Question : IP Helper-Address DHCP over VLAN problems with 3550

We have a medium sized network comprising of a 3550 series switch at the core and 21 2950's supplying desktop access, We currently have the internal subnet 10.95.0.0/21 which we have subnetted further into

10.95.0.0/24 (VLAN 1)
10.95.1.0/24 (VLAN 20)
10.95.2.0/23 (VLAN 30)
10.95.4.0/24 (VLAN 40)
10.95.5.0/24 (VLAN 50)

These are the only subnets listed as they are the only oneswe require at this stage. Each of these subnets represents a VLAN on our network, it is important that one VLAN have 400 addresses so we have aggregated two /24's into the /23 (10.95.2.0-10.95.3.255).

The 3550 is providing the InterVLAN routing and when using statically assigned IP's I am able to contact PC's/Servers on other VLANS perfectly, however, I have a DHCP server @ 10.95.4.14 (VLAN40), and have configured the "ip helper-address" command on each of hte VLAN interfaces on the 3550, I have attached a copy of the 3550's config below.

The problem is that PC's in VLAN 1 and VLAN 20 are able to get an IP addressfrom hte DHCP server with no problems, but PC's on VLAN30, VLAN40 and VLAN50 cannot contact the DHCP server.

Any Ideas...?

EMC-Core#sh run
Building configuration...

Current configuration : 2050 bytes
!
version 12.1
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname EMC-Core
!
enable secret 5 $1$6RsS$3ayLhjIOyPJuLSxAbiC4t/
!
ip subnet-zero
ip routing
ip dhcp smart-relay
ip dhcp relay information trust-all
!
ip multicast-routing
!
spanning-tree mode pvst
spanning-tree extend system-id
!
!
!
interface GigabitEthernet0/1
 switchport mode access
!
interface GigabitEthernet0/2
 switchport mode access
 shutdown
!
interface GigabitEthernet0/3
 switchport access vlan 40
 switchport mode dynamic desirable
!
interface GigabitEthernet0/4
 switchport mode access
!
interface GigabitEthernet0/5
 switchport mode dynamic desirable
 shutdown
!
interface GigabitEthernet0/6
 switchport mode dynamic desirable
 shutdown
!
interface GigabitEthernet0/7
 switchport mode dynamic desirable
 shutdown
!
interface GigabitEthernet0/8
 switchport mode dynamic desirable
 shutdown
!
interface GigabitEthernet0/9
 switchport mode dynamic desirable
 shutdown
!
interface GigabitEthernet0/10
 switchport trunk encapsulation dot1q
 switchport mode trunk
!
interface GigabitEthernet0/11
 switchport mode dynamic desirable
!
interface GigabitEthernet0/12
 switchport mode dynamic desirable
!
interface Vlan1
 description Server Vlan
 ip address 10.95.0.1 255.255.255.0
 ip helper-address 10.95.4.14
!
interface Vlan10
 description Admin Vlan
 ip address 10.40.189.2 255.255.255.0
!
interface Vlan20
 description Staff Vlan
 ip address 10.95.1.1 255.255.255.0
 ip helper-address 10.95.4.14
!
interface Vlan30
 description Students Vlan
 ip address 10.95.2.1 255.255.254.0
 ip helper-address 10.95.4.14
!
interface Vlan40
 description Router and Printers Vlan
 ip address 10.95.4.2 255.255.255.0
!
interface Vlan50
 description Phones
 ip address 10.95.5.1 255.255.255.0
 ip helper-address 10.95.4.14
!
ip classless
ip http server
!
!
snmp-server community emc RO
!
line con 0
 exec-timeout 0 0
 password ********
 logging synchronous
 login
line vty 0 4
 password ********
 login
line vty 5 15
 login
!
end

EMC-Core#

Answer : IP Helper-Address DHCP over VLAN problems with 3550

Yes. It was implicit (I thought) that in my diagram the clients were not directly connected to the 3550 switch. therefore, my suggestion is still up!

You said "That is why I haveth helper addresses set up on hte VLAN interfaces of the 3550.". And I agree with you! I just don't agree with the helper address value ...

So again, my sugestion is that for each vlan ...

interface Vlan20
 description Staff Vlan
 ip address 10.95.1.1 255.255.255.0
 ip helper-address 10.95.4.2

So, once more, I'm assuming that 10.95.4.2 is the address of the vlan40 interface which is where the dhcp server is located.



Rafael.