[strongSwan] Timeout on poor connection

Anvar Kuchkartaev anvar at anvartay.com
Sun Oct 1 01:14:55 CEST 2017



parameters from server side and:


from client side I think most important.

Also you have to do several server optimizations like:


iptables -A INPUT -p esp -j ACCEPT

iptables -A INPUT -p udp -m multiport --dport 500,4500 -j ACCEPT

iptables -A INPUT -p icmp --icmp-type fragmentation-needed -j ACCEPT

iptables -I FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS 


net.ipv4.ip_forward_use_pmtu=1 (I assume you have done rest of the 
sysctl configurations like ip_forward, etc.)

On 30/09/17 19:37, Jamie Stuart wrote:
> Could you post your (redacted) strongswan config Anvar?
>> On 30 Sep 2017, at 00:59, Anvar Kuchkartaev <anvar at anvartay.com> wrote:
>> I also have some clients connecting from central Asia where internet is very poor and restricted. The main optimizations must be done at the server os and firewall not in strongswan. In strongswan try to authenticate server with 2048 bit certificate or higher and watch out IKE ciphers, dos_protection, ikesa_table_size, ikesa_table_segments, ikesa_hashtable_size parameters. Allow only IKEv2 if possible and decrease dpd requests and set dpdaction=restart to restart connection automatically if tunnel fails. From operating system watch out mtu changes because in my case I had a lot of mtu decreases within the provider network in the region client located. Allow icmp fragmentation needed requests from firewall and make tcpmss optimizations. It is also recommended to install proxy server behind VPN server which only possible to connect within the VPN tunnel (so client could configure it's browser to proxy server to enhance connection stability).
>> Anvar Kuchkartaev
>> anvar at anvartay.com
>>    Original Message
>> From: Jamie Stuart
>> Sent: viernes, 29 de septiembre de 2017 05:59 p.m.
>> To: users at lists.strongswan.org
>> Subject: [strongSwan] Timeout on poor connection
>> Hi,
>> We have client (running on LEDE) connecting to a server (Ubuntu). The client is connecting from rural Africa of 2G/3G with high latency and low speed.
>> Often, the connection does not come up, timing out after 5 retracts like the log below:
>> ipsec up {connection}
>> initiating IKE_SA {connection}[2] to {serverip}
>> generating IKE_SA_INIT request 0 [ SA KE No N(NATD_S_IP) N(NATD_S_IP) N(FRAG_SUP) N(HASH_ALG) N(REDIR_SUP)]
>> sending packet: from {clientip}[500] to {serverip}[500] (378 bytes)
>> retransmit 1 of request with message ID 0
>> sending packet: from {clientip}[500] to {serverip}[500] (378 bytes)
>> retransmit 2 of request with message ID 0
>> sending packet: from {clientip}[500] to {serverip}[500] (378 bytes)
>> retransmit 3 of request with message ID 0
>> sending packet: from {clientip}[500] to {serverip}[500] (378 bytes)
>> Is there anything more we can do to make the connection 1) establish more reliably 2) remain ’up’ even over a power quality connection (using MOBIKE already)
>> Thanks in advance!
>> Jamie, onebillion

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