"Healthy" servers issuing leases for length of MCLT

[Matt Causey]

On Sat, Jul 10, 2010 at 1:07 AM, Glenn Satchell
<glenn.satchell at uniq.com.au>wrote:

>
> The initial response to a DHCP DISCOVER will be to issue a lease of MCLT,
> then the next renew will be your specified lease time. It works this way
> because the DHCPOFFER is sent before communicating to the partner server.
>

Thanks for the info.  We have a very short MCLT (300 seconds) and 12 hour
lease time.  I can confirm that our 'normal' clients behave in the way you
describe:

tc at box:~$ sudo udhcpc -i wlan0 --foreground
udhcpc (v1.14.3) started
Sending discover...
Sending discover...
Sending select for 172.24.120.141...
Lease of 172.24.120.141 obtained, lease time 300
deleting routers
route: SIOCDELRT: No such process
adding dns 10.4.4.10
adding dns 172.24.98.22
adding dns 172.24.98.21
adding dns 10.5.40.1
Sending renew...
Sending renew...

<wait...>

Sending renew...
Lease of 172.24.120.141 obtained, lease time 43200
deleting routers
route: SIOCDELRT: No such process
adding dns 10.4.4.10
adding dns 172.24.98.22
adding dns 172.24.98.21
adding dns 10.5.40.1

So, that part looks good.

Now our Cisco access points seem to be actually sending the 300 second lease
time in their DHCPREQUEST:

19:20:06.439558 IP (tos 0x0, ttl 254, id 18499, offset 0, flags [none],
proto: UDP (17), length: 336) CLIENT.bootpc > SERVER.bootps: [udp sum ok]
BOOTP/DHCP, Request from 00:26:0b:c9:eb:e4 (oui Unknown), length: 308,
xid:0x97f, flags:
 [none] (0x0000)
          Client IP: phx3-wap-97-189.phx3.amazon.com
          Client Ethernet Address: 00:26:0b:c9:eb:e4 (oui Unknown)
          Vendor-rfc1048:
            DHCP:REQUEST            MSZ:1152
            CID:[ether]00:26:0b:c9:eb:e4
            LT:300
            HN:"ACCESS-POINT"
            PR:SM+NS+DN+WNS+DG+LOG+SR+T150+VO
            VC:"Cisco AP c1250"

which seems to be followed by the reply containing the 300 second lease
time:

19:20:06.445402 IP (tos 0x0, ttl  64, id 0, offset 0, flags [DF], proto: UDP
(17), length: 331) SERVER.bootps > CLIENT.bootpc: [bad udp cksum aa72!]
BOOTP/DHCP, Reply, length: 303, xid:0x97f, flags: [none] (0x0000)
          Client IP: BLAH
          Your IP: BLAH
          Server IP: BLAH
          Client Ethernet Address: 00:26:0b:c9:eb:e4 (oui Unknown)
          file "filename"
          Vendor-rfc1048:
            DHCP:ACK
            SID:HOST
            LT:300
            SM:255.255.255.0

The DHCPREQUEST from other clients does not ask for a particular lease time,
so they get the 12 hour one from the server.

Soooo, I intend to bug Cisco about their dhcp client implimentation.  But is
there anything I can do to fix this from my end?  I see the min-lease-time
option.  Will that help?

--
Matt
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.isc.org/pipermail/dhcp-users/attachments/20100909/e6ea4994/attachment.html>