How does DHCP Authorized ARP command works?

From: Ismail AlShelh (ishelh@mdsa.com)
Date: Sat Nov 18 2006 - 14:46:18 ART


With reference to the following link :

http://www.cisco.com/en/US/products/ps6441/products_configuration_guide_chapt
er09186a008071c33f.html

R1 E0----------------------------------E0/0 R2

The example is illustrating the use of DHCP Authorized ARP, I have the
following questions :

1  What do we mean by secure ARP entry in the ARP Table, the documentation
said that the update arp command will install a secure ARP entry in its ARP
table

2 How the arp authorized command will stop any dynamic ARP on the
interface? And how R1 which is the DHCP server will know that the first MAC
it receives from R2 is not spoofed?

3- I am afraid that this question can come in a form of scenario in the CCIE
R&S Lab so please let me know if I have to delve into this level and incase
yes then please provide me with some scenarios which can cover this topic
because these commands are not covered in the current IEWB.

Router 1 (DHCP Server)
ip dhcp pool name1
 network 10.0.0.0 255.255.255.0
 lease 0 0 20
 update arp
!
interface Ethernet0
 ip address 10.0.0.1 255.255.255.0
 half-duplex
 arp authorized
 arp timeout 60
! optional command to adjust the periodic ARP probes sent to the peer
 arp probe interval 5 count 15
Router 2 (DHCP Client)

interface Ethernet0/0
 ip address dhcp
 half-duplex

Thanks,
Ismail



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