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VLANS and Helper Addresses

Hello, I have recently installed a Cisco 3750 on my network to give me the ability to create VLAN's to segment my POS system from the rest of my network. I need to configure helper addresses in the switch to relay DHCP from one segment to another. I am copying the current config (no helper addresses) and what I think is the proper commands to configure the helpers. My question is does it look correct? Here is the current config followed by the helper address commands:

! version 12.2 no service pad service timestamps debug uptime service timestamps log datetime no service password-encryption service sequence-numbers !

no aaa new-model clock timezone UTC -6 clock summer-time UTC recurring switch 1 provision ws-c3750g-12s system mtu routing 1500 udld aggressive

ip subnet-zero ! ! mls qos map cos-dscp 0 8 16 26 32 46 46 56 ! ! macro global description cisco-global errdisable recovery cause link-flap errdisable recovery interval 60 no file verify auto ! spanning-tree mode rapid-pvst spanning-tree loopguard default spanning-tree extend system-id ! vlan internal allocation policy ascending ! interface GigabitEthernet1/0/1 ! interface GigabitEthernet1/0/2 ! interface GigabitEthernet1/0/3 ! interface GigabitEthernet1/0/4 switchport access vlan 10 switchport mode access ! interface GigabitEthernet1/0/5 ! interface GigabitEthernet1/0/6 ! interface GigabitEthernet1/0/7 switchport trunk encapsulation dot1q switchport mode trunk macro description cisco-switch auto qos voip trust spanning-tree link-type point-to-point ! interface GigabitEthernet1/0/8 ! interface GigabitEthernet1/0/9 ! interface GigabitEthernet1/0/10 ! interface GigabitEthernet1/0/11 ! interface GigabitEthernet1/0/12 switchport trunk encapsulation dot1q switchport mode dynamic desirable ! interface Vlan1 ip address 172.25.2.26 255.255.254.0 ! interface Vlan10 ip address 172.25.4.10 255.255.255.0 ! ip default-gateway 172.25.2.2 ip classless ip http server ! ! control-plane ! !

end

And the helper address commands:

TSFF-CORE#conf t TSFF-CORE(config)#int GigabitEthernet1/0/4 TSFF-CORE(config-if)#ip helper-address 172.25.2.10 TSFF-CORE(config-if)#exit TSFF-CORE(config)#exit TSFF-CORE#wr mem

TSFF-CORE#conf t TSFF-CORE(config)#int GigabitEthernet1/0/12 TSFF-CORE(config-if)#ip helper-address 172.25.4.20 Server TSFF-CORE(config-if)#ip helper-address 172.25.4.21 Server TSFF-CORE(config-if)#ip helper-address 172.25.4.22 Server TSFF-CORE(config-if)#ip helper-address 172.25.4.30 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.31 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.32 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.33 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.34 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.35 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.36 Register TSFF-CORE(config-if)#exit TSFF-CORE(config)#exit TSFF-CORE#wr mem

Reply to
Pappy
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Hello, I have recently installed a Cisco 3750 on my network to give me the ability to create VLAN's to segment my POS system from the rest of my network. I need to configure helper addresses in the switch to relay DHCP from one segment to another. I am copying the current config (no helper addresses) and what I think is the proper commands to configure the helpers. My question is does it look correct? Here is the current config followed by the helper address commands:

! version 12.2 no service pad service timestamps debug uptime service timestamps log datetime no service password-encryption service sequence-numbers !

no aaa new-model clock timezone UTC -6 clock summer-time UTC recurring switch 1 provision ws-c3750g-12s system mtu routing 1500 udld aggressive

ip subnet-zero ! ! mls qos map cos-dscp 0 8 16 26 32 46 46 56 ! ! macro global description cisco-global errdisable recovery cause link-flap errdisable recovery interval 60 no file verify auto ! spanning-tree mode rapid-pvst spanning-tree loopguard default spanning-tree extend system-id ! vlan internal allocation policy ascending ! interface GigabitEthernet1/0/1 ! interface GigabitEthernet1/0/2 ! interface GigabitEthernet1/0/3 ! interface GigabitEthernet1/0/4 switchport access vlan 10 switchport mode access ! interface GigabitEthernet1/0/5 ! interface GigabitEthernet1/0/6 ! interface GigabitEthernet1/0/7 switchport trunk encapsulation dot1q switchport mode trunk macro description cisco-switch auto qos voip trust spanning-tree link-type point-to-point ! interface GigabitEthernet1/0/8 ! interface GigabitEthernet1/0/9 ! interface GigabitEthernet1/0/10 ! interface GigabitEthernet1/0/11 ! interface GigabitEthernet1/0/12 switchport trunk encapsulation dot1q switchport mode dynamic desirable ! interface Vlan1 ip address 172.25.2.26 255.255.254.0 ! interface Vlan10 ip address 172.25.4.10 255.255.255.0 ! ip default-gateway 172.25.2.2 ip classless ip http server ! ! control-plane ! !

end

And the helper address commands:

TSFF-CORE#conf t TSFF-CORE(config)#int GigabitEthernet1/0/4 TSFF-CORE(config-if)#ip helper-address 172.25.2.10 TSFF-CORE(config-if)#exit TSFF-CORE(config)#exit TSFF-CORE#wr mem

TSFF-CORE#conf t TSFF-CORE(config)#int GigabitEthernet1/0/12 TSFF-CORE(config-if)#ip helper-address 172.25.4.20 Server TSFF-CORE(config-if)#ip helper-address 172.25.4.21 Server TSFF-CORE(config-if)#ip helper-address 172.25.4.22 Server TSFF-CORE(config-if)#ip helper-address 172.25.4.30 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.31 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.32 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.33 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.34 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.35 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.36 Register TSFF-CORE(config-if)#exit TSFF-CORE(config)#exit TSFF-CORE#wr mem

Reply to
Pappy

Hi there

I'm not sure if I understood right, but you probably need to configure ip helper-addresses under interface VLANs, no under physical interfaces.

int vlan 1 ip helper-address

int vlan 10 ip helper-address

Regards, JV

Reply to
Juki

What didn't you understand? I will be more than happy to elaborate.

Reply to
Pappy

That is correct. IP helper addresses go into the VLAN interface configuration because they listen for the broadcast and determine the source subnet ID from the listening interface. The DHCP server might have multiple DHCP scopes but provides a lease based on the source IP address of the listening relay interface.

----- Scott Perry Indianapolis, IN

-----

Reply to
Scott Perry

Hello, I have recently installed a Cisco 3750 on my network to give me the ability to create VLAN's to segment my POS system from the rest of my network. I need to configure helper addresses in the switch to relay DHCP from one segment to another. I am copying the current config (no helper addresses) and what I think is the proper commands to configure the helpers. My question is does it look correct? Here is the current config followed by the helper address commands:

! version 12.2 no service pad service timestamps debug uptime service timestamps log datetime no service password-encryption service sequence-numbers !

no aaa new-model clock timezone UTC -6 clock summer-time UTC recurring switch 1 provision ws-c3750g-12s system mtu routing 1500 udld aggressive

ip subnet-zero ! ! mls qos map cos-dscp 0 8 16 26 32 46 46 56 ! ! macro global description cisco-global errdisable recovery cause link-flap errdisable recovery interval 60 no file verify auto ! spanning-tree mode rapid-pvst spanning-tree loopguard default spanning-tree extend system-id ! vlan internal allocation policy ascending ! interface GigabitEthernet1/0/1 ! interface GigabitEthernet1/0/2 ! interface GigabitEthernet1/0/3 ! interface GigabitEthernet1/0/4 switchport access vlan 10 switchport mode access ! interface GigabitEthernet1/0/5 ! interface GigabitEthernet1/0/6 ! interface GigabitEthernet1/0/7 switchport trunk encapsulation dot1q switchport mode trunk macro description cisco-switch auto qos voip trust spanning-tree link-type point-to-point ! interface GigabitEthernet1/0/8 ! interface GigabitEthernet1/0/9 ! interface GigabitEthernet1/0/10 ! interface GigabitEthernet1/0/11 ! interface GigabitEthernet1/0/12 switchport trunk encapsulation dot1q switchport mode dynamic desirable ! interface Vlan1 ip address 172.25.2.26 255.255.254.0 ! interface Vlan10 ip address 172.25.4.10 255.255.255.0 ! ip default-gateway 172.25.2.2 ip classless ip http server ! ! control-plane ! !

end

And the helper address commands:

TSFF-CORE#conf t TSFF-CORE(config)#int GigabitEthernet1/0/4 TSFF-CORE(config-if)#ip helper-address 172.25.2.10 TSFF-CORE(config-if)#exit TSFF-CORE(config)#exit TSFF-CORE#wr mem

TSFF-CORE#conf t TSFF-CORE(config)#int GigabitEthernet1/0/12 TSFF-CORE(config-if)#ip helper-address 172.25.4.20 Server TSFF-CORE(config-if)#ip helper-address 172.25.4.21 Server TSFF-CORE(config-if)#ip helper-address 172.25.4.22 Server TSFF-CORE(config-if)#ip helper-address 172.25.4.30 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.31 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.32 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.33 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.34 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.35 Register TSFF-CORE(config-if)#ip helper-address 172.25.4.36 Register TSFF-CORE(config-if)#exit TSFF-CORE(config)#exit TSFF-CORE#wr mem

Reply to
Pappy

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