Skip to main content

GET VPN - part seven (NAT)

Today I would like to test how GET VPN cooperates with NAT. I need to say but officially NAT for GET VPN is not supported by Cisco. You can encrypt traffic on a GM, just before encryption/decryption. Anyway I would like to test my below two case scenarios:

1) GM behind NAT

2) KS behind NAT

3) NAT on GM (supported)

I will work on the same design:
 

 

1) GM behind NAT

Now I add a NAT statement on the ASA for GM1 (R3):
 
object network R3-MNG-BN
 host 7.7.7.2
object network R3-MNG-AN
 host 77.77.77.2

nat (spoke1-mng,any) source static R3-MNG-BN R3-MNG-AN

On the ASA I need to add one acl entry:
 
access-list SPOKE1-MNG extended permit udp host 7.7.7.2 host 6.6.6.2 eq 4500
access-list SPOKE1-MNG extended permit udp host 7.7.7.2 host 3.3.3.2 eq 4500

and then we can see:
 
%ASA-6-302015: Built inbound UDP connection 62 for spoke1-mng:7.7.7.2/4500 (77.77.77.2/4500) to keys2:6.6.6.2/4500 (6.6.6.2/4500)

Let’s check the status of R3:
 
R3#sh crypto gdoi
GROUP INFORMATION

    Group Name               : GDOI-GROUP-GREEN
    Group Identity           : 1
    Crypto Path              : ipv4
    Key Management Path      : ipv4
    Rekeys received          : 0
    IPSec SA Direction       : Both

     Group Server list       : 3.3.3.2
                               6.6.6.2

    Group member             : 7.7.7.2          vrf: MNG
       Version               : 1.0.4
       Registration status   : Registered
       Registered with       : 6.6.6.2
       Re-registers in       : 191 sec
       Succeeded registration: 1
       Attempted registration: 6
       Last rekey from       : 0.0.0.0
...

Looks good, status is ‘registered’.

Now KS’ should see the R3 with IP of 77.77.77.2:
 
R2#sh crypto gdoi ks members

Group Member Information :

Number of rekeys sent for group GDOI-GROUP-RED : 0

Group Member ID    : 77.77.77.2  GM Version: 1.0.4
 Group ID          : 2
 Group Name        : GDOI-GROUP-RED
 Key Server ID     : 6.6.6.2
 Rekeys sent       : 0
 Rekeys retries    : 0
 Rekey Acks Rcvd   : 0
 Rekey Acks missed : 0

 Sent seq num : 0       0       0       0
Rcvd seq num :  0       0       0       0

Group Member ID    : 4.4.4.2     GM Version: 1.0.4
 Group ID          : 2
 Group Name        : GDOI-GROUP-RED
 Key Server ID     : 3.3.3.2
 Rekeys sent       : 0
 Rekeys retries    : 0
 Rekey Acks Rcvd   : 0
 Rekey Acks missed : 0

 Sent seq num : 0       0       0       0
Rcvd seq num :  0       0       0       0

Group Member ID    : 5.5.5.2     GM Version: 1.0.4
 Group ID          : 2
 Group Name        : GDOI-GROUP-RED
 Key Server ID     : 3.3.3.2
 Rekeys sent       : 0
 Rekeys retries    : 0
 Rekey Acks Rcvd   : 0
 Rekey Acks missed : 0

 Sent seq num : 0       0       0       0
Rcvd seq num :  0       0       0       0

Number of rekeys sent for group GDOI-GROUP-GREEN : 0

Group Member ID    : 5.5.5.2     GM Version: 1.0.4
 Group ID          : 1
 Group Name        : GDOI-GROUP-GREEN
 Key Server ID     : 6.6.6.2
 Rekeys sent       : 0
 Rekeys retries    : 0
 Rekey Acks Rcvd   : 0
 Rekey Acks missed : 0

 Sent seq num : 0       0       0       0
Rcvd seq num :  0       0       0       0

Group Member ID    : 77.77.77.2  GM Version: 1.0.4
 Group ID          : 1
 Group Name        : GDOI-GROUP-GREEN
 Key Server ID     : 6.6.6.2
 Rekeys sent       : 0
 Rekeys retries    : 0
 Rekey Acks Rcvd   : 0
 Rekey Acks missed : 0

 Sent seq num : 0       0       0       0
Rcvd seq num :  0       0       0       0

Group Member ID    : 4.4.4.2     GM Version: 1.0.4
 Group ID          : 1
 Group Name        : GDOI-GROUP-GREEN
 Key Server ID     : 3.3.3.2
 Rekeys sent       : 0
 Rekeys retries    : 0
 Rekey Acks Rcvd   : 0
 Rekey Acks missed : 0

 Sent seq num : 0       0       0       0
Rcvd seq num :  0       0       0       0

R2#

Let’s test the connectivity:
 
R3#ping vrf RED 20.55.55.55 source 20.33.33.33
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 20.55.55.55, timeout is 2 seconds:
Packet sent with a source address of 20.33.33.33
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 96/102/108 ms
R3#


R3#ping vrf RED 20.44.44.44 source 20.33.33.33
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 20.44.44.44, timeout is 2 seconds:
Packet sent with a source address of 20.33.33.33
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 88/95/100 ms
R3#

Everything works fine. I check the status of ESP sessions on ASA:

asa2(config)# sh conn | i ESP
ESP spoke2-red 20.44.44.44 spoke1-red20.33.33.33, idle 0:00:16, bytes 620
ESP spoke2-red 20.44.44.44 spoke1-red20.33.33.33, idle 0:00:16, bytes 620
asa2(config)#

There is no problem to have one or more GMs behid NAT. I need to only permit UDP/4500. Problems start during re-keying. I don’t know why (I only guess that it happens because GET VPN preserve IP header and addressing:


getvpn-1-IPheader.jpg


the original IP address is still 6.6.6.2 and only IP in a new IP header is 16.16.16.12, the other reason can be synchronization process between KS’, they exchanges GMs list) but even there is no line in the GM1 configuration I see it tries to contact with KS2 using a real IP:


getvpn-1-ws.jpg



2)KS behind NAT

In my second case one KS (r2) is behind NAT. I have to remove first all above changes before I start.

a) NAT - on the ASA I need to add the NAT statement. The second KS will be available with IP: 16.16.16.12: 
 
object network R2-BN
 host 6.6.6.2
object network R2-AN
 host 16.16.16.12

nat (keys1,spoke1-mng) source static R2-BN R-AN

b) GM configuration - I need to add the new KS:
 
!
crypto gdoi group GDOI-GROUP-GREEN
 identity number 1
 server address ipv4 3.3.3.2
 server address ipv4 16.16.16.12
 client registration interface FastEthernet0/0.1
!
crypto gdoi group GDOI-GROUP-RED
 identity number 2
 server address ipv4 3.3.3.2
 server address ipv4 16.16.16.12
 client registration interface FastEthernet0/0.1
!

c) ACL - I see deny messages and I have to add the connection to the ACL
 
%ASA-4-106023: Deny udp src spoke1-mng:7.7.7.2/4500 dst keys2:6.6.6.2/4500 by access-group "SPOKE1-MNG" [0x0]
access-list SPOKE1-MNG extended permit udp host 7.7.7.2 host 6.6.6.2 eq 4500
asa2(config)# sh conn | i 4500
UDP spoke1-mng 7.7.7.2:4500 keys2 6.6.6.2:4500, idle 0:01:35, bytes 2496, flags -
asa2(config)#

I check now if the GM1 is registered:
 
R3#sh crypto gdoi
GROUP INFORMATION

    Group Name               : GDOI-GROUP-GREEN
    Group Identity           : 1
    Crypto Path              : ipv4
    Key Management Path      : ipv4
    Rekeys received          : 2
    IPSec SA Direction       : Both

     Group Server list       : 16.16.16.12

    Group member             : 7.7.7.2          vrf: MNG
       Version               : 1.0.4
       Registration status   : Registered
       Registered with       : 16.16.16.12
       Re-registers in       : 139 sec
       Succeeded registration: 1
       Attempted registration: 2
       Last rekey from       : 6.6.6.2
       Last rekey seq num    : 0
       Unicast rekey received: 2
       Rekey ACKs sent       : 2
       Rekey Rcvd(hh:mm:ss)  : 00:00:34
       allowable rekey cipher: any
       allowable rekey hash  : any
       allowable transformtag: any ESP
...

Looks good. The one thing, as in the first scenario, 'last rekey from’ is 6.6.6.2.

On ASA I see also some attempts despite fact there is no config line with the IP (6.6.6.2).
 
%ASA-4-106023: Deny udp src spoke1-mng:7.7.7.2/848 dst keys2:6.6.6.2/848 by access-group "SPOKE1-MNG" [0x0, 0x0]
%ASA-5-305013: Asymmetric NAT rules matched for forward and reverse flows; Connection for udp src spoke1-mng:7.7.7.2/848 dst keys2:6.6.6.2/848 denied due to NAT reverse path failure

Conclusions - sometimes non-supported solutions are common even in production networks, but for these two cases I wouldn’t take any risk.

3) NAT on GM

I implement NAT for LAN1 (vrf GREEN, subnet 10.33.33.0/24) on the GM1. I need to update the policy on KS’ (access-list 101 permit ip 10.0.0.0 0.255.255.255 10.0.0.0 0.255.255.255). Let’s test it by changing the real IP from 10.33.33.33 to 100.33.33.33 and I keep the same settings on KS’.

Before I start I do one test to be sure the GET VPN work fine:
 
R5#ping vrf GREEN 10.33.33.33 source 10.55.55.55
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.33.33.33, timeout is 2 seconds:
Packet sent with a source address of 10.55.55.55
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 84/93/112 ms
R5#
On ASA I can see:
%ASA-7-609001: Built local-host spoke3-green:10.55.55.55
%ASA-7-609001: Built local-host spoke1-green:10.33.33.33
a) new IP
R3#sh run int loo0
Building configuration...

Current configuration : 91 bytes
!
interface Loopback0
 ip vrf forwarding GREEN
 ip address 100.33.33.33 255.255.255.0
end

R3#

b) routing
 
asa2(config)# route spoke1-green 100.33.33.0 255.255.255.0 17.17.17.2

and test:
 
asa2(config)# ping 100.33.33.33
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 100.33.33.33, timeout is 2 seconds:
?!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 30/32/40 ms
asa2(config)#

and one more test to be sure we don’t receive icmp reply from 10.33.33.33:
 
asa2(config)# ping 10.33.33.33
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.33.33.33, timeout is 2 seconds:
?????
Success rate is 0 percent (0/5)
asa2(config)#

c) NAT
 
R3(config)#ip nat inside source static 100.33.33.33 10.33.33.33 vrf GREEN

R3(config)#interface FastEthernet0/0.2
R3(config-subif)#ip nat outside
R3(config-subif)#
R3(config-subif)#int loo0
R3(config-if)#ip nat inside
R3(config-if)#end
R3#

Let’s do the same test from ASA:
 
asa2(config)# ping 10.33.33.33
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.33.33.33, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 30/32/40 ms
asa2(config)#

On the GM1 we see the translation:
 
R3#sh ip nat translations
Pro Inside global      Inside local       Outside local      Outside global
icmp 10.33.33.33:5313  100.33.33.33:5313  17.17.17.1:5313    17.17.17.1:5313
--- 10.33.33.33        100.33.33.33       ---                ---
R3#

I test it once again from R5:
 
R5#ping vrf GREEN 10.33.33.33 source 10.55.55.55
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.33.33.33, timeout is 2 seconds:
Packet sent with a source address of 10.55.55.55
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 84/105/132 ms
R5#

on the R3 we can see:
 
R3#sh ip nat translations
Pro Inside global      Inside local       Outside local      Outside global
icmp 10.33.33.33:7     100.33.33.33:7     10.55.55.55:7      10.55.55.55:7
icmp 10.33.33.33:8     100.33.33.33:8     10.55.55.55:8      10.55.55.55:8
icmp 10.33.33.33:9     100.33.33.33:9     10.55.55.55:9      10.55.55.55:9
icmp 10.33.33.33:10    100.33.33.33:10    10.55.55.55:10     10.55.55.55:10
icmp 10.33.33.33:11    100.33.33.33:11    10.55.55.55:11     10.55.55.55:11
icmp 10.33.33.33:12    100.33.33.33:12    10.55.55.55:12     10.55.55.55:12
--- 10.33.33.33        100.33.33.33       ---                ---
R3#

I think we can consider above tests as a prove the NAT work fine.
Labels:

Comments

Post a Comment

Popular posts from this blog

What should you know about HA 'override enabled' setting on Fortigate?

High availability is mandatory in most of today's network designs. Only very small companies or branches can run their business without redundancy. When you have Fortigate firewall in your network you have many options to increase network availability. You can use Fortigate Clustering Protocol ( FGCP ) or Virtual Router Redundancy Protocol ( VRRP ). FGCP has two modes: 'override' disabled (default) and 'override' enabled . I'm not going to explain how to set up HA as you can find many resources on Fortinet websites: https://cookbook.fortinet.com/high-availability-two-fortigates-56/ https://cookbook.fortinet.com/high-availability-with-fgcp-56/ Let's recap what is the main difference between them. The default HA setting is 'override' disabled and this is an order of selection an active unit: 1) number of monitored interfaces - when both units have the same number of working (up) interfaces check next parameter 2) HA uptime - an
8 comments
Read more

MAC Authentication Bypass

One of the method to control your network is using MAB feature. It is helpful in case you have devices without dot1x functionality. Today I will try to implement basic configuration and analyze log messages. There is only one switch SW1 and one device attached to port Fa1/0/2.   ! aaa new - model aaa authentication dot1x default group radius ! ! int Fas1 / 0 / 2 authentication host - mode single - host authentication port - control auto mab ! I haven’t configured ACS yet but let’s see what error message I receive:   SW1 ( config - if ) # mab - ev ( Fa1 / 0 / 2 ): Received MAB context create from AuthMgr mab - ev ( Fa1 / 0 / 2 ): Created MAB client context 0x1100000F mab : initial state mab_initialize has enter mab - ev ( Fa1 / 0 / 2 ): Sending create new context event to EAP from MAB for 0x1100000F ( 0000.0000 . 0000 ) mab - sm ( Fa1 / 0 / 2 ): Received event 'MAB_START' on handle 0x1100000F mab : during state mab_initia
Post a Comment
Read more

Inpection of asymmetric sessions on FortiGate

There is one feature available on FortiGate, and I think you should know it, as it modifies a bit what we know about stateful firewalls. In past every packet was treated individually and you had to create policies in both directions. With stateful firewalls we can track connections, and by checking couple of attributes, we can treat them as part of the same session. For example when you initiate connection from a host1 to host2, the returning connection from host2 to host1 will be treated as part of the same connection (session). They have to have the same source/destination and destination/source IPs, port numbers and interfaces.There is an exception from this rule and FortiGate in some specific cases can accept connections on port which was not used in the initial connection. Let me explain how it works on the below example:      The host1 has a default gateway on R1 (10.0.1.2), but you may notice that it is not the optimal path to host2 subnet. When we analyze the packet flo
1 comment
Read more