DHCP not giving out addresses

[jzientek83]

Hello,

Currently we have a Cisco 1921 router that is in a medium business setting.

Data:  40 users, 6 WAP (1142's), 3560 48 port PoE switch, DHCP setup on the Cisco 1921 router, Spectrum business is the ISP

About 3 weeks ago everything was working just fine, now only certain users can gain internet access and any new equipment or users can not gain internet access.  It seems like the DHCP is not responding to the requests send from the clients.

Thank you for any and all help.

We have been unable to connect users for 2 days now.

Thank you again,

Jim

Here are the configs:

CISCO ROUTER       192.168.100.1
CISCO SWITCH    192.168.100.3

ISP settings

IP: 71.83.49.22

DG: 71.83.49.21

GW: 255.255.255.192

------------------------------------------

settings that are in router:

---------------------------------------

BH-ROUTER-01#sho run
Building configuration...

Current configuration : 4811 bytes
!
! Last configuration change at 18:10:42 UTC Wed Sep 9 2015 by MPREP
!
version 15.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname BH-ROUTER-01
!
boot-start-marker
boot-end-marker
!
!
logging buffered 51200 warnings
enable password Alw5y50N)
!
no aaa new-model
!
!
!
!         
!
!
!
!
!
!
!
ip dhcp database BH-ROUTER-01 timeout 180
ip dhcp excluded-address 192.168.100.1
ip dhcp excluded-address 192.168.100.3
ip dhcp excluded-address 192.168.100.199 192.168.100.254
!
ip dhcp pool BH-ROUTER-01
 network 192.168.100.0 255.255.255.192
 default-router 192.168.100.1
 dns-server 208.67.222.222 208.67.222.220
 lease 7

description *** OPEN DNS ADDRESSES ***
!
!
!
ip dhcp global-options
 dns-server 71.10.216.1 71.10.216.2
!         
ip cef
no ipv6 cef
multilink bundle-name authenticated
!
cts logging verbose
!
crypto pki trustpoint TP-self-signed-2609006572
 enrollment selfsigned
 subject-name cn=IOS-Self-Signed-Certificate-2609006572
 revocation-check none
 rsakeypair TP-self-signed-2609006572
!
!
crypto pki certificate chain TP-self-signed-2609006572
 
        quit
license udi pid CISCO1921/K9 sn FTX191380LV
!
!
username Admin privilege 15 secret 5 $1$fjWF$X4ir6ngiQmPQ2e/Ay0P020
username MPREP privilege 15 secret 5 $1$9t89$J.9FBvdH6ZV1j5k6acuaj.
!
redundancy
!
!
!
!
!         
!
interface Embedded-Service-Engine0/0
 no ip address
 shutdown
!
interface GigabitEthernet0/0
 description *** LAN Port ***
 ip address 192.168.100.1 255.255.255.0
 ip nat inside
 ip nat enable
 ip virtual-reassembly in
 duplex auto
 speed auto
!
interface GigabitEthernet0/1
 description *** WAN Port ***
 ip address 71.83.49.22 255.255.255.252
 ip nat outside
 ip nat enable
 ip virtual-reassembly in
 duplex auto
 speed auto
!         
ip forward-protocol nd
!
no ip http server
no ip http secure-server
!
ip nat inside source list 1 interface GigabitEthernet0/1 overload
ip nat inside source static tcp 192.168.100.3 80 interface GigabitEthernet0/1 80
ip route 0.0.0.0 0.0.0.0 71.83.49.21
!
!
!
access-list 1 permit 192.0.0.0 0.255.255.255
!
control-plane
!
!
banner exec ^C
% Password expiration warning.
-----------------------------------------------------------------------
 
Cisco Configuration Professional (Cisco CP) is installed on this device
and it provides the default username "cisco" for  one-time use. If you have
already used the username "cisco" to login to the router and your IOS image
supports the "one-time" user option, then this username has already expired.
You will not be able to login to the router with this username after you exit
this session.
 
It is strongly suggested that you create a new username with a privilege level
of 15 using the following command.
 
username <myuser> privilege 15 secret 0 <mypassword>
 
Replace <myuser> and <mypassword> with the username and password you want to
use.
 
-----------------------------------------------------------------------
^C
banner login ^C

Hello, Welcome to the BH-ROUTER-01, located in Bayer House
^C
banner motd ^C

Welcome to the Cisco 1900 router
^C
!         
line con 0
 password
 logging synchronous
 login local
line aux 0
line 2
 no activation-character
 no exec
 transport preferred none
 transport output pad telnet rlogin lapb-ta mop udptn v120 ssh
 stopbits 1
line vty 0 4
 access-class 23 in
 privilege level 15
 login local
 transport input telnet ssh
line vty 5 15
 access-class 23 in
 privilege level 15
 login local
 transport input telnet ssh
!
scheduler allocate 20000 1000
!
end

[Mark Malone · Accepted solution]

Is the problem there for both wired and wireless users ? These users are on the local lan right as I don't see any helper ip set on the l3 ints?

have you ran  a debug dhcp detail while users are trying to connect to see that the requests are being seen by the router or use a wireshark will tell you aswell which side is not responding router or client

I have seen issues with dhcp before coming from routers where if you remove and reapply the whole pool section (in maintenance window) in configuration it can fix it in case its a bit buggy

what does your show ip dhcp pool show and show ip dhcp binding show

you don't need this line as your only allowing  hosts 192.168.100.0 - 63  ---ip dhcp excluded-address 192.168.100.199 192.168.100.254

[jzientek83]

There is a problem with both wired/wireless.  They are on the local lan.
I have hooked up a computer with wireshark so I can check for requests.
The show ip dchp pool does not show any leases being given out, but a couple of weeks ago it showed 25.

For the helper command - is that needed if the router is the DHCP server?  I thought that was only needed if DHCP was not done by the switch or router?

Thank you

[paul driver]

Hello

Are all these clients receiving a dhcp alocation?
can they access everthing else other than internet?
Is the dhcp scope maxing out due to lan/wifi users alocation?

Do you have a fW between your lan and the internet - Certain Fw/routers can have a licensing count which limits the number of inside hosts allowed to connect through the device?


res

Paul


 

[jzientek83]

Hi,

There is no firewall between LAN & WAN.

There is no lease activity on the router.  I can ping 8.8.8.8 from the router.

Even if I plug into the switch I can not get an IP address.

It seems like a DHCP issue, but everything was working for a few weeks.

Thank you for your help

[Raja_D]

Verify if all the users connected to the switch are part of same vlan or not. If so then go ahead and reconfigure the DHCP configuration on the router by removing the existing configuration. Then verify if the user pc's are able to get the DHCP addresses dynamically or not along with the DNS server ip address information in their TCP/IP properties window.

[Raja_D]

Are those users who are unable to access internet are getting ip's from the DHCP server, and the DNS server ip in their pc's. If they are able to get this info, check if they are able to ping the default gateway and the DNS server or not from there host. Also from the router execute command "show ip dhcp binding" and check for how many pc's are getting the ip's from the router. share the output that you receive on the router.

[jzientek83]

I will get that data first thing Monday, Thanks!!

I did not see any leases on the router which is strange because in the near past I did see the allocations with data.  Someone shut off the router thinking that would reset it, so I was hoping that something didn't get corrupt.

Thank you again,

[Router-support]

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[jzientek83]

Thank you for the information.

Re-entering the dhcp pool did the trick.

Very strange in deed.

Thank you for the quick response

[joojo44]

I encountered a challenge with my Cisco 800 series router, wherein it ceased to allocate IP addresses to devices on my LAN. Upon assigning a static IP address to my PC, I was able to resume work temporarily. Subsequently, I invested significant time and effort in troubleshooting the issue.

However, I eventually resolved the problem by directing my router to synchronize with my NTP (Network Time Protocol) server. This action promptly updated the timezone, date, and time settings, consequently reestablishing the functionality of the DHCP server configuration and enabling proper IP address allocation once again.

I hope this helps you as well