System information

Troubleshooting AppleTalk
Book Title
9-192
Route flapping
(unstable route)
Excessive traffic load on internetworks with many routers can prevent some routers
from sending RTMP
1
updates every 10 seconds as they should. Because routers
begin to age out routes after missing two consecutive RTMP updates, the
inconsistent arrival of RTMP updates can result in constant route changes.
Step 1 Use the show interfaces exec command to check the traffic load. Check
the load for each interface.
The following example is output from the show interfaces command:
Ethernet0 is up, line protocol is up
Hardware is Lance, address is 0000.0c32.49b1 (bia
0000.0c32.49b1)
Internet address is 192.168.52.26/24
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely
255/255, load 1/255
[...]
Route flapping
(unstable route)
The load field displayed in the show interfaces command is the load on
the interface as a fraction of 255 (255/255 is completely saturated),
calculated as an exponential average over five minutes.
Step 2 If the load is less than 50%, reconfiguring timer values might solve the
problem by allowing RTMP updates more time to propagate through the
network.
If the load is more than 50%, you might need to segment the network to
reduce the number of routers (and therefore the amount of traffic) on each
network segment.
Step 3 Use the debug apple events privileged exec command to determine
whether routes are being aged incorrectly. The output should resemble the
following:
Router#debug apple events
AppleTalk Events debugging is on
Router#
%AT-6-PATHNOTIFY: Ethernet0: AppleTalk RTMP path to
250-250 down; reported bad by 200.41
Caution: Because debugging output is assigned high priority in the CPU
process, it can render the system unusable. For this reason, use debug
commands only to troubleshoot specific problems or during
troubleshooting sessions with Cisco technical support staff. Moreover, it
is best to use debug commands during periods of lower network traffic
and fewer users. Debugging during these periods decreases the likelihood
that increased debug command processing overhead will affect system
use.
Step 4 If routes are being aged incorrectly, use the appletalk timers global
configuration command to correct the problem. Suggested timer values
are 10, 30, and 90 to start, but do not exceed 10, 40, and 120. The first
number must always be 10, and the third value should be three times the
second.
You can return the timers to their defaults (10, 20, 60) by using the no
appletalk timers global configuration command.
Timers should be consistently set to the same value throughout the
internetwork, or at a minimum, throughout the backbone of the
internetwork.
Possible Problems Solution