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RIPng Holddown timer

Unanswered Question
Oct 5th, 2009
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Hi All,


I have seen an unusual behavior with RIPng Holddown timer. I setup a lab using two C1760 routers with 12.4(25b) IOS.


Here's the relevant config for the two routers R1 & R2-


R1-


ipv6 unicast-routing

ipv6 cef

!

interface fa 0/0

ipv6 enable

ipv6 address 2001:ABAB::/64 eui-64

ipv6 rip TEST enable

!

ipv6 router rip TEST

timers 30 180 20 120

!


R2-


ipv6 unicast-routing

ipv6 cef

!

interface fa 0/0

ipv6 enable

ipv6 address 2002:ABAB::/64 eui-64

ipv6 rip TEST enable

!

interface Loopback0

ipv6 enable

ipv6 address 2003:ABAB::/64 eui-64

ipv6 rip TEST enable

!

ipv6 router rip TEST

timers 30 180 20 120

!


I shutdown the Loopback0 interface on R2, which triggers an update to all its neighbors with metric 16 for Loopback0 interface prefix 2003:ABAB::/64.


R1 receives this update, deletes the entry from its routing table, starts the holddown timer and garbage-collection timer.


Now before the holddown timer expires, I re-enable Loopback0 interface on R2, which triggers another update to all its neighbor with metric 1. However, R1 ignores this update until Holddown timer expires.


So far so good. All is going well according to the theory. However, before a next periodic update is received from R2 by R1, the holddown timer reaches 0 and sets some ridiculous value to 4294967 and starts decrementing from there. Meanwhile any periodic updates from R2 now are still ignored until garbage-collection timer expires.


This seems to be a bug in the IOS to me.


Just to top it off. Another such experiment, resulted in a very different behavior. When the Holddown timer reached 0, it set the value to 4294967 again. However, the next second, I received the console message "RIPng: Next RIB walk in 99188" and the holddown value was set to 0.


What on earth is a RIB walk?


Please share your thoughts guys.


Regards,

Amit.

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virverma Tue, 10/20/2009 - 17:06
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  • Silver, 250 points or more

not an expert in R&S

but for RIB walk all I know,


The "RIB walk" is the periodic scan of the routing table

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