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Bronze

Advanced ARP & ip helper question

Hello all,

I have a question related to the ARP table and ip helper forwarding. Suppose a VLAN is configured for ip helper forwarding of DHCP requests,

when the DHCP server replies with an offer, it is sent to the forwarding switch, the switch then sends it on to the client on the local LAN.

My question is: when the switch forwards the dhcp offer to the client, does a cisco switch create an ARP entry for this client also at the same time ?

And would this be correct behaviour to create an ARP entry even if the client did not yet DHCP ACK the offer ?

(we forward to several DHCP servers, each offering ip addresses, only one offer is ACKed by the client, but we see ARP entries for the other offers also, this doesnt't seems to be proper behaviour)

regards,

Geert

2 REPLIES
Silver

Advanced ARP & ip helper question

IMHO, a Switch does not have any business in creating ARP entry out of a DHCP reply.

Thanks.

Hall of Fame Super Silver

Advanced ARP & ip helper question

I agree that it is not appropriate to create an ARP entry based on the DHCP OFFER from the server. Until the client sends an ARP response indicating what IP address it is using no ARP entry should be created.

HTH

Rick

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