[c-nsp] DHCP Binding Expiration

[Manaf Al Oqlah]

Hi all,

I am configuring a Cisco 7600 router as DHCP server for my broadband clients. I am using DHCP snooping and ARP inspection for security reasons and the leased time expiration is set for 30 minutes and no excluded-address is configured. The problem is that I still can see  some clients IP addresses lease expiration are Infinite in the DHCP binding! what could be the reason for this behavior and could be this some sort of attack!! 

Here is my configuration of the DHCP server:
!
ip dhcp pool DHCP-POOL
   network 192.168.48.0 255.255.240.0
   default-router 192.168.48.1
   dns-server x.x.x.x x.x.x.x
   domain-name domain.com
   lease 0 0 30
!

and here is the output of the DHCP binding:

R1#show ip dhcp binding | include Infinite
192.168.50.50        001e.e58d.5f27          Infinite                Automatic
192.168.50.93        0017.3f0c.9d47          Infinite                Automatic
192.168.51.5         001e.e595.11b9          Infinite                Automatic
192.168.56.239       001e.e595.1109          Infinite                Automatic
192.168.56.251       0018.392d.94b5          Infinite                Automatic
192.168.57.7         001e.e595.10f9          Infinite                Automatic
192.168.57.77        0018.392d.9473          Infinite                Automatic
192.168.58.76        001f.3c66.6d1d          Infinite                Automatic
192.168.58.133       0014.bf65.80f7          Infinite                Automatic
192.168.58.137       001e.e58d.6671          Infinite                Automatic
192.168.58.151       00c0.020d.91bf          Infinite                Automatic
192.168.58.162       001e.e595.1b23          Infinite                Automatic
192.168.58.191       001e.e58d.6669          Infinite                Automatic
192.168.58.218       0018.3937.a0d7          Infinite                Automatic
192.168.58.231       0016.367b.086d          Infinite                Automatic


Regards,
Manaf