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Forum Discussion
Nighthawk RAX30 - DHCP Client Issues
I've noticed something strange whenever my RAX30 sends DHCP DISCOVER messages to my ISP DHCP server to obtain an IP address. The DHCP specification RFC2131 talks about a field in the DHCP DISCOVER payload called "SECS" that indicates how long a client has been waiting for an IP address. I've found that my RAX30 router never updates the "SECS" field when it sends DISCOVER packets. It is always kept at 0 secs, despite retrying a couple times a couple seconds apart.
While normally this isn't an issue, I've found that this anomalous behavior is keeping my RAX30 router from obtaining an IP address from my ISP's DHCP servers. I'm in contact with the ISP to try and resolve things on their side, but I'm also trying to understand if this is a bug in the RAX30 firmware.
Can anyone help me?
8 Replies
Wonderful job documenting the situation:
- The ISP fails to respond to a DHCP discover with SECS value of 0.
While annoying (and probably inefficient), this may be a typical behavior in certain networking environments.
There being nothing a customer can do to get the ISP to modify their practices (or even get a ticket escalated to someone who actually understands the issue), this is "not good". - The RAX30 does not increase the SECS value on subsequent DHCP requests. Thus, it will never trigger the ISP to respond.
While one would hope that escalating this issue through Netgear support might (eventually) result in updated firmware that functions correctly, there is no guarantee that the problem will ever reach "someone who cares and can DO something".
THANK YOU for investing the time and effort to document this. It seems to me that
- There is little incentive to keep the RAX30. (a) the ISP not likely to change their practice to enable it to connect. (b) there is no way to predict if Netgear will recognize the problem and fix it or how long that might take.
- You have hit a DEAD END.
- There might be some value in publicizing this issue so that others to not make the same mistake. i.e.
o Post on the ISP user forum "Do not attempt to connect a Netgear RAX30 because it will not work"
o When returning the RAX30 for a refund, explain, "it would NOT WORK with ISP xxxx"
o etc. etc.
- The ISP fails to respond to a DHCP discover with SECS value of 0.
Since you have the capability to capture and display the DHCP conversation between router and ISP, it might be interesting to document "what is going on?" with whatever router is working correctly now. (assuming that there IS a working system.) or, even with a random device connected to the ISP (computer, laptop, AppleTV, etc.)
i.e. Does the ISP always ignore the first DHCP request that (by definition) has a SECS value of zero. and then respond to a subsequent request that has an actual value for SECS?
Or, does the ISP respond to the first DHCP request made by devices other than the RAX30?
In my captures and experiments so far, I've yet to see the DHCP server respond to a request that has a 0 SECS value. The working router sends two DISCOVER packets with six seconds between them, and the SECS field is set to 6 accordingly. The DHCP server responds to the second packet with the SECS value of 6.
It's a really strange behavior on the ISP side, and I was trying to look into what configuration might cause this issue, but I haven't turned up anything yet.
Probably time to return the RAX30 and get your money back.
This does appear to be two issues:
- ISP not responding to DHCP Request unless the SECS field is four or greater.
- RAX30 not increasing the SECS number if DHCP Requests do not get a response.
Does this phenomenon appear to happen:
- Only when the RAX30 is powered up?
- Every time the ISP DHCP lease expires and the RAX30 attempts to renew the lease?
Yes, I agree it's two issues. I've been trying to contact the ISP to let them know of the problem on their side, but they are currently putting the blame on NETGEAR, and they do not have enough customers with this problem yet.
The phenomenon with the RAX30 seems to occur as the router attempts to detect the WAN connection. This occurs at startup and when forcing it to try and find the internet connection on setup. It will keep sending three DHCP DISCOVER requests in a row, spaced roughly 2 seconds apart. All these packets will have the SECS field set to 0. After 9 seconds, it will change the transaction id (xid) and then try three more times. All the packets will have the SECS field at 0. It will repeat this until it reports that it can't find an internet connection.
I have packet captures for any of these behaviors.
The ISP does not respond to any of the DHCP Requests?
The ISP DHCP server doesn't seem to respond to DHCP Discover packets unless the SECS field is set to 4 or greater. For other routers, this occurs after one or two retries, but it doesn't work for the RAX30 because the SECS field is stuck at 0. I don't have a good idea what sort of configuration in the DHCP server would cause this behavior, nor why it would be configured that way. This is just what I observed in sending some experimental DHCP packets.
