Skype for Business Online connectivity paths


Recently Microsoft released a blog article to provide awareness and guidance on Simplified port requirements for Skype for Business Online: https://techcommunity.microsoft.com/t5/Skype-for-Business-Blog/Simplified-port-requirements-for-Skype-for-Business-Online/ba-p/77094

which had an updated destination ports to the cloud that makes the high ports TCP and UDP optional.

what concerns us here in this article is any traffic going through the Cloud services; so we will test only the conference media paths.

First lets look on how that is different from On-Premises and how the ICE protocol selects the ports in priorities.

in this scenarios I am going to test the Voice, Video , VBSS and RDP App Share.

I used Netmon to trace the ports and used coloring and marking from the previous blog post https://blogs.msdn.microsoft.com/mahmoud_badran/2017/05/16/netmon-capabilities-for-skype-for-business-online-troubleshooting/

 

Here is an-on premises scenario where the caller dialled to a conference; as you can see here after a series of TURN requests the following Ports were selected ; Client Source Port UDP 50006 and Destination Port UDP 50680

What i am going to do is to add Video for the same call and below is my capture and as seen below Client Source Port is UDP 50036 and Destination Port is UDP 53400

again adding the VBSS (Desktop Share) the following UDP ports were selected Source port UDP 50058 and Destination port UDP 58760

And Finally with Application Sharing the following TCP ports were selected Source Port TCP 50048 and Destination Port 52972.

so in order to enforce the second media path we are going to block all the high ports UDP only from my machine with the Windows Firewall.

 

Now we are going to run the same tests for Audio, Video and VBSS only since they use the UDP high ports and see what happens on Netmon.

for Audio we saw that the second path was Source port 50016 and Destination Port UDP 3478

similar results for Video where the destination was UDP 3478

and similar results for VBSS where the destination was UDP 3478

 

 

Now for the Third Path we are going to Block UDP 3478 from our Firewall and lets see what happens:

Re Run the same Audio, Video and VBSS Scenarios:

Now the interesting Scenario here the TCP high ports are used for Audio, as seen Source Port TCP 50018 and Destination Port TCP 50921

Video as well got established on the TCP high ports, with Source Port TCP 50032 and Destination Port TCP 57669

and Similarly the VBSS was on TCP high ports, here is Client Source port TCP 50052 and Destination port TCP 55464

it is very Important to know that this Scenario you cannot differentiate between VBSS or App Share except from the Snooper Logs

and below is the Snooper logs that proves this session was a TCP VBSS and used H264

06/13/2017|10:28:53.528 45DC:2A20 INFO :: Sending Packet – xx.xx.xx.xx:443 (From Local Address: 192.168.50.121:59364) 3166 bytes:
06/13/2017|10:28:53.528 45DC:2A20 INFO ::
INVITE sip:mbadran@contoso.com;gruu;opaque=app:conf:applicationsharing:id:TLD18BDT SIP/2.0
Via: SIP/2.0/TLS 192.168.50.121:59364
Max-Forwards: 70
From: <sip:mbadran@contoso.com>;tag=dc0670b210;epid=03413c7128
To: <sip:mbadran@contoso.com;gruu;opaque=app:conf:applicationsharing:id:TLD18BDT>;tag=673cc255;epid=361A8A700C
Call-ID: e733471e87ce4f849b9e46122232b0bc
CSeq: 2 INVITE
User-Agent: UCCAPI/16.0.7766.5352 OC/16.0.7766.2091 (Skype for Business)
Supported: ms-dialog-route-set-update
Supported: timer
Supported: histinfo
Supported: ms-safe-transfer
Supported: ms-sender
Supported: ms-early-media
ms-keep-alive: UAC;hop-hop=yes
ms-subnet: 192.168.50.0
ms-endpoint-location-data: NetworkScope;ms-media-location-type=Internet
Proxy-Authorization: TLS-DSK qop=”auth”, realm=”SIP Communications Service”, opaque=”3E0FAC86″, targetname=”contoso.com”, crand=”9ab215e7″, cnum=”166″, response=”9e30cf5b6d03f822abb93d19c2bb10b598e1917d”
Content-Type: application/sdp
Content-Length: 1610

v=0

o=- 0 2 IN IP4 xx.xx.xx.xx

s=session

c=IN IP4 xx.xx.xx.xx

b=CT:99980

t=0 0

a=x-mediabw:applicationsharing-video send=8100;recv=4000

m=applicationsharing 50049 TCP/RTP/SAVP 127

a=ice-ufrag:t8XO

a=ice-pwd:/R1zFbA5Rdy5X4V4YVfem42q

a=candidate:14 1 TCP-ACT 1852570879 24.140.230.224 50049 typ prflx raddr 192.168.50.121 rport 50049

a=x-candidate-info:14 network-type=wlan

a=crypto:2 AES_CM_128_HMAC_SHA1_80 inline:Enb/Q/W9NCW2r/4A+IJzCq90n18lQYiXot3EVgAa|2^31|1:1

a=remote-candidates:1 xx.xx.xx.xx 50336 2 xx.xx.xx.xx 50336

a=setup:active

a=connection:existing

a=rtpmap:127 x-data/90000

a=rtcp-mux

a=x-bwealgorithm:packetpair

a=x-applicationsharing-session-id:1

a=x-applicationsharing-role:sharer

a=x-applicationsharing-media-type:rdp

a=x-applicationsharing-contentflow:sendonly

m=video 50052 TCP/RTP/SAVP 122 123

a=x-ssrc-range:2832877825-2832877924

a=rtcp-fb:* x-message app send:src,x-pli recv:src,x-pli

a=rtcp-rsize

a=label:applicationsharing-video

a=ice-ufrag:NLIp

a=ice-pwd:oX/60lMgeMaJTxar75FhtfCk

a=x-mediasettings:applicationsharing-video=required

a=candidate:11 1 TCP-ACT 1852567295 xx.xx.xx.xx 50052 typ prflx raddr 192.168.50.121 rport 50052

a=x-candidate-info:11 network-type=wlan

a=cryptoscale:1 client AES_CM_128_HMAC_SHA1_80 inline:Enb/Q/W9NCW2r/4A+IJzCq90n18lQYiXot3EVgAa|2^31|1:1

a=remote-candidates:1 xx.xx.xx.xx 55646 2 xx.xx.xx.xx 55646

a=setup:active

a=connection:existing

a=sendonly

a=rtpmap:122 X-H264UC/90000

a=fmtp:122 packetization-mode=1;mst-mode=NI-TC

a=rtpmap:123 x-ulpfecuc/90000

a=rtcp-mux

a=x-bwealgorithm:packetpair

Now we will run the same Session for RDP and see the difference in Snooper, as you see the Source port was TCP 50043 and Destination Port TCP 51039

06/13/2017|10:43:01.703 45DC:2A20 INFO  :: Sending Packet – xx.xx.xx.xx:443 (From Local Address: 192.168.50.121:59364) 2320 bytes:
06/13/2017|10:43:01.703 45DC:2A20 INFO  ::
INVITE sip:mbadran@contoso.com;gruu;opaque=app:conf:applicationsharing:id:Y6FD73H2 SIP/2.0
Via: SIP/2.0/TLS 192.168.50.121:59364
Max-Forwards: 70
From: <sip:mbadran@contoso.com>;tag=dc77454c41;epid=03413c7128
To: <sip:mbadran@contoso.com;gruu;opaque=app:conf:applicationsharing:id:Y6FD73H2>;tag=bbeffade50;epid=D9672F7281
Call-ID: 4d4d16fe0a9643f3ac565ca370b095d7
CSeq: 2 INVITE
Contact: <sip:mbadran@contoso.com;opaque=user:epid:5c4Y0LZ-P16OxFNemnoO7gAA;gruu>
User-Agent: UCCAPI/16.0.7766.5352 OC/16.0.7766.2091 (Skype for Business)
Supported: ms-dialog-route-set-update
Supported: timer
Supported: histinfo
Supported: ms-safe-transfer
Supported: ms-sender
Supported: ms-early-media
ms-keep-alive: UAC;hop-hop=yes
ms-subnet: 192.168.50.0
ms-endpoint-location-data: NetworkScope;ms-media-location-type=Internet
Proxy-Authorization: TLS-DSK qop=”auth”, realm=”SIP Communications Service”, opaque=”3E0FAC86″, targetname=”contoso.com”, crand=”eac0f45a”, cnum=”383″, response=”2e315122a3a496c4abaa2e70d7b154567e64f1a2″
Content-Type: application/sdp
Content-Length: 763
v=0
o=- 0 1 IN IP4 xx.xx.xx.xx
s=session
c=IN IP4 xx.xx.xx.xx
b=CT:99980
t=0 0
m=applicationsharing 50043 TCP/RTP/SAVP 127
a=ice-ufrag:VvoJ
a=ice-pwd:za3jOXA4LzS7Lr4eZCC9appB
a=candidate:14 1 TCP-ACT 1852570879 xx.xx.xx.xx 50043 typ prflx raddr 192.168.50.121 rport 50043
a=x-candidate-info:14 network-type=wlan
a=crypto:2 AES_CM_128_HMAC_SHA1_80 inline:z0oEcJPviJ2Q4CNEXt75fE3PyOrJyDDE33PsRDUe|2^31|1:1
a=remote-candidates:1 xx.xx.xx.xx 51039 2 xx.xx.xx.xx 51039
a=setup:active
a=connection:existing
a=mid:1
a=rtpmap:127 x-data/90000
a=rtcp-mux
a=x-bwealgorithm:packetpair
a=x-applicationsharing-session-id:1
a=x-applicationsharing-role:sharer
a=x-applicationsharing-media-type:rdp
a=x-applicationsharing-contentflow:sendonly

And now Finally if we Blocked all UCP high ports , low ports and TCP high ports the final path will be port TCP 443 for all media types.

Note that i noticed a degradation in voice quality at this point but the SILKWide was still used as a codec, which i found in the VQReport.

Conclusion :

Destination Ports for Skype for Business Online and the alternative paths are different from that of the on-premises.

The tables below illustrate the destination ports and alternative paths in priority for each of the on-premises and cloud.

Outbound Traffic preferred route for On-premises:

 

Media Type Transport Source Port Destination Port
Audio UDP Client Subnet 50000 – 50019 SfB Edge Server IPs OR Client Subnet in P2P 50000 – 59999
Video UDP Client Subnet 50020 – 50039 SfB Edge Server IPs OR Client Subnet in P2P 50000 – 59999
VBSS UDP Client Subnet 50040 – 50059 SfB Edge  Server IPs OR Client Subnet in P2P 50000 – 59999
AppShare RDP TCP Client Subnet 50040 – 50059 SfB Edge  Server IPs OR Client Subnet in P2P 50000 – 59999

 

Alternative Route 2:

Media Type Transport Source Port Destination Port
Audio UDP Client Subnet 50000 – 50019 SfB Edge  Server IPs OR Client Subnet in P2P 3478
Video UDP Client Subnet 50020 – 50039 SfB Edge  Server IPs OR Client Subnet in P2P 3478
VBSS UDP Client Subnet 50040 – 50059 SfB Edge  Server IPs OR Client Subnet in P2P 3478
AppShare RDP TCP Client Subnet 50040 – 50059 SfB Edge  Server IPs OR Client Subnet in P2P 443

 

Alternative Route 3:

Media Type Transport Source Port Destination Port
Audio TCP Client Subnet 50000 – 50019 SfB Edge  Server IPs OR Client Subnet in P2P 50000 – 59999
Video TCP Client Subnet 50020 – 50039 SfB Edge  Server IPs OR Client Subnet in P2P 50000 – 59999
VBSS TCP Client Subnet 50040 – 50059 SfB Edge  Server IPs OR Client Subnet in P2P 50000 – 59999
AppShare RDP TCP Client Subnet 50040 – 50059 SfB Edge Server IPs OR Client Subnet in P2P 443

 

Alternative Route 4:

Media Type Transport Source Port Destination Port
Audio TCP Client Subnet 50000 – 50019 SfB Edge Server IPs OR Client Subnet in P2P 443
Video TCP Client Subnet 50020 – 50039 SfB Edge Server IPs OR Client Subnet in P2P 443
VBSS TCP Client Subnet 50040 – 50059 SfB Edge Server IPs OR Client Subnet in P2P 443
AppShare RDP TCP Client Subnet 50040 – 50059 SfB Edge Server IPs OR Client Subnet in P2P 443

 

 

 

Inbound Traffic preferred route:

Media Type Transport Source Port Destination Port
Audio UDP SfB Edge Server IPs OR Client Subnet in P2P 50000 – 59999 Client Subnet 50000 – 50019
Video UDP SfB Edge Server IPs OR Client Subnet in P2P 50000 – 59999 Client Subnet 50020 – 50039
VBSS UDP SfB Edge Server IPs OR Client Subnet in P2P 50000 – 59999 Client Subnet 50040 – 50059
AppShare RDP TCP SfB Edge Server IPs OR Client Subnet in P2P 50000 – 59999 Client Subnet 50040 – 50059

 

Alternative Route 2:

Media Type Transport Source Port Destination Port
Audio UDP SfB Edge Server IPs OR Client Subnet in P2P 3478 Client Subnet 50000 – 50019
Video UDP SfB Edge Server IPs OR Client Subnet in P2P 3478 Client Subnet 50020 – 50039
VBSS UDP SfB Edge Server IPs OR Client Subnet in P2P 3478 Client Subnet 50040 – 50059
AppShare RDP TCP SfB Edge Server IPs OR Client Subnet in P2P 443 Client Subnet 50040 – 50059

 

Alternative Route 3:

Media Type Transport Source Port Destination Port
Audio TCP SfB Edge Server IPs OR Client Subnet in P2P 50000 – 59999 Client Subnet 50000 – 50019
Video TCP SfB Edge Server IPs OR Client Subnet in P2P 50000 – 59999 Client Subnet 50020 – 50039
VBSS TCP SfB Edge Server IPs OR Client Subnet in P2P 50000 – 59999 Client Subnet 50040 – 50059
AppShare RDP TCP SfB Edge Server IPs OR Client Subnet in P2P 443 Client Subnet 50040 – 50059

 

Alternative Route 4:

Media Type Transport Source Port Destination Port
Audio TCP SfB Edge Server IPs OR Client Subnet in P2P 443 Client Subnet 50000 – 50019
Video TCP SfB Edge Server IPs OR Client Subnet in P2P 443 Client Subnet 50020 – 50039
VBSS TCP SfB Edge Server IPs OR Client Subnet in P2P 443 Client Subnet 50040 – 50059
AppShare RDP TCP SfB Edge Server IPs OR Client Subnet in P2P 443 Client Subnet 50040 – 50059

 

 

 

The Way its configured now in the cloud is Different and below is the table for the cloud media paths:

Outbound Traffic preferred route for Skype for Business Online:

 

Media Type Transport Source Port Destination Port
Audio UDP Client Subnet 50000 – 50019 SfB Online IPs OR Client Subnet in P2P 50000 – 59999
Video UDP Client Subnet 50020 – 50039 SfB Online IPs OR Client Subnet in P2P 50000 – 59999
VBSS UDP Client Subnet 50040 – 50059 SfB Online IPs OR Client Subnet in P2P 50000 – 59999
AppShare RDP TCP Client Subnet 50040 – 50059 SfB Online IPs OR Client Subnet in P2P 443

 

Alternative Route 2:

Media Type Transport Source Port Destination Port
Audio UDP Client Subnet 50000 – 50019 SfB Online IPs OR Client Subnet in P2P 3478
Video UDP Client Subnet 50020 – 50039 SfB Online IPs OR Client Subnet in P2P 3478
VBSS UDP Client Subnet 50040 – 50059 SfB Online IPs OR Client Subnet in P2P 3478
AppShare RDP TCP Client Subnet 50040 – 50059 SfB Online IPs OR Client Subnet in P2P 443

 

Alternative Route 3:

Media Type Transport Source Port Destination Port
Audio TCP Client Subnet 50000 – 50019 SfB Online IPs OR Client Subnet in P2P 443
Video TCP Client Subnet 50020 – 50039 SfB Online IPs OR Client Subnet in P2P 443
VBSS TCP Client Subnet 50040 – 50059 SfB Online IPs OR Client Subnet in P2P 443
AppShare RDP TCP Client Subnet 50040 – 50059 SfB Online IPs OR Client Subnet in P2P 443

 

 

Inbound Traffic preferred route:

Media Type Transport Source Port Destination Port
Audio UDP SfB Online IPs OR Client Subnet in P2P 50000 – 59999 Client Subnet 50000 – 50019
Video UDP SfB Online IPs OR Client Subnet in P2P 50000 – 59999 Client Subnet 50020 – 50039
VBSS UDP SfB Online IPs OR Client Subnet in P2P 50000 – 59999 Client Subnet 50040 – 50059
AppShare RDP TCP SfB Online IPs OR Client Subnet in P2P 443 Client Subnet 50040 – 50059

 

Alternative Route 2:

Media Type Transport Source Port Destination Port
Audio UDP SfB Online IPs OR Client Subnet in P2P 3478 Client Subnet 50000 – 50019
Video UDP SfB Online IPs OR Client Subnet in P2P 3478 Client Subnet 50020 – 50039
VBSS UDP SfB Online IPs OR Client Subnet in P2P 3478 Client Subnet 50040 – 50059
AppShare RDP TCP SfB Online IPs OR Client Subnet in P2P 443 Client Subnet 50040 – 50059

 

Alternative Route 3:

Media Type Transport Source Port Destination Port
Audio TCP SfB Online IPs OR Client Subnet in P2P 443 Client Subnet 50000 – 50019
Video TCP SfB Online IPs OR Client Subnet in P2P 443 Client Subnet 50020 – 50039
VBSS TCP SfB Online IPs OR Client Subnet in P2P 443 Client Subnet 50040 – 50059
AppShare RDP TCP SfB Online IPs OR Client Subnet in P2P 443 Client Subnet 50040 – 50059

 

 

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