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Excluded IP address automatically increasing on Cat3750

Hi there,

I have encountered some weird issue on our Cat3750 running as DHCP Server.

I have exlucded 5 IP addresses only on the running configuration as below.

ip dhcp excluded-address 172.28.196.1 172.28.196.4

ip dhcp excluded-address 172.28.196.62

ip dhcp pool Wireless-business

   network 172.28.196.0 255.255.255.192

   default-router 172.28.196.1

   dns-server 172.28.144.7 172.28.128.3

   netbios-name-server 172.28.144.7 172.28.128.3

   netbios-node-type h-node

However "show ip dhcp pool" is the below and users cannot get new IP addres assigned by this switch anymore.

Why is the number of excluded address 30 even though we set it as 5?

Pool Wireless-business :

Utilization mark (high/low)    : 100 / 0

Subnet size (first/next)       : 0 / 0

Total addresses                : 62

Leased addresses               : 32

Excluded addresses             : 30

Pending event                  : none

1 subnet is currently in the pool :

Current index        IP address range                    Leased/Excluded/Total

0.0.0.0              172.28.196.1     - 172.28.196.62     32    / 30    / 62

When I reset the configuration, then users can get new IP address but,

30 minutes later after I reset the configuration, we’ve got the below already. So soon the same issue will happen again.

Pool Wireless-business :

Utilization mark (high/low)    : 100 / 0

Subnet size (first/next)       : 0 / 0

Total addresses                : 62

Leased addresses               : 25

Excluded addresses             : 26

Pending event                  : none

1 subnet is currently in the pool :

Current index        IP address range                    Leased/Excluded/Total

172.28.196.50        172.28.196.1     - 172.28.196.62     25    / 26    / 62

Actually the below is the current result and users cannot get new IP address from the switch

Pool Wireless-business :

Utilization mark (high/low)    : 100 / 0

Subnet size (first/next)       : 0 / 0

Total addresses                : 62

Leased addresses               : 36

Excluded addresses             : 26

Pending event                  : none

1 subnet is currently in the pool :

Current index        IP address range                    Leased/Excluded/Total

0.0.0.0              172.28.196.1     - 172.28.196.62     36    / 26    / 62

IOS version is c3750-ipbasek9-mz.122-53.SE/c3750-ipbasek9-mz.122-53.SE.bin

Does anyone help us out of this issue?

Everyone's tags (1)
1 REPLY
Cisco Employee

Excluded IP address automatically increasing on Cat3750

Hello,

You can possible have requests leaking between VLANs.

Check

show ip dhcp conflict

first.

If you see any ip in conflict DB, then clear this ip address and try the following:

run wireshark on the client and ran debug ip dhcp server packet, debug ip dhcp server

events, debug arp on the switch (DHCP server).

See iff client sends DHCP discover in one VLAN and switch gets that in different VLAN.

Quick check also can be proxy-arp disable.

Nik

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