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Old 02-02-2011, 07:54 AM   #1
Registered: Aug 2007
Location: The Greate INDIA
Distribution: CentOS, RHEL, Fedora
Posts: 102

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Unhappy UDP: bad checksum. From x.x.x.x:1234 to y.y.y.y:1234 ulen 100

Dear friends,

I am getting the following error sometimes while getting the RTP packets.

UDP: bad checksum. From <ip>:<port> to <ip>:<port> ulen 136
UDP: bad checksum. From <ip>:<port> to <ip>:<port> ulen 40
UDP: bad checksum. From <ip>:<port> to <ip>:<port> ulen 136
any idea ? (I am using centsOS-5.3, kernel-
Old 02-03-2011, 11:11 AM   #2
Registered: Dec 2007
Distribution: cp6
Posts: 44

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I haven't been introduced to RTP(Real-time Transfer Protocol), so I searched wikipedia for the answer and this is what I found.
The Transmission Control Protocol (TCP), although standardized for RTP use, is not normally used in RTP application because TCP favors reliability over timeliness. Instead the majority of the RTP implementations are built on the User Datagram Protocol (UDP)
According to this, I guess what's troubling you is why it uses UDP, and not TCP. Well, I just wrote you the answer - it is implemented so to favor timeliness over reliability. For further reading you may follow my way and ask wikipedia. I presume you'll find the chapter "OVERVIEW" most informative one.

If you're asking why are your packets experiencing problems, and having bad checksums, it could be for various reasons. What I'm going to say now relies on the fact that you said it happens SOMETIMES.
Those corrupted packets could be product of someone's bad intentions, but as well, could be just regular packets that were exposed to interference of any kind(trams/electrical trains passing by your home etc.). After all, that's what the checksums are for - to check if packets were corrupted during transport. At the and I would like to add, I think that, what you are experiencing is normal and I doubt it is anyone's malicious intention.

If it's happening all too often, and significantly reducing your throughput, you should contact your ISP to help you reduce the interference.

Last edited by hogar.strashni; 02-03-2011 at 11:45 AM.
Old 04-14-2011, 07:21 AM   #3
Registered: Aug 2007
Location: The Greate INDIA
Distribution: CentOS, RHEL, Fedora
Posts: 102

Original Poster
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thnx a lot hogar.strashni

My prob is resolved. It was caused by router itself.
anyways, thnx for the reply.
Old 11-30-2013, 04:43 AM   #4
LQ Newbie
Registered: Nov 2013
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bad checksum. From <ip>:<port> to <ip>:<port> ulen 856

Dear vdx,

Could you share me the cause of your router, and how to you fix it! Because i have a error same your error.



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