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DHCP 30s delay


Our server team advise us to check the L2 switch on the issue that the DHCP server running in windows has a 30s delay when leasing an IP address to a workstation. Connection is only through local area network. The DHCP server and the workstation are connected to an L2 switch. All in the same VLAN which is the default.


Average branch has 10 devices/workstation and there are branches that only 2 or 3 workstation that encounter the delay. There are also branches that all workstation encounter the delay and there are branches that do not experience any delay on their workstation. We have around 100+ branches and so far there are 26 confirmed branches that experience this problem. Switch configuration is the same for all switches. I was advise to implement portfast on all access port since we have a pvst spanning tree configured on the switch.


Question: If we implement portfast, why does other workstation/branches doesn't experience the same problem given that all switches has no portfast configured on all ports? How do we resolve this?



17 Replies 17

There are ports on the CISCO switches that do not exhibit the same issue.  PVST is running in cisco switches. Are there reasons why spanning-tree is not running on certain ports given that PVST is configured on the switch and not on per port?


As for the HP2510 models, even if the STP is disabled, there are still 30s delay seen on certain ports on the switch.

I guess we could spend hours doing packet captures and switch debugs to try to work out what is happening or you could just ignore the fact that it is happening on certain ports and set the network up correctly so that it doesn't happen anywhere under normal circumstances.


If you really want an answer as to why, get spanning-tree debug logs and packet captures from a working and non-working port.  Even better, implement DHCP snooping and debug that.  It will tell you exactly what is happening and how and why.  Happy to help with the diagnosis if you need it, but we are really flying blind with very little real information here.


Thanks! Appreciate all the inputs. I'll update once I get an approval to execute the portfast command. Cheers!

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