Refer to the exhibit. The partial configuration foran 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?
ASBR
router ospf 123
redistribute eigrp 1 route-map eigrp-to-ospf
!
route-map eigrp-to-ospf permit 10
match ip address prefix-list private
set tag 255
route-map eigrp-to-ospf permit 20
!
ip prefix-list private permit 10.0.0.0/8 ge 8 le 30
ip prefix-list private permit 172.16.0.0/11 ge 11 le 30
ip prefix-list private permit 192.168.0.0/16 ge 16 le 30
Area 0 ABR
router ospf 123
distribute-list route-map private-filter in
!
route-map private-filter deny 10
match tag 255
route-map private-filter permit 20

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.

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 outthese 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)