DHCP IP Conflict problem on 819 Router

[bsgd]

Hello all,

This is the first time I am actually trying to configure and debug a cisco router, so bear with me. I have a very small business so I have the simplest network there is, nothing fancy here. I have been trying to get a Cisco 819 and a LAP1242 in Autonomous mode to work as my new router and acess point (internet acess is using the routers internal SIM 3G chip), but I've been having several issues related to IP addresses, and I simply cant understand whats going on since my setup here is so simple. Here's the config I have on my 819:

hostname Cisco
!
ip domain name regence
!
clock timezone GMT -3
ip dhcp excluded-address 10.10.10.1
!
ip dhcp pool ccp-pool
network 10.10.10.0 255.255.255.0
default-router 10.10.10.1
dns-server 10.10.10.1
lease 3
!
ip dns server
!
ip dns view default
default dns forwarder
default dns forwarding
default domain lookup
default domain name-server
!
interface Vlan1
ip address 10.10.10.1 255.255.255.0
ip nat inside
!
controller Cellular 0
!
chat-script gsm "" "AT!SCACT=1,1" TIMEOUT 60 "OK"
!
interface cellular 0
ip address negotiated
ip nat outside
ip virtual-reassembly in
encapsulation slip
dialer in-band
dialer string gsm
dialer-group 1
async mode interactive
!
ip route 0.0.0.0 0.0.0.0 Cellular0
ip nat inside source list 1 interface Cellular0 overload
!
dialer-list 1 protocol ip permit
!
access-list 1 permit 10.10.10.0 0.0.0.255
!
line 3
exec-timeout 0 0
password cisco
script dialer gsm
login
modem InOut
no exec
transport input all

I have only 6 clients (2 iphones, 3 Windows 10 computers and the LAP1242) trying to connect to the router, and ALL of them are set to get IPs from DHCP, no static IPs. Usually the first 2 or 3 devices connect fine and get valid IPs, but suddenly, some devices wont conenct corrcetly, and get those standard 169.xxx.xxx.xxx IPs. 

Router is running the original firmware that came with it, Cisco IOS 15.2 (4) M3. I also uploaded a new firmware by TFTP (15.4 (3) M10) but it didint make a difference, same problem.

The SHOW ARP command results in the following:

Cisco#show arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.10.10.3 0 409c.2837.ea32 ARPA Vlan1
Internet 10.10.10.4 0 48bf.6b29.f308 ARPA Vlan1
Internet 10.10.10.5 2 bcdd.c29b.41d4 ARPA Vlan1
Internet 10.10.10.6 2 4485.00a4.cbee ARPA Vlan1
Internet 10.10.10.7 0 Incomplete ARPA

In this case, one of the WINDOWS 10 LAPTOPS (10.10.10.7) did not get a valid IP address. IP CONFIG shows IP 169.254.229.116. I tried using the 'no ip dhcp conflict logging' config but it didnt make a difference as far as I can tell, as some deviced still wouldnt be able to succesfully connect.

Any help? I still dont get why Im having issues on such a straightforward setup, I must be doing something wrong here.

[Jaderson Pessoa]

Hello my friend, laptop is trying to connection through wlan or lan? are you able to test it using lan cable?

[bsgd]

Hi Janderson,

All devices are connecting through WLAN. I did try connecting ONE device using a lan cable and got UNIDENTIFIED NETWORK on Windows. No valid IP.

Forgot to mention something important. Sometimes (not always) I do get a few erros while connected to the router via PUTTY:

%DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 10.10.10.2.
%DHCPD-4-PING_CONFLICT: DHCP address conflict: server pinged 10.10.10.3.

[Jaderson Pessoa]

ok, try it:
ip dhcp excluded-address 10.10.10.1 10.10.10.5
clear ip dhcp binding *
clear ip dhcp conflict *

[bsgd]

OK, so I inserted ip dhcp excluded-address 10.10.10.1 10.10.10.5 inside CONF T and then after leaving config I sent clear ip dhcp binding *
clear ip dhcp conflict *
After that the same problem occurs, heres what I got:
show arp
Internet 10.10.10.3 3 48bf.6b29.f308 ARPA Vlan1
Internet 10.10.10.5 2 409c.2837.ea32 ARPA Vlan1
Internet 10.10.10.6 0 48bf.6b29.f308 ARPA Vlan1
Cisco#
*Jul 6 13:53:18.639: %DHCPD-4-DECLINE_CONFLICT: DHCP address conflict: client 0140.9c28.37ea.32 declined 10.10.10.6.
I have tried resetting and redoing this all over severla times, but still have some serious issues with IP and DHCP. I have even tried 5 completely different windows machines but most of them wont get a valid IP address.

[Jaderson Pessoa]

what access_point model are you using? it directly attached to your router or there is a switch between?

[bsgd]

Im using the AIR-LAP1242AG-A-K9 flashed to autonomous mode.
No swith or any other device on the network, just the LAP connected directly to FE 0 on 819 router.

[Reza Sharifi]

Hi,

What is the output of:

sh ip dhcp binding

sh ip dhcp conflict

HTH

[bsgd]

I have restarted the router and started fresh. Currently I have 5 clients connected, but only one of them 10.10.10.6 has a valid IP address. The others are connect through WLAN but with no internet access and no valid IP.
Output of requested commands:

Cisco#show arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.10.10.1 - 04da.d2b1.a36e ARPA Vlan1
Internet 10.10.10.6 0 48bf.6b29.f308 ARPA Vlan1
Cisco#sh ip dhcp conflict
IP address Detection method Detection time VRF
10.10.10.6 Gratuitous ARP Jul 06 2020 11:27 AM
Cisco#show arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.10.10.1 - 04da.d2b1.a36e ARPA Vlan1
Internet 10.10.10.6 0 48bf.6b29.f308 ARPA Vlan1
Cisco#sh ip dhcp binding
Bindings from all pools not associated with VRF:
IP address Client-ID/ Lease expiration Type
Hardware address/
User name
Cisco#sh ip dhcp conflict
IP address Detection method Detection time VRF
10.10.10.6 Gratuitous ARP Jul 06 2020 11:27 AM
Cisco#

[Reza Sharifi]

So, there is no binding.

Can you add "import all" to the dhcp pool and test again?

Also, does "sh ip dhcp pool" show the correct subnet?

HTH

[bsgd]

So I resent configuration including IMPORT ALL but I noticed an error:

Cisco#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Cisco(config)#hostname Cisco
Cisco(config)#!
Cisco(config)#ip domain name regence
Cisco(config)#!
Cisco(config)#clock timezone GMT -3
Cisco(config)#ip dhcp excluded-address 10.10.10.1 10.10.10.5
Cisco(config)#!
Cisco(config)#ip dhcp pool ccp-pool
Cisco(dhcp-config)#network 10.10.10.0 255.255.255.0
% Subnet overlaps with an existing subnet [10.10.10.0, 255.255.255.248] in this pool.
Cisco(dhcp-config)#default-router 10.10.10.1
Cisco(dhcp-config)#dns-server 10.10.10.1
Cisco(dhcp-config)#import all
Cisco(dhcp-config)#lease 3
Cisco(dhcp-config)#!
Cisco(dhcp-config)#ip dns server
Cisco(config)#!
Cisco(config)#ip dns view default
Cisco(cfg-dns-view)#default dns forwarder
Cisco(cfg-dns-view)#default dns forwarding
Cisco(cfg-dns-view)#default domain lookup
Cisco(cfg-dns-view)#default domain name-server
Cisco(cfg-dns-view)#!
Cisco(cfg-dns-view)#interface Vlan1
Cisco(config-if)#ip address 10.10.10.1 255.255.255.0
Cisco(config-if)#ip nat inside
Cisco(config-if)#!
Cisco(config-if)#controller Cellular 0
Cisco(config-controller)#!
Cisco(config-controller)#chat-script gsm "" "AT!SCACT=1,1" TIMEOUT 60 "OK"
Cisco(config)#!
Cisco(config)#interface cellular 0
Cisco(config-if)#ip address negotiated
Cisco(config-if)#ip nat outside
Cisco(config-if)#ip virtual-reassembly in
Cisco(config-if)#encapsulation slip
Cisco(config-if)#dialer in-band
Cisco(config-if)#dialer string gsm
Cisco(config-if)#dialer-group 1
Cisco(config-if)#async mode interactive
Cisco(config-if)#!
Cisco(config-if)#ip route 0.0.0.0 0.0.0.0 Cellular0
Cisco(config)#ip nat inside source list 1 interface Cellular0 overload
%Dynamic mapping in use, cannot change
Cisco(config)#!
Cisco(config)#dialer-list 1 protocol ip permit
Cisco(config)#!
Cisco(config)#access-list 1 permit 10.10.10.0 0.0.0.255
Cisco(config)#!
Cisco(config)#line 3
Cisco(config-line)#exec-timeout 0 0
Cisco(config-line)#password cisco
Cisco(config-line)#script dialer gsm
Cisco(config-line)#login
Cisco(config-line)#modem InOut
Cisco(config-line)#no exec
Cisco(config-line)#transport input all
Cisco(config-line)#^Z

And here is the output of sh ip dhcp pool

Cisco#sh ip dhcp pool

Pool ccp-pool :
Utilization mark (high/low) : 100 / 0
Subnet size (first/next) : 0 / 0
Total addresses : 6
Leased addresses : 0
Pending event : none
1 subnet is currently in the pool :
Current index IP address range Leased addresses
0.0.0.0 10.10.10.1 - 10.10.10.6 0
Cisco#

[bsgd]

So I resent all configuration including IMPORT ALL. Heres what I got:

Cisco#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Cisco(config)#hostname Cisco
Cisco(config)#!
Cisco(config)#ip domain name regence
Cisco(config)#!
Cisco(config)#clock timezone GMT -3
Cisco(config)#ip dhcp excluded-address 10.10.10.1 10.10.10.5
Cisco(config)#!
Cisco(config)#ip dhcp pool ccp-pool
Cisco(dhcp-config)#network 10.10.10.0 255.255.255.0
% Subnet overlaps with an existing subnet [10.10.10.0, 255.255.255.248] in this pool.
Cisco(dhcp-config)#default-router 10.10.10.1
Cisco(dhcp-config)#dns-server 10.10.10.1
Cisco(dhcp-config)#import all
Cisco(dhcp-config)#lease 3
Cisco(dhcp-config)#!
Cisco(dhcp-config)#ip dns server
Cisco(config)#!
Cisco(config)#ip dns view default
Cisco(cfg-dns-view)#default dns forwarder
Cisco(cfg-dns-view)#default dns forwarding
Cisco(cfg-dns-view)#default domain lookup
Cisco(cfg-dns-view)#default domain name-server
Cisco(cfg-dns-view)#!
Cisco(cfg-dns-view)#interface Vlan1
Cisco(config-if)#ip address 10.10.10.1 255.255.255.0
Cisco(config-if)#ip nat inside
Cisco(config-if)#!
Cisco(config-if)#controller Cellular 0
Cisco(config-controller)#!
Cisco(config-controller)#chat-script gsm "" "AT!SCACT=1,1" TIMEOUT 60 "OK"
Cisco(config)#!
Cisco(config)#interface cellular 0
Cisco(config-if)#ip address negotiated
Cisco(config-if)#ip nat outside
Cisco(config-if)#ip virtual-reassembly in
Cisco(config-if)#encapsulation slip
Cisco(config-if)#dialer in-band
Cisco(config-if)#dialer string gsm
Cisco(config-if)#dialer-group 1
Cisco(config-if)#async mode interactive
Cisco(config-if)#!
Cisco(config-if)#ip route 0.0.0.0 0.0.0.0 Cellular0
Cisco(config)#ip nat inside source list 1 interface Cellular0 overload
%Dynamic mapping in use, cannot change
Cisco(config)#!
Cisco(config)#dialer-list 1 protocol ip permit
Cisco(config)#!
Cisco(config)#access-list 1 permit 10.10.10.0 0.0.0.255
Cisco(config)#!
Cisco(config)#line 3
Cisco(config-line)#exec-timeout 0 0
Cisco(config-line)#password cisco
Cisco(config-line)#script dialer gsm
Cisco(config-line)#login
Cisco(config-line)#modem InOut
Cisco(config-line)#no exec
Cisco(config-line)#transport input all
Cisco(config-line)#^Z
Cisco#

This is what I got from sh ip dhcp pool:

Cisco#sh ip dhcp pool

Pool ccp-pool :
Utilization mark (high/low) : 100 / 0
Subnet size (first/next) : 0 / 0
Total addresses : 6
Leased addresses : 0
Pending event : none
1 subnet is currently in the pool :
Current index IP address range Leased addresses
0.0.0.0 10.10.10.1 - 10.10.10.6 0
Cisco#

[Reza Sharifi]

% Subnet overlaps with an existing subnet [10.10.10.0, 255.255.255.248] in this pool.

Current index IP address range Leased addresses
0.0.0.0 10.10.10.1 - 10.10.10.6 0

There seems to be a conflict somewhere in your config.

Also,

Cisco#sh ip dhcp pool

Pool ccp-pool :
Utilization mark (high/low) : 100 / 0
Subnet size (first/next) : 0 / 0
Total addresses : 6

total addressee should be 254

[Reza Sharifi]

If you can't find the conflict, maybe one option is to save the current config, than erase the config all together, (write erase), reload the router and start all over but this is really the resort option.

HTH

[bsgd]

I will start from scratch. Can I just use the original CONFIGURATION from my original post, without excluding IPs from 10.10.10.1 to 10.10.10.5 from DHCP exclude?