Stuck in Active – stuck in active.
– Active – Dead link.
– Passive – Functional link.
These states can be found in the EIGRP Topological Table!
To see all this, we're going to take concrete examples 🙂
(You may not understand anything otherwise)
– R-00, R1, R11, R12, R21, R22, R23 and R24 are all well configured, work perfectly and use the EIGRP protocol.
– The only LAN that exists is the lan X.X.X.X (we ignore the interconnections networks).
– The R1 router has only one Successor to join the X.X.X.X network.
This is R1's topological table.
P – Passive – Information still valid.
Reaction in the event of a breakdown
– The link between R-00 and R1 falls and R-00 is no longer the R1 Neighoor.
– R1 switches the X.X.X.X network to Active mode.
A – Active – unreachable.
What will R1 do to remedy this problem?
– R1 sends a QUERY package to all these neighbors except its old Successor.
– R1 launches a 3-minute Timer, if it doesn't receive a Reply package from a Neighoor, it will put it in the "STUCK IN ACTIVE" stadium.
– R11 and R12 receive a Query package of R1.
– R11 sends a Query package to R21 and R22.
– R12 sends a Query package to R23 and R24.
– R11 and R12 launch a 3-minute Timer.
R21, R22, R23 and R24
– Receive a Query package.
– Do not own other Neighboor.
– Respond to the Query package with a Reply package.
– R11 and R12 have received a response to all their Query packages.
– R11 and R12 respond to the Query r1 package with a Reply package.
Since no one knows how to join this network, everyone has put an infinite Metric in their Reply.
R1 concludes that this network is no longer reachable at all and removes it from its topological table and thus from its routing table.
If R1 does not receive a Reply
– R1 is too busy.
– Link problem.
– One-way link via fibre optics. (see article on the UDLD).
What's going on:
– R1 removes R12 from its neighboors.
All because R1 didn't process R12's response?
It's all nonsense!
Cisco reacted from IOS 12.1 and created the SIA-Query and SIA-Reply packages.
SIA-Query and SIA-Reply
We are in the same situation, R1 is waiting for the R12 Reply …
After 1 minute and 30 seconds, R1 begins to worry and decides to send an SIA-Query to R12.
R12 responds with an SIA-Reply, R1 is happy, it still doesn't have the information requested but it won't remove R12 from its Neighboor table.
We make a small picture:
– R1 – Professor CM1.
– Other routers – Fifth graders.
The teacher would like to know the phone number of the principal of the school because he lost it and asks his fifth grade class to ask all their friends at the school if anyone knows this phone number…
It's going to be useless because the students only know their parents' phone number.
Well, we're going to tell every student at the school that if someone asks them for a phone number outside their parents' number to answer:
– I don't know any other numbers and my friends like that.
– No unnecessary hubbub in the playground.
– The Teacher knows first-all that he will not get this information from his students.
In order to tell a router to announce only the resins that have authorized it and not to launch unnecessary Query packages, we will set it up in STUB mode.
Hoping this article has been helpful to you! Don't hesitate to let me know!!