dhclient doesn't respond to DHCP OFFER

dhclient doesn't respond to DHCP OFFER

Post by seandarc » Wed, 08 Oct 2003 05:48:42



I have a small old machine I'm setting up to route for my cable
connection with ool. It has two pcmcia nework cards - one connected to
the cable modem, the other to the local hub. Both cards work when
conected to the hub - i.e. other machines on the lan can connect to them.

But...neither card works when I try to run dhclient on the cable modem.
What's weird is that I moved another machine to the cable modem - also
redhat 9.0. It worked! dhclient quickly got the address.

On the first machine, I've flushed iptables, blanked out my hosts.deny,
and changed hosts.allow to ALL:ALL.

I got ethereal to look at what was happening. Here's a bunch of snips.

Almost all of the traffic was ARP requests from the Cisco router from
ool confirming the leases.  Note my machine is getting back DHCP OFFER's
and DHCP ACK's (43,44,120,121,198,199 ) [ there's no DHCPDISCOVER before
the first ACK because ethereal started up a little late.] but dhclient
doesn't respond - it just keeps sending DHCPDISCOVER requests.

At the end Xircom, the adapter, asks if anybody's seen the gateway. It
then pings away, using the address the other machine ( the one that
worked ) uses. No response.

WTF is happening. ool seems to be be doing what it's supposed to. The
adapters are working - else how could ethereal see this stuff.
The firewall is flushed. Both the good machine and the bad machine are
using dhclient - 3.0p12. Both adapters on the bad machine have the same
problem. Both machines are using 2.4.22 kernel. The adapters on the bad
machine work fine on the LAN.

Any help reallly appreciated.

sean

     No. Time        Source                Destination
Protocol Info
       1 0.000000    Cisco_e3:81:56        Broadcast             ARP
   Who has 24.44.12.158?  Tell 24.44.8.1
       2 0.128525    Cisco_e3:81:56        Broadcast             ARP
   Who has 24.44.10.242?  Tell 24.44.8.1
       3 0.207890    Cisco_e3:81:56        Broadcast             ARP
   Who has 67.86.253.152?  Tell 67.86.240.1
.................

      43 5.515039    10.122.208.1          255.255.255.255       DHCP
   DHCP Offer    - Transaction ID 0x1800
      44 5.684118    10.122.208.1          255.255.255.255       DHCP
   DHCP ACK      - Transaction ID 0x1800

..............

      97 12.765007   0.0.0.0               255.255.255.255       DHCP
   DHCP Discover - Transaction ID 0x76db9156

............

     120 15.956841   10.122.208.1          255.255.255.255       DHCP
   DHCP Offer    - Transaction ID 0xfffffba0
     121 16.049819   10.122.208.1          255.255.255.255       DHCP
   DHCP ACK      - Transaction ID 0xfffffba0

.............

  198 27.228633   10.122.208.1          255.255.255.255       DHCP
DHCP Offer    - Transaction ID 0xffffc490
     199 27.318397   10.122.208.1          255.255.255.255       DHCP
   DHCP ACK      - Transaction ID 0xffffc490
     200 27.418549   Cisco_e3:81:56        Broadcast             ARP
        DHCP Discover - Transaction ID 0x76db9156
...........................

     202 27.698475   0.0.0.0               255.255.255.255       DHCP
   DHCP Discover - Transaction ID 0x76db9156
..........................

     291 40.699363   0.0.0.0               255.255.255.255       DHCP
   DHCP Discover - Transaction ID 0x76db9156

........................

     405 56.120297   Xircom_37:6c:9e       Broadcast             ARP
   Who has 67.86.240.1?  Tell 67.86.243.131

...............................

     416 57.119705   67.86.243.131         67.86.240.1           ICMP
   Echo (ping) request

...........................

     428 58.119779   67.86.243.131         67.86.240.1           ICMP
   Echo (ping) request

....................

     435 59.119946   67.86.243.131         67.86.240.1           ICMP
   Echo (ping) request

...................

     441 60.119855   67.86.243.131         67.86.240.1           ICMP
   Echo (ping) request
....................................
     446 61.119908   67.86.243.131         67.86.240.1           ICMP
   Echo (ping) request
..............................
     453 62.119980   67.86.243.131         67.86.240.1           ICMP
   Echo (ping) request
...............................
     460 63.120081   67.86.243.131         67.86.240.1           ICMP
   Echo (ping) request
..........................
     471 64.120133   67.86.243.131         67.86.240.1           ICMP
   Echo (ping) request
..................................
     479 65.120222   67.86.243.131         67.86.240.1           ICMP
   Echo (ping) request
.......................

 
 
 

dhclient doesn't respond to DHCP OFFER

Post by Andrew Schulma » Wed, 08 Oct 2003 18:13:26


Quote:> On the first machine, I've flushed iptables

And set the default policy to ACCEPT?  Sorry, but that's about my only idea
here.

You could use some iptables logging to see whether it sees the incoming
OFFERs and ACKs.

The information you gave about what does and doesn't work on the different
machines is helpful.  It sure makes your problem sound like a firewall
problem.  Okay, here's another idea:  make sure that the policy on all of
the nat and mangle chains is also set to ACCEPT.  I got screwed by this
once-- I set them to REJECT by mistake, and my whole network ground to a
halt until I finally figured it out a week later.  (Including loopback, so
my whole system slowed to a crawl.)

iptables --policy INPUT   ACCEPT
iptables --policy OUTPUT  ACCEPT
iptables --policy FORWARD ACCEPT

iptables -t nat --policy PREROUTING  ACCEPT
iptables -t nat --policy POSTROUTING ACCEPT
iptables -t nat --policy OUTPUT      ACCEPT

iptables -t mangle --policy PREROUTING  ACCEPT
iptables -t mangle --policy INPUT       ACCEPT
iptables -t mangle --policy FORWARD     ACCEPT
iptables -t mangle --policy OUTPUT      ACCEPT
iptables -t mangle --policy POSTROUTING ACCEPT

Good luck,
Andrew.

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