Site to site VPN Fortigate 5.4 and Cisco- NO-PROPOSAL-CHOSEN

[Xander]

Hello,

In our company we have Fortigate 60D (v5.4.1) and I'm trying to setup the VPN with Cisco router. Cisco router is owned by other company and I do not have access to it. Phase 1 seems to work as expected ([...] - text cut for better visibility):

ike 0:phase-1-int:193473: negotiation result
ike 0:phase-1-int:193473: proposal id = 1:
ike 0:phase-1-int:193473: protocol id = ISAKMP:
ike 0:phase-1-int:193473: trans_id = KEY_IKE.
ike 0:phase-1-int:193473: encapsulation = IKE/none
ike 0:phase-1-int:193473: type=OAKLEY_ENCRYPT_ALG, val=AES_CBC, key-len=256
ike 0:phase-1-int:193473: type=OAKLEY_HASH_ALG, val=SHA2_512.
ike 0:phase-1-int:193473: type=AUTH_METHOD, val=PRESHARED_KEY.
ike 0:phase-1-int:193473: type=OAKLEY_GROUP, val=ECP384.
ike 0:phase-1-int:193473: ISAKMP SA lifetime=28800
[...]
ike 0:phase-1-int:193473: VID CISCO-UNITY [...]
ike 0:phase-1-int:193473: peer supports UNITY
[...]
ike 0:phase-1-int:193473: DPD negotiated
ike 0:phase-1-int:193473: NAT not detected
ike 0:phase-1-int:193473: PSK authentication succeeded
ike 0:phase-1-int:193473: authentication OK
ike 0:phase-1-int:193473: established IKE SA [...]

But then I get the error as follows

ike 0:phase-1-int:193473: notify msg received: NO-PROPOSAL-CHOSEN
ike 0:phase-1-int:193473:phase-2-int:4954165: IPsec SPI d888eef3 match
ike 0:phase-1-int:193473:phase-2-int:4954165: delete phase2 SPI d888eef

I've asked the Cisco admin for config details and after comparison we have

Phase_1

the same Diffie-Hellman group the same proposal (aes256 - sha512) the same keylife (in seconds) Phase_2

The same Diffie-Hellman group ("dhgrp" parameter on Fortigate and "pfs" parameter on Cisco)

The same keylife (in kilobytes)

Proposals are:

Fortigate

set proposal aes256-sha512

Cisco

set transform-set esp-aes_256_esp-sha512-hmac
crypto ipsec transform-set esp-aes_256_esp-sha512-hmac esp-aes 256 esp-sha512-hmac

Can anyone tell me what could be wrong?

I'm not network specialist and I don't know even what to ask the mentioned Cisco admin.

Any help appreciated.

Best regards

Alex

[moby]

Hi Alex,

The above Cisco configuration only show the phase 2 (IPSEC) configuration. You should also check the phase 1 configuration for the Cisco router which would been shown in the ISAKMP policy in the configuration of the Cisco router. Also is dead peer detection enabled/disabled at each end?

Moby

[MikePruett]

Making sure things match 100% is my go to. Things like NAT-T, timers being off, encryption / authentication means being incorrect etc.

Remember, the FortiGate will follow RFC perfectly. So if the Cisco side doesn't match 100% it will kill it. For instance, Palo Alto firewalls you can chose the timer as a period of days etc. Even if the FortiGate has the correct number of seconds in the timer that matches said day period of the Palo the connection will fail.

[Xander]

The below config is all that I've got from the Cisco admin.

The parts marked [in square braces] were changed by me to anonymize some entries

crypto isakmp policy ###
encr aes 256
hash sha512
authentication pre-share
group 20
lifetime 28800

crypto map [name] [##] ipsec-isakmp
set peer [1.2.3.4]
set security-association lifetime kilobytes 512000
set transform-set esp-aes_256_esp-sha512-hmac
set pfs group20
match address [ac-name]
reverse-route

crypto ipsec transform-set esp-aes_256_esp-sha512-hmac esp-aes 256 esp-sha512-hmac

Regarding the DPD: I don't know if it is turned on on Cisco side but I can see something like this in the logs:

ike 0:phase-1-int:193469: sent IKE msg (R-U-THERE): 1.2.3.4:500->5.6.7.8:500, len=140, id=[...]
ike 0:phase-1-int:193469: notify msg received: R-U-THERE-ACK

Does indicates that DPD works fine or not necessarily?

My config is as follows

phase-1-int

config vpn ipsec phase1-interface
edit "phase-1-int"
set interface "wan1"
set local-gw [1.2.3.4]
set keylife 28800
set proposal aes256-sha512
set dpd on-idle
set dhgrp 20
set remote-gw [5.6.7.8]
set psksecret ENC (encrypted)
set dpd-retryinterval 10
next
end

phase-2-int

config vpn ipsec phase2-interface
edit "phase-2-int"
set phase1name "phase-1-int"
set proposal aes256-sha512
set dhgrp 20
set auto-negotiate enable
set keylife-type kbs
set src-addr-type ip
set keylifekbs 512000
set src-start-ip [9.10.11.12]
next
end

[neonbit]

Config looks ok except for the following on the Cisco side:

set security-association lifetime kilobytes 512000

Would it be possible for them to change this to:

set security-association lifetime seconds 512000

Since the FGTs keylife is in seconds.

[ede_pfau]

nope, both firewalls use KBs in phase2 as configured.

FortiOS supports both, default is seconds.

[neonbit]

ops sorry didn't see he changed the keylife type, pls diregard!

[Xander]

Hi All

Thanks for all the replies and hints. Problem still exists but I'll send the suggestions to the mentioned admin and wait for his reply. I'll post the solution here if I found one.

BR

Alex

[kadkwai]

Hi Alex,

I'm having the same issue! Were you able to resolve this problem ? 

Thank you,

[Xander · Accepted solution]

Hi Kadkwai

I've solved the problem after a lot of troubleshooting together with very skilled friend of mine.

I had to solve 2 issues:

1 - We had to NAT the traffic before it went into the tunnel (office lan -> NAT -> VPN tunnel)

2 - Than we received information that on the Cisco side the phase2 interface is configured to match specified IP addresses that are on the access list only (we specified the addresses before so we knew them all)

match address ac-list

My final configs are as follows Phase1

edit "vpn-p1"
 set interface "wan1"
 set keylife 28800
 set proposal aes256-sha512
 set dhgrp 20
 set mesh-selector-type subnet <- this allows to provide several addresses "remote-networks-on-ac-list", see phase2 below
 set remote-gw [1.2.3.4]
 set psksecret ENC secret
 next

Phase 2

edit "vpn-p2"
 set phase1name "vpn-p1"
 set proposal aes256-sha512
 set dhgrp 20
 set auto-negotiate enable
 set keylife-type kbs
 set src-addr-type name <- we need that to NAT our traffic
 set dst-addr-type name <- we need that to mach the IP put on cisco access list
 set keylifekbs 512000
 set src-name "our-nat-ip" <- we need that to NAT our traffic
 set dst-name "remote-networks-on-ac-list" <- we need that to mach the IP put on cisco access list
 next

src-name and dst-name you can define in

config firewall address

e.g.

edit "our-nat-ip"
 set subnet 3.4.5.6 255.255.255.255
next
edit "network-1"
 set subnet 192.168.1.0 255.255.255.0
next
edit "network-2"
 set subnet 192.168.2.0 255.255.255.0
next

and

config firewall addrgrp

e.g.

edit "remote-networks-on-ac-list"
 set member "network-1" "network-2"
 set allow-routing enable
 next

Hope this helps!

BR

Alex