IP DHCP Helper Address and IP ARP

[DAVID]

If you add an additional IP helper address to an existing SVI so that the new address is first in the list above the existing helper addresses, do you still need to clear the ip arp on the switch for those IP addresses associated on the SVI?

[merij2787]

https://community.cisco.com/t5/discusiones-general/%F0%9D%94%B8-%F0%9D%94%B8-how-do-i-get-a-human-at-%F0%9D%94%B8merica%F0%9D%95%9F-%F0%9D%94%B8%F0%9D%95%9A%F0%9D%95%A3lines-immediately-us/m-p/5125357#M29271 https://community.cisco.com/t5/discusiones-general/aa-ask-how-do-i-get-a-human-at-%F0%9D%94%B8merica%F0%9D%95%9F-%F0%9D%94%B8irli%F0%9D%95%9Fes-immediately-us/m-p/5125372#M29281
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https://community.cisco.com/t5/discusiones-general/%EF%B8%8F-ask-how-do-i-speak-to-american-customer-service-google-rank/m-p/5125389#M29290 https://community.cisco.com/t5/discusiones-general/get-%EF%B8%8Fcontact-how-do-i-speak-to-american-customer-service-usa-tr/m-p/5125401#M29294
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https://community.cisco.com/t5/discusiones-general/a-quot-a-how-do-i-get-a-human-at-%F0%9D%94%B8merica%F0%9D%95%9F-%F0%9D%94%B8%F0%9D%95%9A%F0%9D%95%A3lines-immediately/m-p/5125368#M29279 https://community.cisco.com/t5/discusiones-general/a-a-how-do-i-get-a-human-at-%F0%9D%94%B8merica%F0%9D%95%9F-%F0%9D%94%B8irli%F0%9D%95%9Fes-immediately-24x7/m-p/5125374#M29282
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https://community.cisco.com/t5/discusiones-general/call-how-do-i-get-a-human-at-%F0%9D%94%B8merica%F0%9D%95%9F-%F0%9D%94%B8%F0%9D%95%9A%F0%9D%95%A3lines-immediately-us/m-p/5125362#M29275 https://community.cisco.com/t5/discusiones-general/aa-how-do-i-get-a-human-at-%F0%9D%94%B8merica%F0%9D%95%9F-%F0%9D%94%B8%F0%9D%95%9A%F0%9D%95%A3lines-immediately-us/m-p/5125369#M29280
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[Andrea Testino · Accepted solution]

David,

Adding an additional IP helper address to an SVI on a Cisco device primarily affects DHCP traffic forwarding and does not directly impact the ARP protocol or the ARP table on the device. The IP helper addresses are used to forward DHCP Requests received on the L3 interface to the specified remote DHCP servers, allowing clients on a subnet configured on the SVI to receive DHCP services from servers not located on that same subnet. This essentially acts as a DHCP Relay. In short, configuring a new IP helper address above the existing ones does not generally necessitate clearing the ARP table. Are you seeing any behaviors or symptoms that lead you to think otherwise? Happy to help.

I hope that helps!

[DAVID]

No.  Another engineer and I were having a discussing and he mentioned about clearing the IP ARP cache. I thought it wasn't necessary but I just was not too sure.  Both DHCP server IP addresses are Windows DHCP servers that replicate with one another and our DHCP admin stated that the new DHCP server already has the endpoints showing in the various DHCP pools.  So it looks like that was an easy one.

[MHM Cisco World]

If you add two ip helper 

The  SW will send dhcp request to both IP helper whatever it top or button config.

And so arp have no issue here 

MHM