Cisco Systems Router 1800 Series User Manual

							 
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Chapter 7      Configuring VPNs Using an IPSec Tunnel and Generic Routing Encapsulation
  Configure a VPN
Enable Policy Lookup
Perform these steps to enable policy lookup through AAA, beginning in global configuration mode:
Step 4domain name
Example:
Router(config-isakmp-group)# domain 
company.com
Router(config-isakmp-group)# 
Specifies group domain membership.
Step 5exit
Example:
Router(config-isakmp-group)# exitRouter(config)# 
Exits IKE group policy configuration mode, and 
enters global configuration mode.
Step 6ip local pool {default | poolname} 
[low-ip-address [high-ip-address]]
Example:
Router(config)# ip local pool dynpool 
30.30.30.20 30.30.30.30
Router(config)# 
Specifies a local address pool for the group.
For details about this command and additional 
parameters that can be set, see the
 Cisco IOS Dial 
Technologies Command Reference.
Command or Action Purpose
Command or ActionPurpose
Step 1aaa new-model
Example:
Router(config)# aaa new-modelRouter(config)# 
Enables the AAA access control model.
Step 2aaa authentication login {default | list-name} 
method1 [method2...] 
Example:
Router(config)# aaa authentication login 
rtr-remote local
Router(config)# 
Specifies AAA authentication of selected users at 
login, and specifies the method used.
This example uses a local authentication database. 
You could also use a RADIUS server for this. See 
the
 Cisco IOS Security Configuration Guide and 
the Cisco IOS Security Command Reference for 
details. 
						

							
 
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Chapter 7      Configuring VPNs Using an IPSec Tunnel and Generic Routing Encapsulation
  Configure a VPN
Configure IPSec Transforms and Protocols
A transform set represents a certain combination of  security protocols and algorithms. During IKE 
negotiation, the peers agree to use a particular transform set for protecting data flow. 
During IKE negotiations, the peers search in multiple transform sets for a transform that is the same at 
both peers. When such a transform set is found, it is  selected and applied to the protected traffic as a part 
of both peers’ configurations. 
Perform these steps to specify the IPSec transform se t and protocols, beginning in global configuration 
mode:
Command or ActionPurpose
Step 1crypto ipsec transform-set  transform-set-name 
transform1  [transform2 ] [transform3 ] 
[ transform4 ]
Example:
Router(config)#  crypto ipsec transform-set 
vpn1 esp-3des esp-sha-hmac
Router(config)# 
Defines a transform set—An acceptable 
combination of IPSec security protocols and 
algorithms.
See the  Cisco IOS Security Command Reference  
for detail about the valid transforms and 
combinations.
Step 2crypto ipsec security-association lifetime  
{ seconds  seconds  | kilobytes  kilobytes }
Example:
Router(config)#  crypto ipsec 
security-association lifetime seconds 86400
Router(config)# 
Specifies global lifetime values used when 
negotiating IPSec security associations.
See the  Cisco IOS Security Command Reference  
for details.
Step 3aaa authorization {network  | exec  | commands 
level  | reverse-access  | configuration } {default  | 
list-name } [method1  [ method2... ]]
Example:
Router(config)#  aaa authorization network 
rtr-remote local
Router(config)# 
Specifies AAA authorization of all 
network-related service requests, including PPP, 
and the method used to do so.
This example uses a loca l authorization database. 
You could also use a RADIUS server for this. See 
the
 Cisco IOS Security Configuration Guide and 
the Cisco IOS Security Command Reference for 
details.
Step 4username  name  {nopassword  | password  
password  | password  encryption-type  
encrypted-password }
Example:
Router(config)#  username Cisco password 0 
Cisco
Router(config)# 
Establishes a username-b ased authentication 
system.
This example implements a username of  Cisco 
with an encrypted password of  Cisco.
Command or Action Purpose 
						

							
 
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Chapter 7      Configuring VPNs Using an IPSec Tunnel and Generic Routing Encapsulation   Configure a VPN
NoteWith manually established security associations, there is no negotiation with the peer, and both sides 
must specify the same transform set. 
Configure the IPSec Crypto Method and Parameters
A dynamic crypto map policy processes  negotiation requests for new security associations from remote 
IPSec peers, even if the router do es not know all the crypto map para meters (for example, IP address).
Perform these steps to configure the IPSec crypto method, beginning in global configuration mode:
Command or ActionPurpose
Step 1crypto dynamic-map dynamic-map-name 
dynamic-seq-num
Example:
Router(config)#  crypto dynamic-map dynmap 1
Router(config-crypto-map)# 
Creates a dynamic crypto map entry, and enters 
crypto map configuration mode.
See the Cisco IOS Security Command Reference  
for more detail about this command.
Step 2set transform-set transform-set-name 
[ transform-set-name2 ...transform-set-name6 ] 
Example:
Router(config-crypto-map)#  set 
transform-set vpn1
Router(config-crypto-map)# 
Specifies which transform sets can be used with 
the crypto map entry.
Step 3reverse-route
Example:
Router(config-crypto-map)#  reverse-routeRouter(config-crypto-map)# 
Creates source proxy information for the crypto 
map entry.
See the Cisco IOS Security Command Reference  
for details.
Step 4exit
Example:
Router(config-crypto-map)# exit
Router(config)# 
Enters global configuration mode.
Step 5crypto map map-name seq-num  [ipsec-isakmp ] 
[ dynamic  dynamic-map-name ] [discover ] 
[ profile  profile-name ] 
Example:
Router(config)#  crypto map static-map 1 
ipsec-isakmp dynamic dynmap
Router(config)# 
Creates a crypto map profile. 
						

							
 
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Chapter 7      Configuring VPNs Using an IPSec Tunnel and Generic Routing Encapsulation
  Configure a GRE Tunnel
Apply the Crypto Map to the Physical Interface
The crypto maps must be applied  to each interface through which IPSec traffic flows. Applying the 
crypto map to the physical interface instructs the rout er to evaluate all the traffic against the security 
associations database. With the default configuratio ns, the router provides secure connectivity by 
encrypting the traffic sent between remote sites. Howeve r, the public interface still allows the rest of the 
traffic to pass and provides connectivity to the Internet.
Perform these steps to apply a crypto map to an interface, beginning in global configuration mode:
Command or ActionPurpose
Step 1interface  type number
Example:
Router(config)#  interface fastethernet 0Router(config-if)# 
Enters interface configuration mode for the 
interface to which you want to apply the crypto 
map.
Step 2crypto map map-name
Example:
Router(config-if)#  crypto map static-map
Router(config-if)# 
Applies the crypto map to the interface.
See th e Cisco IOS Security Command Reference  
for more detail about this command.
Step 3exit
Example:
Router(config-if)# exitRouter(config)# 
Enters global configuration mode.
Configure a GRE Tunnel
Perform these steps to configure a GRE tunnel, beginning in global configuration mode: 
Command or ActionPurpose
Step 1interface type number
Example:
Router(config)#  interface tunnel 1Router(config-if)# 
Creates a tunnel interface and enters interface 
configuration mode.
Step 2ip address ip-address mask
Example:
Router(config-if)#  10.62.1.193 
255.255.255.252
Router(config-if)# 
Assigns an address to the tunnel. 
						

							 
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  Configure a GRE Tunnel
Step 3tunnel source interface-type number
Example:
Router(config-if)# tunnel source 
fastethernet 2
Router(config-if)# 
Specifies the source endpoint of the router for the 
GRE tunnel.
Step 4tunnel destination default-gateway-ip-address
Example:
Router(config-if)# tunnel destination 
192.168.101.1
Router(config-if)# 
Specifies the destination endpoint of the router for 
the GRE tunnel.
Step 5crypto map map-name
Example:
Router(config-if)# crypto map static-mapRouter(config-if)# 
Assigns a crypto map to the tunnel.
NoteDynamic routing or static routes to the 
tunnel interface must be configured to 
establish connectivity between the sites. 
See the
 Cisco IOS Security Configuration 
Guide for details. 
Step 6exit
Example:
Router(config-if)# exit
Router(config)# 
Exits interface configuration mode, and returns to 
global configuration mode.
Step 7ip access-list {standard | extended} 
access-list-name 
Example:
Router(config)# ip access-list extended 
vpnstatic1
Router(config-acl)# 
Enters ACL configuration mode for the named 
ACL that is used by the crypto map. 
Step 8permit protocol source source-wildcard 
destination destination-wildcard 
Example:
Router(config-acl)# permit gre host 
192.168.100.1 host 192.168.101.1
Router(config-acl)# 
Specifies that only GRE traffic is permitted on the 
outbound interface. 
Step 9exit
Example:
Router(config-acl)# exitRouter(config)# 
Returns to global configuration mode.
Command or Action Purpose 
						

							 
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  Configuration Example
Configuration Example
The following configuration example shows a portion of the configuration file for a VPN using a GRE 
tunnel scenario described in the preceding sections.
!aaa new-model
!
aaa authentication login rtr-remote localaaa authorization network rtr-remote local
aaa session-id common
!username cisco password 0 cisco
!
interface tunnel 1ip address 10.62.1.193 255.255.255.252
tunnel source fastethernet 2
tunnel destination interface 192.168.101.1
ip route 20.20.20.0 255.255.255.0 tunnel 1
crypto isakmp policy 1
encryption 3desauthentication pre-share
group 2
!crypto isakmp client configuration group rtr-remote
key secret-password
dns 10.50.10.1 10.60.10.1domain company.com
pool dynpool
!crypto ipsec transform-set vpn1 esp-3des esp-sha-hmac
!
crypto ipsec security-association lifetime seconds 86400!
crypto dynamic-map dynmap 1
set transform-set vpn1reverse-route
!
crypto map static-map 1 ipsec-isakmp dynamic dynmapcrypto map dynmap isakmp authorization list rtr-remote
crypto map dynmap client configuration address respond
!crypto isakmp policy 1 ! defines the key association and authentication for ipsec tunnel.
hash md5 
authentication pre-sharecrypto isakmp key cisco123 address 200.1.1.1
!
!crypto ipsec transform-set set1 esp-3des esp-md5-hmac ! defines encryption and transform 
set for the ipsec tunnel.
!crypto map to_corporate 1 ipsec-isakmp ! associates all crypto values and peering address 
for the ipsec tunnel.
 set peer 200.1.1.1 set transform-set set1 
 match address 105
!!!
interface vlan 1 ! VLAN 1 is the internal home network 
						

							 
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  Configuration Example
 ip address 10.1.1.1 255.255.255.0 ip nat inside
 ip inspect firewall in ! inspection examines outbound traffic
crypto map static-mapno cdp enable
!
interface fastethernet 0! FE0 is the outside or internet exposed interface ip address 210.110.101.21 255.255.255.0
 ip access-group 103 in ! acl 103 permits ipsec traffic from the corp. router as well as 
denies internet initiated traffic inbound. ip nat outside
 no cdp enable
 crypto map to_corporate ! applies the ipsec tunnel to the outside interface.!
ip nat inside source list 102 interface Ethernet1 overload ! utilize nat overload in order 
to make best use of the single address provided by the isp.ip classless
ip route 0.0.0.0 0.0.0.0 210.110.101.1
no ip http server!
!
! acl 102 associated addresses used for nat.access-list 102 permit ip 10.1.1.0 0.0.0.255 any
! acl 103 defines traffic allowed from the peer for the ipsec tunnel.
access-list 103 permit udp host 200.1.1.1 any eq isakmp
access-list 103 permit udp host 200.1.1.1 eq isakmp anyaccess-list 103 permit esp host 200.1.1.1 any
access-list 103 permit icmp any any ! allow icmp for debugging but should be disabled due 
to security implications.access-list 103 deny ip any any ! prevents internet initiated traffic inbound.
! acl 105 matches addresses for the ipsec tunnel to/from the corporate network.
access-list 105 permit ip 10.1.1.0 0.0.0.255 192.168.0.0 0.0.255.255no cdp run 
						

							 
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CH A P T E R
 
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8
Configuring a Simple Firewall
The Cisco 1800 integrated services routers support network traffic filtering by means of access lists. The 
router also supports packet inspection and dynamic temporary access lists by means of Context-Based 
Access Control (CBAC).
Basic traffic filtering is limited to configured access list implementations that examine packets at the 
network layer or, at most, the transport layer, permitting or denying the passage of each packet through 
the firewall. However, the use of inspection rules in CBAC allows the creation and use of dynamic 
temporary access lists. These dynamic lists allow temp orary openings in the configured access lists at 
firewall interfaces. These openings are created when tr affic for a specified user session exits the internal 
network through the firewall. The openings allow returning traffic for the specified session (that would 
normally be blocked) back through the firewall.
See the  Cisco IOS Security Configuration Guide, Release 12.3 , for more detailed information on traffic 
filtering and firewalls.
Figure 8-1 shows a network deployment using PPPoE or PPPoA with NAT and a firewall.
Figure 8-1 Router with Firewall Configured
121781
2
3
7
56
1
4 
						

							
1Multiple networked devices—Desktops, laptop PCs, switches
2Fast Ethernet LAN interface (the inside interface for NAT)
3PPPoE or PPPoA client and firewall implementation—Cisco 1811/1812 or Cisco 1801/1802/1803 
series integrated services router, respectively
4Point at which NAT occurs
5Protected network
6Unprotected network
7Fast Ethernet or ATM WAN interf ace (the outside interface for NAT)
 
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Chapter 8      Configuring a Simple Firewall
  
In the configuration example that follows, the firewall is applied to the outside WAN interface (FE0) on 
the Cisco
 1811 or Cisco 1812 and protects the Fast Ethernet LAN  on FE2 by filtering and inspecting all 
traffic entering the router on the Fa st Ethernet WAN interface FE1. Note  that in this example, the network 
traffic originating from the corporate network, networ k address 10.1.1.0, is considered safe traffic and 
is not filtered.
Configuration Tasks
Perform the following tasks to configure this network scenario:
 Configure Access Lists
 Configure Inspection Rules
 Apply Access Lists and Inspection Rules to Interfaces
An example showing the results of these configuration tasks is shown in the section “ Configuration 
Example.”
NoteThe procedures in this chapter assume that you have already configur ed basic router features as well as 
PPPoE or PPPoA with NAT. If you have not pe rformed these configurations tasks, see 
Chapter 1, “Basic 
Router Configuration,” Chapter 3, “Configuring PPP over Ethernet with NAT,” and Chapter 4, 
“Configuring PPP over ATM with NAT,” as appropriate for your router. You may have also configured 
DHCP, VLANs, and secure tunnels.