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Slow DHCP on 5500G-EI

roo5ter
Occasional Advisor

Slow DHCP on 5500G-EI

I have recently upgraded our core switch to a 3Com 5500G-EI (24 port, no PoE). I have roughly 20 routed VLANs and the 5500 is providing DHCP across nearly every one. Since the changeover, we have been having very slow DHCP responses (sometimes 30-45 seconds). This is on devices directly connected to the switch and hanging off our various edge switches. We see this on our NBX phones (on layer 3) as well as workstations. The devices generally time out when looking for an IP. Is there any obvious fix? Thanks.
3 REPLIES
Shirin
Frequent Advisor

Re: Slow DHCP on 5500G-EI

Do you mean that the switch is relaying udp ports 67 and 68 OR do you mean that the switch is the DHCP server ?



In the first case you require to configure as following, for each vlan where no dhcp is available



dhcp-server 1 ip ip_address-first_dhc-server ip_address-second_dhcp-server

interface vlanx

dhcp-server 1



In the second case you may want to look at the software version the switch is running and compare with what is available on the web site of 3com;

Maybe you can do some sniffing and open a case with 3com



Hope it helps!

roo5ter
Occasional Advisor

Re: Slow DHCP on 5500G-EI

The core switch discussed is the DHCP server. We do have the scopes configured as noted; however a consultant just recommended we enable RSTP & STP to see if we can fix the DHCP slowdowns. The DHCP timeouts tend to happen on PCs connected edge switches (Baseline 2226s with RSTP enabled already) directly connected to the core. This is what code was added:



#

stp mode rstp

stp instance 0 root primary

#



Any idea if this could fix the issue? It will take a few days to test.

roo5ter
Occasional Advisor

Re: Slow DHCP on 5500G-EI

It appears that enabling RSTP on the 5500G-EI as noted in my earlier message fixed the issue.