dhcp binding database

[suthomas1]

Hello,

One of our switches host dhcp server for a set of hosts. There are about 55 of these hosts , currently in operation.

However the dhcp binding table only shows four of them. 

(note- these are not manual bindings).

Is there any specific reason for this output? Should it not show me all ip's from the pool that are currently leased/being used?

Thank you.

[johnd2310]

Hi,

The database should show all leased addresses. Have you checked that all you PCs are actually getting addresses from that particular dhcp server?

Thanks

John

[luis_cordova]

Hi @suthomas1 ,

could you share the DHCP settings and the command used to see the DCHP table and its result?

Regards

[suthomas1]

following is the pool & output. 

As you see, only 4 hosts are listed in the table. However, there are another 55 hosts who are live on this network & i can ping them.

ip dhcp pool hosts
network 192.168.100.0 255.255.255.128
dns-server 192.168.200.1
default-router 192.168.100.1
lease 120

switch-3560#show ip dhcp binding
Bindings from all pools not associated with VRF:
IP address Client-ID/ Lease expiration Type State Interface
Hardware address/
User name
192.168.100.11 xx.xx.xx.xx July 12 2019 07:37 AM Automatic Active Vlan100
192.168.100.15 xx.xx.xx.xx July 10 2019 12:12 AM Automatic Active Vlan100
192.168.100.18 xx.xx.xx.xx July 14 2019 04:56 AM Automatic Active Vlan100
192.168.100.21 xx.xx.xx.xx July 20 2019 06:01 AM Automatic Active Vlan100

[Seb Rupik]

Hi there,

As @johnd2310 mentions, can you confirm where these 'missing' hosts are getting there IP address information from?

If they are windows hosts, ipconfig /all will tell us what we need. Is "DHCP Enabled" yet to Yes. If so, is the address listed next to "DHCP Server" the router SVI (192.168.100.1) on the subnet the hosts are connected to?

cheers,

Seb.

[suthomas1]

These are not windows hosts, they are some scanner sort of things. 
I rebooted one of the working ones & it picked the right ip from the pool soon after. 

However on the binding list, there is no difference.

[Seb Rupik]

Hi there,

What is the output of:

show ip dhcp server stat

Also to confirm that the router is handing out the leases, issue the command debug ip dhcp server events , and reboot one of these scanner nodes. Hopefully the debug log will show the Desc, Offer, Req and Ack sequence of messages. Please share the log.

cheers,

Seb.

[suthomas1]

---

This is the output of stat output. Please note, there other dhcp pools so it is reflecting all of these.

I tried restarting one of the devices & once it came up online , its entry does appear on the binding table.

Wondering why otherwise it is not showing full entry for other hosts which already have IP.

sh ip dhcp server statistics
Memory usage 22331
Address pools 3
Database agents 0
Automatic bindings 11
Manual bindings 0
Expired bindings 10
Malformed messages 0
Secure arp entries 0
Renew messages 816
Relay bindings 0
Relay bindings active 0
Relay bindings terminated 0
Relay bindings selecting 0

Message Received
BOOTREQUEST 0
DHCPDISCOVER 134761
DHCPREQUEST 28415
DHCPDECLINE 1
DHCPRELEASE 0
DHCPINFORM 44
DHCPVENDOR 0
BOOTREPLY 0
DHCPOFFER 1323
DHCPACK 25985
DHCPNAK 14

Message Sent
BOOTREPLY 0
DHCPOFFER 504
DHCPACK 924
DHCPNAK 136

Message Forwarded
BOOTREQUEST 0
DHCPDISCOVER 4677
DHCPREQUEST 101767
DHCPDECLINE 5
DHCPRELEASE 0
DHCPINFORM 205
DHCPVENDOR 0
BOOTREPLY 0
DHCPOFFER 1323
DHCPACK 25985
DHCPNAK 14

[Seb Rupik · Accepted solution]

OK, so the other two DHCP pools you have configured are going to pollute these stats for the purpose that we need them for.

The next option is as I suggested earlier, run a DHCP server debug whilst rebooting one of the scanners, and see if the DHCP DORA sequence appears in the logs and that the scanner is then present in the bindings. If you see the Discover and Offer, but not the Request and Accept, then you possible have another DHCP server present on the segment. 

Have you thought about configuring DHCP snooping on the access layer which these scanners are attached to?

cheers,

Seb.