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SPLIT: DHCP MaxDHCPMessageSize


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#1 NameOfTheDragon

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Posted 16 July 2015 - 06:13 AM

I don't think this is related to the stopping-on-the-hour issue, but in the process of investigating that I caught a DHCP broadcast and noticed this error message (attached) - might be something to look into...
Attached File  MaxDHCPMessageSize.PNG   582.2KB   1 downloads
I noticed that on Technet there is a documentation mistake, which says "The maximum legal value for this option is 576". That is incorrect, 576 is the minimum value, per RFC2132:
 
"The code for this option is 57, and its length is 2. The minimum legal value is 576 octets".
 
I believe that is the link layer size and includes 64 octets header and 512 octets payload, that's the smallest link layer packet that hosts are supposed to accept.
 
Regards,
Tim

#2 Chris Walker

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Posted 06 August 2015 - 03:30 AM

Thanks Tim. There are some rules around IPv4 vs IPv6 packet sizes, min buffers, etc. The stack will always take minimum-sized TCP packets (and defaults to larger, regular size IPv4 frames).

Could you post this as an Issue on the Netduino.IP GitHub repo, and then we'll double-check the broadcast minimum DHCP message size?

Unless you're not getting an IP address via DHCP, this setting is unlikely to cause any issues--but in any case we want to make sure the stack is nice and standards-compliant throughout :)

Thanks Tim,

Chris

#3 NameOfTheDragon

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Posted 07 August 2015 - 09:40 PM

Thanks Tim. There are some rules around IPv4 vs IPv6 packet sizes, min buffers, etc. The stack will always take minimum-sized TCP packets (and defaults to larger, regular size IPv4 frames).

Could you post this as an Issue on the Netduino.IP GitHub repo, and then we'll double-check the broadcast minimum DHCP message size?

Unless you're not getting an IP address via DHCP, this setting is unlikely to cause any issues--but in any case we want to make sure the stack is nice and standards-compliant throughout :)

Thanks Tim,

Chris

 

Issue created on GitHub. They're building up... ;-)

--Tim



#4 Chris Walker

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Posted 18 September 2015 - 07:22 AM

Hi Tim,

Fixed in Netduino.IP v1.0.1 (in the 4.3.2.3 firmware).

Whew, no more outstanding issues for Netduino.IP on GitHub :)

Please let me know how the updated firmware works for you! And thanks again for surfacing this issue.

Chris




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