# ARP binding or DHCP Address reservation.



## sveken

I was going threw my router, and i found these two things, ARP binding, and theres DHCP  address reservation, whats the deference? do we do the same thing and if so why do they need them both there? I am looking to just give a PC the same IP everytime, the help thing on the router page says they both do that but is there any diference? or advantage to useing one over the other? my router is a netcom NB504.


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## pym

DHCP reservations are used to set aside IP addresses, in order that they not be handed out upon DHCP request to computers that they're not meant for.

For example, you have a server on your network and you want it always to use 192.168.1.2 because you have scripts configured to use that IP address.  Even if you have the static address 192.168.1.2 configured on the server, the address might be handed to another machine if the server is down for any appreciable amount of time.  Then, when the server came up again, there would be two computers with the same IP Address.

DHCP reservation avoids this by telling the router/DHCP server to hold that address.  On Windows Server, you create a reservation for an IP address and assign to the reservation the MAC address of the computer that should receive it.  When any computer comes online, the MAC address is checked and if it matches the reservation, it receives that IP address.

I'm not familiar with ARP binding, but a quick search suggests that it's a security precaution against ARP poisoning.  In ARP poisoning, a rogue computer sends ARP messages that associate an existing and legitimate IP address with its own MAC address.  I think the ARP binding that you're referring to involves an independent, trusted database kept on the router that checks ARP requests and prevents traffic from being routed to a rogue host.

I hope that helps.  But check the manual for your router:  http://media.netcomm.com.au/public/assets/pdf_file/0015/14244/BP504_UG.pdf


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## Cromewell

pym said:


> DHCP reservations are used to set aside IP addresses, in order that they not be handed out upon DHCP request to computers that they're not meant for.
> 
> For example, you have a server on your network and you want it always to use 192.168.1.2 because you have scripts configured to use that IP address.  Even if you have the static address 192.168.1.2 configured on the server, the address might be handed to another machine if the server is down for any appreciable amount of time.  Then, when the server came up again, there would be two computers with the same IP Address.
> 
> DHCP reservation avoids this by telling the router/DHCP server to hold that address.  On Windows Server, you create a reservation for an IP address and assign to the reservation the MAC address of the computer that should receive it.  When any computer comes online, the MAC address is checked and if it matches the reservation, it receives that IP address.
> 
> I'm not familiar with ARP binding, but a quick search suggests that it's a security precaution against ARP poisoning.  In ARP poisoning, a rogue computer sends ARP messages that associate an existing and legitimate IP address with its own MAC address.  I think the ARP binding that you're referring to involves an independent, trusted database kept on the router that checks ARP requests and prevents traffic from being routed to a rogue host.
> 
> I hope that helps.  But check the manual for your router:  http://media.netcomm.com.au/public/assets/pdf_file/0015/14244/BP504_UG.pdf


Normally I'd say the same about ARP Binding but I took a quick look at the manual and in this case it seems to do the exact same thing as reserving the address. It takes a MAC/IP address pairing just like the address reservation. I would use IP Reservation though, I'm not 100% on what ARP binding will do, it may mess up your routing if it doesn't force the same address to get assigned.


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## sveken

Thank you you for you'r help  i used the address reservation


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