Jeff Doyle vs Debugs ..concerning RIP

Routing TCP/IP volume 1 >>> somewhere it mentions (i think while explaining simple split horizon) that a router send the RIP packet to its neighbor with a hop count of 0  and the neighbor receives the route and increments hop count to 1 .so router B would send router A an update about network 5 with hop 0. Router A would increment the hop count to 1 and compare it to the routing table. There router A finds network 5 as connected (essentially hop count 0) and discards the update

router A------------------network5--------------router b

 

DEBUGS>> however the debugs i see in the solutions on WB1 show that a router increments the hop count before sending it


question>> is this a cosmetic issue and doyle is right or is the router actually increasing the hop count before sending out updates??

 

thankyou

Comments

  • I would believe a debug over any text pretty much all the time.

     

  • Hi Toxic,




    In my experience, the router always increases the hop by 1 before sending it out. If what you stated is actually in the vol 1 book then its most likely an error or true with the code Jeff used ( which is most likely a very old ios code:-)).



    Hope this helps,


    Olushile 





    -----Original Message-----

    From: ToxicAvenginator <[email protected]>

    To: olushile <[email protected]>

    Sent: Fri, Nov 4, 2011 11:32 am

    Subject: [CCIE R&S] Jeff Doyle vs Debugs ..concerning RIP













    Routing TCP/IP volume 1 >>> somewhere it mentions (i think while explaining simple split horizon) that a router send the RIP packet to its neighbor with a hop count of 0  and the neighbor receives the route and increments hop count to 1 .so router B would send router A an update about network 5 with hop 0. Router A would increment the hop count to 1 and compare it to the routing table. There router A finds network 5 as connected (essentially hop count 0) and discards the update


    router A------------------network5--------------router b


     


    DEBUGS>> however the debugs i see in the solutions on WB1 show that a router increments the hop count before sending it




    question>> is this a cosmetic issue and doyle is right or is the router actually increasing the hop count before sending out updates??


     


    thankyou






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  • Hi Toxic,




    In my experience, the router always increases the hop by 1 before sending it out. If what you stated is actually in the vol 1 book then its most likely an error or true with the code Jeff used ( which is most likely a very old ios code:-)).



    Hope this helps,

    Olushile 






     

    Thankyou...appreciate the responce...i've found quite a few differences with doyles explaination and how it actually works..regarding RIP..

     

    for example...Doyle claims that a RIP route goes into hold down when an increase in metric happens..which is not true..the ONLY time a cisco router puts a route in holddown is when the update timer expires..

    anyhow..cheers!

     

    Tox

     

  • Thats right from my testing experience as well, cisco running RIP router always increases the hop by 1 before sending it out. It was also explained by Brian in ATC. 

  • Hi all,

       Normally, a DV should advertise its own metric for a prefix, like EIGRP does  (this is why probably in Jeff Doyle book it shows this). However, RIP on Cisco routers increase the metric of the prefix before advertising it out: so if i have a directly connected prefix which i advertise it in RIP, i advertise it with metric of 1.

    @Toxic, the route goes into holddown when the invalid timer expires (not the update timer), and stays in the hold down state aproximately flash-invalid timer(regardless of the value you set on hold down).

    Good luck with your studies!

  • Hi all,

       Normally, a DV should advertise its own metric for a prefix, like EIGRP does  (this is why probably in Jeff Doyle book it shows this). However, RIP on Cisco routers increase the metric of the prefix before advertising it out: so if i have a directly connected prefix which i advertise it in RIP, i advertise it with metric of 1.

    @Toxic, the route goes into holddown when the invalid timer expires (not the update timer), and stays in the hold down state aproximately flash-invalid timer(regardless of the value you set on hold down).

    Good luck with your studies!

    lol i meant 6 times update timer by default lol...yanno i should pay more attention when i type responces here!

     

    thankyou for the correction!   >>

     

    what is flash-invalid timer?  is it configurable?  

  • Hi Toxic,

       It is flash timer minus invalid timer, so as you can modify both flash and invalid timer values, the result is "configurable".

    Good luck with your studies!

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