First, I think there is an error in DSG. Second, I stumbled into an interesting
behavior of the "distance" command.
This is a task about RIP route poisoning. We can go for offset-list method or
distance one. The WB goes for distance, ok.
DSG says that we should enter "distance 255 150.100.12.2 255.255.255.255 1"
which IMHO is wrong. The context help and command reference agree that we
should enter wilcard there, and not the subnet mask. So, it should be
"150.100.12.2 0.0.0.0".
That can be confirmed with "sh run | i distance" which then show that the
router automatically converted the distance command into "distance 255 0.0.0.0
255.255.255.255 1" because of the "ANY" wildcard used.
So, I think it is definite that we should use wildcard. Anyway, I tried it this
way and it worked. But...
Now, about the second part of my email. I would really love somebody to explain
why is this happening.
When I corrected the "distance" command, I noticed that the update timer has
not been reset anymore. The route just slowly started to dissapear. That
confused me and I thought all this is not working. That is why I changed the
distance to "254" in order to be able to see the route in the table even after
the command. All other routes behaved normal, just this one. So, i chose to
wait and saw that the distance command did have the effect, but only after the
flush timer has expired, the route got deleted from the table, and another RIP
update came after that. Only then the AD got changed to 254... Why the router
is not changing the distance immediately after the next RIP update? Why the
flush timer and all?
See for yourself:
R1(config-router)#do sho access-l 1
Standard IP access list 1
10 permit 200.0.0.9 (75 matches)
R1(config-router)#do sh run | i dista
distance 254 150.100.12.2 0.0.0.0 1
.... and we still have the old "120" distance...
R1(config-router)#do sro 200.0.0.9
Routing entry for 200.0.0.9/32
Known via "rip", distance 120, metric 3
Redistributing via rip
Last update from 150.100.12.2 on FastEthernet0/0, 00:00:28 ago
..... time is passing...
R1(config-router)#do sro 200.0.0.9
Routing entry for 200.0.0.9/32
Known via "rip", distance 120, metric 3
Redistributing via rip
Last update from 150.100.12.2 on FastEthernet0/0, 00:02:54 ago
... some more...
R1(config-router)#do sro 200.0.0.9
Routing entry for 200.0.0.9/32
Known via "rip", distance 120, metric 4294967295 (inaccessible)
Redistributing via rip
Last update from 150.100.12.2 on FastEthernet0/0, 00:04:01 ago
.... and here it is, the new AD...
R1(config-router)#do sro 200.0.0.9
Routing entry for 200.0.0.9/32
Known via "rip", distance 254, metric 3
Redistributing via rip
Last update from 150.100.12.2 on FastEthernet0/0, 00:00:20 ago
Best Regards,
Bojan Zivancevic
Network Engineer
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