DHCP timeout events - A lot of DHCP requests almost every 2 minutes

[hara12386]

Hello,

We have CoreSwitches configured as DHCP servers and Layer3 for several Vlans but we started noticing DHCP timeouts and after analysis we found out that devices are sending a DHCP request almost every 2 minutes even if the lease time is configured for 8days and they have already an IP

The configuration is basic:

ip dhcp pool Vlan40
network 10.152.104.128 255.255.255.128
default-router 10.152.104.129
dns-server X.X.X.X X.X.X.
domain-name test.com

Debug dhcp packet detail is showing the following result when the DHCP timeout event is detected:

028493: Sep 23 22:34:24 GMT+1: DHCPD: Reload workspace interface Vlan40 tableid 0.

028494: Sep 23 22:34:24 GMT+1: DHCPD: tableid for 10.152.104.129 on Vlan40 is 0

028495: Sep 23 22:34:24 GMT+1: DHCPD: client's VPN is .

028496: Sep 23 22:34:24 GMT+1: DHCPD: DHCPREQUEST received from client 011e.f4c4.53db.ad.

028497: Sep 23 22:34:24 GMT+1: DHCPD: Finding a relay for client 011e.f4c4.53db.ad on interface Vlan40.

But we don't see any response from the Switch regarding those requests

We have :

- Modified the lease time

- tested with the remember command

- Rebooted the switch

- Issue is happening in several sites and with almost all devices

- in the network we have coreSwitches 3560 versions 3.6.4 and 3.6.6 and 9300 with version 17.12.X and they both showing same issue

Many thanks

[David Ruess]

Hello,

Do you have any other configuration related to DHCP such as DHCP snooping? Can you provide the full device configuration?

Are these PCs that are trying to get an IP address or other network devices?

How many switches/devices are between the DHCP configured network device as a server and the client?

-David

[hara12386]

Hello @David Ruess 

Yes DHCP snooping is configured, below is the DHCP configuration in the switch : 

SwitchCore#sh run | s dhcp
ip dhcp snooping vlan 1-4094
no ip dhcp snooping information option
ip dhcp snooping database flash:dhcp-database
ip dhcp snooping
ip dhcp excluded-address 10.152.107.1
ip dhcp excluded-address 10.152.104.251 10.152.104.254
ip dhcp excluded-address 10.152.104.65 10.152.104.75
ip dhcp excluded-address 172.31.82.1 172.31.82.14
ip dhcp excluded-address 172.31.82.101 172.31.82.105
ip dhcp excluded-address 172.31.82.201 172.31.82.254

ip dhcp pool Vlan40
utilization mark high 90 log
network 10.152.104.128 255.255.255.128
default-router 10.152.104.129
dns-server 172.31.82.105 10.246.6.1
domain-name test.com
ip dhcp pool Vlan75
network 10.152.104.64 255.255.255.192
default-router 10.152.104.65
dns-server 172.31.82.105 10.246.6.1
domain-name test.com
ip dhcp pool Vlan90
network 172.31.82.0 255.255.255.0
default-router 172.31.82.254
dns-server 172.31.82.105 10.246.6.1
domain-name test.com

errdisable recovery cause dhcp-rate-limit
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust
ip dhcp snooping trust

Issue is impacting mainly Android devices but only some PCs WIFI and Wired

there is only one access switch and an access point for WIFI devices.

Many thanks,

[Giuseppe Larosa]

Hello @hara12386 ,

this message:

028497: Sep 23 22:34:24 GMT+1: DHCPD: Finding a relay for client 011e.f4c4.53db.ad on interface Vlan40.

if the switch is a DHCP server in VLAN40 it should not look for a DHCP relay

The second note is that you have DHCP snooping enabled on all VLANs . It may be better to enable only on selected VLANs

Third note: there are several threads about issues of Android clients with DHCP server runing on Cisco devices some of them related to AP roaming that should not apply to your case if the AP is only one.

Hope to help

Giuseppe

[paul driver]

Hello
A short lease time for dhcp enabled IOT wifi clients I would say best practices especially due to their roaming capabilities 

Also disabling proxy between the dhcp server and and its clients would be applicable to negate any false replies sent to the client /server 

[hara12386]

Hello @paul driver 

I already played with the lease time but issue remains and proxy is disabled in the L3 interface.

Many thanks,

[Htonieto]

I had a strange DHCP issue recently with Catalyst 9K, you can check the entire topic here.

The only thing that solved the issue was upgrading from 17.03.05 to 17.12.05.

[pieterh]

if the coreswitch itself is the DHCP server, then I don't think you need any "dhcp snooping trust" configuration here
this command is only neccessary on a switches interface leading to where the DHCP server can be found
like on the uplink of an accessswitch connecting to this coreswitch

On a Cisco Catalyst 9000 series switch (Cat9k), the DHCP snooping database is a dynamic table of IP-to-MAC bindings learned from client devices on untrusted ports,

as you have a LOT of dhcp-snooping trust commands in your configuration, it looks like you trust allmost ALL of your interfaces ?
if so then there will be NO entries in your DHCP-snooping database.

[MHM Cisco World]

This issue solved ?

MHM

[hara12386]

Hello,

No issue is still not yet fixed, a case is in progress with TAC but no improvement!

Many thanks