DHCP Issues with SG350 switches

[douchey604]

Hi, We have an ongoing issue with the SG350 range of switches when using them to allocate DHCP addresses.  The issue is that sometimes they will not fully issue an IP Address to the Laptops that are connecting into the Switch via Ethernet.  When we look at the Address Binding table it shows that it has allocated an address, but actually, it hasn't.  Also, the address Type shows as MAC Address when all the others, that are actually working, show as Client Identifier.  The only way around this and for the switch to actually complete the address issue is to disconnect the laptop, delete that address binding, Admin the port down, Admin the port up, re-connect the laptop and then most of the time it will get an address and function correctly.  We have now seen the same type issue with our Windows Deployment Server setup, whereas a PC will pxe boot fine, get through the first stage of deployment, then reboot, then it fails to get an IP with the same address binding issue, and again this is fixed by deleting the binding from the DHCP table on the switch.

It has happened across multiple different switches, across multiple sites, the firmware is all latest except one site which was retrograded as a test.

Thanks in advance.

[Georg Pauwen]

Hello,

are these random clients (laptops) with random Nics, or is there a pattern (e.g. only Apple laptops, only laptops with certain network cards) ?

[douchey604]

Hi, Multiple HP Probooks, Elitebooks and now Dell Optiplex desktops. Thanks

[Georg Pauwen]

Hello,

are these Windows machines ?

Looking at what you said earlier:

--> Also, the address Type shows as MAC Address when all the others, that are actually working, show as Client Identifier.

Check the registry on the failing clients:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\SkipClientID

By default, this registry entry is set to 0 (False),and therefore the option is included in outgoing DHCP requests.
Check if by any chance this value is set to 1 (True), which would prevent the option from being sent in the DHCP requests.

[balaji.bandi]

Can you post the config to look, also give us information - where is the DHCP Server (same switch or other DHCP Server ?)

[douchey604]

We have these SG350 switches at multiple branch sites and all seem to have the same issue, I will gather a config and post later, thanks 

[MHM Cisco World]

one Q. are you config dhcp snooping & dhcp server in same SW?

if yes then try disable snooping and try again 

[crackedHead]

Yes. I am using 2.5.5.47.

The problem is that the Cisco switch is not putting the "NTP Server" or "bootfile" in the DHCP response. Configuration is:

ip dhcp pool host myhost
address 1.1.1.2 255.255.255.0 hardware-address 00:11:22:33:44:55
client-name myhost
next-server 1.2.1.3
bootfile pxelinux.0
default-router 1.1.1.1
time-server 1.1.1.1

Response has:

Your-IP 1.1.1.3
Server-IP 1.2.1.3
Client-Ethernet-Address 00:11:22:33:44:55
Vendor-rfc1048 Extensions
  Magic Cookie
    DHCP-Message Option 53, length 1: ACK
    Server-ID Option 4, length 4: 1.1.1.2
    Lease-Time Option 51, length 4
    DN Option 58, length 4: 4294967295
    RB Option 58, length 4: 4294967295
    Hostname Option 12, length 6: myhost
    Subnet-Mask Option 1, length 4: 255.255.255.0
    default-Gateway Option 3, length 4: 1.1.1.1

The options missing:

- NTP server

- Boot File

[paul driver]

Hello
Do you have the correct file path for the boot file and its the nxt-server reachable, you could also try using the option value instead of the custom name.

example: time (4) next server(12)  ntp (42) pxefile(67)
ip dhcp pool static
option 4 ip x.x.x.x

option 12 ip x.x.x.x
option 42 ip x.x.x.x
option 67 ascii /pxelinux.0

[crackedHead]

The SG350X does not support the configuration syntax you are using above. I tried and anything that it has a keyword for it will reject, e.g:

switch(config-dhcp)#option 4 ip 1.2.3.4
This code 4 is supported explicitly. Please use appropriate command.

The problem isn't that there is a problem with the configuration, the problem is that the dhcp server code in the SG350 switch is not returning all of the options specified in the configuration stanza.

[paul driver]

Hello

---

@crackedHead wrote:
PC will pxe boot fine, get through the first stage of deployment, then reboot, then it fails to get an IP with the same address binding issue, and again this is fixed by deleting the binding from the DHCP table on the switch.

---

Does this switch have a option to turn off ip dhcp conflict logging?

conf t
no ip dhcp conflict logging

[crackedHead]

The SG350X does not support the command "no ip dhcp conflict logging".