Nextelco:ASA VPN DHCPrelay

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DHCP through VPN

Is time to set up something really useful. In our general schema we have some site to site VPNs between ASA devices sitting on Africa and Norway. In order to have a centralized DHCP server it is necessary to configure ASAs in order to provide DHCP requests and replies through the VPN. In the following Figure we can see the configuration details.

Nextelco ASA DHCP VPN.png


In order to set the DHCP configuration, first we need to set up the initial configuration and the VPN between these two ASAs. In order to set up the initial configuration refer to the following configuration steps.


At this point, it is necessary to understand how DHCP and specially DHCP relay works in order to know how to set up everything. So, these are the necessary steps:

  1. The client, user machine, broadcasts a DHCP DISCOVER packet.
    • IP source: 0.0.0.0
    • IP destination: 255.255.255.255
    • Port source: 68
    • Port destination: 67
    • Relay agent IP address: 0.0.0.0


  2. ASA2 takes the packet and based on its DHCP relay configuration it sends the DHCP DISCOVER packet directly to the DCHP server.
    • IP source: 10.10.10.2
    • IP destination: 192.168.1.2
    • Port source: 67
    • Port destination: 67
    • Relay agent IP address: 192.168.2.1


  3. The DCHP server takes the DHCP DISCOVER packet and it replies with a DHCP OFFER. It sends the offer to the RELAY AGENT (ASA2).
    • IP source: 192.168.1.2
    • IP destination: 192.168.2.1
    • Port source: 67
    • Port destination: 67
    • Relay agent IP address: 192.168.2.1
    • Your IP address: 192.168.2.2


  4. ASA2 takes the DHCP OFFER and it sends to the client.
    • IP source: 192.168.2.1
    • IP destination: 192.168.2.2
    • Port source: 67
    • Port destination: 68
    • Relay agent IP address: 192.168.2.1
    • Your IP address: 192.168.2.2


  5. The client starts with the DCHP REQUEST.
    • IP source: 0.0.0.0
    • IP destination: 255.255.255.255
    • Port source: 68
    • Port destination: 67
    • Relay agent IP address: 0.0.0.0
    • DHCP server: 192.168.1.2
    • Requested IP address: 192.168.2.2


  6. ASA2 takes the REQUEST and it forwards to the DHCP server.
    • IP source: 10.10.10.2
    • IP destination: 192.168.1.2
    • Port source: 67
    • Port destination: 67
    • Relay agent IP address: 192.168.2.1
    • DHCP server: 192.168.1.2
    • Requested IP address: 192.168.2.2


  7. The DHCP server takes the REQUEST and replies with a DHCP ACK.
    • IP source: 192.168.1.2
    • IP destination: 192.168.2.1
    • Port source: 67
    • Port destination: 67
    • Relay agent IP address: 192.168.2.1
    • DHCP server: 192.168.1.2
    • Your IP address: 192.168.2.2


  8. Last step. ASA2 takes the ACK and it forwards to the client.
    • IP source: 192.168.2.1
    • IP destination: 192.168.2.2
    • Port source: 67
    • Port destination: 68
    • Relay agent IP address: 192.168.2.1
    • DHCP server: 192.168.1.2
    • Your IP address: 192.168.2.2


In order to allow DHCP traffic through the VPN it is necessary to set up both, ASA1 and ASA2. These are the configuration files of both of them.


ASA1 

: Saved 
: 
ASA Version 8.2(5) 
! 
hostname ASA1 
enable password 8Ry2YjIyt7RRXU24 encrypted
passwd 2KFQnbNIdI.2KYOU encrypted
names
! 
interface Ethernet0/0
 switchport access vlan 2
!
interface Ethernet0/1
!
interface Ethernet0/2
 shutdown
!
interface Ethernet0/3
 shutdown
!
interface Ethernet0/4
 shutdown
!
interface Ethernet0/5
 shutdown
!             
interface Ethernet0/6
 shutdown
!
interface Ethernet0/7
 shutdown
!
interface Vlan1
 nameif inside
 security-level 100
 ip address 192.168.1.1 255.255.255.0 
!
interface Vlan2
 nameif outside
 security-level 0
 ip address 10.10.10.1 255.255.255.0 
!
ftp mode passive 
object-group network DHCP_SERVER
 description DHCP server IP address.
 network-object host 192.168.1.2
object-group network ASA1_INSIDE_NET
 description ASA1 inside network address.
 network-object 192.168.1.0 255.255.255.0
object-group network ASA2_INSIDE_NET
 description ASA2 inside network address.
 network-object 192.168.2.0 255.255.255.0
object-group network ASA2_OUTSIDE_IP
 description ASA2 outside interface IP address.
 network-object host 10.10.10.2
access-list CRYPTO_LAN_TO_LAN extended permit ip object-group DHCP_SERVER object-group ASA2_OUTSIDE_IP 
access-list CRYPTO_LAN_TO_LAN extended permit ip object-group ASA1_INSIDE_NET object-group ASA2_INSIDE_NET 
access-list INSIDE_NAT_OUTSIDE extended permit ip object-group ASA1_INSIDE_NET any 
access-list CRYPTO_NO_NAT extended permit ip object-group DHCP_SERVER object-group ASA2_OUTSIDE_IP 
access-list CRYPTO_NO_NAT extended permit ip object-group ASA1_INSIDE_NET object-group ASA2_INSIDE_NET 
pager lines 24 
mtu inside 1500
mtu outside 1500
icmp unreachable rate-limit 1 burst-size 1
no asdm history enable
arp timeout 14400
global (outside) 1 interface
nat (inside) 0 access-list CRYPTO_NO_NAT
nat (inside) 1 access-list INSIDE_NAT_OUTSIDE
route outside 192.168.2.0 255.255.255.0 10.10.10.2 1
timeout xlate 3:00:00
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 icmp 0:00:02
timeout sunrpc 0:10:00 h323 0:05:00 h225 1:00:00 mgcp 0:05:00 mgcp-pat 0:05:00
timeout sip 0:30:00 sip_media 0:02:00 sip-invite 0:03:00 sip-disconnect 0:02:00
timeout sip-provisional-media 0:02:00 uauth 0:05:00 absolute
timeout tcp-proxy-reassembly 0:01:00
timeout floating-conn 0:00:00 
dynamic-access-policy-record DfltAccessPolicy 
aaa authentication ssh console LOCAL 
no snmp-server location
no snmp-server contact
snmp-server enable traps snmp authentication linkup linkdown coldstart
crypto ipsec transform-set ESP-3DES-SHA esp-des esp-sha-hmac 
crypto ipsec security-association lifetime seconds 28800
crypto ipsec security-association lifetime kilobytes 4608000
crypto map MAP_CRYPTO_LAN_TO_LAN 1 match address CRYPTO_LAN_TO_LAN
crypto map MAP_CRYPTO_LAN_TO_LAN 1 set pfs group1
crypto map MAP_CRYPTO_LAN_TO_LAN 1 set peer 10.10.10.2 
crypto map MAP_CRYPTO_LAN_TO_LAN 1 set transform-set ESP-3DES-SHA
crypto map MAP_CRYPTO_LAN_TO_LAN interface outside
crypto isakmp enable outside
crypto isakmp policy 10
 authentication pre-share
 encryption 3des
 hash sha
 group 2
 lifetime 86400
crypto isakmp policy 65535
 authentication pre-share
 encryption 3des
 hash sha
 group 2
 lifetime 86400
telnet timeout 5
ssh 192.168.1.0 255.255.255.0 inside
ssh timeout 5
console timeout 0

threat-detection basic-threat
threat-detection statistics access-list
no threat-detection statistics tcp-intercept
username basicinternet password UVFcpWay5BJPKJFl encrypted privilege 15
tunnel-group 10.10.10.2 type ipsec-l2l
tunnel-group 10.10.10.2 ipsec-attributes
 pre-shared-key *****
!
class-map inspection_default
 match default-inspection-traffic
!
!
policy-map type inspect dns preset_dns_map
 parameters   
  message-length maximum client auto
  message-length maximum 512
policy-map global_policy
 class inspection_default
  inspect dns preset_dns_map 
  inspect ftp 
  inspect h323 h225 
  inspect h323 ras 
  inspect ip-options 
  inspect netbios 
  inspect rsh 
  inspect rtsp 
  inspect skinny  
  inspect esmtp 
  inspect sqlnet 
  inspect sunrpc 
  inspect tftp 
  inspect sip  
  inspect xdmcp 
  inspect icmp 
!
service-policy global_policy global
prompt hostname context 
no call-home reporting anonymous
call-home
 profile CiscoTAC-1
  no active
  destination address http https://tools.cisco.com/its/service/oddce/services/DDCEService
  destination address email callhome@cisco.com
  destination transport-method http
  subscribe-to-alert-group diagnostic
  subscribe-to-alert-group environment
  subscribe-to-alert-group inventory periodic monthly
  subscribe-to-alert-group configuration periodic monthly
  subscribe-to-alert-group telemetry periodic daily
Cryptochecksum:fac7c4dec8271bb4b049cfd63b0e2a71
: end


ASA2 

: Saved
: 
ASA Version 8.0(5) 
! 
hostname ASA2
enable password 8Ry2YjIyt7RRXU24 encrypted
passwd 2KFQnbNIdI.2KYOU encrypted
names
! 
interface Vlan1
 nameif inside
 security-level 100
 ip address 192.168.2.1 255.255.255.0 
!
interface Vlan2
 nameif outside
 security-level 0
 ip address 10.10.10.2 255.255.255.0 
!
interface Ethernet0/0
 switchport access vlan 2
!
interface Ethernet0/1
!
interface Ethernet0/2
 shutdown     
!
interface Ethernet0/3
 shutdown
!
interface Ethernet0/4
 shutdown
!
interface Ethernet0/5
 shutdown
!
interface Ethernet0/6
 shutdown
!
interface Ethernet0/7
 shutdown
! 
boot system disk0:/asa805-k8.bin
ftp mode passive
object-group network DHCP_SERVER
 description DHCP server IP address.
 network-object host 192.168.1.2 
object-group network ASA1_INSIDE_NET
 description ASA1 inside network address.
 network-object 192.168.1.0 255.255.255.0
object-group network ASA2_INSIDE_NET
 description ASA2 inside network address.
 network-object 192.168.2.0 255.255.255.0
object-group network ASA2_OUTSIDE_IP
 description ASA2 outside interface IP address.
 network-object host 10.10.10.2
access-list INSIDE_NAT_OUTSIDE extended permit ip object-group ASA2_INSIDE_NET any 
access-list CRYPTO_NO_NAT extended permit ip object-group ASA2_OUTSIDE_IP object-group DHCP_SERVER 
access-list CRYPTO_NO_NAT extended permit ip object-group ASA2_INSIDE_NET object-group ASA1_INSIDE_NET 
access-list CRYPTO_LAN_TO_LAN extended permit ip object-group ASA2_OUTSIDE_IP object-group DHCP_SERVER 
access-list CRYPTO_LAN_TO_LAN extended permit ip object-group ASA2_INSIDE_NET object-group ASA1_INSIDE_NET 
pager lines 24
mtu inside 1500
mtu outside 1500
icmp unreachable rate-limit 1 burst-size 1
no asdm history enable
arp timeout 14400
global (outside) 1 interface
nat (inside) 0 access-list CRYPTO_NO_NAT
nat (inside) 1 access-list INSIDE_NAT_OUTSIDE
route outside 192.168.1.0 255.255.255.0 10.10.10.1 1
timeout xlate 3:00:00
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 icmp 0:00:02
timeout sunrpc 0:10:00 h323 0:05:00 h225 1:00:00 mgcp 0:05:00 mgcp-pat 0:05:00
timeout sip 0:30:00 sip_media 0:02:00 sip-invite 0:03:00 sip-disconnect 0:02:00
timeout sip-provisional-media 0:02:00 uauth 0:05:00 absolute
timeout tcp-proxy-reassembly 0:01:00 
dynamic-access-policy-record DfltAccessPolicy
aaa authentication ssh console LOCAL 
no snmp-server location
no snmp-server contact
snmp-server enable traps snmp authentication linkup linkdown coldstart
crypto ipsec transform-set ESP-3DES-SHA esp-des esp-sha-hmac 
crypto ipsec security-association lifetime seconds 28800
crypto ipsec security-association lifetime kilobytes 4608000
crypto map MAP_CRYPTO_LAN_TO_LAN 1 match address CRYPTO_LAN_TO_LAN
crypto map MAP_CRYPTO_LAN_TO_LAN 1 set pfs group1
crypto map MAP_CRYPTO_LAN_TO_LAN 1 set peer 10.10.10.1 
crypto map MAP_CRYPTO_LAN_TO_LAN 1 set transform-set ESP-3DES-SHA
crypto map MAP_CRYPTO_LAN_TO_LAN interface outside
crypto isakmp enable outside
crypto isakmp policy 10
 authentication pre-share
 encryption 3des
 hash sha
 group 2
 lifetime 86400
crypto isakmp policy 65535
 authentication pre-share
 encryption 3des
 hash sha
 group 2
 lifetime 86400
no crypto isakmp nat-traversal
telnet timeout 5
ssh 192.168.2.0 255.255.255.0 inside
ssh timeout 5
console timeout 0
dhcprelay server 192.168.1.2 outside
dhcprelay enable inside
dhcprelay timeout 60

threat-detection basic-threat
threat-detection statistics access-list
no threat-detection statistics tcp-intercept
username basicinternet password UVFcpWay5BJPKJFl encrypted privilege 15
tunnel-group 10.10.10.1 type ipsec-l2l
tunnel-group 10.10.10.1 ipsec-attributes
 pre-shared-key *
!
class-map inspection_default
 match default-inspection-traffic
!
!
policy-map type inspect dns preset_dns_map
 parameters
  message-length maximum 512
policy-map global_policy
 class inspection_default
  inspect dns preset_dns_map 
  inspect ftp 
  inspect h323 h225 
  inspect h323 ras 
  inspect netbios 
  inspect rsh 
  inspect rtsp 
  inspect skinny  
  inspect esmtp 
  inspect sqlnet 
  inspect sunrpc 
  inspect tftp 
  inspect sip  
  inspect xdmcp 
  inspect icmp 
!
service-policy global_policy global
prompt hostname context 
Cryptochecksum:d1cc3c831f3b6d6cf2c4df715e57b9b7
: end


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