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Bug: Netduino DHCP requests not asking for DNS


Best Answer DaveRVW, 10 July 2013 - 05:48 PM

More news.

 

I called net.EnableDynamicDns() [font="arial, helvetica, sans-serif;"]and now DNS is working again, including requesting and receiving DNS servers during DHCP.  My Netduino was recently reset and I had to reset the MAC address.  Not sure why the default would be to not ask for DNS servers in this state.[/font]

 

[font="arial, helvetica, sans-serif;"]So the original complaint is not complete, but there is something not quite right here that I have to call EnableDynamicDns() from this state.  This is not expected.[/font]

 

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#1 DaveRVW

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Posted 10 July 2013 - 04:12 PM

My Netduino Plus 2 (v4.2.2.2 Jan 26 2013) is working at home with networking, then I bring it to work today and network time protocol requests are failing.  I do some digging, and the DNS entry is my home router, not my work DNS.  DHCP is enabled, and the other parameters are okay (IP, subnet, router, etc.)

 

So I used WireShark to capture the relevant DHCP packets.  Netduino should be requesting DNS options but is not.  The BOOTP option 55 only includes Subnet Mask, Router, and Broadcast Address.  It should also include DNS as a requested parameter.  The DHCP server at home supplies the DNS entry anyways, but the DHCP server at work appears to be strictly complying with the parameter request and doesn't supply the DNS entry if not requested.

 

Option: (55) Parameter Request List Length: 3 Parameter Request List Item: (1) Subnet Mask Parameter Request List Item: (3) Router Parameter Request List Item: (28) Broadcast Address

 

There should be at least one more item included:

  Parameter Request List Item: (6) Domain Name Server

 

Relevant packet dump from work is attached.

Attached Files



#2 DaveRVW

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Posted 10 July 2013 - 05:48 PM   Best Answer

More news.

 

I called net.EnableDynamicDns() [font="arial, helvetica, sans-serif;"]and now DNS is working again, including requesting and receiving DNS servers during DHCP.  My Netduino was recently reset and I had to reset the MAC address.  Not sure why the default would be to not ask for DNS servers in this state.[/font]

 

[font="arial, helvetica, sans-serif;"]So the original complaint is not complete, but there is something not quite right here that I have to call EnableDynamicDns() from this state.  This is not expected.[/font]

 



#3 ziggurat29

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Posted 11 July 2013 - 04:21 PM

It is interesting, I have never had to do this, and I can attest that I use a dns name to reach my server from the netduino (which is on the Internet, not the lan), and I use dhcp to get all my config.  I would think that would mean that I must be using dns to resolve the name, and that since there is no specific configuration of the dns server name, that it must have come in through dhcp, automatically, without explicit programmatic action.  FWIW I am using 4.2.2.1.

 

Your mention that, at work, that you find that "the DNS entry is my home router, not my work DNS" is interesting.  What do you mean by that?  There's not a power-cycle-to-power-cycle persistent storage of a dynamically assigned dns name.



#4 nakchak

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Posted 11 July 2013 - 06:16 PM

Depends on your works network setup, if its a relatively secure setup it may well be blackholing unknown mac addresses... If that's the case denying dns info as its a good way to mitigate against unknown devices, you probably find the firewall blackholes it as well. You could always use googles public dns servers and hard code the ip's 8.8.8.8 & 8.8.4.4 Nak.

#5 DaveRVW

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Posted 12 July 2013 - 05:33 AM

Your mention that, at work, that you find that "the DNS entry is my home router, not my work DNS" is interesting.  What do you mean by that?  There's not a power-cycle-to-power-cycle persistent storage of a dynamically assigned dns name.

 

DNS server(s) appears to be up to two IP addresses.  Took my Netduino to work, and while it was using DHCP and the IP showed up in the proper 192.168.x.x range, it kept my home DNS in the 10.x.y.z. range.   I had been switching between static and dynamic IPs, and/or lost my network settings a few times too.  But I don't remember changing to static DNS.  The "fix" to call EnableDynamicDns() was unexpected.

 

Now everything is working fine.






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