Learning by Doing: CISCO Certified Network ... - SCN Research

(VLSM/CIDR). OSPF on a wider scale is better left to upper-level courses. You are
only getting a brief overview here.
Quick overview: Wildcard Masks
A while back you learned about subnet masks. We use wildcard masks to instruct our
devices to “only pay attention” to certain information. The easiest way I know to explain
how to set up a wildcard mask is: a wildcard mask is usually the exact opposite of a
subnet mask (in terms of binary one’s and zero’s). One last note: a wildcard mask, unlike
a subnet mask, does not have to contain contiguous one’s…more on this later). Let’s
look at an example:
If we had a network 172.16.1.0/24 and wanted to use a routing protocol:
• With RIP, IGRP, EIGRP, BGP (with subnet mask):
o network 172.16.1.0 255.255.255.0
o let’s see that subnet mask in binary:
• 11111111.11111111. 11111111.00000000
• With OSPF (with wildcard mask):
o network 172.16.1.0 0.0.0.255
o let’s see that wildcard mask in binary:
• 00000000.00000000. 00000000.11111111
Step-By-Step Instructions:
1. Set up and cable the lab as shown. Do not use any routing protocol. Notice
how our addresses extend beyond our address class boundary. OSPF will pass
subnet information.
2. Now let’s add in our OSPF routing protocol. We use the number 0 because
OSPF requires at least one “area” be numbered 0. Yes…the number “1” is an
autonomous system number too.
wash(config)#router ospf 1
wash(config-router)#network 172.16.1.0 0.0.0.255 area 0
wash(config-router)#network 172.16.2.0 0.0.0.255 area 0
leung(config)#router ospf 1
leung(config-router)#network 172.16.2.0 0.0.0.255 area 0
leung(config-router)#network 172.16.3.0 0.0.0.255 area 0
3. We can use some show commands too:
wash#sh ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
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