HP-UX Mobile IPv4 A.03.01 Administrator's Guide

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Chapter 8
99
Home or Foreign Agent Cannot Get the Mobile Node’s Link Address (failed to
get link addr)
If a Mobile Node is not registering with a Foreign Agent or if the Mobile Node is not
de-registering when it returns to its home network, check the Foreign Agent’s syslog
file (for registration problems) or the Home Agent’s syslog file (for de-registration
problems). Look for errors indicating that the Foreign or Home Agent is unable to get the
Mobile Node’s link address from the Registration Request packet. (The Foreign Agent
must extract the Mobile Node’s link address at registration time so it can forward the
de-capsulated packets to the Mobile Node. The Home Agent must extract the Mobile
Node’s link address at de-registration time so it can send a proxy ARP message with the
Mobile Node’s link address.)
Look for log entries similar to the following:
Mar 21 08:22:43 ERROR: registration_process: failed to get link addr
from Registration Request message
Mar 21 08:22:43 ERROR: MN=192.15.15.3, HA=192.15.15.4,
COA=10.10.10.2
Solution The most likely cause of these entries is that the link was brought down, then
back up (using ifconfig) while the Mobile IPv4 daemon was running. To fix this
problem, use the mipadmin -stop and mipadmin -start commands to stop and restart
the daemon.
The reason for this problem is that the Home or Foreign Agent must extract the link
address of the Mobile Node from the link-level protocol header of the packet that
contains the Registration Request. To do this, the NOFASTPATH option for the link must
be enabled. By default, the nofastpath option is disabled when ifconfig brings up a
link. The HP-UX Mobile IPv4 startup script (which is executed by the mipadmin utility)
enables the NOFASTPATH option on the links configured for Mobile IPv4. (The HP-UX
Mobile IPv4 shutdown script and mipadmin the disable the NOFASTPATH option when the
HP-UX Mobile IPv4 software is shutdown.)
To determine if the nofastpath option is enabled, use the following ndd command to
view the interface information:
ndd /dev/ip ip_ill_config_status
In the example below, lan1 is being used for Mobile IPv4 so the NOFASTPATH option is set.
The interface lan0 is not being used for Mobile IPv4, so it does not have the NOFASTPATH
option set:
# ndd /dev/ip ip_ill_config_status
Interface Configuration options
lan1 NOPOINTOPOINT ARP PLAINSAP NOFASTPATH
lan0 NOPOINTOPOINT ARP PLAINSAP