Refer to the exhibit. The partial configuration for an OSPF ASBR and an Area 0 ABR is shown. Assume the OSPF configurations throughout the network are operable.
Which statement about these configurations is true?
Select the best response.
A.
The ASBR route-maps are basically useless, because there are no deny prefix-lists.
B.
LSA Type 5s will not be received by the ABR from the ASBR.
C.
The OSPF backbone will not learn any RFC 1918 addresses.
D.
The matched prefix-list addresses will be given a metric of 255, which is essentially unreachable.
Answer: C
Explanation
The ASBR accepts RFC 1918 addresses and set these networks to “tag 255″ but when advertising into Area 0, the ABR Area 0 filters out these networks because they match “tag 255″ so the OSPF backbone will not learn any RFC 1918 addresses.
Note that if you use an ACL in a route-map deny clause, routes that are permitted by the ACL are not redistributed.
All the networks with “tag 255″ are blocked by the clause 10 while all other networks are permitted by the clause 20 of the route-map (if a match command is not present, all routes match the clause).
Note:
RFC 1918 addresses include:
+ Class A: 10.0.0.0 – 10.255.255.255 (10/8 prefix)
+ Class B: 172.16.0.0 – 172.31.255.255 (172.16/12 prefix)
+ Class C: 192.168.0.0 – 192.168.255.255 (192.168/16 prefix)
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