topic Re: DHCP timeout on a vlan in Switching

DHCP timeout on a vlan

jasonmeyer — Fri, 21 Jan 2022 15:40:44 GMT

Have a Cat9404 configure with several VLAN and each having Ip helper-address DHCP IP configured for each. Seems as though one VLAN DHCP requests for clients are timing out, though somewhat sporadically. I don't believe its a rogue DHCP server on the VLAN and as far as i know, only happening on one VLAN.

Here is the DHCP section of a Show Tech DHCPV4

Message Received
BOOTREQUEST 1
DHCPDISCOVER 377041
DHCPREQUEST 970508
DHCPDECLINE 1783
DHCPRELEASE 680
DHCPINFORM 209273
DHCPVENDOR 0
BOOTREPLY 1
DHCPOFFER 361080
DHCPACK 1075473
DHCPNAK 236

Message Sent
BOOTREPLY 0
DHCPOFFER 0
DHCPACK 0
DHCPNAK 0

Message Forwarded
BOOTREQUEST 10
DHCPDISCOVER 3478790
DHCPREQUEST 9280023
DHCPDECLINE 17433
DHCPRELEASE 6361
DHCPINFORM 2025488
DHCPVENDOR 0
BOOTREPLY 1
DHCPOFFER 361080
DHCPACK 1075473
DHCPNAK 236

Shouldn't the received and forwarded be the same?

Re: DHCP timeout on a vlan

balaji.bandi — Fri, 21 Jan 2022 15:45:47 GMT

what vlan is that, what is the config on it ? how would you come that it was timing out, what is the observation here ?

Re: DHCP timeout on a vlan

jasonmeyer — Fri, 21 Jan 2022 16:10:34 GMT

Config is pretty straight forward.

interface Vlan2103
ip address x.x.x.x 255.255.0.0
ip helper-address DHCP IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip directed-broadcast 101
ip wccp 90 redirect in
ip wccp 92 redirect in

Well clients are self assigning addresses. On a windows client in the CLI I do an ipconfig /renew and it takes awhile but eventually returns a DHCP timeout error.

The apple netboot servers are for imagine Mac laptops and desktops, wish I didn't have to have so many. I have checked with the Apple admins and they say DHCP is not configured to hand out IPs, just boot info.

Re: DHCP timeout on a vlan

Georg Pauwen — Fri, 21 Jan 2022 16:46:17 GMT

Hello,

what is the DHCP server (e.g. Windows 2012) ?

Re: DHCP timeout on a vlan

jasonmeyer — Fri, 21 Jan 2022 16:57:53 GMT

Window 2016.

Re: DHCP timeout on a vlan

Georg Pauwen — Fri, 21 Jan 2022 17:32:55 GMT

Hello,

is there a specific reason for ip directed-broadasts to be enabled ? If not, try and disable that:

interface Vlan2103
ip address x.x.x.x 255.255.0.0
ip helper-address DHCP IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
ip helper-address apple netboot IP
--> no ip directed-broadcast 101
ip wccp 90 redirect in
ip wccp 92 redirect in

Re: DHCP timeout on a vlan

balaji.bandi — Fri, 21 Jan 2022 17:51:09 GMT

As per i know i do not believe so many helper address works, i have tesed some time back, more than 4 helper address, the TTL expires, never reaches the DHCP Server., make it simple with ip helper address and test it.

Re: DHCP timeout on a vlan

jasonmeyer — Fri, 21 Jan 2022 18:01:57 GMT

Thats in my other VLANs and not causing any issues there.

Re: DHCP timeout on a vlan

jasonmeyer — Fri, 21 Jan 2022 18:03:15 GMT

Hmmm Ok I can see that, but other vlans have the exact same config and have been that way for several years and even different hardware and never had an issue.

Re: DHCP timeout on a vlan

balaji.bandi — Fri, 21 Jan 2022 19:47:41 GMT

i can not comment on how others working, just test as advice to see if that resolves your issue?

before we get to how others working with same config - we try to resolve the issue here.

Re: DHCP timeout on a vlan

jasonmeyer — Fri, 21 Jan 2022 20:13:57 GMT

I did pull it out, just for fun.

Re: DHCP timeout on a vlan

jasonmeyer — Fri, 21 Jan 2022 20:14:49 GMT

Which 4 would you pull out? The last 4?

Re: DHCP timeout on a vlan

balaji.bandi — Fri, 21 Jan 2022 20:38:02 GMT

Try with only 1 DHCP which is reachable and working and keep adding more after testing.

Re: DHCP timeout on a vlan

MHM Cisco World — Fri, 21 Jan 2022 23:30:07 GMT

friend, I think it issue of routing from DHCP server to host VLAN, you need to check the return traffic. try ping and see if it success.

Re: DHCP timeout on a vlan

jasonmeyer — Mon, 24 Jan 2022 15:21:01 GMT

If i statically assign an IP in the subnet, i can ping the DHCP server just fine.

Re: DHCP timeout on a vlan

MHM Cisco World — Wed, 26 Jan 2022 15:17:29 GMT

ping without specify source make router/switch select the one nearest the destination.
to check ping DHCP server using the VLAN interface.