ICND1 Key Areas to focus on.

1.OSPF:
          ip ospf cost,BW varies for serial gig FE, auto-cost,
          DR/BDR election,priority,router-id,loopback
          passive interface,passive interface default

2.NAT:
         Translation occurs twice a packet going out.
         and coming back in,viz ICMP Ping.
        
3.access-list ,adding a deny statement even with
   implicit deny enables logging.
   DNS acl port is UDP 53,though TCP also used.

4.Switching , Native VLAN, Enabled VLAN's.

5.Most important show commands , whose output
    one must be a Jedi Master of.

   show ip route
   show ip ospf neighbors
   show interface g0/0
   show interface g0/0 switchport
   show vlan brief
   show cdp neighbors detail
   show cdp entry *
   show ipv6 route
   show ipv6 ospf neighbors
   show ip nat statistics
   show ip nat translations
   show ip access-list
   show ip interface
   show access-lists
   show controllers
   show ip arp