The Bryant Advantage CCNP ROUTE Study Guide

Chris Bryant, CCIE #12933

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The Remote Workplace, Part I: VPNs And IPSec
VPN Terminology Data Encryption Technologies Key Encryption Schemes The IPSec Architecture Configuring Site-to-Site VPNs Creating An IKE Policy Configuring Transform Sets Crypto ACLs Configuring Site-to-Site VPNs with SDM Dead Peer Detection GRE Over IPSec Tunnels Configuring GRE Over IPSec Tunnels with SDM Easy VPN Server and Client Configuring Easy VPN Server In SDM Configuring Easy VPN Client

In a previous section, we discussed different methods of allowing mobile users and remote offices communicate with a central location ("HQ"). These days, it's not enough to have communication - we need secure communication. Virtual Private Networks (VPNs) are a great way to secure these transmissions.

It's the "private" part of VPNs that brings us that security. Configuring VPNs gives us the opportunity to apply security to a connection that is using a shared technology such as Frame Relay - in other words, to treat this connection as though it were on a private network. What's A VPN? VPNs are often referred to as tunnels. We can apply security rules and policies to this tunnel without applying them to other WAN communications. For example, when we configure commands directly on the Serial0 interface, all communications using that interface are subject to those commands. When we create a VPN, it's actually seen as a separate interface - you'll see this when we configure one - and we can apply rules to the VPN that are not applied to other communications using Serial0. In the following exhibit, a VPN has been created between two routers. Security policies can be enforced on the VPN between those two routers without affecting any WAN communications involving the bottom router.

There are some VPN terms that are sometimes used interchangeably, but they don't refer to the same feature. Let's take a close look at these terms. VPNs offer three vital functions. Note that two of these occur at the receiver, and one at the sender. Data origin authentication allows the receiver to guarantee the source of the packet.

Encryption is just that - the sender encrypts the packets before sending them. If an intruder picks them off the wire, they will have no meaning.

Integrity is the receiver's ability to ensure that the data was not affected or altered in any fashion as it traveled across the VPN.

There are three different protocols we can use to create this tunnel. Originally defined in RFC 1701, Generic Routing Encapsulation enables a Cisco router to encapsulate a packet in an IP header. When the packet reaches the remote router, the header is stripped off. GRE's drawback is that there's no encryption scheme, and that's a pretty big drawback. Defined in RFC 2661, The Layer 2 Tunneling Protocol (L2TP) is actually a hybrid of Microsoft's Point-to-Point Tunneling Protocol (PPTP) and Cisco's own Layer 2 Forwarding (L2F). Again, the major drawback is that L2TP doesn't have an encryption scheme either.

This giant flaw is corrected by IP Security, generally referred to as IPSec. IPSec does offer encryption along with authentication, and that's why you'll see more IPSec in today's networks than L2TP or GRE. That's also why we're going to spend the majority of this section working with IPSec. VPN Terminology Before we get to a more specific discussion of VPNs, there are some general terms you should know. We'll review the terms from the beginning of this section as well. Data Confidentiality means that only the devices that should see the data in an unencrypted form will see the data that way. Generally, this is achieved by one endpoint encrypting the data and sending it across the link in that fashion, with the second endpoint unencrypting the data. Data Integrity means that the recipient of the data can guarantee that the received data is the same as the transmitted data - in short, that the data was not altered during transport. Data Origin Authentication guarantees that the data originated from a specific endpoint. Anti-replay protection (sometimes just called "replay protection") protects against replay attacks, a malicious repeat and/or delay of a valid transmission. Replay attacks can begin innocently enough. In this example, Router C requests proof of identity from Router A. Router A responds with proof of identity.

The problem is, an Intruder is listening to the conversation and copies Router A's proof of identity.

After A and C are done with their conversation, the Intruder starts a

These data blocks are usually 64 bits in size. Variations of symmetric encryption include stream algorithms. Symmetric encryption is sometimes called secret key encryption. a repeated sequence number will be rejected. DES keys can be broken in any time frame from 24 hours to ten minutes. pretending to be A. When C asks for proof of identity.conversation with C. The main issue is that the key used by DES to encrypt data is only 56 bits in size. To me. (A key is a random string of binary Key Encryption Schemes Symmetric encryption is an algorithm where the key that is used for encryption is also used for decryption. If you'd like to take a peek at how it works . Triple DES (3DES) is just what it sounds like . and C will accept it. Anti-replay protection can use several different methods of defeating such an attack. and a few problems have developed with DES since then. where one bit or byte is encrypted/decrypted at a time. where blocks of data are encrypted/decrypted as a whole.the DES encryption procedure is run three times..wikipedia. . Both DES and 3DES use symmetric encryption. The actual function of AES is far beyond the scope of this exam. http://en.) Thirty years ago. that was fine. but it really is quite fascinating.. and block algorithms. DES was developed in 1976. AES can run on any Cisco router that has IPSec DES/3DES capability. anyway.. with three different 56-bit DES keys. including the one-time use of tokens for the proof of identity or by using sequence numbers. The Advanced Encryption Standard (AES) is being rapidly adopted by governments and organizations around the world. but the effective security provided is considered to be only 112 bits. Data Encryption Technologies For data to be encrypted. the Intruder submits A's ID. it follows that something's got to perform this encryption! One such encryption tool is the Data Encryption Standard (DES). That's a total of 168 bits. but then again floppy disks used to be the largest storage unit any of us needed! Depending on which documentation you read.

or it may be a CA in your very own organization. Now that the CA has verified Dan and Bob. Dan will actually use Bob's public key to encrypt the message. The digital certificate is a combination of Dan's public key and the CA's private root key. If "Dan" has a public key. Exchanging Secret Keys Over A Non-Secure Connection It seems like quite a Catch-22. The CA may be global. The email is then sent to Bob. The IPSec Architecture IPSec is a combination of three following protocols: . asymmetric encryption involves two keys for both the sender and receiver. and the CA will then issue a digital certificate saying just that.but it's still in use today in networks around the world. In contrast. who will use his private key to de-encrypt the email. the public key should be certified by a third party called a Certificate Authority (CA). making it that much easier for an intruder to discover the Before starting the actual encryption process. Dan will send an email to Bob using In this example. The key here (no pun intended) is that you better trust your CA. but since the VPN doesn't exist yet. this protocol was also designed in 1976 . to create the VPN. This public key encryption scheme involves a public and private key for each user. because the entire public key encryption process is built around the CA verifying users and their public keys. we need the endpoints to exchange secret keys. public key encryption can be put into use.The drawback to symmetric encryption is that the key is used for two purposes. the CA will make sure Dan is who he says he is. Referred to in some documentation as exponential key agreement. the secret keys must be exchanged over a non-secure connection! The DiffieHellman algorithm allows the exchange of secret keys over a non-secure communications channel. such as www.

ESP requires strong cryptography. which defines a method for authenticating.Authentication Header (AH). which isn't available and/or allowed everywhere. AH may meet all your requirements. That's because some of the IP fields can't be correctly predicted by the receiver . which negotiates the security parameters and authentication keys The IPSec Packet Format Defined in RFC 2402. the data. you might be wondering why you'd ever choose AH over ESP. there is an ESP Header and ESP Trailer surrounding. AH does offer: data origin authentication data integrity anti-replay protection (optional) AH does not offer data confidentiality. Here are a few things to consider: ESP is more processor-intensive than you can see from the IPSec packet illustration. The drawback with AH is that the authentication it provides for the IP Header is not complete. which authentication and securing data defines a method for Encapsulating Security Payload (ESP).these are mutable fields which may change during transmission. provides data origin authentication as well as offering optional anti-replay protection. which is really what we're interested in. To sum it up. ESP offers all of the following: data origin authentication anti-replay protection data confidentiality Comparing AH and ESP. AH has no such requirement. AH will successfully protect the IP packet's payload. the entire IPSec process is . Both ESP and AH can be run in one of two modes . The Encapsulating Security Payload (ESP) does just that . or encapsulating. If your data does not require data confidentiality. though. Authentication Header (AH) offers solid security -.Tunnel Mode and Transport Mode. and encrypting data Internet Key Exchange (IKE). In Tunnel mode.

The tunnel mode process encrypts the entire IP packet. there will be six messages overall. At this point. Transport mode encrypts the IP payload. As a result: There is no protection for the original IP address The original IP address will be used for routing Only data from the Transport layer up is protected by IPSec (easy enough to remember!) Configuring Site-to-Site IPSec VPNs Configuring a site-to-site VPN is basically a five-step process. This interesting traffic initializes the IPSec requires interesting traffic to be sent by a host. and then that encrypted packet is placed into another IP packet. Assuming we're running Main mode. right?) IKE Phase 1 (IKE SA negotiation) IKE Phase 2 (IPSec SA negotiation) Data Transfer Tunnel Termination IPSec doesn't just start working by itself . and it's those tunnel IP addresses that will be used to route the packet.transparent to the end hosts. We'll configure one later in this section. uninteresting kind. Process Initialization via "interesting traffic" (as opposed to the usual. but the IPSec header is inserted directly after the IP header in the packet. IKE's looking for an ISAKMP policy that's a match at both endpoints. . The initiator will first transmit proposals for the encryption and authentication schemes to be used. That encapsulating packet will have the IP addresses configured on the tunnel endpoints. The routers will now enter IKE Phase I. A crypto access-list will define interesting traffic for our VPN. specialized IPSec gateway devices handle the IPSec workload.

the devices will exchange DiffieHellman public keys. the rest of the negotiation is encrypted. using an encrypted form of their IP addresses. The IKE SA is then established and Phase II can begin. including its Diffie-Hellman public key. from this point on. The initiator and recipient authenticate each other in the third exchange of Phase I.In the second exchange of IKE Phase I. . (If we had chosen to run IKE in Aggressive Mode. ) The initiator packets everything needed for the SA negotiation in the first message. this would have been a three-message process.

The recipient responds with the acceptable parameters and authentication information. With the IPSec SA in place. the recipient responds with a list of acceptable parameters. and its Diffie-Hellman public key. This message is called proof of liveness. the hosts can now exchange data. The initiator proposes parameters for the IPSec SA. and we're done! IKE Phase 2 has one mode. This is also a three-message process. . and the initiator then transmits a message that lets the responder know that message 2 was received and processed. Quick mode. The initiator then sends a confirmation that it received that information.

with 1 being the highest priority. Creating An IKE Policy Before configuring the IKE policy. or perhaps after the tunnel have been up for a certain number of seconds. There is no default. as shown below by IOS Help. The lower the number. but we all know how that is! R1(config)#crypto isakmp enable To display the current IKE policies. . the higher the priority. no volume limit We're not going to use the default.Once the data exchange is complete. We'll create a custom policy with the crypto isakmp policy command. the tunnel can be torn down.a new Security Association can be agreed upon while the existing one is still in place. however. R1(config)#crypto isakmp policy ? <1-10000> Priority of protection suite R1(config)#crypto isakmp policy 100 IOS Help shows the options for the IKE policy. It's supposed to be on by default.Data Encryption Standard (56 bit keys). make sure ISAKMP is enabled with the crypto isakmp enable command. R1#show crypto isakmp policy Global IKE policy Default protection suite encryption algorithm: DES . This tunnel termination can be configured to occur after a certain number of bytes have passed through the tunnel. Policies can be assigned priorities. run show crypto isakmp policy. hash algorithm: Secure Hash Standard authentication method: Rivest-Shamir-Adleman Signature Diffie-Hellman group: #1 (768 bit) lifetime: 86400 seconds. But what if traffic is flowing through the tunnel at the same time the tunnel's supposed to be torn down? No fear .

AES.Data Encryption Standard (56 bit keys).The options for authentication are preshared keys. The default is group 1. The default is DES. The default is RSA Signature.Advanced Encryption Standard. R1(config-isakmp)#group ? 1 Diffie-Hellman group 1 2 Diffie-Hellman group 2 5 Diffie-Hellman group 5 R1(config-isakmp)#group The hash algorithm will be either MD5 or SHA. We'll use 3DES.400 seconds. we need to set the SA lifetime. and 3DES (TDES). The default is the maximum number of seconds.400.the default and the one we just wrote. R1(config-isakmp)#lifetime ? <60-86400> lifetime in seconds R1(config-isakmp)#lifetime 42400 show crypto isakmp policy displays both policies on the router . which equals 24 hours. . 86. R1(config-isakmp)#encryption ? 3des Three key triple DES aes AES . R1(config-isakmp)#encryption 3des We do have options for the Diffie-Hellman group. so we'll use group 5. and RSA Encryption. des DES . so we'll set the policy to MD5. We'll set that to 42. R1(config-isakmp)#authentication ? pre-share Pre-Shared Key rsa-encr Rivest-Shamir-Adleman Encryption rsa-sig Rivest-Shamir-Adleman Signature R1(config-isakmp)#authentication pre-share The options for encryption are DES. The default is SHA. RSA Signature. We'll configure the policy to use preshared keys. R1(config-isakmp)#hash ? md5 Message Digest 5 sha Secure Hash Standard R1(config-isakmp)#hash md5 Finally.

The exact same policy has been configured on R3. R2 then checks its Policy 200. the initiator sends its policies to the receiver. If that policy doesn't match. R2 checks its own policies for a match with the policy sent by the initiator. R1 and R3 are on the same Serial segment. Policy 300 matches all the requirements.0 /24. and the receiver starts this search with its lowest numbered policy.12. That policy requires SHA and the incoming policy names MD5. It's vital to remember that just because the first policy comparison doesn't result in a match. but that's not quite true. so the negotiation is successful. R3(config)#crypto isakmp policy 100 R3(config-isakmp)#hash md5 R3(config-isakmp)#lifetime 42400 R3(config-isakmp)#group 5 R3(config-isakmp)#authentication pre-share R3(config-isakmp)#encryption 3des When IKE Phase 1 negotiation begins. R1. Here's a list of the parameters . R2 begins with its lowest-numbered policy. and that does not match the incoming policy. In the following example. 172. 100. so there's no match. You'd think that all five values would have to match for the negotiation to be successful. The receiver will then attempt to find a match for that policy among its own policies.12. the receiver checks its next lowest numbered policy. with their router number as the last octet. which requires DES. the recipient will continue to search for a match.

We can verify this with show crypto isakmp sa. If Phase I is successful.and what has to happen for successful negotiation. Along with the key itself. there's nothing to show! The ISAKMP SA doesn't exist until the entire IPSec configuration is in place and interesting traffic has started the process. but you really can't test it until the entire thing is done. Watch the syntax with this command. Trust me. . as it differs between IOS versions. if the output of a show command shows nothing. IOS Help shows that the options are slightly different between the IOS versions we're using. the lower value is used. Since our policies referred to preshared keys. If less. That's one frustrating thing about IPSec . this is something you need to get used to. an ISAKMP SA will be created. the IP address of the remote peer must be configured. Hash: exact match Encryption: exact match Authentication: exact match DH Group number: exact match Lifetime: Remote peer policy must have lifetime equal to or less than initiator. we better create them! The crypto isakmp key command does this. As a CCNP and world-class Cisco engineer. Not all versions have the 0 / 6 option you'll see below on R1.there's a good deal of configuration. R3#show crypto isakmp sa dst src R3# state conn-id slot As always.

Options are shown with IOS Help. the IPSec process continues. the process is terminated and the session torn down. As with ISAKMP policies. If there's an exact match.crypto access lists. IPSec SA Lifetimes The default lifetime of an IPSec SA is 1 hour. if there's no match. the IPSec SA will be built. The endpoints must agree exactly on which encryption and algorithms will be used to create the IPSec SA. . The below command sets this value to 30 minutes (1800 seconds). The SA lifetime can also be based on volume. as shown here on R3. A transform set is built with the crypto ipsec transform-set command. Always use IOS Help to double-check the measuring unit in use by any given command. but IOS Help reveals that the command that changes this value on a global basis sets the IPSec SA lifetime in seconds.Configuring The IPSec Transform Sets An IPSec Transform Set is simply a group of individual parameters that will enforce a security policy. The remote peer will compare each set received against its own transform sets. and then the exact same transform set is configured on R1. and when a match is found. Crypto Access Lists Remember way back when I mentioned that interesting traffic triggers the IPSec process? We're finally getting to the part of IPSec that identifies this interesting traffic . multiple transform sets can be configured and sent to a remote peer. Crypto ACLs are used to define the traffic that is protected by IPSec.

matched traffic is permitted and unmatched traffic denied (by the implicit deny). matched traffic is encrypted and unmatched traffic is unencrypted but still transmitted. Outbound crypto ACLs identify the traffic to be secured by IPSec. If inbound Crypto ACLs are configured. but there's a major difference in operation between the two. Extended ACLs can serve as Crypto ACLs. With Extended ACLs. unprotected traffic that matches the ACL is dropped . they can also be configured to affect inbound traffic. and traffic not named by the crypto ACL will be sent in clear text. Inbound crypto ACLs can identify traffic that should have been protected by IPSec. Such traffic will be discarded.While most of the Crypto ACLs you write will be configured to affect outbound traffic. With Crypto ACLs. Let's use the following network to show you what I mean.simply because it's unprotected. . The trickiest part of writing Crypto ACLs for IPSec peers is making sure they're symmetrical rather than identical. but wasn't.

0 0. we need them to be mirror images.0.1.255 172.0 0.255 When you're configuring IPSec and concentrating on the many details we've discussed in this chapter. We don't want the two ACLs to be an exact copy of each other . R3(config)#crypto <1-65535> client isakmp isakmp-profile local-address map CCNP ? Sequence to insert into crypto map entry Specify client configuration settings Specify isakmp configuration settings Specify isakmp profile to use Interface to use for local address for this crypto map R3(config)#crypto map CCNP 100 ? ipsec-isakmp IPSEC w/ISAKMP ipsec-manual IPSEC w/manual keying <cr> R3(config)#crypto map CCNP 100 ipsec-isakmp ? dynamic Enable dynamic crypto map support profile Enable crypto map as a crypto-profile <cr> R3(config)#crypto map CCNP 100 ipsec-isakmp R3(config-crypto-map)# We've successfully created a crypto map named CCNP. where the ACL.0 0. I'll just write the ACL on one router and then copy and paste it to the other. exact reverses of each other. We're now in crypto map configuration mode.1.if they're identical.0." Always double-check your ACLs . R2's ACL will look like this: access-list 123 permit ip 172.0.255 For traffic on R2's ethernet segment to be protected by IPSec if it's destined for the ethernet segment on R1.0. transform sets.0.rather.5.5. Any SA lifetime value configured here overrides the globally configured . that will use ISAKMP to establish the IPSec Security Associations. Let's look at the basic command to write a Crypto Map along with some options.10. That's just one purpose of a Crypto Map. R1's ACL will look like this: access-list 123 permit ip 172.To have traffic on R1's ethernet segment protected by IPSec if it's destined for the ethernet segment on R2. Once the Crypto ACLs are written.0.255 172. it's time to apply them to the appropriate interfaces. courtesy of IOS Help. and security association lifetime for this particular crypto map can be set.10. it's really easy to think "Hey. sequence number 100.10. peers.10. there is a problem.0.0 0.0. IPSEC(initialize_sas): .579: IPSEC(validate_proposal_request): proposal part #1.3. protocol= AH.12.1 Type escape sequence to abort. msg.value. (key eng.12. conn_id= 0. remote= 172.591: IPSEC(key_engine): got a queue event with 2 kei messages *Jun 6 23:51:17.12.1 protocol : 0 src port : 0 dst port : 0 *Jun 6 23:51:17. keysize= 0.) INBOUND local= 172. (key eng.!!! Success rate is 60 percent (3/5).12. remote= 172. Sending 5. keysize= 0. *Jun 6 23:51:17.) INBOUND local= 172.12. remote= 172.12. Near the bottom of the debug output. but we'll leave that value alone for now.12. keysize= 0. lifedur= 1800s and 4608000kb. .1. flags= 0x2 *Jun 6 23:51:17.12. we'll enable debug crypto ipsec on R3 to allow us to see the details of the SA negotiations.3. lifedur= 1800s and 4608000kb.12.12. conn_id= 0.3. lifedur= 0s and 0kb. R1(config)#crypto map CCNP 100 ipsec-isakmp % NOTE: This new crypto map will remain disabled until a peer and a valid access list have been configured. R3#debug crypto ipsec Crypto IPSEC debugging is on R3#ping 172. protocol= AH. flags= 0x400A.999: IPSEC(sa_request): .583: Crypto mapdb : proxy_match src addr : 172. transform= ah-md5-hmac (Tunnel). transform= ah-md5-hmac (Tunnel).12. 100-byte ICMP Echos to 172.) OUTBOUND local= 172. round-trip min/avg/max = 48/49/52 ms R2#. msg.1. transform= ah-md5-hmac (Tunnel).12.12.1 R3(config-crypto-map)#set transform-set R3_TRANSFORM_SET R3(config-crypto-map)#set security-association lifetime ? kilobytes Volume-based key duration seconds Time-based key duration R3(config)#int s0/1 R3(config-if)#crypto map CCNP R3(config-if)# *Mar 1 04:10:12. msg. R1(config-crypto-map)#match address 123 R1(config-crypto-map)#set peer 172.807: %CRYPTO-6-ISAKMP_ON_OFF: ISAKMP is ON R3(config)#crypto map CCNP 100 ipsec-isakmp R3(config-crypto-map)#match address 123 R3(config-crypto-map)#set peer 172. spi= 0x91791CF(152539599).12. spi= 0x91791CF(152539599). protocol= AH. timeout is 2 seconds: *Jun 6 23:51:14. (key eng.12.12. you can see that two separate unidirectional SAs have been built.591: IPSEC(initialize_sas): .12. flags= 0x2 *Jun 6 23:51:17.3 dst addr : 172.2 R1(config-crypto-map)#set transform-set R1_TRANSFORM_SET R1(config-crypto-map)#interface serial 0/1 R1(config-if)#crypto map CCNP R1(config-if)# *Apr 1 17:27:04.260: %CRYPTO-6-ISAKMP_ON_OFF: ISAKMP is ON Before sending interesting traffic to start the entire process. spi= 0x0(0).12. conn_id= 0. 172. A common error message is MM_NO_STATE. conn_id= 0.3 dst addr : 172.) OUTBOUND local= 172. spi= 0x945FCBB6(2489306038).(key eng.595: IPSEC(crypto_ipsec_sa_find_ident_head): reconnecting with the same proxies and 172.12. keysize= 0.599: IPSEC(create_sa): sa created. sa_spi= 0x945FCBB6(2489306038).1 Extended IP access list 123 access-list 123 permit ip host 172.3. transform= ah-md5-hmac (Tunnel).1.12. sa_proto= 51. sa_conn_id= 2001 *Jun 6 23:51: host 172. sa_trans= ah-md5-hmac . sa_proto= 51. remote= 172. dest_port 0 *Jun 6 23:51:17. Crypto mapdb : proxy_match src addr : 172.12. and if you think that sounds bad. } Interfaces using crypto map CCNP: Serial0/1 . protocol= AH.1 *Jun 6 23:51:17. you're right! This indicates a fundamental problem with Phase I.12.12.12. sa_conn_id= 2002 By running show crypto isakmp sa.123.12. lifedur= 1800s and 4608000kb. most likely a mismatch of attributes between peers.123.12. along with a quick explanation of each courtesy of Cisco's website. R2#show crypto map Crypto Map "CCNP" 100 ipsec-isakmp Peer = 172.1 Current peer: 172. msg.595: IPSEC(policy_db_add_ident): src 172.12.3. (sa) sa_dest= 172.12. Two other excellent IPSec troubleshooting commands are show crypto map and show crypto ipsec transform-set. sa_trans= ah-md5-hmac .12.595: IPSec: Flow_switching Allocated flow for sibling 80000002 *Jun 6 23:51:17. here are a few other potential messages we don't want to see. (sa) sa_dest= 172.123.12. R2#show crypto isakmp sa dst src 172. dest 172.2 state QM_IDLE conn-id 1 slot 0 status ACTIVE QM_IDLE is what we do want to see.599: IPSEC(create_sa): sa created.1 protocol : 0 src port : 0 dst port : 0 *Jun 6 23:51:17.123.12. and this message can also be generated by a misconfigured pre-shared key.1 Security association lifetime: 4608000 kilobytes/1800 seconds PFS (Y/N): N Transform sets={ R2_TRANSFORM_SET. sa_sp i= 0x91791CF(152539599). MM_KEY_EXCH can indicate a misconfiguration of the peer's IP address.12. flags= 0xA *Jun 6 23:51:17. we can see that the SA is in place and is active.

because you can always block ports that are needed by network services or applications. you're going to have to be very careful with your access lists. *Jun 7 00:48:18. protocol number 50 AH.074: IPSEC(key_engine_delete_sas): rec'd delete notify from ISA KMP *Jun 7 00:50:10.123. because three primary IPSec protocols use ports that must not be blocked by ACLs: ESP. *Jun 7 00:50:10.AND applied it to the proper interface Made sure our ACLs allowed the appropriate port numbers . sa_trans= ah-md5-hmac .086: IPSEC(delete_sa): deleting SA sa_spi= 0x877193DD(2272367581). sa_spi= 0xF8BA8F2(260810994). sa_conn_id= 2003.12. protocol number 51 IKE. exp iring in 111 seconds IPSEC(lifetime_expiry): SA lifetime threshold *Jun 7 00:50:10. (identity) local= 172.1. sa_conn_id= 2004.090: IPSec: Flow_switching Deallocated flow for sibling 8000000 A Warning About ACLs And IPSec As you work with more complex combinations of Cisco technologies. }. Transform set R2_TRANSFORM_SET: { ah-md5-hmac will negotiate = { Tunnel.R2#show crypto ipsec transform-set Transform set R3_TRANSFORM_SET: { ah-md5-hmac will negotiate = { Tunnel. } } To let you see what the IPSec process looks like when the SA expires.123.2. This is particularly true with IPSec. here's the process we used to create this site-to-site IPSec VPN: Created the ISAKMP policy Created the IPSec transform set Defined interesting traffic with the crypto access-list Created the crypto map . You should especially be careful with port ranges in ACLs. I left the debug running until the one we built in this chapter expired.078: IPSEC(key_engine_delete_sas): delete SA with spi 0x877193D *Jun 7 00:50:10. *Jun 7 00:50:10.12.086: IPSEC(delete_sa): deleting SA.270: reached.074: IPSEC(key_engine): got a queue event with 1 kei messages *Jun 7 00:50:10. sa_trans= ah-md5-hmac . To review. }. UDP port 500 Make sure your network's ACLs are not inadvertently blocking these ports and protocol numbers anywhere you have IPSec running. remote= 172.

IPSec is very secure.we've got to run a combination of IPSec and GRE. always make sure to apply the crypto map to the interface! Hey. the crypto ACL indicates the traffic to be encrypted GRE over IPSec allows the transmission of dynamic routing protocol multicast traffic Whether you use the CLI or SDM. commonly called GRE over IPSec. Combined with a lack of strong security features. Cisco's website recommends the use of transport mode over tunnel mode with GRE over IPSec. IPSec couldn't carry multicast traffic. Using transport mode results in less total overhead.the first IOS release that allowed IPSec to carry multicast traffic was 12. Interestingly enough. and then that encapsulation is encapsulated again. Multicast traffic generated by OSPF and EIGRP can't be carried by basic IPSec .The Return Of GRE The Generic Routing Encapsulation (GRE) tunneling has actually made a comeback. and vice versa. and from there choose VPN. we'll start by clicking the Configure button. In effect. . Our old friends tunnel mode and transport mode are still around as well. by IPSec. By combining GRE and IPSec. but it does have drawbacks. we have a GRE tunnel inside an IPSec tunnel.2(4)T. and there are plenty of routers out there running an earlier IOS. We used to love GRE's multiprotocol capabilities. since GRE can do things that IPSec can't do. but that's not as important to us in today's networks as it once was. that's enough talking about GRE over IPSec. Let's configure it with SDM! Configuring A GRE Tunnel Over IPSec Via SDM (PDQ) As always. and you may still run into some trouble with that in the field . which IPSec does not offer Why call it "GRE over IPSec" rather than "IPSec over GRE"? Because the GRE encapsulation happens first. Originally. and we're all in favor of that! To review Just as with a site-to-site VPN. GRE was pretty much dead for quite a while. The latest IOS versions can't handle all multicast traffic. each protocol helps to compensate for the other's limitation: IPSec adds data integrity and confidentiality that GRE does not offer GRE offers the ability to carry routing protocol traffic. however.

too! . After clicking Launch the selected task. The Site-toSite VPN window gives us two main choices: When I choose the GRE over IPSec option. we're given some reminders of why we're using GRE .good review material for your exam.From the main VPN window. we'll select Site-to-Site VPN. this illustration is shown.

The next screen asks us for some required GRE-over-IPSec information. but if we did. namely the tunnel source and destination and the address of the tunnel itself. we can specify either the interface or the IP address. it's good information to have in mind for the tunnel config. We don't have any of these features on this interface. where the only option for destination is the IP address. Note that for the source. Did you notice the Details button in the previous screen? Clicking that gives you quite a bit of information regarding that interface. .

but the next screen gives us the option to do so.Now back to the config! We're not going to create a backup tunnel. and we'll accept the . The next window prompts us for the pre-shared key or to indicate the use of digital certificates. The next window is the IKE Proposal selection area.

If you're running a routing protocol over the tunnels. for example. For EIGRP. We're then prompted to identify the routing protocol that will run over the tunnel. and we'll accept the default there as well. we had the opportunity to create a backup tunnel.default IKE policy. Earlier in this section. With static . The next window is the Transform Set selection area. you may need to alter some metrics so that one tunnel is preferred over the other. I'd suggest working with the delay option rather than the other metrics as it's easier to get the result you want.

the VPN is down.routing. we're presented with a Summary of the configuration we've chosen. should you run into that problem in the real world. Cisco's website offers several solutions to this issue.0. using Split Tunneling with NAT and PAT on the same router can cause problems. We now have the option of tunneling all traffic. We'll enable ST here and configure traffic destined for 10. As always. At this point. Real-world note: By default.0 /8 to use the tunnel. or using Split Tunneling to send select traffic through the tunnel. you could alter the AD of the routes with the distance option. since we haven't configured the other side of it! .0.

Here's the mirror configuration: crypto isakmp policy 1 authentication pre-share encr 3des hash sha group 2 lifetime 86400 exit crypto isakmp key secretkey address 172.31. along with warnings about how this config should be used only as a guide and should not be pasted into the remote router.the Generate Mirror button! Real-world note: If you can't find something in SDM.1.1 crypto ipsec transform-set ESP-3DES-SHA esp-sha-hmac esp-3des mode tunnel exit ip access-list extended SDM_1 remark SDM_ACL Category=4 permit gre host 10. After clicking Generate Mirror. that connects to this router.a mirror image .1. set transform-set ESP-3DES-SHA set peer 172.1 .31.2 host 172.We need an exact reverse of this configuration . SDM has a great tool to create this mirror at the verrrrrry bottom of the screen . I'm going to do just what they told me not to do.1. Since we're in a lab environment.1. always look at the very bottom of the screen. we get that mirror place on the downstream router. and save this config and then paste it into the downstream router.1 exit crypto map SDM_CMAP_1 1 ipsec-isakmp description Apply the crypto map on the peer router's interface having IP address 10.

3600. As a result. the Clients have the most up-to-date policies without the network admins .match address SDM_1 set security-association lifetime seconds 3600 set security-association lifetime kilobytes 4608000 exit After copying that config to the downstream router. the Edit Site-to-Site VPN screen shows the VPN is now up. For your exam and when reading Cisco documentation. After the policy acceptance.1700 routers w/ 12.255.0 ip mtu 1420 tunnel source FastEthernet0/1 tunnel destination 10. Quite a few different Cisco devices can act as Easy VPN Servers.2(8)T or later The Easy VPN Remote device can be a Cisco router.2(8)T IOS Many Cisco 800 series routers running 12. and the Server responds with the acceptance of a matching proposal. and that's how I'll refer to them for the rest of this video. I will not list each here. What's So "Easy" About Easy VPN? Easy VPN consists of the following: Easy VPN Server Easy VPN Remote Sounds easy enough! Seriously.that's you and me . or VPN concentrator as well. I applied that crypto map to the physical interface and created a tunnel interface manually: interface Tunnel0 ip address 10.having to visit them individually.7200.1 Going back to the original router.1. . remember that "Remote" and "Client" refer to the same device. The basics of the VPN construction will look familiar at this point! First. "Easy VPN Remote" devices are often referred to as "Easy VPN Clients". the real benefit of Easy VPN is that security policies written at the Server level can then be pushed out to Clients. the Client will send ISAKMP proposals to the Server.1.2600. the ISAKMP SA is in place.255.2.2 255. PIX.1. but here are the more common ones: VPN 3000 concentrators Cisco 7500.7100.

but keep in mind that we can use these security protocols in addition to local authentication. The Server will now send a challenge to the Client. the Client requests the necessary configuration details from the Server. We can use several methods to set up this authentication: Local (using the username/password command) RADIUS TACACS Xauth (Extended Authentication) We'll take a closer look at RADIUS and TACACS in another section. Once the Client has successfully authenticated. This information can include: IP address information (required) internal DNS and WINS server addresses split tunneling configuration information Split tunneling allows the Client to have a secure tunnel to the Server and simultaneous non-secure connections to other networks. the process enters Mode configuration. At this stage. According to Cisco's website.The next step is a little different from what we've seen in other VPNs. the Reverse Route Injection stage begins. Once Mode configuration is completed. prompting the Client to send a username and password to the Server. "Reverse route injection (RRI) is the .

and we'll select Easy VPN Server.ability for static routes to be automatically inserted into the routing process for those networks and hosts protected by a remote tunnel endpoint". The description screen shows the following. After RRI. and we're all set. You'll see a list of topics under "VPN". Configuring Easy VPN Server In SDM We'll start our Easy VPN server config by clicking the VPN button in the Configure section of SDM. Note the prerequisite task. . we're almost there! IPSec Quick Mode then negotiates the IPSec SA.

so I'll click that. . we're presented with this message: We do want to enable AAA.There's a link to enable AAA on that screen. After clicking the enable AAA link. Note that the Enable Easy VPN button is grayed out since AAA is not yet enabled. so we'll click Yes and move on.

we can enable Easy VPN Server. Welcome to the Easy VPN Server Wizard! Good exam review material on this screen as well! Here's the next window: .Once the AAA commands are delivered.

We could create custom policies by clicking Add. and we'll accept the default there as well. but you see that we can use key. but here we'll use the default. digital certificates. . so I'll choose that in the drop-down box. The Transform Set selection window is next.The interface facing the workstation is Fast 0/0. We'll use pre-shared keys as well. the next window asks us for the IKE proposal. or both. After making those selections.

The next window prompts us for the group authorization method. Actually. . we'll indicate local authentication for users. and we'll use local authentication only. the local database is the only option you have! In the next window. I like the summary description here. if you don't have a RADIUS or TACACS server in your network.

Note the pre-shared key appears as a series of asterisks. we'll click Add since a group has not yet been created. .In the next window. The Add Group Policy window opens to the following tab. and you can see the information I entered for yourself.

255.0. which is disabled by default. When I clicked that check box.We'll enable Split Tunneling.0 network with a wildcard mask of 0. the Enter the protected subnets selection window enabled.255. I'll click Add and enter the 10. .255.0.

The policy has been added. the commands are delivered to the router. we're presented with the Summary window. and the Easy VPN Server side of the configuration is complete! Configuring The Easy VPN Client . Finally. After clicking Finish at the bottom of that screen. note that you can specify an idle timer for the tunnel. At the bottom of this screen.

we'd need to import a valid root certificate. I'll enter the IP address of the Easy VPN Server. We're not going to configure Mutual Group Authentication. I'll click Connect. and we'll be prompted for a username / password combination that I configured before the lab began.Now to the workstation! I'll launch the Cisco VPN Client and click New. Group Authentication is selected by default. along with the group name and password (which again appears only as a series of asterisks). Now the HQ connection appears under Connection Entry. The connection is then completed! Note that a lock now appears next to . but if we chose that option.

This is the first place I check when a VPN configuration isn't working correctly.. You can also test the connection from the Server side. and at the very bottom of the screen.. the message Connected to HQ appears in the bottom left of the window. Go to the Edit Easy VPN Server screen. . select Test Easy VPN Server.. If something isn't well. you'll get some great information on the issue here. and you'll get check marks when all is well. . Click Start in the Troubleshooting VPN screen.. and the overall connection time appears in the bottom right of the window.the HQ connection.

and you're there. Naturally. Let's look at an SDM screen we haven't visited yet . This screen has buttons on the left-hand side as well. .the Monitor screen.You'll also receive the following confirmation that all is well. Just click the Monitor button at the top of SDM. we'll select VPN Status.

The IPSec Tunnels tab verifies that the tunnel is up. The Easy VPN Server tab verifies it as well. The IKE SA tab shows the SA is in QM_IDLE mode. along with the number of encrypted and decrypted packets. which is just what we want! .

access to local network files. You must remove any pre-existing NAT and PAT configuration before configuring Easy VPN Remote.Other Easy VPN Options In the Easy VPN Client software. If this is enabled on both the Server and Client. A Note About NAT Easy VPN Client does support NAT and PAT. Copyright © 2011 The Bryant Advantage. So what's the catch? Actually. printers. and that can be a problem for Easy VPN. and access-list commands will not appear in the starting and running configurations. Enabling transparent tunneling enables us to work around potential issues with NAT and PAT. and other resources is allowed without going through the tunnel. . According to Cisco documentation. you'll see an option to Allow Local LAN Access. Client will autoconfigure the necessary NAT and PAT commands and access-lists. When you have a router serving as a firewall that also happens to be between the Easy VPN Client and Server. the admin only needs to configure our old friends ip nat inside and ip nat outside. All Rights Reserved. you'll want to enable this option. but with a twist. you'll see an option for transparent tunneling. On the same tab in SDM. Thankfully. there are two of them: The autoconfigured NAT. you can see them with the show access-list and show ip nat statistics commands. Why? That gateway is likely running NAT and/or PAT. PAT.

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