# DHCP: "no ServerID" messages + no lease

## brainwash

Hi,

recently, my wlan Adapter has trouble acquiring a lease. This happens only occassionally:

Nov 10 12:40:29 mosquito dhcpcd[9612]: wlan0: dhcpcd 4.0.15 starting                                                                                                                                                                         

Nov 10 12:40:29 mosquito dhcpcd[9612]: wlan0: broadcasting for a lease                                                                                                                                                                       

Nov 10 12:40:29 mosquito dhcpcd[9612]: wlan0: offered 192.168.178.23 from 192.168.178.1                                                                                                                                                      

Nov 10 12:40:29 mosquito dhcpcd[9612]: wlan0: ignoring message; no Server ID                                                                                                                                                                 

Nov 10 12:40:34 mosquito dhcpcd[9612]: wlan0: ignoring message; no Server ID                                                                                                                                                                 

Nov 10 12:40:34 mosquito ntpd[5056]: Deleting interface #6 wlan0, 169.254.189.52#123, interface stats: received=0, sent=0, dropped=0, active_time=7500 secs                                                                                  

Nov 10 12:40:37 mosquito dhcpcd[9612]: wlan0: ignoring message; no Server ID                                                                                                                                                                 

Nov 10 12:40:38 mosquito kernel: wlan0: no IPv6 routers present                                                                                                                                                                              

Nov 10 12:40:40 mosquito dhcpcd[9612]: wlan0: ignoring message; no Server ID                                                                                                                                                                 

Nov 10 12:40:43 mosquito dhcpcd[9612]: wlan0: ignoring message; no Server ID                                                                                                                                                                 

Nov 10 12:40:48 mosquito dhcpcd[9612]: wlan0: ignoring message; no Server ID                                                                                                                                                                 

Nov 10 12:40:57 mosquito kernel: No probe response from AP 00:1c:4a:03:d5:35 after 500ms, disconnecting.                                                                                                                                     

Nov 10 12:40:57 mosquito kernel: cfg80211: Calling CRDA to update world regulatory domain                                                                                                                                                    

Nov 10 12:40:59 mosquito dhcpcd[9612]: wlan0: timed out                                                                                                                                                                                      

Nov 10 12:40:59 mosquito dhcpcd[9612]: wlan0: trying to use old lease in `/var/lib/dhcpcd/dhcpcd-wlan0.lease'                                                                                                                                

Nov 10 12:40:59 mosquito dhcpcd[9612]: wlan0: checking 169.254.189.52 is available on attached networks                                                                                                                                      

Nov 10 12:41:04 mosquito dhcpcd[9612]: wlan0: using IPv4LL address 169.254.189.52

My Adapter is an Intel 3945 ABG using the iwl3945 driver. My AP/Router is a Speedport W701V modded with Freetz 29.04.80freetz-1.1.3, which is roughly equivalent to a Fritz!Box 7170. Rebooting the router and reloading the iwl3945 allows me to get a lease again. Only reloading the kernel module or rebooting the router does not help. This problem has started appearing only recently (approximately a week ago), and happens only once a day. I did not make any changes to my Gentoo or Router config and have not installed any Software updates. 

Does anyone have an idea what could be causing this Problem?

Thanks in advance,

brainwash

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## Jaglover

May it be there is another access point in proximity which is connected to another router?

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## brainwash

This is a single-router home setup. There are other APs near, but they use different ESSIDs and I have set up wpa_supplicant to only connect to my ESSID.

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## Jaglover

Well, Google tells this problem occurs with poorly written DHCP servers. You can edit dhcpcd sources and remove server ID check if you want to.

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## brainwash

Yes, but this still does not explain why wlan0 won't accept the offered lease. It should just ignore the fact that no ServerId is present. Or does the absence of the ServerID also imply that any DHCP lease from that Server will be ignored? And why do I sometimes get a lease if this is a case of misconfigured DHCP Server?

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## Jaglover

This may explain it.

It appears new versions of dhcpcd consider NAK messages without ServerID invalid.

I'm no fan of wireless and DHCP myself, can't tell from experience.

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## UberLord

The code has changed a little bit since then.

The ServerID requirement is now enforced in /etc/dhcpcd.conf by default - the user can remove this themselves now so they can work with faulty DHCP servers.

And before anyone goes "bla bla bla dhcpcd is at fault" it is a DHCP requirement that DHCP servers transmit a correct ServerID so that clients know which DHCP server to renew/release their leases from. We can't assume that that computer that sent the message is the DHCP server as that would break DHCP bridges.

The Fritz! box is also a PITA as it enforces a ClientID being present in the DISCOVER/REQUEST which is not a requirement.

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## brainwash

Hi,

thanks for the explanation. The really weird part was this: The problem only occurred when I booted my machine. Then, after restarting the router and reloading the wlan module (causing a restart of dhcpcd) everything would work fine. Maybe I would have tried changing the setting in dhcpcd.conf, but the problem already got on my nerves enough that I decided to replace the DHCP Server of Fritz!' multid with the dnsmasq provided by freetz. Works fine so far.

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