Reverse arp between Vlans

Unanswered Question
Jun 6th, 2007


I have a Unix station on Vlan X and Unix-based DHCP server on Vlan Y. The Unix station needs to address the DHCP server (that located on different vlan) with Reverse arp (sending it's MAC in order to get it's pridefined IP address from the server). Does anybody have any idea how it may be done on CAT6500 switch (with layer3 capabilities)?




There is routing between these vlans. Vlan interfaces are located on the same switch.

I have this problem too.
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Jon Marshall Wed, 06/06/2007 - 03:02

Hi Tim

Under the vlan interface that the client machine is on on the 6500 switch you need to add

vlan 10

ip helper-address "address of DHCP server"

(vlan 10 just used as an example - substitute you client vlan here )



Timor_SSS Wed, 06/06/2007 - 03:54

Guys, ip-helper doesn't resolve this issue. It does help when it deals with a regular ARP (regular broadcast sending ff:ff:ff:ff:ff:ff in the destination MAC address with unknown destination IP)...

In this case it sends it's hardware MAC address in the destination MAC field with L3 broadcast.

Jon Marshall Wed, 06/06/2007 - 05:33


Sorry about that, should have read the question properly. You can use the following command under the interface configuration

int vlan x

ip rarp-server "rarp server"

Problem is, as far as i know, the RARP server needs to be on the same vlan.


Timor_SSS Thu, 06/07/2007 - 03:11


After lots of reading and researching, I've found out that Cisco simply doesn't have a solution for this issue. The only sulution by Cisco, is to bridge the Vlans, but that solution is practically a joke.

Other vendors (such as Nortel) have various solutions, for example: Protocol based Vlans, MAC-based Vlans, Port-based Vlans and subnet-based Vlans. In this case, according to Nortel, the solution is creation of RARP Vlan (protocol-based vlan)- on top of port-based Vlan. The whole vlan logic is different in Nortel and has much more possibilities.

In my case, ;-\

Thanks for your reply


tvlaanderen Wed, 06/06/2007 - 03:28

First guess: configure on interface vlan x "ip helper address "

Regards, Jo.


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