Router Forwarding Decision

Unanswered Question
Jan 18th, 2009

Hi Everybody,

I am little confused in a basic routing concept. I have a router with routing table as below (mention as example)

D 192.168.32.0/24 [90/12345] via 10.1.1.1

R 192.168.32.0/26 [120/4] via 10.1.1.2

O 192.168.32.0/19 [110/3] via 10.1.1.3

If the packet comes with destination address of 192.168.32.1,

How the router decides which path to take.

I want to know how the router decides the forwarding decision. In which order Administrative Distance, Prefix , Metrics are verified for forwarding decision.

Can any body gives me a clear picture. If available document also please

R.B.Kumar

I have this problem too.
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Paolo Bevilacqua Sun, 01/18/2009 - 08:28

Hi,

AD, metrics, etc only decides what it is installed in routing table. One in routing table, "longest matching route" is used.

You can read a book like http://books.google.it/books?id=9LBQAB2L6QgC&pg=PA198&lpg=PA198&dq=ios+routing+primer&source=bl&ots=jLZkwmXMNs&sig=YbdC_hAoJLLUHsolV10-w3zmvIo&hl=it&sa=X&oi=book_result&resnum=3&ct=result#PPP1,M1

or there are many documents, use a search engine to find.

hclisschennai Sun, 01/18/2009 - 08:39

Hi,

Thanks for your prompt response. In fact i have tried various literatures in Cisco. None gave me this clear information

Thanks for your input. I helped me to great extend.

Paolo Bevilacqua Sun, 01/18/2009 - 09:57

You are welcome. In fact, I should have written:

Once in routing table, "longest matching route" is used. If more than one is found, then, load balancing happens according the method configured.

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