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DHCP for VLAN on 4507; IP Conflicts too often

I have seen a few similar posts, but nothing so far that fits my scenario, I think.

I keep getting random users in this VLAN reporting IP conflicts. These desktop systems are left on 24/7. Right now, we only have one VLAN DHCP being served from this core switch.

There are only 29 computers pulling DHCP on this VLAN, but I have a large range allocated to them for growth. These are desktop systems, so they don't swap network ports, and they don't have dual NICs, nor do they have WiFi. So I am at a lose as to why we would be seeing IP conflicts with such an obvious open pool of IPs, and with MAC addresses not changing. It has been my experience that pretty much unless something happens(offline for several days, NIC replacement, etc.) to the MAC every IP renewal gives the same IP back.

Core#sho ip dhcp pool OUR-Workstations

Pool OUR-Workstations :

Utilization mark (high/low)    : 100 / 0

Subnet size (first/next)       : 0 / 0

Total addresses                : 254

Leased addresses               : 28

Excluded addresses             : 49

Pending event                  : none

1 subnet is currently in the pool :

Current index        IP address range                    Leased/Excluded/Total

10.1.32.183          10.1.32.1        - 10.1.32.254       28    / 49    / 254

Core#sho ip dhcp binding

Bindings from all pools not associated with VRF:

IP address      Client-ID/              Lease expiration        Type       State      Interface

                Hardware address/

                User name

10.1.32.50      0180.1f02.5f5e.b6       Dec 18 2013 11:34 PM    Automatic  Active     Vlan32

10.1.32.51      01f0.4da2.2e9f.06       Dec 19 2013 07:57 AM    Automatic  Active     Vlan32

10.1.32.54      01b8.ac6f.45b4.27       Dec 19 2013 09:54 AM    Automatic  Active     Vlan32

10.1.32.55      0100.2564.c8bd.ea       Dec 19 2013 09:33 AM    Automatic  Active     Vlan32

10.1.32.58      01b8.ac6f.45c4.97       Dec 19 2013 04:18 AM    Automatic  Active     Vlan32

10.1.32.61      01b8.ac6f.3693.05       Dec 19 2013 05:12 AM    Automatic  Active     Vlan32

10.1.32.62      01b8.ac6f.35f0.eb       Dec 19 2013 05:18 AM    Automatic  Active     Vlan32

10.1.32.63      0100.2564.c8c7.ae       Dec 19 2013 12:26 AM    Automatic  Active     Vlan32

10.1.32.65      01f0.4da2.2fba.66       Dec 19 2013 01:44 AM    Automatic  Active     Vlan32

10.1.32.66      01b8.ac6f.46eb.b8       Dec 19 2013 01:05 AM    Automatic  Active     Vlan32

10.1.32.67      01b8.ac6f.45c9.7a       Dec 18 2013 10:54 PM    Automatic  Active     Vlan32

10.1.32.68      01b8.ac6f.45c3.dc       Dec 19 2013 07:12 AM    Automatic  Active     Vlan32

10.1.32.70      01b8.ac6f.35f1.48       Dec 19 2013 05:15 AM    Automatic  Active     Vlan32

10.1.32.88      01b8.ac6f.37bc.3e       Dec 19 2013 06:37 AM    Automatic  Active     Vlan32

10.1.32.97      01b8.ac6f.368f.f5       Dec 19 2013 06:42 AM    Automatic  Active     Vlan32

10.1.32.101     01b8.ac6f.45bb.9e       Dec 19 2013 06:17 AM    Automatic  Active     Vlan32

10.1.32.110     01f0.4da2.2d47.5a       Dec 19 2013 06:17 AM    Automatic  Active     Vlan32

10.1.32.118     01f0.1faf.1d37.97       Dec 19 2013 07:19 AM    Automatic  Active     Vlan32

10.1.32.121     0100.2564.c95a.c1       Dec 19 2013 06:53 AM    Automatic  Active     Vlan32

10.1.32.144     01b8.ac6f.1d37.34       Dec 19 2013 09:16 AM    Automatic  Active     Vlan32

10.1.32.167     0100.2564.c94e.f0       Dec 19 2013 07:34 AM    Automatic  Active     Vlan32

10.1.32.170     01e0.db55.e9d7.01       Dec 19 2013 07:38 AM    Automatic  Active     Vlan32

10.1.32.171     0100.03ff.2eba.66       Dec 18 2013 01:20 PM    Automatic  Active     Vlan32

10.1.32.178     0124.7703.f1c2.e5       Dec 18 2013 10:02 AM    Automatic  Selecting  Vlan32

10.1.32.235     01f0.4da2.2c92.33       Dec 19 2013 09:53 AM    Automatic  Active     Vlan32

10.1.32.238     01b8.ac6f.3649.aa       Dec 19 2013 05:21 AM    Automatic  Active     Vlan32

10.1.32.241     01b8.ac6f.1d2a.2f       Dec 18 2013 10:08 PM    Automatic  Active     Vlan32

10.1.32.247     01b8.ac6f.45b5.8f       Dec 19 2013 05:15 AM    Automatic  Active     Vlan32

Not sure what the SELECTING status is for 10.1.32.178, but I assume I caught this at a point IP renewal.

Core#sho ip dhcp server stat

Memory usage         22449

Address pools        1

Database agents      0

Automatic bindings   28

Manual bindings      0

Expired bindings     1178

Malformed messages   294

Secure arp entries   0

Renew messages       2368

Relay bindings                 0

Relay bindings active          10

Relay bindings terminated      0

Relay bindings selecting       10

Message              Received

BOOTREQUEST          171602

DHCPDISCOVER         2931675

DHCPREQUEST          2680462

DHCPDECLINE          271

DHCPRELEASE          26

DHCPINFORM           951950

DHCPVENDOR           0

BOOTREPLY            0

DHCPOFFER            126

DHCPACK              0

DHCPNAK              0

Message              Sent

BOOTREPLY            0

DHCPOFFER            8196

DHCPACK              353198

DHCPNAK              12769

Message      Forwarded

BOOTREQUEST          0

DHCPDISCOVER         0

DHCPREQUEST          0

DHCPDECLINE          0

DHCPRELEASE          0

DHCPINFORM           0

DHCPVENDOR           0

BOOTREPLY            0

DHCPOFFER            0

DHCPACK              0

DHCPNAK              0

  • LAN Switching and Routing
Everyone's tags (6)
1 REPLY
Purple

DHCP for VLAN on 4507; IP Conflicts too often

Hi,

Cisco IOS DHCP service doesn't reallocate the same IP to a client that is renewing its binding, it will try to offer the next IP available that is not excluded manually or that either didn't receive a DHCPDECLINE or a positive reply to an icmp echo test or ARP test.It will circle like this upto end of pool and starting at start of pool again.

Regards

Alain

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