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DHCP lab issue

Andrew White
Level 2
Level 2

Hello,

I'm trying to build a typology similar to my work in GNS3, I'm using routers with the NM-16ESW module for 16 switch ports.  Anyway I'm trying to get the host on the VLAN 90 switch an IP address via DHCP but it's having none of it. Core 1 and 2 are using HSRP for all our VLANs, I though the best way to add a DHCP server using a router would be to add it to both cores and using /30 subnets and advertise into OSPF and add the ip-helper address to the VLANs on each core.  Someone did suggest  making the 2 ports for the DHCP server a port channel, but I wasn't sure how I woudl configure this on the to cores.

 

Host 1

no ip routing

!
interface FastEthernet0/0
 ip address dhcp
 no ip route-cache
 duplex auto
 speed auto

90-Switch (layer 2)

 

no ip routing

!
interface FastEthernet1/0

 Description Host 1
 switchport access vlan 90
 duplex full
 speed 100

!

interface FastEthernet1/14

 switchport trunk native vlan 23
 switchport trunk allowed vlan 1,23,90,1002-1005
 switchport mode trunk
 duplex full
 speed 100
!
interface FastEthernet1/15
 switchport trunk native vlan 23
 switchport trunk allowed vlan 1,23,90,1002-1005
 switchport mode trunk
 duplex full
 speed 100

!
interface Vlan1
 no ip address
 no ip route-cache
 shutdown
!
interface Vlan23
 ip address 192.168.23.90 255.255.255.0

 

Core1

interface Port-channel1
 switchport mode trunk

!

interface FastEthernet1/0
 switchport mode trunk
 duplex full
 speed 100
 channel-group 1 mode on
!
interface FastEthernet1/1
 switchport mode trunk
 duplex full
 speed 100
 channel-group 1 mode on

interface FastEthernet1/4
 description DHCP Server
 no switchport
 ip address 192.168.41.2 255.255.255.252
 duplex full
 speed 100

interface FastEthernet1/13
 switchport trunk native vlan 23
 switchport trunk allowed vlan 1,2,23,100,1002-1005
 switchport mode trunk
 duplex full
 speed 100
!
interface FastEthernet1/15
 switchport trunk native vlan 23
 switchport trunk allowed vlan 1,2,23,90,1002-1005
 switchport mode trunk
 duplex full
 speed 100

!
interface Vlan1
 no ip address
 shutdown
!
interface Vlan2
 ip address 128.101.10.69 255.255.0.0
 standby 2 ip 128.101.10.70
 standby 2 preempt
!
interface Vlan20
 ip address 192.168.20.253 255.255.255.0
 standby 20 ip 192.168.20.254
 standby 20 preempt
!
interface Vlan21
 ip address 192.168.21.253 255.255.255.0
 ip helper-address 192.168.21.1
 standby 21 ip 192.168.21.254
 standby 21 preempt
!
interface Vlan23
 ip address 192.168.23.253 255.255.255.0
 standby 23 ip 192.168.23.254
 standby 23 preempt
!
interface Vlan30
 ip address 192.168.30.253 255.255.255.0
 standby 30 ip 192.168.30.254
 standby 30 preempt
!
interface Vlan40
 ip address 192.168.40.253 255.255.255.0
 standby 40 ip 192.168.40.254
 standby 40 preempt
!
interface Vlan50
 ip address 192.168.50.253 255.255.255.0
 standby 50 ip 192.168.50.254
 standby 50 preempt
!
interface Vlan60
 ip address 192.168.60.253 255.255.255.0
 standby 60 ip 192.168.60.254
 standby 60 preempt
!
interface Vlan70
 ip address 192.168.70.253 255.255.255.0
 standby 70 ip 192.168.70.254
 standby 70 preempt
!
interface Vlan80
 ip address 192.168.80.253 255.255.255.0
 standby 80 ip 192.168.80.254
 standby 80 preempt
!
interface Vlan90
 ip address 192.168.90.253 255.255.255.0
 ip helper-address 192.168.41.1
 standby 90 ip 192.168.90.254
 standby 90 preempt
!
interface Vlan100
 ip address 192.168.100.253 255.255.255.0
 ip helper-address 192.168.41.1
 standby 100 ip 192.168.100.254
 standby 100 preempt
!
router ospf 1
 router-id 1.1.1.1
 log-adjacency-changes
 network 192.168.41.0 0.0.0.3 area 0
 network 192.168.90.0 0.0.0.255 area 0
 network 192.168.100.0 0.0.0.255 area 0

Core 2

interface Port-channel1
 switchport mode trunk

!

interface FastEthernet1/0
 switchport mode trunk
 duplex full
 speed 100
 channel-group 1 mode on
!
interface FastEthernet1/1
 switchport mode trunk
 duplex full
 speed 100
 channel-group 1 mode on

!

interface FastEthernet1/4
 description DHCP Server
 no switchport
 ip address 192.168.41.6 255.255.255.252
 duplex full
 speed 100

!

interface FastEthernet1/14
 switchport trunk native vlan 23

 switchport trunk allowed vlan 1,2,23,90,1002-1005
 switchport mode trunk
 duplex full
 speed 100
!
interface FastEthernet1/15
 switchport trunk native vlan 23

 switchport trunk allowed vlan 1,2,23,100,1002-1005
 switchport mode trunk
 duplex full
 speed 100

interface Vlan2
 ip address 128.101.10.68 255.255.0.0
 standby 2 ip 128.101.10.70
 standby 2 priority 109
 standby 2 preempt
!
interface Vlan20
 ip address 192.168.20.252 255.255.255.0
 standby 20 ip 192.168.20.254
 standby 20 priority 109
 standby 20 preempt
!
interface Vlan21
 ip address 192.168.21.252 255.255.255.0
 standby 21 ip 192.168.21.254
 standby 21 priority 109
 standby 21 preempt
!
interface Vlan23
 ip address 192.168.23.252 255.255.255.0
 standby 23 ip 192.168.23.254
 standby 23 priority 109
 standby 23 preempt
!
interface Vlan30
 ip address 192.168.30.252 255.255.255.0
 standby 30 ip 192.168.30.254
 standby 30 priority 109
 standby 30 preempt
!
interface Vlan40
 ip address 192.168.40.252 255.255.255.0
 standby 40 ip 192.168.40.254
 standby 40 priority 109
 standby 40 preempt
!
interface Vlan50
 ip address 192.168.50.252 255.255.255.0
 standby 50 ip 192.168.50.254
 standby 50 priority 109
 standby 50 preempt
!
interface Vlan60
 ip address 192.168.60.252 255.255.255.0
 standby 60 ip 192.168.60.254
 standby 60 priority 109
 standby 60 preempt
!
interface Vlan70
 ip address 192.168.70.252 255.255.255.0
 standby 70 ip 192.168.70.254
 standby 70 priority 109
 standby 70 preempt
!
interface Vlan80
 ip address 192.168.80.252 255.255.255.0
 standby 80 ip 192.168.80.254
 standby 80 priority 109
 standby 80 preempt
!
interface Vlan90
 ip address 192.168.90.252 255.255.255.0
 ip helper-address 192.168.41.5
 standby 90 ip 192.168.90.254
 standby 90 priority 109
 standby 90 preempt
!
interface Vlan100
 ip address 192.168.100.252 255.255.255.0
 ip helper-address 192.168.41.5
 standby 100 ip 192.168.100.254
 standby 100 priority 109
 standby 100 preempt
!
router ospf 1
 router-id 2.2.2.2
 log-adjacency-changes
 network 192.168.41.4 0.0.0.3 area 0
 network 192.168.90.0 0.0.0.255 area 0
 network 192.168.100.0 0.0.0.255 area 0

On the host 1 if I run a "shut" , "no shut" on fa 0/0 and run DHCP debug commands on the DHCP server I get this:

*Mar  1 00:36:19.915: DHCPD: Sending notification of DISCOVER:

*Mar  1 00:36:19.915:   DHCPD: htype 1 chaddr cc0a.3714.0000
*Mar  1 00:36:19.919:   DHCPD: remote id 020a0000c0a8290100000000
*Mar  1 00:36:19.919:   DHCPD: circuit id 00000000
*Mar  1 00:36:19.919: DHCPD: DHCPDISCOVER received from client 0063.6973.636f.2d63.6330.612e.3337.3134.2e30.3030.302d.4661.302f.30 on interface FastEthernet0/0.
*Mar  1 00:36:19.919: DHCPD: Seeing if there is an internally specified pool class:
*Mar  1 00:36:19.919:   DHCPD: htype 1 chaddr cc0a.3714.0000
*Mar  1 00:36:19.919:   DHCPD: remote id 020a0000c0a8290100000000
*Mar  1 00:36:19.919:   DHCPD: circuit id 00000000
*Mar  1 00:36:19.919: DHCPD: there is no address pool for 192.168.41.1.
*Mar  1 00:36:19.935: DHCPD: Sending notification of DISCOVER:
*Mar  1 00:36:19.935:   DHCPD: htype 1 chaddr cc0a.3714.0000
*Mar  1 00:36:19.935:   DHCPD: remote id 020a0000c0a8290501000000
*Mar  1 00:36:19.935:   DHCPD: circuit id 00000000
*Mar  1 00:36:19.935: DHCPD: DHCPDISCOVER received from client 0063.6973.636f.2d63.6330.612e.3337.3134.2e30.3030.302d.4661.302f.30 on interface FastEthernet0/1.
*Mar  1 00:36:19.935: DHCPD: Seeing if there is an internally specified pool class:
*Mar  1 00:36:19.935:   DHCPD: htype 1 chaddr cc0a.3714.0000
*Mar  1 00:36:19.935:   DHCPD: remote id 020a0000c0a8290501000000
*Mar  1 00:36:19.935:   DHCPD: circuit id 00000000
*Mar  1 00:36:19.935: DHCPD: there is no address pool for 192.168.41.5.

Thanks

17 Replies 17

petenixon
Level 3
Level 3

Can you show the configuration of the DHCP server router?

Here it is:

 

ip dhcp pool VLAN90
   network 192.168.90.0 255.255.255.0
   default-router 192.168.90.254 
!
ip dhcp pool VLAN100
   network 192.168.100.0 255.255.255.0
   default-router 192.168.90.254 

!

interface FastEthernet0/0
 ip address 192.168.41.1 255.255.255.252
 duplex auto
 speed auto
!
interface FastEthernet0/1
 ip address 192.168.41.5 255.255.255.252
 duplex auto
 speed auto

!

router ospf 1
 log-adjacency-changes
 network 192.168.41.0 0.0.0.3 area 0
 network 192.168.41.4 0.0.0.3 area 0

Just wondered if you had any ideas?

Nothing is jumping out at me to be honest! What happens if you try and create a reservation using client-identifier?

Not tried that before, how do I do that?

Something like this?

Host1#sh int fa 0/0
FastEthernet0/0 is up, line protocol is up 
  Hardware is AmdFE, address is cc0a.1d4c.0000 (bia cc0a.1d4c.0000)

Host1:

ip dhcp pool VLAN90
   network 192.168.90.0 255.255.255.0
   default-router 192.168.90.254 

ip dhcp pool host1

 host 192.168.90.123 255.255.255.0

 client-identifier  cc0a.1d4c.0000

 client-name host1

 

That mac address didn't appear on the DHCP debug though.

 

That is correct. Just something I did notice, you don't have any ip dhcp excluded addresses configured on the DHCP router. Is this just missing from your output or are they not configured? You would need to exclude any addresses from the pool that have already been assigned.

Andrew White
Level 2
Level 2

Yes excluded IPs are included as part of the DHCP pool, sorry I should of mentioned.

It's as if the DHCP discovers are not reaching the DHCP server.

 

No problem.

Would it be possible for you to disable HSRP and drop all the connections from Core 1 except to the DHCP server and from the DHCP server to your root primary?

 

Is it normal to add a DHCP server this way using a router, should I be using a trunk from the router to the 2 cores instead?

Andrew White
Level 2
Level 2

Same issue I'm afraid.  I just added a router on Core 2 on vlan 90 and made it a DHCP server and added a scope for the 192.168.90.x subnet and it was ok.  It just seems the IP helper address isn't forwarding the offers.

 

I wondered if the host 1 could reach the DHCP router so I added a static IP and it can ping 192.168.41.1 and 192.168.41.5.

 

 

Hi.

I just lab'd this in GNS3 and managed to get it working. I wasn't able to replicate your topology fully as my laptop is not powerful enough! I used two routers (DHCP server and host) and a single "multilayer" switch, and I didn't use OSPF.

On the DHCP server, disable IP routing, or as in your topology, make sure there is a route back to the .90 vlan on your DHCP server router.

On the link between the host router and the layer 2 switch, I changed to a trunk on the layer 2 switch, and a sub-interface with the encapsulation set to vlan 90:

int fa0/0.1
encapsulation dot1q 90
ip address dhcp
speed 100
duplex full
no shut

Can you give that a try and let me know?

This is for the host?

int fa0/0.1

encapsulation dot1q 90
ip address dhcp
speed 100
duplex full
no shut

What happened when you tried the lab as layer 3 and not layer 2?

Yep, the sub-interface should be configured on the host router.

The switch was set up as a layer 2 trunk (for the host router) and layer 3 interface (for the DHCP router) as well as the SVI for vlan 90.

It made me think (from an ROAS perspective) that the interface on the host router would be considered to be in the native vlan (1). This would not match the vlan 90 configuration.

Hello

What model is the layer2 switch?

also try this:


host
int fa1/0
ip address dhcp client-id fastEthernet 1/0
exit

ip route 0.0.0.0 0.0.0.0 dhcp


renew dhcp fa1/0

res

Paul
 

 


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Kind Regards
Paul
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