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Author Topic: Short packets  (Read 829 times)

Weaver

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  • Retd s/w dev; A&A; 3x7km lines; Firebrick; IPv6
Short packets
« on: March 03, 2020, 12:13:31 PM »

Say someone sends me an IPv4 TCP packet and it is less than 40 bytes long, or any IPv4 packet that is less than 20 bytes long (do I have the minimum lengths correct?), then what does that do to operating system <x>? Are there still bugs in operating systems relating to checking for this and other similar evils?

I ask because I was reading about a switch that offers checking for such things and I wondered if there is still any need for such external checks. Of course a stateful firewall provides a guard against evildoers anyway unless they are already inside your LAN that is.
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petef

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Re: Short packets
« Reply #1 on: March 03, 2020, 02:00:17 PM »

You are correct about the minimum packet sizes. Shorter packets might be caused by transmission errors or malicious construction. Both of those should be caught by the link layer. I hesitate to say that all current OSs are bug free but it would surprise me if there were handling errors in network drivers. Many years ago I found a bug in IBM's IP handling which had been causing NFS errors. That was an exception which proves the rule.

A switch allows you to offload processing onto separate hardware. Any lift will depend on how many dodgy packets need to be dealt with.
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niemand

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Re: Short packets
« Reply #2 on: March 03, 2020, 03:50:43 PM »

Discarded as junk. Error counter will increment as packet/frame is considered corrupted.
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niemand

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Re: Short packets
« Reply #3 on: March 03, 2020, 03:52:08 PM »

NB switch won't care, or shouldn't as it should be inspecting Ethernet headers only, router will discard.
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