[ECOS] Re: DHCP crash with Novell Server

[Grant Edwards <grante at visi dot com>]

On Tue, Jun 19, 2001 at 02:33:04PM -0500, Grant Edwards wrote:

> However, when used with a Novell Netware 5.0 server it crashes
> (the board resets) when the IP lease expires (600 seconds in
> the example below).

[...]

>   1.  Novell server doesn't send T1 renewal time (option 58)
>   2.  Novell server doesn't send T2 rebind time (option 59)

Here's what seems to be happening:

 1) The code in dhcp_proto.c:new_lease() doesn't check the
    return status of get_bootp_option().  Since there are no
    rebind (T2) and renewal (T1) time options, it ends up
    reusing the IP lease time value for those two.

    We end up with least->t1 == lease->t2 == lease->expiry.
    
 2) Set an alarm for now+lease->t1
 
 3) Alarm goes off.
 
 4) alarm_function() gets called.  

    It sets a new alarm for lease->t2 
    (same as lease->t1, IOW: now.)
    
    It enables the alarm.
    
    note: It hasn't yet changed the state variable lease->next.
    
    goto 3)
    
 After 40-50 nested calls to alarm_function(), the stack blows.



Here are the fixes I plan on trying:

 1) in alarm_function() change the state variable _before_
    re-enabling the alarm.  That will limit the nesting level
    to 3.

    With no other changes, this will cause the lease to expire
    (AFAICT).

 2) in new_lease(), check the return value of
    get_bootp_option() and set default values for T1 and T2 if
    the server doesn't provide them.

My understanding of the RFCs is that a server is required to
provide an IP lease expiry time, but is not required to specify
T1 and T2.

I don't know if client behavior in absence of T1/T2 options is
defined.  In a different client, I've defaulted T1 and T2 to
1/2 expiry and 3/4 expiry.

Perhaps the proper behavior is just to wait for the IP lease to
expire and start from scratch (start with a DISCOVERY rather
than a REQUEST), but it doesn't appear that this is what the
eCos routines do when the lease expires.  Rather, they shut
down the interface and give up, right?

Stay tuned...

-- 
Grant Edwards
grante@visi.com