http://www.tp-link.com/en/faq-444.html
Here is a FAQ about how to set L2TP VPN, you can double check your configuartion.

Hello thanks for the link.

I followed the steps very closely, but when I try to connect I get the following error.

"the L2TP connection attempt failed because the security layer could not negotiate compatible parameters with the remote computer"

Any ideas??

Thanks

CES

The same problem here...

These releases add support for Diffie-Hellman (DH) Group 14 and 5 to L2TP over IPSec, and Diffie-Hellman Group 14 to Cisco IPSec. The new supported key exchange proposals are:
DH Group 14 14 14 14 5 5 5
Encryption algorithm AES256 AES256 AES256 AES256 AES256 AES256 AES256
Hash algorithm SHA256 SHA1 MD5 SHA512 SHA256 SHA1 MD5
Previous versions of iOS, OS X and Server supported DH Group 2 (only) for L2TP over IPSec. Previous versions of iOS also supported DH group 5 and 2 for Cisco IPSec, with DH group 2 for aggressive mode.
DH Group 2 is still supported but it has the lowest priority when finding a proposal match. Both L2TP over IPSec and Cisco IPsec now support DH Groups 14, 5, 2, in that order of preference. For aggressive mode, the VPN client will try first with DH Group 14; if it fails, it will try again with DH Group 2. Apple recommends using Group 14 or Group 5 since they provide stronger security than Group 2, which may be vulnerable to compromise.


Firmware Version: 1.1.0 Build 20150416 Rel.35252
Hardware Version: TL-ER6020 v1.0

Hi , I have found a beta firmware for thisrouter,it is s solution for the L2TP VPN at Apple .

http://static.tp-link.com/resources/software/TL-ER6020v1_en_1.1.1_20160628-rel58934_up.zip

You may need to reconfigure the router after the firmware upgrade.

Hello marcelotq

Thanks for providing the link for the beta firmware for the TL-ER6020v1. I'm having the same issue with router TL-ER604W V1.0 was wondering if you can please provide a beta firmware for this model as well.

Thanks.

Carlos Sosa

cacososa wrote

Hello marcelotq

Thanks for providing the link for the beta firmware for the TL-ER6020v1. I'm having the same issue with router TL-ER604W V1.0 was wondering if you can please provide a beta firmware for this model as well.

Thanks.

Carlos Sosa

Hi, you can found here:
http://tp-link-support.de/firmware/

Or, direct access:
http://tp-link-support.de/firmware/TL-ER604W/TL-ER604Wv1_160622.beta.Apple-L2TP.zip

Hello,

Thanks for the link. I was able to download the firmware just fine, however when I try updating the router, I get "UPDATE FAILED" Message. Is there a specific set of instructions I need to be following in order to update the firmware?

Any help would be greatly appreciate it.

Regards
Carlos Sosa

Has the firmware you are trying to install officially been released by TP-Link yet?
It's not easily found unless you have that specific link..

Well, the reason that it is not easily found is because it is a BETA firmware therefore it has not been officially released.