entry states that this traffic must be IPsec-protected.)
For static crypto map entries, if outbound traffic matches a permit statement in an access list and the corresponding SA is not yet established, the router initiates new SAs with the remote peer. In the case of dynamic crypto map entries, if no SA existed, the traffic would simply be dropped (because dynamic crypto maps are not used for initiating new SAs).
Note |
Be careful when using the any keyword in permit entries in dynamic crypto maps. If it is possible for the traffic covered by such a permit entry to include multicast or broadcast traffic, the access list should include deny entries for the appropriate address range. Access lists should also include deny entries for network and subnet broadcast traffic, and for any other traffic that should not be IPsec protected. |
For redundancy, you could apply the same crypto map set to more than one interface. The default behavior is as follows:
If you apply the same crypto map set to multiple interfaces for redundancy purposes, you need to specify an identifying interface. One suggestion is to use a loopback interface as the identifying interface. This has the following effects:
The use of manual security associations is a result of a prior arrangement between the users of the local router and the IPsec peer. The two parties may begin with manual SAs and then move to using SAs established via IKE, or the remote party's system may not support IKE. If IKE is not used for establishing the SAs, there is no negotiation of SAs, so the configuration information in both systems must be the same in order for traffic to be processed successfully by IPsec.
The local router can simultaneously support manual and IKE-established SAs, even within a single crypto map set.
There is very little reason to disable IKE on the local router (unless the router only supports manual SAs, which is unlikely).
Note |
Access lists for crypto map entries tagged as ipsec-manual are restricted to a single permit entry and subsequent entries are ignored. In other words, the SAs established by that particular crypto map entry are only for a single data flow. To be able to support multiple manually established SAs for different kinds of traffic, define multiple crypto access lists, and then apply each one to a separate ipsec-manual crypto map entry. Each access list should include one permit statement defining what traffic to protect. |
After at least one crypto access list is created, a transform set needs to be defined as described in the section "Defining Transform Sets."
Next the crypto access lists need to be associated to particular interfaces when you configure and apply crypto map sets to the interfaces are configured and applied (following instructions in the sections "Creating Crypto Map Sets" and "Applying Crypto Map Sets to Interfaces").
Perform this task to define a transform set that is to be used by the IPsec peers during IPsec security association negotiations with IKE.
Command or Action | Purpose | |
---|---|---|
|
Example: Router> enable |
Enables privileged EXEC mode. |
|
Example: Router# configure terminal |
Enters global configuration mode. |
|
Example: Router(config)# crypto ipsec transform-set aesset esp-aes 256 esp-sha-hmac |
Defines a transform set and enters crypto transform configuration mode. There are complex rules defining which entries you can use for the transform arguments. These rules are explained in the command description for the crypto ipsec transform-set command, and the table in the About Transform Sets section provides a list of allowed transform combinations. |
|
Example: Router(cfg-crypto-tran)# mode transport |
(Optional) Changes the mode associated with the transform set. The mode setting is applicable only to traffic whose source and destination addresses are the IPsec peer addresses; it is ignored for all other traffic. (All other traffic is in tunnel mode only.) |
|
Example: Router(config)# exit |
Exits global configuration mode. |
|
Example: Router# clear crypto sa |
(Optional) Clears existing IPsec security associations so that any changes to a transform set takes effect on subsequently established security associations. Manually established SAs are reestablished immediately. |
|
Example: Router# show crypto ipsec transform-set |
(Optional) Displays the configured transform sets. |
After you have defined a transform set, you should create a crypto map as specified in the Creating Crypto Map Sets section.
When IKE is used to establish SAs, the IPsec peers can negotiate the settings they use for the new security associations. This means that you can specify lists (such as lists of acceptable transforms) within the crypto map entry.
Perform this task to create crypto map entries that use IKE to establish the SAs.
Command or Action | Purpose | |||
---|---|---|---|---|
|
Example: Router> enable |
Enables privileged EXEC mode. |
||
|
Example: Router# configure terminal |
Enters global configuration mode. |
||
|
Example: Router(config)# crypto map static-map 1 ipsec-isakmp |
Names the crypto map entry to create (or modify) and enters crypto map configuration mode. |
||
|
Example: Router(config-crypto-m)# match address vpn-tunnel |
Names an extended access list. This access list determines which traffic should be protected by IPsec and which traffic should not be protected by IPsec security in the context of this crypto map entry. |
||
|
Example: Router(config-crypto-m)# set-peer 192.168.101.1 |
Specifies a remote IPsec peer, the peer to which IPsec protected traffic can be forwarded. Repeat for multiple remote peers. |
||
|
Example: Router(config-crypto-m)# set transform-set aesset |
Specifies which transform sets are allowed for this crypto map entry. List multiple transform sets in order of priority (highest priority first). |
||
|
Example: Router (config-crypto-m)# set security-association lifetime seconds 2700 |
(Optional) Specifies an SA lifetime for the crypto map entry. By default, the SAs of the crypto map are negotiated according to the global lifetimes. |
||
|
Example: Router(config-crypto-m)# set security-association level per-host |
(Optional) Specifies that separate SAs should be established for each source and destination host pair. By default, a single IPsec "tunnel" can carry traffic for multiple source hosts and multiple destination hosts.
|
||
|
Example: Router(config-crypto-m)# set pfs group2 |
(Optional) Specifies that IPsec either should ask for perfect forward secrecy (PFS) when requesting new SAs for this crypto map entry or should demand PFS in requests received from the IPsec peer. By default, PFS is not requested. If no group is specified with this command, group1 is used as the default. |
||
|
Example: Router(config-crypto-m)# end |
Exits crypto-map configuration mode and returns to privileged EXEC mode. |
||
|
Example: Router# show crypto map |
Displays your crypto map configuration. |
Certain configuration changes take effect only when negotiating subsequent SAs. If you want the new settings to take immediate effect, you must clear the existing SAs so that they are reestablished with the changed configuration. If the router is actively processing IPsec traffic, it is desirable to clear only the portion of the SA database that would be affected by the configuration changes (that is, clear only the SAs established by a given crypto map set). Clearing the full SA database should be reserved for large-scale changes, or when the router is processing very little other IPsec traffic.
To clear IPsec SAs, use the clear crypto sa command with appropriate parameters. (Omitting all parameters clears out the full SA database, which clears active security sessions.)
After you have successfully created a static crypto map, you must apply the crypto map set to each interface through which IPsec traffic flows. To complete this task, see the section "Applying Crypto Map Sets to Interfaces."
Perform this task to create dynamic crypto map entries that use IKE to establish the SAs.
Note |
Dynamic crypto map entries specify crypto access lists that limit traffic for which IPsec SAs can be established. A dynamic crypto map entry that does not specify an access list is ignored during traffic filtering. A dynamic crypto map entry with an empty access list causes traffic to be dropped. If there is only one dynamic crypto map entry in the crypto map set, it must specify acceptable transform sets. |
Command or Action | Purpose | |||
---|---|---|---|---|
|
Example: Router> enable |
Enables privileged EXEC mode. |
||
|
Example: Router# configure terminal |
Enters global configuration mode. |
||
|
Example: Router(config)# crypto dynamic-map test-map 1 |
Creates a dynamic crypto map entry and enters crypto map configuration mode. |
||
|
Example: Router(config-crypto-m)# set transform-set aesset |
Specifies which transform sets are allowed for the crypto map entry. List multiple transform sets in order of priority (highest priority first). This is the only configuration statement required in dynamic crypto map entries. |
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Example: Router(config-crypto-m)# match address 101 |
(Optional) Accesses list number or name of an extended access list. This access list determines which traffic should be protected by IPsec and which traffic should not be protected by IPsec security in the context of this crypto map entry.
If access lists are configured, the data flow identity proposed by the IPsec peer must fall within a permit statement for this crypto access list. If access lists are not configured, the router accepts any data flow identity proposed by the IPsec peer. However, if access lists are configured but the specified access list does not exist or is empty, the router drops all packets. This scenario is similar to static crypto maps because they also require that an access list be specified. Care must be taken if the any keyword is used in the access list, because the access list is used for packet filtering as well as for negotiation. You must configure a match address; otherwise, the behavior is not secure. |
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Example: Router(config-crypto-m)# set peer 192.168.101.1 |
(Optional) Specifies a remote IPsec peer. Repeat for multiple remote peers.
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Example: Router (config-crypto-m)# set security-association lifetime seconds 7200 |
(Optional) Overrides (for a particular crypto map entry) the global lifetime value, which is used when negotiating IPsec SAs. |
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Example: Router(config-crypto-m)# set pfs group2 |
(Optional) Specifies that IPsec should ask for PFS when requesting new security associations for this crypto map entry or should demand PFS in requests received from the IPsec peer. By default, PFS is not requested. If no group is specified with this command, group1 is used as the default. |
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Example: Router(config-crypto-m)# end |
Exits crypto-map configuration mode and returns to privileged EXEC mode. |
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Example: Router# show crypto dynamic-map |
(Optional) Displays information about dynamic crypto maps. |
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Example: Router# configure terminal |
Returns to global configuration mode. |
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Example: Router(config)# crypto map static-map 1 ipsec-isakmp dynamic test-map |
(Optional) Adds a dynamic crypto map to a crypto map set. You should set the crypto map entries referencing dynamic maps to the lowest priority entries in a crypto map set. |
Certain configuration changes take effect only when negotiating subsequent SAs. If you want the new settings to take immediate effect, you must clear the existing SAs so that they are reestablished with the changed configuration. If the router is actively processing IPsec traffic, it is desirable to clear only the portion of the SA database that would be affected by the configuration changes (that is, clear only the SAs established by a given crypto map set). Clearing the full SA database should be reserved for large-scale changes, or when the router is processing very little other IPsec traffic.
To clear IPsec SAs, use the clear crypto sa command with appropriate parameters. (Omitting all parameters clears the full SA database, which clears active security sessions.)
After you have successfully created a crypto map set, you must apply the crypto map set to each interface through which IPsec traffic flows. To complete this task, see the section "Applying Crypto Map Sets to Interfaces."
To create crypto map entries to establish manual SAs (that is, when IKE is not used to establish the SAs), perform this task.
Command or Action | Purpose | |||
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Example: Router> enable |
Enables privileged EXEC mode. |
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Example: Router# configure terminal |
Enters global configuration mode. |
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Example: Router(config)# crypto map mymap 10 ipsec-manual |
Specifies the crypto map entry to create or modify and enters crypto map configuration mode. |
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Example: Router(config-crypto-m)# match address 102 |
Names an IPsec access list that determines which traffic should be protected by IPsec and which traffic should not be protected by IPsec in the context of this crypto map entry. (The access list can specify only one permit entry when IKE is not used.) |
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Example: Router(config-crypto-m)# set peer 10.0.0.5 |
Specifies the remote IPsec peer. This is the peer to which IPsec protected traffic should be forwarded. (Only one peer can be specified when IKE is not used.) |
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Example: Router(config-crypto-m)# set transform-set someset |
Specifies which transform set should be used. This must be the same transform set that is specified in the remote peer's corresponding crypto map entry.
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Example: Router(config-crypto-m)# set session-key inbound ah 256 98765432109876549876543210987654 Example: Router(config-crypto-m)# set session-key outbound ah 256 fedcbafedcbafedcfedcbafedcbafedc |
Sets the AH security parameter indexes (SPIs) and keys to apply to inbound and outbound protected traffic if the specified transform set includes the AH protocol. (This manually specifies the AH security association to be used with protected traffic.) |
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Example: Router(config-crypto-m)# set session-key inbound esp 256 cipher 0123456789012345 Example: Router(config-crypto-m)# set session-key outbound esp 256 cipher abcdefabcdefabcd |
Sets the ESP SPIs and keys to apply to inbound and outbound protected traffic if the specified transform set includes the ESP protocol. Specifies the cipher keys if the transform set includes an ESP cipher algorithm. Specifies the authenticator keys if the transform set includes an ESP authenticator algorithm. (This manually specifies the ESP security association to be used with protected traffic.) |
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Example: Router(config-crypto-m)# end |
Exits crypto-map configuration mode and returns to privileged EXEC mode. |
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Example: Router# show crypto map |
Displays your crypto map configuration. |
For manually established SAs, you must clear and reinitialize the SAs for the changes to take effect. To clear IPsec SAs, use the clear crypto sa command with appropriate parameters. (Omitting all parameters clears the full SA database, which clears active security sessions.)
After you have successfully created a crypto map set, you must apply the crypto map set to each interface through which IPsec traffic flows. To complete this task, see the section "Applying Crypto Map Sets to Interfaces."
You need to apply a crypto map set to each interface through which IPsec traffic flows. Applying the crypto map set to an interface instructs the router to evaluate all the interface's traffic against the crypto map set and to use the specified policy during connection or security association negotiation on behalf of traffic to be protected by crypto.
Perform this task to apply a crypto map to an interface.
Command or Action | Purpose | |
---|---|---|
|
Example: Router> enable |
Enables privileged EXEC mode. |
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Example: Router# configure terminal |
Enters global configuration mode. |
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Example: Router(config)# Interface FastEthernet 0/0 |
Configures an interface and enters interface configuration mode. |
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Example: Router(config-if)# crypto map mymap |
Applies a crypto map set to an interface. |
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Example: Router(config-if)# exit |
Exits interface configuration mode and returns to global configuration mode. |
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Example: Router(config)# crypto map mymap local-address loopback0 |
(Optional) Permits redundant interfaces to share the same crypto map using the same local identity. |
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Example: Router(config)# exit |
(Optional) Exits global configuration mode. |
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Example: Router# show crypto map |
(Optional) Displays your crypto map configuration |
The following example is a portion of the show running-config command. This example shows how to configure a static crypto map and define AES as the encryption method.
crypto isakmp policy 10 encryption aes 256 authentication pre-share lifetime 180 crypto isakmp key cisco123 address 10.0.110.1 ! ! crypto ipsec transform-set aesset esp-aes 256 esp-sha-hmac mode transport ! crypto map aesmap 10 ipsec-isakmp set peer 10.0.110.1 set transform-set aesset match address 120 ! ! ! voice call carrier capacity active ! ! mta receive maximum-recipients 0 ! ! interface FastEthernet0/0/1 ip address 10.0.110.2 255.255.255.0 ip nat outside no ip route-cache no ip mroute-cache duplex auto speed auto crypto map aesmap ! interface Serial0/0 no ip address shutdown ! interface FastEthernet0/1/1 ip address 10.0.110.1 255.255.255.0 ip nat inside no ip route-cache no ip mroute-cache duplex auto speed auto ! ip nat inside source list 110 interface FastEthernet0/0/1 overload ip classless ip route 0.0.0.0 0.0.0.0 10.5.1.1 ip route 10.0.110.0 255.255.255.0 FastEthernet0/0/1 ip route 172.18.124.0 255.255.255.0 10.5.1.1 ip route 172.18.125.3 255.255.255.255 10.5.1.1 ip http server ! ! access-list 110 deny ip 10.0.110.0 0.0.0.255 10.0.110.0 0.0.0.255 access-list 110 permit ip 10.0.110.0 0.0.0.255 any access-list 120 permit ip 10.0.110.0 0.0.0.255 10.0.110.0 0.0.0.255 !
Related Topic |
Document Title |
---|---|
IKE configuration |
|
IKE, IPsec, and PKI configuration commands: complete command syntax, command mode, defaults, usage guidelines, and examples |
Standards |
Title |
---|---|
None |
-- |
MIBs |
MIBs Link |
---|---|
To locate and download MIBs for selected platforms, Cisco IOS XE releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs |
Title |
---|---|
RFC 2401 |
Security Architecture for the Internet Protocol |
RFC 2402 |
IP Authentication Header |
RFC 2403 |
The Use of HMAC-MD5-96 within ESP and AH |
RFC 2404 |
The Use of HMAC-SHA-1-96 within ESP and AH |
RFC 2405 |
The ESP DES-CBC Cipher Algorithm With Explicit IV |
RFC 2406 |
IP Encapsulating Security Payload (ESP) |
RFC 2407 |
The Internet IP Security Domain of Interpretation for ISAKMP |
RFC 2408 |
Internet Security Association and Key Management Protocol (ISAKMP) |
Description |
Link |
---|---|
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 3 | Feature Information for Configuring Security for IPsec VPNs |
Feature Name |
Releases |
Feature Information |
---|---|---|
Advanced Encryption Standard (AES) |
Cisco IOS XE Release 2.1 |
This feature adds support for the new encryption standard AES, which is a privacy transform for IPsec and IKE and has been developed to replace DES. The following sections provide information about this feature: The following commands were modified by this feature: crypto ipsec transform-set, encryption (IKE policy), show crypto ipsec transform-set, show isakmp policy. |
IKE Shared Secret Using AAA Server |
Cisco IOS XE Release 2.1 |
The IKE Shared Secret Using AAA Server feature enables key lookup from a AAA server. This feature was implemented on Cisco ASR 1000 Series Routers. |
anti-replay-- Security service where the receiver can reject old or duplicate packets to protect itself against replay attacks. IPsec provides this optional service by use of a sequence number combined with the use of data authentication. Cisco IOS XE IPsec provides this service whenever it provides the data authentication service, except for manually established SAs (that is, SAs established by configuration and not by IKE).
data authentication --Verification of the integrity and origin of the data. Data authentication can refer either to integrity alone or to both of these concepts (although data origin authentication is dependent upon data integrity).
data confidentiality -- Security service in which the protected data cannot be observed.
data flow -- Grouping of traffic, identified by a combination of source address or mask, destination address or mask, IP next protocol field, and source and destination ports, where the protocol and port fields can have the values of any. IPsec protection is applied to data flows.
peer -- In the context of this module, a "peer" is a router or other device that participates in IPsec.
PFS --perfect forward secrecy. Cryptographic characteristic associated with a derived shared secret value. With PFS, if one key is compromised, previous and subsequent keys are not compromised, because subsequent keys are not derived from previous keys.
SA --security association. Description of how two or more entities use security services in the context of a particular security protocol (AH or ESP) to communicate securely on behalf of a particular data flow. The transform and the shared secret keys are used for protecting the traffic.
SPI --security parameter index. A number which, together with a destination IP address and security protocol, uniquely identifies a particular security association. Without IKE, the SPI is manually specified for each security association.
transform -- List of operations performed on a dataflow to provide data authentication, data confidentiality, and data compression. For example, one transform is the ESP protocol with the HMAC-MD5 authentication algorithm; another transform is the AH protocol with the 56-bit DES encryption algorithm and the ESP protocol with the HMAC-SHA authentication algorithm.
tunnel -- In the context of this module, "tunnel" is a secure communication path between two peers, such as two routers. It does not refer to using IPsec in tunnel mode.
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R)
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.