Configure ISE 2.2 IPSEC to Secure NAD (IOS) Communication

Introduction

This document describes how to configure and troubleshoot TACACS IPSEC to secure Cisco Identity Service Engine (ISE) 2.2 - Network Access Device (NAD) communication. TACACS traffic can be encrypted with site-to-site (LAN-to-LAN) IPSec Internet Key Exchange Version 2 (IKEv2) tunnel between Router and ISE. This document does not cover TACACS configuration part.

Prerequisites

Requirements

Cisco recommends that you have knowledge of these topics:

• ISE
• Cisco Router
• General IPSec concepts
• General TACACS concepts

Components Used

The information in this document is based on these software and hardware versions:

• Cisco ISR4451-X Router that runs software Version 15.4(3)S2
• Cisco Identity Service Engine version 2.2
• Windows 7 Service Pack 1

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Background Information

The goal is to secure protocols which use insecure MD5 hash, Radius and TACACS with IPSec. Few facts to take into consideration:

• Cisco ISE supports IPSec in Tunnel and Transport modes.
• When you enable IPSec on a Cisco ISE interface, an IPSec tunnel is created between Cisco ISE and the NAD to secure the communication.
• You can define a pre-shared key or use X.509 certificates for IPSec authentication.
• IPSec can be enabled on Eth1 through Eth5 interfaces. You can configure IPSec on only one Cisco ISE interface per PSN.

ISE IPSec Architecture

Once encrypted packets are received by GE-1 ISE interface, Embedded Services Router (ESR) intercepts them on Eth0/0 interface.

interface Ethernet0/0
 description e0/0->connection to external NAD
 ip address 10.48.17.87 255.255.255.0
 ip nat outside
 ip virtual-reassembly in
 no ip route-cache
 crypto map radius

ESR decrypts them and according to preconfigured NAT rules performs address translation. Outgoing (towards NAD) RADIUS/TACACS packets are translated to Ethernet0/0 interface address and encrypted afterwards.

ip nat inside source list 1 interface Ethernet0/0 overload
ip nat inside source static udp 10.1.1.2 1645 interface Ethernet0/0 1645
ip nat inside source static udp 10.1.1.2 1646 interface Ethernet0/0 1646
ip nat inside source static udp 10.1.1.2 1812 interface Ethernet0/0 1812
ip nat inside source static udp 10.1.1.2 1813 interface Ethernet0/0 1813
ip nat inside source static tcp 10.1.1.2 49 interface Ethernet0/0 49
access-list 1 permit 10.1.1.0 0.0.0.3

Packets which are destined to Eth0/0 interface on RADIUS/TACACS ports should be forwared via Eth0/1 interface to 10.1.1.2 ip address, which is internal address of ISE. ESR configuration of Eth0/1

interface Ethernet0/1
 description e0/1->tap0 internal connection to ISE
 ip address 10.1.1.1 255.255.255.252
 ip nat inside
 ip virtual-reassembly in
 no ip route-cache

ISE configuration of internal Tap-0 interface:

ISE22-1ek/admin# show interface | b tap0
tap0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.1.1.2  netmask 255.255.255.252  broadcast 10.1.1.3
        inet6 fe80::6c2e:37ff:fe5f:b609  prefixlen 64  scopeid 0x20<link>
        ether 6e:2e:37:5f:b6:09  txqueuelen 500  (Ethernet)
        RX packets 81462  bytes 8927953 (8.5 MiB)
        RX errors 0  dropped 68798  overruns 0  frame 0
        TX packets 105  bytes 8405 (8.2 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Network Diagram

The information in this document uses this network setup:

Configure ikev1 ipsec vpn using pre-shared key (out of the box)

This section describes how to complete the IOS CLI and ISE configurations.

IOS Router CLI Configuration

Configure the Interfaces

If the IOS router interfaces are not yet configured, then at least the WAN interface should be configured. Here is an example:

interface GigabitEthernet0/0/0
 ip address 10.48.23.68 255.255.255.0
 negotiation auto
 no shutdown
! 

Ensure that there is connectivity to the remote peer that should be used in order to establish a site-to-site VPN tunnel. You can use a ping in order to verify basic connectivity.

Configure the ISAKMP (IKEv1) Policy

In order to configure the ISAKMP policies for the IKEv1 connections, enter the crypto isakmp policy <priority> command in global configuration mode. Here is an example:

crypto isakmp policy 10
 encr aes
 hash sha256
 authentication pre-share
 group 16

Note: You can configure multiple IKE policies on each peer that participates in IPSec. When the IKE negotiation begins, it attempts to find a common policy that is configured on both of the peers, and it starts with the highest priority policies that are specified on the remote peer.

Configure a Crypto ISAKMP Key

In order to configure a preshared authentication key, enter the crypto isakmp key command in global configuration mode:

crypto isakmp key Krakow123 address 10.48.17.87

Configure an ACL for VPN Traffic of Interest

Use the extended or named access list in order to specify the traffic that should be protected by encryption. Here is an example:

access-list 101 permit ip 10.48.23.68 0.0.0.0 10.48.17.87 0.0.0.0 

Note: An ACL for VPN traffic uses the source and destination IP addresses after NAT.

Configure a Transform Set

In order to define an IPSec transform set (an acceptable combination of security protocols and algorithms), enter the crypto ipsec transform-set command in global configuration mode. Here is an example:

crypto ipsec transform-set SET esp-aes esp-sha256-hmac 
 mode transport

Configure a Crypto Map and Apply it to an Interface

In order to create or modify a crypto map entry and enter the crypto map configuration mode, enter the crypto map global configuration command. In order for the crypto map entry to be complete, there are some aspects that must be defined at a minimum:

• The IPsec peers to which the protected traffic can be forwarded must be defined. These are the peers with which an SA can be established. In order to specify an IPSec peer in a crypto map entry, enter the set peer command.
• The transform sets that are acceptable for use with the protected traffic must be defined. In order to specify the transform sets that can be used with the crypto map entry, enter the set transform-set command.
• The traffic that should be protected must be defined. In order to specify an extended access list for a crypto map entry, enter the match address command.

Here is an example:

crypto map MAP 10 ipsec-isakmp
 set peer 10.48.17.87
 set transform-set SET
 match address 101

The final step is to apply the previously defined crypto map set to an interface. In order to apply this, enter the crypto map interface configuration command:

interface GigabitEthernet0/0
 crypto map MAP 

IOS Final Configuration

Here is the final IOS router CLI configuration:

aaa group server tacacs+ ISE_TACACS
 server name ISE22
!
aaa authentication login default group ISE_TACACS
aaa authorization exec default group ISE_TACACS
!
crypto isakmp policy 10
 encr aes
 hash sha256
 authentication pre-share
 group 16
!
crypto isakmp key Krakow123 address 10.48.17.87
!
crypto ipsec transform-set SET esp-aes esp-sha256-hmac 
 mode transport
!
crypto map MAP 10 ipsec-isakmp
 set peer 10.48.17.87
 set transform-set SET
 match address 101
!
access-list 101 permit ip 10.48.23.68 0.0.0.0 10.48.17.87 0.0.0.0 
!
interface GigabitEthernet0/0/0
 ip address 10.48.23.68 255.255.255.0
 negotiation auto
 no shutdown
!
crypto map MAP 10 ipsec-isakmp
 set peer 10.48.17.87
 set transform-set SET
 match address 101
!
tacacs server ISE22
 address ipv4 10.48.17.87
 key cisco

ISE Configuration

Configure IP address on  ISE

Address should be configured on interface GE1-GE5 from the CLI, GE0 is not supported.

interface GigabitEthernet 1
  ip address 10.48.17.87 255.255.255.0
  ipv6 address autoconfig
  ipv6 enable

Note: Application restarts after IP address is configured on the interface:
% Changing the IP address might cause ISE services to restart
Continue with IP address change?  Y/N [N]: Y

Add NAD to IPSec Group on ISE

Navigate to Administration > Network Resources > Network Devices. Click Add. Ensure you configure the Name, IP Address, Shared Secret. To terminate IPSec tunnel from the NAD select YES against IPSEC Network Device Group.

Once NAD is added, additional route should be created on ISE, to ensure that RADIUS traffic goes through ESR and get encrypted:

ip route 10.48.23.68 255.255.255.255 gateway 10.1.1.1

Enable IPSEC on ISE

Navigate to Administration > System > Settings. Click on Radius and further on IPSEC. Select PSN (Single/Multiple/All) Select Enable option, pick the Interface and Select Authentication Method. Click Save. Services restart on the selected node at this point.

Note, that after services restart ISE CLI configuration shows configured interface without IP address and in shutdown state, it is expected as ESR (Embedded Services Router) takes control of ISE interface.

interface GigabitEthernet 1
  shutdown
  ipv6 address autoconfig
  ipv6 enable

Once services are restarted, ESR functionality is enabled. To login to ESR type esr in the command line:

ISE22-1ek/admin# esr
% Entering ESR 5921 shell
% Cisco IOS Software, C5921 Software (C5921_I86-UNIVERSALK9-M), Version 15.5(2)T2, RELEASE SOFTWARE (fc3)
% Technical Support: http://www.cisco.com/techsupport
% Copyright (c) 1986-2015 Cisco Systems, Inc.

Press RETURN to get started, <CTRL-C> to exit

ise-esr5921>en
ise-esr5921#

ESR comes with this crypto configuration, which is enough to have the ipsec tunnel terminated with pre-shared keys:

crypto keyring MVPN-spokes
  pre-shared-key address 0.0.0.0 0.0.0.0 key Krakow123
!
crypto isakmp policy 10
 encr aes
 hash sha256
 authentication pre-share
 group 16
!
crypto isakmp policy 20
 encr aes
 hash sha256
 authentication pre-share
 group 14
!
crypto isakmp key Krakow123 address 0.0.0.0
!
crypto isakmp profile MVPN-profile
   description LAN-to-LAN for spoke router(s) connection
   keyring MVPN-spokes
   match identity address 0.0.0.0
!
crypto ipsec transform-set radius esp-aes esp-sha256-hmac
 mode tunnel
crypto ipsec transform-set radius-2 esp-aes esp-sha256-hmac
 mode transport
!
crypto dynamic-map MVPN-dynmap 10
 set transform-set radius radius-2 
!
crypto map radius 10 ipsec-isakmp dynamic MVPN-dynmap

 Make sure ESR has a route to send encrypted packets out:

ip route 0.0.0.0 0.0.0.0 10.48.26.1

Set Tacacs Policy on ISE

Verify

IOS Router

Before ssh session is initiated to the Router, there is no active VPN connections:

ISR4451#sh cry isa sa
IPv4 Crypto ISAKMP SA
dst             src             state          conn-id status

IPv6 Crypto ISAKMP SA

 Client connects to Router, as an authentication source ISE 2.2 is used.

EKORNEYC-M-K04E:~ ekorneyc$ ssh alice@10.48.23.68
Password:
ISR4451#

IOS sends a TACACS Packet, which triggers VPN session establishment, once the tunnel is up the this output is seen on the Router. It confirms that the phase 1 of the tunnel is up:

ISR4451#sh cry isa sa
IPv4 Crypto ISAKMP SA
dst             src             state          conn-id status
10.48.17.87     10.48.23.68     QM_IDLE           1962 ACTIVE

IPv6 Crypto ISAKMP SA

ISR4451#

Phase 2 is up, and packets are encrypted and decrypted:

ISR4451#sh cry ipsec sa

interface: GigabitEthernet0/0/0
    Crypto map tag: MAP, local addr 10.48.23.68

   protected vrf: (none)
   local  ident (addr/mask/prot/port): (10.48.23.68/255.255.255.255/0/0)
   remote ident (addr/mask/prot/port): (10.48.17.87/255.255.255.255/0/0)
   current_peer 10.48.17.87 port 500
     PERMIT, flags={origin_is_acl,}
    #pkts encaps: 48, #pkts encrypt: 48, #pkts digest: 48
    #pkts decaps: 48, #pkts decrypt: 48, #pkts verify: 48
    #pkts compressed: 0, #pkts decompressed: 0
    #pkts not compressed: 0, #pkts compr. failed: 0
    #pkts not decompressed: 0, #pkts decompress failed: 0
    #send errors 0, #recv errors 0

     local crypto endpt.: 10.48.23.68, remote crypto endpt.: 10.48.17.87
     plaintext mtu 1458, path mtu 1500, ip mtu 1500, ip mtu idb GigabitEthernet0/0/0
     current outbound spi: 0x64BD51B8(1690128824)
     PFS (Y/N): N, DH group: none

     inbound esp sas:
      spi: 0xFAE51DF8(4209319416)
        transform: esp-aes esp-sha256-hmac ,
        in use settings ={Transport, }
        conn id: 2681, flow_id: ESG:681, sibling_flags FFFFFFFF80004008, crypto map: MAP
        sa timing: remaining key lifetime (k/sec): (4607998/3127)
        IV size: 16 bytes
        replay detection support: Y
        Status: ACTIVE(ACTIVE)

     inbound ah sas:

     inbound pcp sas:

     outbound esp sas:
      spi: 0x64BD51B8(1690128824)
        transform: esp-aes esp-sha256-hmac ,
        in use settings ={Transport, }
        conn id: 2682, flow_id: ESG:682, sibling_flags FFFFFFFF80004008, crypto map: MAP
        sa timing: remaining key lifetime (k/sec): (4607997/3127)
        IV size: 16 bytes
        replay detection support: Y
        Status: ACTIVE(ACTIVE)

     outbound ah sas:

     outbound pcp sas:
ISR4451#

ESR

Same outputs can be checked on ESR, phase one is up:

ise-esr5921#sh cry isa sa
IPv4 Crypto ISAKMP SA
dst             src             state          conn-id status
10.48.17.87     10.48.23.68     QM_IDLE           1002 ACTIVE

IPv6 Crypto ISAKMP SA

ise-esr5921#

Phase 2 is up, packets are encrypted and decrypted successfully:

ise-esr5921#sh cry ipsec sa

interface: Ethernet0/0
    Crypto map tag: radius, local addr 10.48.17.87

   protected vrf: (none)
   local  ident (addr/mask/prot/port): (10.48.17.87/255.255.255.255/0/0)
   remote ident (addr/mask/prot/port): (10.48.23.68/255.255.255.255/0/0)
   current_peer 10.48.23.68 port 500
     PERMIT, flags={}
    #pkts encaps: 48, #pkts encrypt: 48, #pkts digest: 48
    #pkts decaps: 48, #pkts decrypt: 48, #pkts verify: 48
    #pkts compressed: 0, #pkts decompressed: 0
    #pkts not compressed: 0, #pkts compr. failed: 0
    #pkts not decompressed: 0, #pkts decompress failed: 0
    #send errors 0, #recv errors 0

     local crypto endpt.: 10.48.17.87, remote crypto endpt.: 10.48.23.68
     plaintext mtu 1458, path mtu 1500, ip mtu 1500, ip mtu idb Ethernet0/0
     current outbound spi: 0xFAE51DF8(4209319416)
     PFS (Y/N): N, DH group: none

     inbound esp sas:
      spi: 0x64BD51B8(1690128824)
        transform: esp-aes esp-sha256-hmac ,
        in use settings ={Transport, }
        conn id: 3, flow_id: SW:3, sibling_flags 80000000, crypto map: radius
        sa timing: remaining key lifetime (k/sec): (4242722/3056)
        IV size: 16 bytes
        replay detection support: Y
        Status: ACTIVE(ACTIVE)

     inbound ah sas:

     inbound pcp sas:

     outbound esp sas:
      spi: 0xFAE51DF8(4209319416)
        transform: esp-aes esp-sha256-hmac ,
        in use settings ={Transport, }
        conn id: 4, flow_id: SW:4, sibling_flags 80000000, crypto map: radius
        sa timing: remaining key lifetime (k/sec): (4242722/3056)
        IV size: 16 bytes
        replay detection support: Y
        Status: ACTIVE(ACTIVE)

     outbound ah sas:
          
     outbound pcp sas:
ise-esr5921#

ISE

Live Authentication indicates regular PAP_ASCII authentication:

Captures taken on GE1 interface of ISE and filtered with ESP or Tacacs, confirm that there is no Tacacs in clear text, and all traffic is encrypted:

Troubleshoot

Common VPN Troubleshooting technique can be applied to troubleshoot issues related to IPSEC. You can find useful documents below:

IOS IKEv2 Debugs for Site-to-Site VPN with PSKs Troubleshooting TechNote

ASA IKEv2 Debugs for Site-to-Site VPN with PSKs

IPsec Troubleshooting: Understanding and Using debug Commands

Configure FlexVPN Site-to-Site (DVTI to SVTI) between NAD and ISE 2.2

It is also possible to protect RADIUS traffic with FlexVPN. The following topology is used in the example below:

FlexVPN configuration is straightforward. More details can be found here:

http://www.cisco.com/c/en/us/support/docs/security/flexvpn/115782-flexvpn-site-to-site-00.html

Advantages of Flex VPN design

• You can run Flex along all your previous IPsec VPNs. Most scenarios allow coexistence of previous configuration and flex.
• Flex VPN is based on IKEv2 and not IKEv1, which improves almost all aspects of negotiation and protocol stability.
• Multiple functionalities achievable with one framework.
• Ease of configuration by using sane defaults - you do not need to define policies, transform sets etc, IKEv2 has built in defaults that make sense and are updated.

Router Configuration

aaa new-model
!
!
aaa group server tacacs+ ISE_TACACS
 server name ISE22_VRF
ip vrf forwarding TACACS
!
aaa authentication login default group ISE_TACACS
aaa authorization exec default group ISE_TACACS 
aaa authorization network default local 
!
crypto ikev2 authorization policy default
 route set interface Loopback0
 no route set interface
!
!
crypto ikev2 keyring mykeys
 peer ISE22
  address 10.48.17.87
  pre-shared-key Krakow123
 !
!
!
crypto ikev2 profile default
 match identity remote address 10.48.17.87 255.255.255.255 
 authentication remote pre-share (with the command authentication remote pre-share key <key> in place keyring is not required)
 authentication local pre-share
 keyring local mykeys
 aaa authorization group psk list default default
!
!
ip tftp source-interface GigabitEthernet0
!
!
!
crypto ipsec profile default
 set ikev2-profile default (it is default configuration)
!
!
!
interface Loopback0
ip vrf forwarding TACACS
 ip address 100.100.100.100 255.255.255.0
!
interface Tunnel0
ip vrf forwarding TACACS
 ip address 10.1.12.1 255.255.255.0
 tunnel source GigabitEthernet0/0/0
 tunnel mode ipsec ipv4
 tunnel destination 10.48.17.87
 tunnel protection ipsec profile default
!
interface GigabitEthernet0/0/0
 ip address 10.48.23.68 255.255.255.0
 negotiation auto
!
!
ip route 0.0.0.0 0.0.0.0 10.48.23.1
ip tacacs source-interface Loopback0
!
!
tacacs server ISE22_VRF
 address ipv4 10.1.1.2
 key cisco
!
ISR4451# 

ESR Configuration on ISE

ise-esr5921#sh run
Building configuration...

Current configuration : 5778 bytes
!
! Last configuration change at 17:32:58 CET Thu Feb 23 2017
!
version 15.5
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
service call-home
!
hostname ise-esr5921
!
boot-start-marker
boot host unix:default-config
boot-end-marker
!
!
!
no aaa new-model
bsd-client server url https://cloudsso.cisco.com/as/token.oauth2
clock timezone CET 1 0
mmi polling-interval 60
no mmi auto-configure
no mmi pvc
mmi snmp-timeout 180
call-home
 ! If contact email address in call-home is configured as sch-smart-licensing@cisco.com
 ! the email address configured in Cisco Smart License Portal will be used as contact email address to send SCH notifications.
 contact-email-addr sch-smart-licensing@cisco.com
 profile "CiscoTAC-1"
  active
  destination transport-method http
  no destination transport-method email
!
!
!
!
!
!
!
!


!         
!
!
!
ip cef
no ipv6 cef
!
multilink bundle-name authenticated
!
!
!
!
!
!
!
!
!
crypto pki trustpoint SLA-TrustPoint
 enrollment pkcs12
 revocation-check crl
!
!
crypto pki certificate chain SLA-TrustPoint
 certificate ca 01
  30820321 30820209 A0030201 02020101 300D0609 2A864886 F70D0101 0B050030 
  32310E30 0C060355 040A1305 43697363 6F312030 1E060355 04031317 43697363 
  6F204C69 63656E73 696E6720 526F6F74 20434130 1E170D31 33303533 30313934 
  3834375A 170D3338 30353330 31393438 34375A30 32310E30 0C060355 040A1305 
  43697363 6F312030 1E060355 04031317 43697363 6F204C69 63656E73 696E6720 
  526F6F74 20434130 82012230 0D06092A 864886F7 0D010101 05000382 010F0030 
  82010A02 82010100 A6BCBD96 131E05F7 145EA72C 2CD686E6 17222EA1 F1EFF64D 
  CBB4C798 212AA147 C655D8D7 9471380D 8711441E 1AAF071A 9CAE6388 8A38E520 
  1C394D78 462EF239 C659F715 B98C0A59 5BBB5CBD 0CFEBEA3 700A8BF7 D8F256EE 
  4AA4E80D DB6FD1C9 60B1FD18 FFC69C96 6FA68957 A2617DE7 104FDC5F EA2956AC 
  7390A3EB 2B5436AD C847A2C5 DAB553EB 69A9A535 58E9F3E3 C0BD23CF 58BD7188 
  68E69491 20F320E7 948E71D7 AE3BCC84 F10684C7 4BC8E00F 539BA42B 42C68BB7 
  C7479096 B4CB2D62 EA2F505D C7B062A4 6811D95B E8250FC4 5D5D5FB8 8F27D191 
  C55F0D76 61F9A4CD 3D992327 A8BB03BD 4E6D7069 7CBADF8B DF5F4368 95135E44 
  DFC7C6CF 04DD7FD1 02030100 01A34230 40300E06 03551D0F 0101FF04 04030201 
  06300F06 03551D13 0101FF04 05300301 01FF301D 0603551D 0E041604 1449DC85 
  4B3D31E5 1B3E6A17 606AF333 3D3B4C73 E8300D06 092A8648 86F70D01 010B0500 
  03820101 00507F24 D3932A66 86025D9F E838AE5C 6D4DF6B0 49631C78 240DA905 
  604EDCDE FF4FED2B 77FC460E CD636FDB DD44681E 3A5673AB 9093D3B1 6C9E3D8B 
  D98987BF E40CBD9E 1AECA0C2 2189BB5C 8FA85686 CD98B646 5575B146 8DFC66A8 
  467A3DF4 4D565700 6ADF0F0D CF835015 3C04FF7C 21E878AC 11BA9CD2 55A9232C 
  7CA7B7E6 C1AF74F6 152E99B7 B1FCF9BB E973DE7F 5BDDEB86 C71E3B49 1765308B 
  5FB0DA06 B92AFE7F 494E8A9E 07B85737 F3A58BE1 1A48A229 C37C1E69 39F08678 
  80DDCD16 D6BACECA EEBC7CF9 8428787B 35202CDC 60E4616A B623CDBD 230E3AFB 
  418616A9 4093E049 4D10AB75 27E86F73 932E35B5 8862FDAE 0275156F 719BB2F0 
  D697DF7F 28
        quit
license udi pid CISCO5921-K9 sn 98492083R3X
username lab password 0 lab
!
redundancy
!
!
! 
crypto keyring MVPN-spokes  
  pre-shared-key address 0.0.0.0 0.0.0.0 key Krakow123
crypto ikev2 authorization policy default
 route set interface
 route set remote ipv4 10.1.1.0 255.255.255.0
!
!
!
crypto ikev2 keyring mykeys
 peer ISR4451
  address 10.48.23.68
  pre-shared-key Krakow123
 !
!
!
crypto ikev2 profile default
 match identity remote address 0.0.0.0 
 authentication remote pre-share
 authentication local pre-share
 keyring local mykeys
 aaa authorization group psk list default default local
 virtual-template 1
!
!
crypto isakmp policy 10
 encr aes
 hash sha256
 authentication pre-share
 group 16
!
crypto isakmp policy 20
 encr aes
 hash sha256
 authentication pre-share
 group 14 
crypto isakmp key Krakow123 address 0.0.0.0        
crypto isakmp profile MVPN-profile
   description LAN-to-LAN for spoke router(s) connection
   keyring MVPN-spokes
   match identity address 0.0.0.0 
!
!
crypto ipsec transform-set radius esp-aes esp-sha256-hmac 
 mode tunnel
crypto ipsec transform-set radius-2 esp-aes esp-sha256-hmac 
 mode transport
!
!
!
crypto dynamic-map MVPN-dynmap 10
 set transform-set radius radius-2 
!
!
crypto map radius 10 ipsec-isakmp dynamic MVPN-dynmap 
!
!
!
!         
!
interface Loopback0
 ip address 10.1.12.2 255.255.255.0
!
interface Ethernet0/0
 description e0/0->connection to external NAD 
 ip address 10.48.17.87 255.255.255.0
 ip nat outside
 ip virtual-reassembly in
 no ip route-cache
 crypto map radius
!
interface Ethernet0/1
 description e0/1->tap0 internal connection to ISE
 ip address 10.1.1.1 255.255.255.252
 ip nat inside
 ip virtual-reassembly in
 no ip route-cache
!
interface Ethernet0/2
 description e0/2->connection to CSSM backend license server
 no ip address
 ip virtual-reassembly in
 no ip route-cache
!
interface Ethernet0/3
 no ip address
 shutdown
!
interface Virtual-Template1 type tunnel
 ip unnumbered Loopback0
 tunnel source Ethernet0/0
 tunnel mode ipsec ipv4
 tunnel protection ipsec profile default
!
ip forward-protocol nd
!
!
no ip http server
no ip http secure-server
ip nat inside source list 1 interface Ethernet0/0 overload
ip nat inside source static udp 10.1.1.2 1645 interface Ethernet0/0 1645
ip nat inside source static udp 10.1.1.2 1646 interface Ethernet0/0 1646
ip nat inside source static udp 10.1.1.2 1812 interface Ethernet0/0 1812
ip nat inside source static udp 10.1.1.2 1813 interface Ethernet0/0 1813
ip nat inside source static tcp 10.1.1.2 49 interface Ethernet0/0 49
ip route 0.0.0.0 0.0.0.0 10.48.17.1
!
!
!
access-list 1 permit 10.1.1.0 0.0.0.3
!
control-plane
!
 !
 !
 !
 !
!
!
!
!
!
!
!
line con 0
 logging synchronous
line aux 0
line vty 0 4
 login
 transport input none
!
!
end

FlexVPN Design Considerations

• In most cases Radius connection should be terminated on G0/1 interface of ISE, which is E0/0 interface of ESR. While using crypto maps, interesting traffic should be defined with access-lists, with SVTI - using routing. It will not work, if two routers are configured to ISE interface one via Tunnel (encrypted) and one via interface (Tunnel establishment). The same issue applies to the Router configuration.
• For this reason interesting traffic (Encrypted Radius) is communicated between Lo0 interface of the router, and Tap0 interface of ISE (no nat is needed in this case on ESR). Because of this, ip route can be configured, to force Radius traffic to go through the tunnel and get encrypted.
• Since ip address of Tap0 interface of the ISE is fixed (10.1.1.2) it can be placed in VRF on Router, to ensure communication to this ip address happens only for TACACS and only through the tunnel.