2 Dhcp pool´s for 2 vlans - only 1 work

[Pedro Lima]

Hello sir´s.

I have a follow scenario

Route 1721 -> 2950 -> 2950 -> 2950-> my device

Im tryng to get dhcp over vlan 3 but isnt work. If I insert static IP work very well.

If I change vlan to 2 work normally with dhcp.

I dont know where is the problem. I made agian the pool and still the problem.

I think the problem its on router. All traffic, if is set static IP, work very well by the switchs. Only the DHCP isnt gived in vlan 3.

Thanks anyway,

Follow Router config.

!
version 12.3
service timestamps debug datetime msec
service timestamps log datetime msec
service password-encryption
!
hostname Router-Interno
!
boot-start-marker
boot-end-marker
!
!
mmi polling-interval 60
no mmi auto-configure
no mmi pvc
mmi snmp-timeout 180
no aaa new-model
ip subnet-zero
ip cef
!
!
ip dhcp excluded-address 172.16.10.30 255.255.255.224
!
ip dhcp pool VLAN003
   network 172.16.20.0 255.255.255.224
   default-router 172.16.20.1
   dns-server 8.8.8.8
!
ip dhcp pool VLAN002
   network 172.16.10.0 255.255.255.224
   default-router 172.16.10.1
   dns-server 8.8.8.8
!
ip dhcp pool Ips-Fix
   host 172.16.10.30 255.255.255.224
   client-identifier 0000.aaaa.2222
   default-router 172.16.10.1
   dns-server 8.8.8.8
   lease infinite
!
ip domain name
no ftp-server write-enable
!
!
!
!
interface BRI0
 no ip address
 shutdown
!
interface FastEthernet0
 no ip address
 speed auto
!
interface FastEthernet0.1
!
interface FastEthernet0.2
 description Workstat
 encapsulation dot1Q 2
 ip address 172.16.10.1 255.255.255.224
 ip access-group 102 in
 ip nat inside
!
interface FastEthernet0.3
 description Guest-Wifi
 encapsulation dot1Q 3
 ip address 172.16.20.1 255.255.255.224
  ip helper-address 172.16.20.1
 ip nat inside
!
interface FastEthernet0.4
 description Routers
 encapsulation dot1Q 4
 ip address 172.16.4.5 255.255.255.248
 ip access-group 104 in
!
interface FastEthernet0.5
 description test
 encapsulation dot1Q 5
!
interface FastEthernet0.6
 description Clonezilla
 encapsulation dot1Q 6
!
interface FastEthernet0.7
 description Cloud
 encapsulation dot1Q 7
 ip address 192.168.0.2 255.255.255.252
 ip access-group 105 in
 ip nat outside
!
interface FastEthernet0.8
 description PrinterScan
 encapsulation dot1Q 8
 ip address 10.10.10.1 255.255.255.240
 ip access-group 106 in
!
interface FastEthernet0.20
 encapsulation dot1Q 20 native
!
interface Serial0
 no ip address
 shutdown
!
ip nat inside source list 1 interface FastEthernet0.7 overload
ip classless
ip route 0.0.0.0 0.0.0.0 192.168.0.1
no ip http server
!

[John Blakley]

Hi Pedro,

On the interface, you don't need to specify a helper address since the scope is on the router itself. 

interface FastEthernet0.3
 description Guest-Wifi
 encapsulation dot1Q 3
 ip address 172.16.20.1 255.255.255.224
  ip helper-address 172.16.20.1 << --- Try removing this line
 ip nat inside

HTH,

John

[Richard Burts · Accepted solution]

I believe that your issue is a misunderstanding about configuring excluded addresses. Your configuration has this

ip dhcp excluded-address 172.16.10.30 255.255.255.224

but the excluded address should specify starting and ending address rather than address and mask as you have it. Try changing it to this and let us know if it works better

ip dhcp excluded-address 172.16.10.30 172.16.10.255

HTH

Rick

[John Blakley]

That's a great catch Rick... I didn't notice that...

** Edit **

I labbed this up, and sure enough you can kill the scope by excluding the subnet. Using debugs, you can see where the scope is exhausted. The version of ios that I'm using doesn't give you the option of a mask as the second part of the range. I have the option of low ip and high ip address, but since it doesn't specifically state mask...Rated! :)

Thanks,

John

[Pedro Lima]

Hey Rick, try to explain me that. But the network 172.16.10.X work normally, the problem is on .20 network :S

I remove the excluded address and work well.

But I dont understanding why the excluded address 172.16.10.x /224 is blocking the network .20

Please, could you explain me if u have some little time?

Thanks, very thanks!

[Richard Burts]

I am not clear whether you are still confused about the issue. So let me offer this explanation. When you configure dhcp excluded address specifying two parameters (two addresses) IOS will start at the first address and exclude everything up to the second address. So as you had it originally configured IOS would exclude starting at 172.16.10.30 and going all the way up to 255.255.255.224. Clearly that range includes 172.16.20.0 and so your second scope was excluded.

HTH

Rick

[Pedro Lima]

omg, of course!

Thanks, very thanks to explain me! :D

[Pedro Lima]

Hello John, I put this command to try help my problem, but isnt work too, removing still same :(

Im usnig wireshark to try resolve this problem.

On netwrok172.16.10.x work fine!

On network 172.16.20.x  I just receive ANK, no more :/