Slow DHCP Responses
Gruher, Joseph R
joseph.r.gruher at intel.com
Thu Aug 8 18:43:01 UTC 2013
>Behalf Of Simon Hobson
>"Gruher, Joseph R" wrote:
>> My problem is DHCP requests take a very long time, generally around 30-40
>> This is consistent across different clients and across different sources of the
>DHCP request (Linux, Windows, BIOS PXE, iPXE).
>> They do always complete eventually but it seems like they should only take
>far, far less time.
>Yes, it should be "nearly instant".
>As Steve says, have a look at your switch ports first - I've been caught out with
>this in the past when using a managed switch that defaults to Spanning Tree
>turned on :( One very quick way round this is to attach your device to a really
>basic "dumb" switch.
This sounds on the right track. The client shows as waiting on DHCP starting around 11:34:30 but looking at tcpdump the DHCP request doesn't come in on the DHCP server until 11:35:05 and then it is actually serviced very quickly. I'll investigate the switch settings. I'm using a Cisco Nexus 5010 switch basically straight out of the box. Thanks for the help!
11:35:05.214869 IP 0.0.0.0.bootpc > 255.255.255.255.bootps: BOOTP/DHCP, Request from 00:15:17:9e:29:a8 (oui Unknown), length 548
11:35:05.215241 IP 184.108.40.206.bootps > 255.255.255.255.bootpc: BOOTP/DHCP, Reply, length 300
11:35:06.873861 STP 802.1d, Config, Flags [Topology change], bridge-id 8001.c8:4c:75:e8:f5:00.8001, length 43
11:35:08.874054 STP 802.1d, Config, Flags [Topology change], bridge-id 8001.c8:4c:75:e8:f5:00.8001, length 43
11:35:09.224355 IP 0.0.0.0.bootpc > 255.255.255.255.bootps: BOOTP/DHCP, Request from 00:15:17:9e:29:a8 (oui Unknown), length 548
11:35:09.224558 IP 220.127.116.11.bootps > 255.255.255.255.bootpc: BOOTP/DHCP, Reply, length 300
11:35:09.229344 ARP, Request who-has 18.104.22.168 tell 22.214.171.124, length 46
11:35:09.229363 ARP, Reply 126.96.36.199 is-at 00:1b:21:71:8d:88 (oui Unknown), length 28
11:35:09.229429 IP 188.8.131.52.ah-esp-encap > 184.108.40.206.tftp: 30 RRQ "undionly.kpxe" octet tsize 0
11:35:09.230710 IP 220.127.116.11.41957 > 18.104.22.168.ah-esp-encap: UDP, length 14
11:35:09.230781 IP 22.214.171.124.ah-esp-encap > 126.96.36.199.41957: UDP, length 17
11:35:09.232516 IP 188.8.131.52.acp-port > 184.108.40.206.tftp: 35 RRQ "undionly.kpxe" octet blksize 1456
>Also, as a side note, unless you are part of Alascom, Inc, you shouldn't be
>using their IP allocation (220.127.116.11/17). You should stick to RFC1918 addresses
>(10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) which are explicitly set aside for
>private use. Even if this is a completely isolated network, it's bad practice to
>use someone elses addresses - one day you'll forget and it'll bite you on the
Thanks, I'll change those.
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