Devices not reaching the DHCP server... bad switch gateway to blame?
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@Dashrender said in Devices not reaching the DHCP server... bad switch gateway to blame?:
@Jason said in Devices not reaching the DHCP server... bad switch gateway to blame?:
Depends on how the switch is running but if you have Macros on the switch or it's in Layer3 mode (even if on the same subnet) it can affect things.
Also if this is cisco switch you might want to enable RSTP (spanning-tree mode rapid-pvst)
what is macro on a switch?
What in a layer 3 mode would prevent a DHCP request from making it through a switch when we know there are no VLANs?
What does STP have to do with this? Clearly the PC isn't a loopback to the switch.@Dashrender said in Devices not reaching the DHCP server... bad switch gateway to blame?:
@Jason said in Devices not reaching the DHCP server... bad switch gateway to blame?:
Depends on how the switch is running but if you have Macros on the switch or it's in Layer3 mode (even if on the same subnet) it can affect things.
Also if this is cisco switch you might want to enable RSTP (spanning-tree mode rapid-pvst)
what is macro on a switch?
Some SDN switches run a full blown OS, you can do pretty much everything on them.
What in a layer 3 mode would prevent a DHCP request from making it through a switch when we know there are no VLANs?
A firewall? For example: https://www.juniper.net/documentation/en_US/junos13.3/topics/concept/firewall-filter-ex-series-overview.html
What does STP have to do with this? Clearly the PC isn't a loopback to the switch.
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I'm on the call looking at this. What a pain. I'll try to post what we are finding....
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DHCP Renewals appear to be working just fine from anywhere. New DHCP Leases appear to never work, possibly not for a week or more. It is only that today there are new things going onto the network.
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Looked at the logs, there does not appear to be any issues with the pool being exhausted. Both logs and manually looking at DHCP Service confirm that IP addresses are available.
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Could you pinpoint the place where the packets get dropped? Wireshark before / behind the switch?
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@thwr said in Devices not reaching the DHCP server... bad switch gateway to blame?:
Could you pinpoint the place where the packets get dropped? Wireshark before / behind the switch?
Potentially, I just mentioned that on the call as a potential next step.
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@scottalanmiller said in Devices not reaching the DHCP server... bad switch gateway to blame?:
@thwr said in Devices not reaching the DHCP server... bad switch gateway to blame?:
Could you pinpoint the place where the packets get dropped? Wireshark before / behind the switch?
Potentially, I just mentioned that on the call as a potential next step.
Probably your best bet. Don't know the Netgears or how smart (dumb) they are, but you never know.
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Is this a wired or wireless connection through this switch having a problem?
I wonder if there is a latency issue on that specif cable?
tried restarting the DHCP service - Gene said it's on the same device as the gateway, so probably not a windows box.. so might require a reboot of the whole gateway.
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@Dashrender said in Devices not reaching the DHCP server... bad switch gateway to blame?:
Is this a wired or wireless connection through this switch having a problem?
I wonder if there is a latency issue on that specif cable?
tried restarting the DHCP service - Gene said it's on the same device as the gateway, so probably not a windows box.. so might require a reboot of the whole gateway.
Wired for sure, but AFAIK eveyrthing has been tested at this point.
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@Dashrender said in Devices not reaching the DHCP server... bad switch gateway to blame?:
tried restarting the DHCP service - Gene said it's on the same device as the gateway, so probably not a windows box.. so might require a reboot of the whole gateway.
It's not. It's on the main AD server along with AD and DNS.
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@Dashrender said in Devices not reaching the DHCP server... bad switch gateway to blame?:
I wonder if there is a latency issue on that specif cable?
We thought that that was the case, but appears not to be.
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@art_of_shred said in Devices not reaching the DHCP server... bad switch gateway to blame?:
I should note that the gateway and DHCP server are one and the same.
I mispoke.. it was Art, not Gene.
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Scope out of IPs?
First thing I would check if renewals work but new isn't
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@Dashrender said in Devices not reaching the DHCP server... bad switch gateway to blame?:
What does STP have to do with this? Clearly the PC isn't a loopback to the switch.
by default STP on most switches puts ports in blocking mode then in fowarding mode after it checks it. RSTP does a better job of handling and fowards first then checks and blocks if need. if you don't enable rapid-pvst on most cisco switches you will have issues with DHCP once in a while but you will always have issues with PXE etc.
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Have you restarted the DHCP server? It's hosted on a Windows box I wonder if there is some rot or an update that needs to be applied.
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Maybe sure the Whitelist isn't enabled on the DHCP server.
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@scottalanmiller said in Devices not reaching the DHCP server... bad switch gateway to blame?:
@Dashrender said in Devices not reaching the DHCP server... bad switch gateway to blame?:
tried restarting the DHCP service - Gene said it's on the same device as the gateway, so probably not a windows box.. so might require a reboot of the whole gateway.
It's not. It's on the main AD server along with AD and DNS.
how is a DC the default gateway?
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Looks like split brain. That's a guess.
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@Jason said in Devices not reaching the DHCP server... bad switch gateway to blame?:
@scottalanmiller said in Devices not reaching the DHCP server... bad switch gateway to blame?:
@Dashrender said in Devices not reaching the DHCP server... bad switch gateway to blame?:
tried restarting the DHCP service - Gene said it's on the same device as the gateway, so probably not a windows box.. so might require a reboot of the whole gateway.
It's not. It's on the main AD server along with AD and DNS.
how is a DC the default gateway?
It's not. No relationship.
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I was having a brain fart when I said the gateway was the dhcp server. The primary dc is the server. It ended up being that it was set up to failover to a secondary dc (dhcp, that is) but the config wasn't completed on the second dc. It must have tried to failover and got stuck. It would renew leases just fine, but no new leases handed out. Removed that config and it recovered instantly. Problem solved.
