vlan and ip helper adddress

Answered Question
May 16th, 2014
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Hi everyone,

 

I was configuring a new vlan for users.

Vlan was SVI say with IP 192.168.40.x subnet.

There was routing configured for this vlan to access specfic subnets.

DHCP server for this vlan had IP 172.16.x.x

 

Users were supposed to get IP in the 192.168.40 which was defined in the DHCP scope.

 

USers were not getting IP untill i config the ip helper on the svi vlan.

Need to understand 2 things here

1>Say if DHCP server had IP 192.168.40.10 then we do not need ip helper address  command on svi vlan right?as they are on same subnet?

2>Traffic flow from user PC to get the DHCP IP from DHCP server flows lile this--

From switch port the request for IP goes to SVI vlan and as ip helper address is configured with DHCP server IP then from vlan it goes to DHCPserver via routing configured on the switch?

 

Regards

MAhesh

Correct Answer by Reza Sharifi about 3 years 3 months ago

Hi Mahesh,

Long time no hear.

1>Say if DHCP server had IP 192.168.40.10 then we do not need ip helper address  command on svi vlan right?as they are on same subnet?

You are correct.  If the DHCP server is in the subnet as 192.168.40.0 then you don't need helper address.

2>Traffic flow from user PC to get the DHCP IP from DHCP server flows lile this--

From switch port the request for IP goes to SVI vlan and as ip helper address is configured with DHCP server IP then from vlan it goes to DHCPserver via routing configured on the switch?

That is correct.

Reza

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Correct Answer
Reza Sharifi Fri, 05/16/2014 - 19:25
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    2017 LAN

Hi Mahesh,

Long time no hear.

1>Say if DHCP server had IP 192.168.40.10 then we do not need ip helper address  command on svi vlan right?as they are on same subnet?

You are correct.  If the DHCP server is in the subnet as 192.168.40.0 then you don't need helper address.

2>Traffic flow from user PC to get the DHCP IP from DHCP server flows lile this--

From switch port the request for IP goes to SVI vlan and as ip helper address is configured with DHCP server IP then from vlan it goes to DHCPserver via routing configured on the switch?

That is correct.

Reza

mahesh18 Fri, 05/16/2014 - 20:09
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Hi Reza,

 

How are you doing?

In this job i am mostly working on Cisco ASA and VPN stuff.So busy in learning about Cisco ASA.

Regards

MAhesh

 

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