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

  • 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!

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