LinuxQuestions.org
Visit Jeremy's Blog.
Go Back   LinuxQuestions.org > Forums > Linux Forums > Linux - Networking
User Name
Password
Linux - Networking This forum is for any issue related to networks or networking.
Routing, network cards, OSI, etc. Anything is fair game.

Notices


Reply
  Search this Thread
Old 04-10-2018, 03:08 AM   #1
eSelix
Senior Member
 
Registered: Oct 2009
Location: Wroclaw, Poland
Distribution: Arch, Kubuntu
Posts: 1,261

Rep: Reputation: 315Reputation: 315Reputation: 315Reputation: 315
Skype stays offline and TCP Retransmission


Hi, I have a problem with Skype. I am using Pidgin with skypeweb plugin and Microsoft Skype for Windows on Virtualbox. Both works in certain situation, but does not in other. By not working I mean that Skype is connecting, all my contacts are displayed, but are offline, I am offline for others and I cannot send text messages to others and vice versa. Real Skype has showing animated circular arrows icon forever. This started few months ago, ealier works good long time.

I tested it on 3 networks: primary company WAN1 (ADSL), secondary company WAN2 (LTE), home network WAN3 (Broadband Ethernet). My company network is: modem (WAN1) or LTE modem with router and NAT (WAN2) (changed by metric in next router route table) -> Mikrotik router (NAT, firewall disabled for my IP) -> PC with Ubuntu (firewall disabled).

When it does not work:
Pidgin running on Ubuntu when I am connected to WAN1. (This is option which I need)
Skype or Pidgin on Virtualbox when I am connected to WAN1 (virtual net in NAT mode).

When it works:
Skype or Pidgin on Virtualbox when I am connected to WAN1 or WAN2 (virtual net in bridge mode).
Skype or Pidgin on Virtualbox when I am connected to WAN2 (virtual net in NAT mode) - but not with WAN1.
Pidgin running on Ubuntu when I am connected to WAN2 - but not with WAN1.
Skype on real Windows 10 with WAN1 or WAN2.
Pidgin running on Arch Linux when I am connected to WAN3.

Ubuntu was tested on 2 devices: PC and laptop - behave the same. Other services: www, mail, etc. works ok. I captured some packets with Wireshark when it does not work, there is always DUP ACK and then TCP Retransmission multiple times. I am not good with network packets deciphering. It seems that during one connection some packets are blocked. Can somebody help me to start Skype working or investigate whats is going on the network?

Click image for larger version

Name:	Pidgin-wireshark.png
Views:	21
Size:	84.6 KB
ID:	27426
Attached Files
File Type: txt Pidgin-k12_wireshark_format.txt (100.9 KB, 4 views)

Last edited by eSelix; 04-10-2018 at 06:03 AM.
 
Old 04-10-2018, 02:49 PM   #2
nini09
Senior Member
 
Registered: Apr 2009
Posts: 1,607

Rep: Reputation: 138Reputation: 138
Based on sniffer, device in uplink path has problem to handle HTTPS traffic. TCP sequence and ACK number is jumping.
 
Old 04-11-2018, 01:11 AM   #3
eSelix
Senior Member
 
Registered: Oct 2009
Location: Wroclaw, Poland
Distribution: Arch, Kubuntu
Posts: 1,261

Original Poster
Rep: Reputation: 315Reputation: 315Reputation: 315Reputation: 315
But how to explain, that it works in VirtualBox with bridge mode and not in real system on the same machine?
 
Old 04-12-2018, 03:04 PM   #4
nini09
Senior Member
 
Registered: Apr 2009
Posts: 1,607

Rep: Reputation: 138Reputation: 138
You can compare TCP options and HTTPS parameters. These things could be different.
 
Old 04-16-2018, 01:46 AM   #5
eSelix
Senior Member
 
Registered: Oct 2009
Location: Wroclaw, Poland
Distribution: Arch, Kubuntu
Posts: 1,261

Original Poster
Rep: Reputation: 315Reputation: 315Reputation: 315Reputation: 315
I just discovered that changing MTU on my PC interface to 1484 allows Skype to works immediately. So, maybe some component on the route blocks all ICMP (these Microsoft servers does not respond to ping request at all) or can't fragment packets. Now, how to find which one it is? Is it something on my network or in the Internet? I logged ICMP packets passing through router, but don't saw any of type 3/4 (fragmentation required).
 
Old 04-16-2018, 04:10 PM   #6
nini09
Senior Member
 
Registered: Apr 2009
Posts: 1,607

Rep: Reputation: 138Reputation: 138
The MTU doesn't match each other.
 
Old 04-17-2018, 01:09 AM   #7
eSelix
Senior Member
 
Registered: Oct 2009
Location: Wroclaw, Poland
Distribution: Arch, Kubuntu
Posts: 1,261

Original Poster
Rep: Reputation: 315Reputation: 315Reputation: 315Reputation: 315
Sorry, I do not understand.
 
Old 04-17-2018, 03:12 PM   #8
nini09
Senior Member
 
Registered: Apr 2009
Posts: 1,607

Rep: Reputation: 138Reputation: 138
Skype packet is HTTPS. If the packet size is too big and middle router can't sent out based its MTU, it should do fragment normally. But HTTPS packet can't do it because encrypted.
 
Old 04-18-2018, 02:20 AM   #9
eSelix
Senior Member
 
Registered: Oct 2009
Location: Wroclaw, Poland
Distribution: Arch, Kubuntu
Posts: 1,261

Original Poster
Rep: Reputation: 315Reputation: 315Reputation: 315Reputation: 315
I didn't heard about fragmentation of encrypted packets. Anyway, these packets are send with DF set and in that case this router should answer with proper ICMP packet telling that sent packet was too large and sender than can decrease its length - that not happens. How to resolve that without lowering MTU for whole LAN due some misconfigured distant router? Or maybe in my network is something wrong?
 
Old 04-19-2018, 03:19 PM   #10
nini09
Senior Member
 
Registered: Apr 2009
Posts: 1,607

Rep: Reputation: 138Reputation: 138
If you want to discover MTU automatically, you can try mechanism of path MTU discovery. But it requests all device in path to support it.
 
Old 04-23-2018, 07:48 AM   #11
eSelix
Senior Member
 
Registered: Oct 2009
Location: Wroclaw, Poland
Distribution: Arch, Kubuntu
Posts: 1,261

Original Poster
Rep: Reputation: 315Reputation: 315Reputation: 315Reputation: 315
That's what I'm talking about - PMTU does not work due some misconfigured device. I see no problem in my network. If I lower MTU on router WAN interface, it is properly discovered by other devices. On the other hand it's hard to believe, that no one encounter this problem during connection with Skype network. Anyway I see no other solution as lowering MTU on my own router.
 
  


Reply

Tags
offline, skype, tcp retransmission


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off



Similar Threads
Thread Thread Starter Forum Replies Last Post
tcp retransmission ping.vat Linux - Networking 1 10-05-2014 06:47 PM
Unexpected TCP Retransmission. $ubbu Linux - Networking 10 06-01-2012 02:09 PM
ssh hangs upon tcp errors or retransmission wastingtime Linux - Software 1 03-10-2009 08:13 PM
TCP Retransmission in Information tab of Ethereal Linuxfan0001 Linux - Networking 1 06-18-2008 03:28 PM
TCP retransmission and duplicated ack enjoyzj Linux - Networking 0 06-05-2004 06:19 PM

LinuxQuestions.org > Forums > Linux Forums > Linux - Networking

All times are GMT -5. The time now is 09:15 PM.

Main Menu
Advertisement
My LQ
Write for LQ
LinuxQuestions.org is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
Syndicate
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration