EIGRP SIA re transmission timer ...just need a math check
i'm just reading/reviewing my notes and i believe i have a mistake in them...so i'm asking IEOC before i make the correction since i have enough space on that page in my notes to make this correction once...
about halfway thru the active timer(3 mins) in EIGRP a router sends a SIA query ie 90 seconds (SIA retransmission timer)
if a SIA response is recieved then the active timer and the SIA retransmission timer are both reset.
this happens 3 times.
then my notes say and i quote " The neighbor wont be declared SIA for up to 6 mins"
how did i get 6 mins (i dont remember the source)...
90+90+90 (the 3 times the SIA retransmission and active time is reset)+ 180 (3 mins of active time after the last reset) = 450seconds or 7.5mins
thanx for any help
Tox!
Comments
Hello,
Since this is a top result on google I'll try to bump it.
I found this statement in 'Routing TCP/IP Volume 1 Second Edition' on page 327.
I can't think of how to test this, but I agree with your math over the book's. In practice I would think that the SIA-Query will almost always accomplish its purpose the first time through and reset the neighbor that does not reply.
i'll have AD 90 for "things that go bump"! Alex
Tox!
The process you mentioned starts after 90s. So the calculation goes something like this...
3 tries (or reset of those timers) makes it 270.
After the 3rd reset it waits for another 90 seconds for the Active timer to expire. This makes it 270+90=360=6 minutes.
Vikram Parmar
after the 3rd reset why would it wait ONLY 90 seconds..
upon reception of a SIA-response BOTH SIA retransmission timer and Active timer are reset
the 3rd reset takes it down to time Time = 0
at this point you need the active timer to expire ...which is 3 minutes...
i'm not arguing i'm just trying to understand this...obviously i have a hole in my knowledge
Tox!
Check out this link:
https://supportforums.cisco.com/thread/2094474
After 90 s or 1.5 mins, the router send an SIA query ONLY to the neighbor from which it did not receive a reply. The neighbor which just sent a reply (saying its still waiting for a reply) then starts this process again and repeats the process. The idea is to reset only the neighbor from which the response is not coming , it may be multiple hops away instead of resetting the immediate neighbor.
Now if you go by this, you will see that this adds up to 360 seconds. ( 3 times wait for 1.5 mins AFTER the initial SIA query after 1.5 mins). At least this is what I understand. I may be wrong. You can double check on this.
I went ahead and ordered this book...
i'll know for sure soon enough
http://www.amazon.com/EIGRP-Network-Design-Solutions-Definitive/dp/1578701651
Tox!