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Routing Control Practice Questions

15 original questions covering ENARSI 1.1 to 1.5. Most give you an exhibit and ask for the fault or the fix, as the exam does. Answer every one before opening any explanation. Target: 12 of 15 (80%).

1. Blueprint 1.1

Refer to the exhibit. The engineer wants R1 to prefer RIP over OSPF for the prefixes that R5 advertises into OSPF, but nothing changed after the configuration was applied. R5's OSPF interface toward R1 is 10.1.15.5 and its router ID is 10.255.255.5.

router ospf 1
 distance 125 10.1.15.5 0.0.0.0 R5-NETS
!
ip access-list standard R5-NETS
 permit 10.50.0.0 0.0.255.255

R1# show ip route 10.50.1.0
Routing entry for 10.50.1.0/24
  Known via "ospf 1", distance 110, metric 2, type intra area
  Last update from 10.1.15.5 on GigabitEthernet0/2, 00:22:41 ago
  Routing Descriptor Blocks:
  * 10.1.15.5, from 10.255.255.5, 00:22:41 ago, via GigabitEthernet0/2

What is the fix?

  • A. Change the ACL to an extended ACL
  • B. Use distance ospf intra-area 125 instead
  • C. Clear the OSPF process; distance changes need a reset
  • D. Change the source address in the distance command to 10.255.255.5
Answer: D

For OSPF, the address in the source-based distance command is matched against the router ID of the router that originated the route, which show ip route prints after "from". 10.1.15.5 is R5's interface address, so nothing matches. B would also raise the AD but for every intra-area route from every router, which is broader than required. No reset is needed (C), and a standard ACL is the correct type (A).

2. Blueprint 1.1

Two sites are connected by a private 10 Gbps link running EIGRP and also by eBGP through an Internet provider. Site B's LAN 172.16.50.0/24 is reached through the provider from site A. Which change on site A's router fixes this with the smallest impact?

  • A. distance eigrp 15 170 under EIGRP
  • B. network 172.16.50.0 mask 255.255.255.0 backdoor under BGP
  • C. distance bgp 200 200 200 under BGP
  • D. Remove the eBGP session
Answer: B

The eBGP route (AD 20) beats EIGRP internal (AD 90). The backdoor keyword gives the eBGP-learned copy of that one prefix AD 200 so EIGRP wins, without changing anything else and without originating the prefix into BGP. A would work, but it changes the EIGRP internal AD for every prefix on the router, which is far broader than needed. C changes every eBGP route. D removes redundancy.

3. Blueprint 1.1

Refer to the exhibit. 192.168.70.0/24 is redistributed into EIGRP by another router and normally reached through EIGRP. The static route was added as a backup. What does R2 use while EIGRP is healthy?

ip route 192.168.70.0 255.255.255.0 10.2.9.9 150

R2# show ip eigrp topology 192.168.70.0/24 | include route is
      Composite metric is (130816/128256), route is External
  • A. The EIGRP route, because EIGRP was configured first
  • B. The static route, because its AD of 150 is lower than the EIGRP external AD of 170
  • C. Both, with equal-cost load sharing
  • D. The EIGRP route, because a floating static route only installs when its next hop is unreachable
Answer: B

The prefix is an EIGRP external, which has AD 170, not 90. A "floating" static at 150 floats above internal EIGRP but beats external EIGRP, so it is used all the time. The backup AD must be higher than 170 for this prefix. Routes from different sources never load-share (C).

4. Blueprint 1.2

Refer to the exhibit. The intent is to redistribute every OSPF route into EIGRP except 10.30.0.0/16 and its subnets. R4, an EIGRP neighbor, still receives 10.30.5.0/24. Why?

ip prefix-list NO-30 seq 5 deny 10.30.0.0/16 le 32
ip prefix-list NO-30 seq 10 permit 0.0.0.0/0 le 32
!
route-map O2E permit 10
 match ip address prefix-list NO-30
 set tag 110
route-map O2E permit 20
!
router eigrp 100
 redistribute ospf 1 metric 100000 10 255 1 1500 route-map O2E
  • A. Prefix lists cannot use le 32
  • B. 10.30.5.0/24 fails sequence 10 because the prefix list denies it, then matches the catch-all sequence 20 and is redistributed without a tag
  • C. EIGRP needs distribute-list to filter redistributed routes
  • D. The tag overrides the prefix list
Answer: B

A deny in a prefix list used by a route map only means "does not match this sequence". The route falls through to sequence 20, which has no match line and permits everything. Either delete sequence 20, or invert the logic: a prefix list that permits 10.30.0.0/16 le 32, matched in a route map deny sequence, followed by a permit sequence.

5. Blueprint 1.2

Which two prefixes are matched by ip prefix-list P permit 10.64.0.0/10 le 16? (Choose two.)

  • A. 10.64.0.0/10
  • B. 10.100.0.0/16
  • C. 10.128.0.0/16
  • D. 10.70.1.0/24
  • E. 10.0.0.0/8
Answer: A, B

The first 10 bits must equal those of 10.64.0.0 (second octet 64 to 127), and the length must be from 10 to 16. 10.64.0.0/10 and 10.100.0.0/16 qualify. C has second octet 128, outside the /10. D is inside the range but has length 24. E has length 8, below the minimum of 10.

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