ARP Questions

[vpalania]

Hi,

1)In what cases does a host connected to an Ethernet no need to use ARP or an ARP Cache fot better transmitting IP ?

2)Suppose Router C receives a request from Router A looking for Router B's Physical Address,suppose C has the bind IP to Phy., should C answer the question ?

Thanks,

Vijay

[lgijssel]

Please check the following document.

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080094adb.shtml

It contains the answer about your 2nd question and some general info to the workings of the ARP protocol.

Regards,

Leo

[pkhatri]

Hi Vijay,

1. The only time a host does not need to use ARP is when transmitting broadcast/multicast packets where you can easily translate network-layer addresses to MAC addresses. In all other cases, the host will need to determine the MAC address using ARP (or its cache)

2. As per the link from Leo, Router B will answer this query but only if:

- the address being ARPed for is not on the subnet between router A and router C

- C has a route to that subnet

- proxy-ARP is enabled on C's interface to A

However, C will respond with it's own MAC address, not that of router B. This is the concept of Proxy ARP.

Hope that helps - pls rate the post if it does.

Paresh