confusion over route selected from routing table

[Garegin88]

Packets received by the router from BGP enter via a serial interface at 209.165.201.10. Each route is present within the routing table. Which interface is used to forward traffic with a destination IP of 10.10 10 24?

People are saying that the answer is F0/11. I don't understand why since F0/13 has the lowest AD. 

[Giuseppe Larosa]

Hello @Garegin88 ,

the scenario is not real world but it is used to make you understand how the routing table choices the best path.

However, in square brackets [AD  Metric]  so the right answer is out of Fas0/11 because of the lowest AD and the lowest metric between the routes with the same AD 90.

out FAS0/13 you have an OSPF route with AD=110 and metric = 20 but route out Fas0/11 has AD=90 and metric= 144 and it is selected for its lower AD.

Edit:

in any case the most specific route is selected first and usually this is part of the selection.  Then AD, then metric

Hope to help

Giuseppe

[Garegin88]

hold on. I thought in #/#, the first number is the default AD and the second one is the one specified by admin. So in this case the admin left all default ADs?  

[Giuseppe Larosa]

Hello @Garegin88 ,

in the []   we have AD / metric there is no concept of an AD defined by user. This has been this way all the time long.

if you change the AD of EIGRP it will be reflected on the left number before the /

Hope to help

Giuseppe

[MHM Cisco World]

Same prefix for multi IGP/BGP?

This not real network?

MHM

[Garegin88]

No, it’s a practice question

[MHM Cisco World]

Ok' then the 

Router use belwo rules to inject prefix into RIB

1- prefix the lowest AD

If tie 

2- prefer lowest metric 

If tie

3- multipath is config

If Yes add all prefix 

If No here the router can select old one.

MHM