08-19-2021 01:31 AM
we have many APs controlled by cisco wlc 5520
We found some mobile phone roaming from one AP to another AP, DCHP problem
for example
when one mobile phone assotiate to one AP and obtain an IP adress A.A.A.A(from dhcp server running on catalyst 9400)
after this mobile phone move to another AP , we can find this mobile phone send DHCP request (source adress is 0.0.0.0,but option 50 request ip address is a new ip address B (not seen anywhere ,not seen another dhcp server assign this IP B),
DHCP server has old binding ip address A.A.A.A, so dhcp server send DHCP NAK to mobile phone, and release old bingding A.A.A.A
after while, mobile phone begin a new dhcp discover process , DHCP server a new IP C.C.C.C
I have found when this happened .mobile join another AP is 802.11 associate request (not reassociate), then dhcp request happened
Has any one saw this mobile phone weired DHCP request behavor?
why during associate another AP, mobile phone send a not seen new ip B.B.B.B dchp request ? you can see attach
I found dhcp debug on android phone same behavior
thank you
Tom
08-19-2021 01:47 AM
New Mobiles has randomised MAC Address, check every time new IP address (is the MAC Address same ?)
before go deep of the problem.
08-20-2021 04:24 AM
No, mac address is same I check android phone
08-19-2021 01:48 AM
How many clients are affected by this issue? Do you see the option 50 only sporadically (after roaming), or also during initial association of that client? Is it possible that address B.B.B.B is configured as static IP address on the phone?
I have not seen this behavior before. But for me this is a typical client problem and not caused by the networking infrastructure.
You stated that you use the DHCP server on Catalyst 9400. I think the DHCP server cannot be configured to "ignore option 50" or something similar.
08-20-2021 04:24 AM
many client afftect, adroid ,iphone , but I found many happened on android mobile phone, but It didn't happen every time. May be I hold a phone walking from 1st floor to 4th floor, maybe happen 1 time or 2.
today we capture packest on 45 and 94 switch interface connect to many APs,. I found same behavior happened, when one phone send dhcp request to 94 switch dhcp server , the other phone send dhcp request to 45 dhcp server, two phone send dhcp request ( option 50 has one weired new ip eath phone(weired , I didn't find where came from, I didn't find a new dhcp server),
45 and 94 send dhcp nak to client, two mobile phone the begin a new dhcp discover, but 94 then send a new c.c.c.c address, 45 send old a.a.a.a address ( 45 94 dhcp server didn't config remember option) , So I found 45 switch and 94 switch 's behavior is different. So customer found ip address had changed when he change dhcp server from 45 to 94 switch
I add remember option on 94 dhcp config
I found when this happened, WLC capute can find deassociate /deauthenticate 802.11 frame then client associate a new ap , then dhcp request send from client(take weired ip)
It's weired
thank you
Tom
09-03-2021 11:47 AM
I am seeing this issue as well on Meraki Wireless. Seems to be affecting newer Android devices only. All other clients are happy and get DHCP Address no issue. I have packet captures showing the DHCP Discover from the client then an Offer from the server, but the client doesn't send a Request. Again, ONLY newer Android clients are seeing this behavior.
Any help is appreciated.
Thanks,
09-06-2021 09:16 PM
last week we used android studio adb connect to one android phone got some logcat logging.
found this issue may be caused by android dhcpclient
we can find at first android 11 phone get an dhcp offer from dhcp serverand
DhcpClient: DhcpRequestingState -1CMD_RECEIVED_PACKET 0 0 02:xx:33:xx:76:xx ACK: your new IP /192.168.1.xxx, netmask /255.255.255.0 DNS servers: /192.168.6.xxx /192.168.6.xxx , lease time 43200
this dhcp offer address was confirmed , I think this dhcp binding is ok in dhcp server
DhcpClient: Received packet.
DhcpClient: Confirmed lease.
DhcpClient: Received ACK, returning to fast ARP checking
but afterwhile customer hold android phone move from upstaire to downstaire
found phone dhcpclient send dhcp request after rejoining one AP
DhcpClient: connect to saved AP, transitionTo mDhcpRequestingState directly
but dhcpserver send nak
DhcpClient: DhcpRequestingState 0CMD_RECEIVED_PACKET 0 0 02:xx:33:xx:76:xx NAK, reason (none)
from wireshark we can oberserve androdi dhcpclient send a totally different ip in dhcp request
but 94 switch and 45 switch as dhcp server behavior is not same, 45 send dhcp nak and not release dhcp binding
but 94 switch as dhcp server after send dhcp nak release dhcp binding immediately, so 94 send a new dhcp offer to phone so customer observe his phone ip address changed as connect to 94 dhcp server ,not changed connect to 45 dhcp server
I found this link to report android old software bug
Android 2.1 - 4.1.1 Allows DHCP Lease to Expire, Keeps Using IP Address (princeton.edu)
https://www.net.princeton.edu/android/android-stops-renewing-lease-keeps-using-IP-address-11236.html
DHCP client ignores lease time [36921335] - Visible to Public - Issue Tracker (google.com)
https://issuetracker.google.com/issues/36921335
this bug reported on google web decade ago ,I found reopen this year, My god
But our customer report apple iphone has same problem, but I tested whole day haven't found this problem
windows pc didn't find this problem
thank you
Tom
09-22-2021 04:23 PM
I was able to find a fix for at least our network. The issue was we had Option 108 enabled in the DHCP options for the DHCP scope for the wireless network. Removing Option 108 resolved the issue with Android clients not receiving DHCP.
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