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Table Of Contents
Cisco Group Encrypted Transport VPN
Prerequisites for Cisco Group Encrypted Transport VPN
Restrictions for Cisco Group Encrypted Transport VPN
Information About Cisco Group Encrypted Transport VPN
Cisco Group Encrypted Transport VPN Overview
Cisco Group Encrypted Transport VPN Architecture
Key Distribution: Group Domain of Interpretation
Cisco Group Encrypted Transport VPN Features
Group Member Access Control List
Enhanced Solutions Manageability
Support with VRF-Lite Interfaces
How to Configure Cisco Group Encrypted Transport VPN
Setting up RSA Keys to Sign Rekey Messages
Setting up the Group ID, Server Type, and SA Type
Setting up an IPsec Lifetime Timer
Setting up an ISAKMP Lifetime Timer
Setting Up the Group Name, ID, and Key Server IP Address
Applying the Crypto Map to an Interface to Which the Traffic Has to Be Encrypted
Verifying and Troubleshooting Cisco Group Encrypted Transport VPN
Verifying Active Group Members on a Key Server
Verifying Rekey-Related Statistics
Verifying IPsec SAs That Were Created by GDOI on a Key Server
Verifying Cooperative Key Server States and Statistics
Verifying Anti-Replay Pseudotime-Related Statistics
Configuration Examples for Cisco Group Encrypted Transport VPN
Key Server and Group Member Case Study
Feature Information for Cisco Group Encrypted Transport VPN
Cisco Group Encrypted Transport VPN
First Published: November 17, 2006
Last Updated: June 18, 2007
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Effective with Cisco IOS 12.4(11)T, the Multicast Rekeying feature information (originally published as Cisco IOS Release 12.4(6)T [titled Secure Multicast]) has been integrated into this document.
Today's networked applications, such as voice and video, are accelerating the need for instantaneous, branch-interconnected, and Quality of Service- (QoS-) enabled WANs. The distributed nature of these applications results in increased demands for scale. At the same time, enterprise WAN technologies force businesses to trade off between QoS-enabled branch interconnectivity and transport security. As network security risks increase and regulatory compliance becomes essential, Cisco Group Encrypted Transport VPN (GET VPN) eliminates the need to compromise between network intelligence and data privacy.
GET VPN eliminates the need for tunnels. By removing the need for point-to-point tunnels, meshed networks are able to scale higher while maintaining network-intelligence features that are critical to voice and video quality, such as QoS, routing, and multicast. GET VPN offers a new standards-based IP security (IPsec) security model that is based on the concept of "trusted" group members. Trusted member routers use a common security methodology that is independent of any point-to-point IPsec tunnel relationship.
GET VPN is a set of features that are necessary to secure IP multicast group traffic or unicast traffic over a private WAN that originates on or flows through a Cisco IOS device. GET VPN combines the keying protocol Group Domain of Interpretation (GDOI) with IPsec encryption to provide users with an efficient method to secure IP multicast traffic or unicast traffic. GET VPN enables the router to apply encryption to nontunneled (that is, "native") IP multicast and unicast packets and eliminates the requirement to configure tunnels to protect multicast and unicast traffic.
Cisco Group Encrypted Transport VPN provides the following benefits:
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Finding Feature Information in This Module
Your Cisco IOS software release may not support all of the features documented in this module. To reach links to specific feature documentation in this module and to see a list of the releases in which each feature is supported, use the "Feature Information for Cisco Group Encrypted Transport VPN" section.
Finding Support Information for Platforms and Cisco IOS and Catalyst OS Software Images
Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Contents
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Prerequisites for Cisco Group Encrypted Transport VPN
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Restrictions for Cisco Group Encrypted Transport VPN
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Information About Cisco Group Encrypted Transport VPN
To configure GET VPN, you should understand the following concepts:
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Cisco Group Encrypted Transport VPN Overview
Today's networked applications, such as voice and video, are accelerating the necessity for instantaneous, branch-interconnected, and QoS-enabled WANs. And the distributed nature of these applications results in increased demands for scale. At the same time, enterprise WAN technologies force businesses to trade off between QoS-enabled branch interconnectivity and transport security. As network security risks increase and regulatory compliance becomes essential, GET VPN, a next-generation WAN encryption technology, eliminates the need to compromise between network intelligence and data privacy.
With the introduction of GET, Cisco now delivers a new category—tunnel-less VPN—that eliminates the need for tunnels. By removing the need for point-to-point tunnels, meshed networks can scale higher while maintaining network-intelligence features critical to voice and video quality. GET offers a new standards-based security model that is based on the concept of "trusted" group members. Trusted member routers use a common security methodology that is independent of any point-to-point IPsec tunnel relationship. By using trusted groups instead of point-to-point tunnels, "any-any" networks can scale higher while maintaining network-intelligence features (such as QoS, routing, and multicast), which are critical to voice and video quality.
GET-based networks can be used in a variety of WAN environments, including IP and Multiprotocol Label Switching (MPLS). MPLS VPNs that use this encryption technology are highly scalable, manageable, and cost-effective, and they meet government-mandated encryption requirements. The flexible nature of GET allows security-conscious enterprises either to manage their own network security over a service provider WAN service or to offload encryption services to their providers. GET simplifies securing large Layer 2 or MPLS networks that require partial or full-mesh connectivity.
Cisco Group Encrypted Transport VPN Architecture
GET VPN is an enhanced solution that encompasses Multicast Rekeying, a Cisco solution for enabling encryption for "native" multicast packets, and unicast rekeying over a private WAN. Multicast Rekeying and GET VPN is based on GDOI as defined in Internet Engineering Task Force (IETF) RFC 3547. In addition, there are similarities to IPsec in the area of header preservation and SA lookup. Dynamic distribution of IPsec SAs has been added, and tunnel overlay properties of IPsec have been removed. Figure 1 further illustrates the concepts of GET VPN and their relationships among one another.
Figure 1 GET VPN Concepts and Relationships
This section includes the following subsections:
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Key Distribution: Group Domain of Interpretation
GDOI
GDOI is defined as the Internet Security Association Key Management Protocol (ISAKMP) Domain of Interpretation (DOI) for group key management. In a group management model, the GDOI protocol operates between a group member and a group controller or key server (GCKS), which establishes security associations (SAs) among authorized group members. The ISAKMP defines two phases of negotiation. GDOI is protected by a Phase 1 ISAKMP security association. The Phase 2 exchange is defined in IETF RFC 3547. The topology shown in Figure 2 and the corresponding explanation show how this protocol works.
Group Member
The group member registers with the key server to get the IPsec SA or SAs that are necessary to communicate with the group. The group member provides the group ID to the key server to get the respective policy and keys for this group. These keys are refreshed periodically, and before the current IPsec SAs expire, so that there is no loss of traffic.
Key Server
The responsibilities of the key server include maintaining the policy and creating and maintaining the keys for the group. When a group member registers, the key server downloads this policy and the keys to the group member. The key server also rekeys the group before existing keys expire.
The key server has two modes: servicing registration requests and sending rekeys. A group member can register at any time and receive the most current policy and keys. When a group member registers with the key server, the key server verifies the group ID that the group member is attempting to join. If this ID is a valid group ID, the key server sends the SA policy to the group member. After the group member acknowledges that it can handle the downloaded policy, the key server downloads the respective keys.
There are two types of keys that the key server can download: the key encryption key (KEK) and the traffic encryption key (TEK). The TEK becomes the IPsec SA with which the group members within the same group communicate. The KEK encrypts the rekey message.
The GDOI server sends out rekey messages either because of an impending IPsec SA expiration or because the policy has changed on the key server (using command-line interface [CLI]). The rekey messages may also be retransmitted periodically to account for possible packet loss. Packet loss can occur because rekey messages are sent without the use of any reliable transport. There is no efficient feedback mechanism by which receivers can indicate that they did not receive a rekey message, so retransmission seeks to bring all receivers up to date.
Figure 2 Protocol Flows That Are Necessary for Group Members
to Participate in a Group
The above topology shows the protocol flows that are necessary for group members to participate in a group, which are as follows:
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How Protocol Messages Work with the Cisco IOS
Multicast Rekeying uses the GDOI protocol (IETF RFC 3547) to distribute the policy and keys for the group. The GDOI protocol is between a key server and a group member. The key server creates and maintains the policy and keys, and it downloads the policy and keys to the authenticated group members. The group members are authenticated by the key server and communicate with other authenticated group members that are in the same group using the IPsec SAs that the group members have received from the key server.
The GDOI protocol is protected by an ISAKMP Phase 1 exchange. The GDOI key server and the GDOI group member must have the same ISAKMP policy. This Phase 1 ISAKMP policy should be strong enough to protect the GDOI protocol that follows. The GDOI protocol is a four-message exchange that follows the Phase 1 ISAKMP policy. The Phase 1 ISAKMP exchange can occur in main mode or aggressive mode.
Figure 3 shows the ISAKMP Phase 1 exchange.
Figure 3 ISAKMP Phase 1 Exchange and GDOI Registration
The above messages (the ISAKMP Phase 1 messages and the four GDOI protocol messages) are referred to as the GDOI registration, and the entire exchange that is shown above is a unicast exchange between the group member and the key server.
After the registration is successful, the key server sends a multicast rekey to all the group members that have registered within a group. During the registration, the group member receives the address of the multicast group and registers with the multicast group that is required to receive the multicast rekeys.
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IPsec
IPsec is a well-known RFC that defines an architecture to provide various security services for traffic at the IP layer. The components and how they fit together with each other and into the IP environment are described in IETF RFC 2401.
Communication Flow Between Key Servers and Group Members to Update IPsec SAs
Key servers and group members are the two components of the GET VPN architecture. The key server holds and supplies group authentication keys and IPsec SAs to the group members.
Group members provide encryption service to the interesting traffic (traffic that is worthy of being encrypted and secured by IPsec).
Communication among the key server and group members is encrypted and secured. GDOI supports the use of two keys: The TEK and the KEK. The TEK is downloaded by the key server to all the group members. The downloaded TEK is used by all the group members to communicate securely among each other. This key is essentially the group key that is shared by all the group members. The group policies and IPsec SAs are refreshed by the key server using periodic rekey messages to the group members. The KEK is also downloaded by the key server and is used by the group members to decrypt the incoming rekey messages from the key server.
The key server generates the group policy and IPsec SAs for the GDOI group. The information generated by the key server includes multiple TEK attributes, traffic encryption policy, lifetime, source and destination, a Security Parameter Index (SPI) ID that is associated with each TEK, and the rekey policy (one KEK).
Figure 4 illustrates the communication flow between group members and the key server. The key server, after receiving registration messages from a group member, generates the information that contains the group policy and new IPsec SAs. The new IPsec SA is then downloaded to the group member. The key server maintains a table that contains the IP address of each group member per group. When a group member registers, the key server adds its IP address in its associated group table, thus allowing the key server to monitor an active group member. A key server can support multiple groups. A group member can be part of multiple groups.
Figure 4 Communication Flow Between Group Members and the Key Server
IPsec and ISAKMP Timers
IPsec and ISAKMP SAs are maintained by the following timers:
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Routing
GET VPN routing is explained in the following section.
Header Preservation
As shown in Figure 5, IPsec-protected data packets carry the original source and destination in the outer IP header rather than replacing them with tunnel endpoint addresses. This technique is known as IPsec Tunnel Mode with Address Preservation.
Figure 5 Header Preservation
Address preservation allows GET VPN to use the routing functionality present within the core network. Address preservation allows routing to deliver the packets to any customer-edge device (CE) in the network that advertises a route to the destination address. Any source and destination matching the policy for the group will be treated in a similar manner. In the situation where a link between IPsec peers is not available, address preservation also helps combat traffic "black-hole" situations.
Header preservation also maintains routing continuity throughout the enterprise address space and in the WAN. As a result, end host addresses of the campus are exposed in the WAN (for MPLS, this applies to the edge of the WAN). For this reason, GET VPN is applicable only when the WAN network acts as a "private" network (for example, in a MPLS network).
Secure Data Plane Multicast
The multicast sender uses the TEK that is obtained from the key server and encrypts the multicast data packet with header preservation before it switches out the packet. The replication of the multicast packet is carried out in the core on the basis of the (S,G) state that is retained in the multicast data packet. This process is illustrated in Figure 6.
Figure 6 Secure Data Plane Multicast Process
Secure Data Plane Unicast
The unicast sender uses the TEK that is obtained from the key server and encrypts the unicast data packet with header preservation before it switches out the packet to the destination. This process is illustrated in Figure 7.
Figure 7 Secure Data Plane Unicast Process
Cisco Group Encrypted Transport VPN Features
This section includes the following subsections:
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Rekeying
Rekey messages are used to refresh IPsec SAs. When the IPsec SAs or the rekey SAs are about to expire, one single rekey message for a particular group is generated on the key server. No new IKE sessions are created for the rekey message distribution. The rekey messages are distributed by the key server over an existing IKE SA.
Rekeying can use multicast or unicast messages. GET VPN supports both unicast and multicast rekeying.
Multicast Rekeying
Multicast rekeys are sent out using an efficient multicast rekey. Following a successful registration, the group member registers with a particular multicast group. All the group members that are registered to the group receives this multicast rekey. Multicast rekeys are sent out periodically on the basis of the configured lifetime on the key server. Multicast rekeys are also sent out if the IPsec or rekey policy is changed on the key server. Triggered by the configuration change, the rekey sends out the new updated policy to all the group members with an efficient multicast rekey.
Unicast Rekeying and SAs
In a large unicast group, to alleviate latency issues, the key server generates rekey messages for only a small number of group members at a time. The key server is ensured that all group members receive the same rekey messages for the new SA before the expiration of the old SA. Also, in a unicast group, after receiving the rekey message from the key server, a group member sends an encrypted acknowledge (ACK) message to the key server using the keys that were received as part of the rekey message. When the key server receives this ACK message, it notes this receipt in its associated group table, which accomplishes the following:
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In addition, in a unicast group, the key server removes the group member from its active list and stops sending the rekey messages to that particular group member if the key server does not receive an ACK message for three consecutives rekeys. If no ACK message is received for three consecutive rekeys, the group member has to fully reregister with the key server after its current SA expires if the group member is still interested in receiving the rekey messages. The ejection of a nonresponsive group member is accomplished only when the key server is operating in the unicast rekey mode. The key server does not eject group members in the multicast rekey mode because group members cannot send ACK messages in that mode.
As in multicast rekeying, if retransmission is configured, each rekey will be retransmitted the configured number of times.
Rekey transport modes and authentication can be configured under a GDOI group.
If unicast rekey transport mode is not defined, multicast is applied by default.
If the TEK rekey is not received, the group member reregisters with the key server 60 seconds before the current IPsec SA expires. The key server has to send out the rekey before the group member reregistration occurs. If no retransmission is configured, the key server sends the rekey 90 seconds before the SA expires. If retransmission is configured, the rekey occurs earlier thant 90 seconds to let the last retransmission be sent 90 seconds before the SA expires.
The key server uses the formula in the example below to calculate when to start sending the rekey to all unicast group members. The unicast rekey process on the key server sends rekeys to unicast group members in groups of 50 within a loop. The time spent within this loop is estimated to be 5 seconds.
A key server rekeys group members in groups of 50, which equals two loops. For example, for 100 group members:
Number of rekey loops = (100 group members)/50 = 2 loops
Time it takes to rekey one loop (estimation) = 5 seconds
Time to rekey 100 group members in two loops of 50: 2 * 5 seconds = 10 seconds
So, the key server pushes the rekey time back as follows:
If the TEK timeout is 300: 300 - 10 = 290
But, the start has to be earlier than the TEK expiry (as in the multicast case).
So, 90 seconds is subtracted from the actual TEK time: 290 - 90 = 200 seconds.
If retransmissions are configured, the rekey timer is moved back more.
For three retransmissions every 10 seconds: 200 - (3 * 10) = 170.
IPsec SA Usage on the Group Members
When a rekey is received and processed on a group member, the new IPsec SA (the Security Parameter Index [SPI]) is installed. There is a period of time when the old and the new IPsec SAs are used. After a certain specified interval, the old IPsec SA is deleted. This overlap is ensures that all group members receive the current rekey and insert the new IPsec SAs. This behavior is independent of the transport method (multicast or unicast rekey transport) for the rekeys from the key server.
On the group member, approximately 30 seconds before the old SA expires, the group member starts to use the new SA in the outbound direction to encrypt the packet. Approximately 60 seconds before the old SA expires, if no new SA is received on the group member side via a rekey from the key server, the group member reregisters.
Figure 8 IPsec SA Usage on a Group Member
In Figure 8, time T2 is when the old SA expires. T1 is 30 seconds before T2, which is when the group member (GM) starts to use the new SA in the outbound direction. T0 is another 30 seconds before T2. If no new SA is received at T0, the group member has to reregister. T is another 30 seconds from T0. The key server (KS) should send a rekey at T.
Configuration Changes Can Trigger a Rekey By a Key Server
Configuration changes on a key server can trigger a rekey by the key server. Please refer to the following sample configuration as you read through the events that will or will not cause a rekey.
crypto ipsec transform-set gdoi-p esp-3des esp-sha-hmac!crypto ipsec profile gdoi-pset security-association lifetime seconds 900set transform-set gdoi-p!crypto gdoi group diffintidentity number 3333server localrekey algorithm aes 128rekey address ipv4 121rekey lifetime seconds 3600no rekey retransmitrekey authentication mypubkey rsa mykeyssa ipsec 1profile gdoi-pmatch address ipv4 120replay counter window-size 3Changes That Will Trigger a Rekey on a Key Server
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Changes That Will Not Trigger a Rekey on a Key Server
The following configuration changes on the key server will not trigger a rekey from the key server:
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Group Member Access Control List
For GET VPN, the traffic that has to be protected is defined statically on the key server using the access control list (ACL). The group member gets information about what has to be protected from the key server. This structure allows the key server to choose and change the policy dynamically as needed. In Secure Multicast, the key server ACL is defined inclusively. The ACL includes only the exact traffic that should be encrypted, with an implicit deny causing all other traffic to be allowed in the clear (that is, if there is no permit, all other traffic is allowed).
GET VPN employs a different philosophy: the definition of which packets should be encrypted is delivered independently. GET VPN supports only statically defined traffic selectors. Policy can be defined by using both deny and permit ACLs on the key server. Only the deny ACL is allowed to be manually configured on a group member. The policies that are downloaded from the key server and configured on the group member are merged. Any ACL that is configured on the group member has predominance over what is downloaded from the key server.
After the group member gets the ACL from the key server, the group member creates a temporary ACL and inserts it into the database. This ACL will be deleted if the group member is removed from the GDOI group for any reason. The packets that are going out of the interface are dropped by the group member if a packet matches the ACL but no IPsec SA exists for that packet.
The key server can send a set of traffic selectors, which may not exactly match the group member ACL on the group member. If such differences occur, the differences have to be merged and resolved. Because the group member is more aware of its topology than the key server, the downloaded ACLs are appended at the end of the group member ACL. The group member ACL (except the implicit deny) is inserted into the database first, followed by the downloaded key server ACL. The database is prioritized, and the database search stops whenever a matched entry is found.
For information about configuring a group member ACL, see "Setting up Group Member ACLs" section."
Time-Based Anti-Replay
Anti-replay is an important feature in a data encryption protocol such as IPSec (RFC 2401). Anti-replay prevents a third party from eavesdropping on an IPsec conversation, stealing packets, and injecting those packets into a session at a later time. The time-based anti-replay mechanism helps ensure that invalid packets are discarded by detecting the replayed packets that have already arrived at an earlier time.
GET VPN uses the Synchronous Anti-Replay (SAR) mechanism to provide anti-replay protection for multisender traffic. SAR is independent of real-world Network Time Protocol (NTP) clock or sequential-counter mechanisms (which guarantee packets are received and processed in order). A SAR clock advances regularly. The time tracked by this clock is called pseudotime. The pseudotime is maintained on the key server and is sent periodically to the group members within a rekey message as a timestamp field called pseudoTimeStamp. GET VPN uses a Cisco proprietary protocol called Metadata to encapsulate the psuedoTimeStamp. Group members have to be resynchronized to the pseudotime of the key server periodically. The pseudotime of the key server starts ticking from when the first group member registers. Initially, the key server sends the current pseudotime value of the key server and window size to group members during the registration process. New attributes, such as time-based replay-enabled information, window size, and the pseudotime of the keyserver, is sent under the SA payload (TEK).
The group members use the pseudotime to prevent replay as follows: the pseudoTimeStamp contains the pseudotime value at which a sender created a packet. A receiver compares the pseudotime value of senders with its own pseudotime value to determine whether a packet is a replayed packet. The receiver uses a time-based anti-replay "window" to accept packets that contain a timestamp value within that window. The window size is configured on the key server and is sent to all group members.
Figure 9 illustrates an anti-replay window in which the value PTr denotes the local pseudotime of the receiver, and W is the window size.
Figure 9 Anti-Replay Window
Keeping Clocks Synchronized
It is possible for the clocks of the group members to slip and lose synchronization with the key server. To keep the clocks synchronized, a rekey message (multicast or unicast, as appropriate), including the current pseudotime value of the key server, is sent periodically (either in a rekey message or at a minimum of every 30 minutes to the group member. If a packet fails this anti-replay check, the pseudotime of both the sender and receiver is printed, an error message is generated, and a count is increased.
To view anti-replay statistics, use the show crypto gdoi group group-name gm replay command on both the sender and receiver devices. If the configuration is changed by the administrator to affect the replay method of the size configuration, the key server initiates a rekey message.
Interval Duration
A tick is the interval duration of the SAR clock. Packets sent in this duration have the same pseudoTimeStamp. The tick is also downloaded to group members, along with the psuedotime from the key server. For example, as shown in Figure 10, packets sent between T0 and T1 would have the same pseudoTimeStamp T0. SAR provides loose anti-replay protection. The replayed packets are accepted if they are replayed during the window. The default window size is 100 seconds. It is recommended that you keep the window size small to minimize packet replay.
Figure 10 SAR Clock Interval Duration
Anti-Replay Configurations
The Anti-Replay feature can be enabled under IPsec SA on a key server by using the following commands:
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Cooperative Key Server
Figure 11 illustrates cooperative key server key distribution. The text below the illustration explains the Cooperative Key Server feature.
Figure 11 Cooperative Key Server Key Distribution
Cooperative key servers provide redundancy to GET VPN. Multiple key servers are supported by GET VPN to ensure redundancy, high availability, and fast recovery if the primary key server fails. Cooperating GDOI key servers jointly manage the GDOI registrations for the group. Each key server is an active key server, handling GDOI registration requests from group members. Because the key servers are cooperating, each key server distributes the same state to the group members that register with it. Load balancing is achieved because each of the GDOI key servers can service a portion of the GDOI registrations.
The primary key server is responsible for creating and distributing group policy. The primary key server periodically sends out (or broadcasts) group information updates to all other key servers to keep those servers in synchronization. If the secondary key servers somehow miss the updates, they contact the primary key server to directly request information updates. The secondary key servers mark the primary key server as unreachable (that is, "dead") if the updates are not received for an extended period of time.
When a new policy is created on a primary key server, regardless of which key server a group member may be registered with, it is the responsibility of the primary key server to distribute rekey messages to GDOI group members.
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Announcement Messages
Announcement messages are secured by IKE Phase 1 and are sent as IKE notify messages. Authentication and confidentiality that are provided by IKE is used to secure the messaging between the key servers. Anti-replay protection is provided by the sequence numbers in the announcement messages. Announcement messages are periodically sent from primary to secondary key servers.
Announcement messages include the following components that help maintain the current state.
Sender Priority of a Key Server
This value describes the priority of the sender, which is configurable using the CLI. The key server with the highest priority becomes the primary key server. If the priority values are the same, the key server with the highest IP address becomes the primary key server.
Maintaining the Role of the Sender
During the synchronization period, if the key servers are at geographically dispersed locations, they may suffer a network-partitioning event. If a network-partitioning event occurs, it is possible that more than one key server can become the primary key server for a period of time. When the network is operating normally again and all the key servers find each other, they need to be told the current role of the sender so the key servers can attain their proper roles.
Request for a Return Packet Flag
All messages are defined as one-way messages. When needed, a key server can request the current state from a peer to find out its role and/or request the current state of the group.
Group Policies
The group policies are the policies that are maintained for a group, such as group member information and IPsec SAs and keys.
Anti-replay functionalities and incorporated Cooperative announcement messages are supported. The primary key server updates the pseudotime value, sending it to all secondary key servers in the group. The secondary key servers should synchronize their SAR clocks to this updated value.
Receive Only SA
For multicast traffic using the GDOI protocol, bidirectional SAs are installed. The Receive Only feature enables an incremental deployment so that only a few sites can be verified before bringing up an entire network. To test the sites, one of the group members should send encrypted traffic to all the other group members and have them decrypt the traffic and forward the traffic "in the clear." Receive Only SA mode allows encryption in only the inbound direction for a period of time. (See the steps below for the Receive Only SA process.) If you configure the sa receive-only command on the key server, Steps 2 and 3 happen automatically.
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This action allows the group members to install SAs in the inbound direction only. Receive-only SAs can be configured under a crypto group. (See "Setting up the Group ID, Server Type, and SA Type" section.")
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If the sa receive-only command is configured, all TEKs under this group are going to be marked "receive only" by the key server when they are sent to the group member.
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Every time a GDOI group member receives an IPsec SA from the key server that is marked as "receive only," the group member installs this IPsec SA only in the inbound direction rather than in both incoming and outgoing directions.
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Local Conversion
First, individually convert each of the group members to passive mode (this change tells the outbound check that there is a valid SA ) and then to bi-directional mode.
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The following method can be used when the testing phase is over and "receive only" SAs have to be converted to bi-directional SAs.
Global Conversion
Remove the sa receive-only command under the group. Removing the sa receive-only command creates new IPsec SAs for this group and causes a rekey. On receipt, group members reinstall the SA in both directions and begin to use it in passive mode. Because the SA cannot remain in passive mode forever, the group members change those SAs to receive or send mode if there is no rekey in 5 minutes. The conversion from passive mode to bidirectional encryption mode is automatic and does not require the administrator to do anything.
Enhanced Solutions Manageability
Several show and debug commands are supported to help verify functionality. See the "Verifying and Troubleshooting Cisco Group Encrypted Transport VPN" section for the details.
Support with VRF-Lite Interfaces
VRF-Lite application supports segmentation of traffic in the control and forwarding planes by keeping the routing tables separate for each user group (or VPN) and forwards the traffic on the associated or dedicated interfaces of each user group.
There are some deployment scenarios in which remote sites that are connecting to an MPLS VPN network might be extending segmentation from a campus to the WAN. In such an extended segmentation case, a CE-PE interface on a CE (group member or key server) device "bounds" to its associated Virtual Routing Forwarding (VRF) instance. This VRF interface connects to an MPLS PE device where it is directly mapped to its associated Border Gateway Protocol (BGP) VRF process, in which case the crypto map is applied to a VRF interface. No other configuration changes are necessary.
End-User Considerations
Multicast rekeying can be used with all modes of multicast. The rekey retransmit command should be used whenever the Protocol Independent Multicast-sparse mode (PIM-SM) is configured because the PIM-SM shortest path tree (SPT) can be torn down if it does not receive continuing traffic. When traffic resumes, PIM-SM must reestablish the SPT. Retransmitting rekey packets increases the chance that group members receive the rekeys when PIM-SM is setting up the SPT.
System Error Messages
For a list of system error messages, see Appendix I: System Messages.
How to Configure Cisco Group Encrypted Transport VPN
This section includes the following required and optional tasks:
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Setting up a Key Server
To set up a key server, perform the steps in the following five subtasks.
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Prerequisites
Before creating the GDOI group, you must first configure IKE and the IPsec transform set, and you must create an IPsec profile. For information about how to configure IKE and the IPsec transform set and to create an IPsec profile, see the "Related Documents" subsection of the "Additional References" section.
Setting up RSA Keys to Sign Rekey Messages
To set up RSA keys that will be used to sign rekey messages, perform the following steps.
If you want to configure anti-replay, use the replay time window-size and replay counter window-size commands (see Steps 4 and 5 below).
Note
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SUMMARY STEPS
1.
2.
3.
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5.
DETAILED STEPS
What to Do Next
Set up the group ID, server type, and SA type. (See the section "Setting up the Group ID, Server Type, and SA Type" section.)
Setting up the Group ID, Server Type, and SA Type
To set up the group ID, server type, and SA type, perform the following steps.
Note
SUMMARY STEPS
1.
2.
3.
4.
or
identity address ipv4 address
5.
6.
DETAILED STEPS
What to Do Next
Remove the receive-only configuration on the key server so that the group members are now operating in bidirectional receive and send mode.
Setting up the Rekey
Rekey is used in the control plane by the key server to periodically refresh the policy and IPsec SAs of the group. On the group-member side, instead of fully reregistering when timers expire for any other reasons, refreshing the registration with a rekey is more efficient. The initial registration is always a unicast registration.
The key server can be configured to send rekeys in unicast or multicast mode. The rekey transport mode is determined by whether the key server can use IP multicast to distribute the rekeys. If multicast capability is not present within the network of the customer, the key server will have to be configured to send rekeys using unicast messages.
Additional options for rekey use the rekey authentication, rekey retransmit, and rekey address ipv4 commands. If unicast transport mode is configured, the source address command will have to be included to specify the source address of this unicast rekey message.
Multicast is the default transport type for rekey messages. The following bulleted items explain when to use rekey transport type mulitcast or unicast:
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Note
The reregistering forces the default transport type to multicast. If no transport type was configured previously, the multicast transport type will apply by default.
Prerequisites
Before configuring the rekey authentication command, you must have configured the router to have a RSA key generated using the crypto key generate rsa command and general-keys and label keywords (for example, "crypto key generate rsa general-key label my keys").
Setting up a Unicast Rekey
To set up a unicast rekey, perform the following steps.
Note
SUMMARY STEPS
1.
2.
3.
4.
or
identity address ipv4 address
5.
6.
7.
8.
9.
10.
Setting up a Multicast Rekey
To set up a multicast rekey, perform the following steps.
SUMMARY STEPS
1.
2.
3.
4.
or
identity address ipv4 address
5.
6.
7.
8.
9.
10.
11.
12.
