SSL VPN poor speed

[Jirka1]

Hello,

we having trouble with throughput the SSL VPN on Windows Latency from the client to the Fortigate is about 20ms and bandwidth in Fortigate site is 1Gbps and client site is 100Mbbps First, when connecting locally over the internal gigabit network (with near-zero latency), performance easily exceeds about 60Mbps for download on the client. I verified through trace routes, the route table, and Task Manager that tested traffic was indeed flowing through SSL VPN. This tells me that the underlying hardware is capable. However, when testing from off-site (at least 100Mbps and 20ms latency), the performance changes. From the client' s perspective, the download rate through SSL VPN is about 13Mbps and the upload is the problem in that it cannot exceed about 2-3Mbps.It seems that the increased latency is the contributing factor. Given that the SSL VPN uses TCP, my guess is that there' s an issue with TCP window scaling of the SSL VPN connection itself, especially when the client is sending data to the Fortigate.

I tried disable all UTM, change IP on wan. wan has no errors, MTU 1500, speed 1GbitFD (fix).

Important: If I configured IPsec VPN and test it, throughput from the corporate LAN to the client is over 80Mbps on both sides. And also traffic to the internet (through the Fortigate, no split-tunnel) reaches maximum client line (about 90Mbps).

Has anyone else been able to achieve better performance on either Windows SSL VPN clients? Our clients need good throughput in both directions from corporate LAN and Internet-based sources where latency far from zero...

My testing has included Windows 7 and Windows 10 Transfer tests included iperf (tcp and udp modes), SMB, FTP, Speedtest.net (and similar tools hosted by the ISP). Fortigate 100D running on v5.4.3,build1111 and FortiClient 5.4.2.0860

config vpn ssl settings
set reqclientcert disable
set sslv3 disable
set tlsv1-0 disable
set tlsv1-1 enable
set tlsv1-2 enable
unset banned-cipher
set ssl-big-buffer disable
set ssl-insert-empty-fragment enable
set https-redirect disable
set ssl-client-renegotiation disable
set force-two-factor-auth disable
set servercert "**********"
set algorithm high
set idle-timeout 0
set auth-timeout 28800
set tunnel-ip-pools "*********"
set dns-suffix "*******.local"
set dns-server1 172.22.91.100
set dns-server2 172.22.91.101
set wins-server1 172.22.91.100
set wins-server2 172.22.91.101
set ipv6-dns-server1 ::
set ipv6-dns-server2 ::
set ipv6-wins-server1 ::
set ipv6-wins-server2 ::
set route-source-interface disable
set url-obscuration disable
set http-compression disable
set http-only-cookie enable
set port 443
set port-precedence enable
set auto-tunnel-static-route enable
set header-x-forwarded-for add
set source-interface "wan1"
set source-address "all"
set source-address-negate disable
set source-address6 "all"
set source-address6-negate disable
set default-portal "web-access"
set dtls-tunnel enable
set check-referer disable
set http-request-header-timeout 20
set http-request-body-timeout 30

config system interface
    edit "wan1"
        set vdom "root"
        set mode static
        set dhcp-relay-service disable
        set ip ********* 255.255.255.240
        set allowaccess ping https ssh snmp http fgfm
        set fail-detect disable
        set pptp-client disable
        set arpforward enable
        set broadcast-forward disable
        set bfd global
        set l2forward disable
        set icmp-redirect enable
        set vlanforward enable
        set stpforward disable
        set ips-sniffer-mode disable
        set ident-accept disable
        set ipmac disable
        set subst disable
        set substitute-dst-mac 00:00:00:00:00:00
        set status up
        set netbios-forward disable
        set wins-ip 0.0.0.0
        set type physical
        set netflow-sampler disable
        set sflow-sampler disable
        set scan-botnet-connections disable
        set sample-rate 2000
        set polling-interval 20
        set sample-direction both
        set explicit-web-proxy disable
        set explicit-ftp-proxy disable
        set tcp-mss 0
        set inbandwidth 0
        set outbandwidth 0
        set spillover-threshold 0
        set ingress-spillover-threshold 0
        set weight 0
        set external disable
        set description "WAN"
        set alias "WAN"
        set security-mode none
        set device-identification disable
        set lldp-transmission vdom
        set fortiheartbeat disable
        set estimated-upstream-bandwidth 0
        set estimated-downstream-bandwidth 0
        set vrrp-virtual-mac disable
        set role wan
        set snmp-index 2
        set secondary-IP disable
        set auto-auth-extension-device disable
        set ap-discover enable
        set fortilink disable
        config ipv6
            set ip6-mode static
            unset ip6-allowaccess
            set ip6-reachable-time 0
            set ip6-retrans-time 0
            set ip6-hop-limit 0
            set dhcp6-prefix-delegation disable
            set ip6-address ::/0
            set ip6-send-adv disable
            set autoconf disable
            set dhcp6-relay-service disable
            set speed 1000full
            set mtu-override disable
            set wccp disable
            set drop-overlapped-fragment disable
            set drop-fragment disable

We are faced with this problem from the beginning (I think FortiOS version 5.0) and we hope to improve with each new version of FortiOS or FortiClient :/ If anyone has any idea how this fix it, I will be grateful.

Thanks!

[Jirka1]

Yes, i tried enable/disabled DTSL and sniff traffic from FortiClient to FortiGate and still connect on port 443 and TCP :\ No UDP. 

[Sebastiaan_Koopmans]

Thanks for your reply: sigmasoftcz Because its an known issue we have to wait to an final fix arrive.

When we receive an update in our ticket , we will let you know

[HA]

Hello,

Can you try to adjust the tcp-mss (on Fortigate) ?? Set it 1350...

Regards,

HA

[Jirka1]

Yes,

we tried set tcp-mms send and recieve. It was first advice from Fortinet support.

[Sebastiaan_Koopmans]

FYI Case is still pending Bugfix release.

[ITGuy11]

I have had this problem for months.  I have a ticket open with support that is also PendBugfix.  I'm not holding my breath...

https://forum.fortinet.com/tm.aspx?m=143253

[recha]

Still no news about a fix for this bug ?

Does someone tried fortios 5.4.4 ?

[Jirka1]

Hi Recha,

I've spoken with Forinet support yesterday and they confirmed, that problem is probably at FortiClient.

DTLS not working properly. I gave them login to our box and made himself an experimental mouse  :) I'll keep you informed.

Jirka

[recha]

Hi Jirka and thanks for the info :)

[Jimmy]

The same applies to the MacOS version unfortunately as we see the same issues here, so we'll be following this topic as well :)