Redistribution, Route Maps & PBR Practice Questions

Answers and explanations appear when you work through the set above.

1. A router redistributes OSPF routes into EIGRP. The redistribute ospf command is configured, no route-map or distribute-list is filtering anything, yet no redistributed routes appear in the EIGRP topology table. What should be checked first?

   • Whether an EIGRP seed metric was supplied, since EIGRP requires bandwidth, delay, reliability, load, and MTU values on redistributed routes
   • Whether OSPF has a virtual link configured
   • Whether the EIGRP router ID is duplicated
   • Whether BGP synchronization is enabled

2. A route-map has only sequence 10 configured as permit, matching match ip address prefix-list PL-A. A candidate route does not match any prefix in PL-A. When this route map filters redistributed routes, what happens to that route?

   • It is permitted anyway because sequence 10 says permit
   • It falls through to an implicit deny because no other sequence exists to catch it, so it is filtered out
   • It gets evaluated against the routing table as a fallback
   • It is permitted, just without any set actions applied

3. A route-map sequence contains match ip address prefix-list A B on one line and a separate match tag 50 line. What logic must a candidate route satisfy to match this sequence?

   • It must match prefix-list A and prefix-list B and tag 50, all three
   • It must match either prefix-list A or prefix-list B (values on the same match line are ORed), and it must also satisfy the separate match tag 50 line (different match statements are ANDed)
   • It only needs to satisfy any one of the three conditions
   • Only the first listed condition in the sequence is actually evaluated

4. During mutual redistribution planning, why is it generally safer to filter or tag routes at redistribution boundaries rather than relying solely on administrative distance differences between the two protocols?

   • Administrative distance is compared per-hop and does not, by itself, stop a route from re-entering the domain it originated from and looping through the redistribution points
   • Administrative distance always prevents redistribution loops on its own
   • Route tagging is slower to converge than relying on AD
   • AD values cannot be changed on Cisco routers

5. A network engineer redistributes EIGRP routes into OSPF without specifying subnets. Internal EIGRP subnetted routes stop appearing in the OSPF domain even though the redistribute command succeeded. What is the likely cause?

   • The redistribute eigrp <as-number> command under OSPF needs the subnets keyword; without it, only classful networks are redistributed
   • OSPF cannot redistribute EIGRP routes at all
   • The EIGRP AS number must match the OSPF process ID
   • Route summarization is mandatory before redistribution

6. Routes redistributed from EIGRP into OSPF show up in the OSPF database as E2 external routes with the metric set to a flat default value rather than each route's original EIGRP composite metric. Why does this happen by default?

   • OSPF external metrics use a fixed default seed metric (20 for redistribution, apart from BGP which defaults to 1) unless overridden by default-metric or a route-map set metric
   • OSPF automatically recalculates a full SPF-equivalent cost for each redistributed route
   • E2 routes always inherit the EIGRP delay value directly as their OSPF cost
   • OSPF cannot carry any metric information for redistributed routes

7. A route-map used in a redistribute command has two sequences: seq 10 deny matching a specific prefix list, and seq 20 permit with no match statements at all. What is the net effect of seq 20 having no match conditions?

   • Seq 20 denies everything because a match statement is mandatory
   • Seq 20 matches every remaining route unconditionally, since a permit sequence with no match clause matches all traffic that reaches it
   • Seq 20 is skipped entirely and treated as if it did not exist
   • The router rejects the route map as invalid configuration

8. An OSPF-learned external route gets redistributed into BGP. What origin code does that route typically carry in the BGP table, and why?

   • IGP, because OSPF is technically classified as an interior gateway protocol
   • Incomplete, because the route entered BGP through redistribution rather than a network statement or direct EGP peering
   • EGP, because it crossed a protocol boundary
   • Origin code is not applied to redistributed routes

9. A route-map applies set tag 100 to routes redistributed from OSPF into EIGRP at R1. At R3, the reverse redistribution from EIGRP back into OSPF uses a route-map with match tag 100 paired with deny, followed by a permit-all catch-all sequence. What is the intended design here?

   • To increase the metric of tagged routes rather than block them
   • To deny only the routes that originated in OSPF from looping back into OSPF at R3, while still permitting genuinely EIGRP-native routes to redistribute into OSPF
   • To force all tagged routes to become intra-area routes
   • To disable redistribution entirely at R3

10. A route-map sequence includes match tag 50 but the redistributed route being evaluated was never tagged by anything upstream (its tag value is 0/unset). Does this sequence match?

    • Yes, an unset tag always satisfies any match tag statement
    • No, the route fails the match tag 50 condition since its actual tag does not equal 50
    • It depends on whether the route is external type 1 or type 2
    • Tag matching is ignored for routes redistributed from EIGRP

11. An administrator configures policy-based routing on an interface with route-map PBR-POLICY, whose only sequence is a permit with set ip next-hop 10.1.1.1. A packet arrives that does not match the sequence's match conditions. What happens to that packet?

    • It is dropped because PBR sequences that do not match always discard the packet
    • It falls through to normal destination-based routing, since PBR only overrides the next hop for packets that actually match a permit sequence
    • It is forwarded to 10.1.1.1 anyway as a fallback
    • PBR halts processing for every subsequent packet on the interface

12. A route-map sequence used for PBR is configured as deny, matching traffic from a particular source subnet, with no set clause. What is the effect on packets that match that sequence?

    • The packet is policy-routed using the default gateway
    • The packet is exempted from policy routing for this sequence and instead falls through to standard routing-table forwarding
    • The router drops the packet immediately
    • Deny sequences are illegal in a PBR route map and cause a configuration error

13. PBR is applied with ip policy route-map PBR-POLICY on interface GigabitEthernet0/0 to redirect transit traffic that enters that interface. Traffic that originates on the router itself (locally generated, such as a ping sourced from the router) does not follow this policy. What must be configured to also policy-route locally originated traffic?

    • A separate local policy route-map applied with ip local policy route-map
    • A second ip policy route-map statement on a loopback interface
    • PBR automatically covers locally generated traffic once applied to any interface
    • Increase the route-map sequence number for locally sourced packets

14. A PBR route-map sets both set ip next-hop 192.168.1.1 and set interface Null0 in the same sequence for verification testing. If 192.168.1.1 is reachable, which set action takes effect and forwards the matched traffic?

    • Both are applied simultaneously and the packet is duplicated
    • set ip next-hop takes effect when its target is reachable; a verify-availability style Null0 drop is typically used only as a fallback when the primary next hop is down
    • set interface Null0 always wins regardless of reachability
    • Neither applies unless a route-map continue clause is added

15. A route map used in a BGP outbound policy has sequence 10 permit with a continue 20 clause, plus a set community action, followed by sequence 20 permit with a different match condition. What does the continue clause change about how BGP processes this route?

    • It causes the route to be evaluated only against sequence 10 and nothing else
    • After applying sequence 10's set actions, processing continues on to evaluate sequence 20 against the same route instead of stopping, letting both sequences apply their actions cumulatively
    • It skips sequence 10 entirely and jumps straight to 20
    • continue is not a valid route-map keyword

16. R2 redistributes both OSPF and static routes into EIGRP with a single redistribute command line for each source protocol, each pointing at route-map RM-FILTER. RM-FILTER has one sequence: permit matching only a specific prefix list built from OSPF-learned subnets. What happens to the static routes when this route map is applied to the static redistribution too?

    • Static routes are automatically exempted from the route map's match conditions
    • Static routes that do not match the OSPF-only prefix list fall through the same implicit deny and are filtered out
    • Static routes bypass route-map filtering entirely because they use a different administrative distance
    • The redistribute static command silently ignores any attached route-map

17. Two ASBRs, R1 and R4, both redistribute OSPF into EIGRP for redundancy, and mutual redistribution is intentionally allowed to run in both directions at each router without tagging. Which risk is most directly created by that design choice?

    • Increased CPU load from LDP label allocation
    • A suboptimal-routing or looping condition where a route can be readvertised back into its protocol of origin, since neither router has any tag or filter to recognize where a route first came from
    • Loss of BGP community propagation
    • OSPF area 0 partitioning

18. A route-map sequence uses match ip address prefix-list PFX-DENY-ME configured as deny, and the prefix-list itself is written with permit clauses matching the prefixes to exclude. What overall effect does combining a permit-based prefix-list with a route-map deny sequence produce?

    • The prefixes listed in the prefix list end up being denied by the route map, since the route-map sequence action (deny) governs the outcome for anything the prefix list matches (permits)
    • The prefix list's own permit action overrides the route map's deny action
    • Combining permit and deny this way always causes a configuration error
    • Only prefixes NOT listed in the prefix list get denied

19. During redistribution troubleshooting, show ip protocols confirms the redistribute command is present, and the route-map referenced by it shows hit counts of 0 for every sequence via show route-map. What does a zero hit count across all sequences most likely indicate?

    • The route map is working correctly and simply has nothing to filter
    • The route map is likely not actually being invoked by the redistribution, or no candidate routes are reaching it at all, since a working, invoked route map should show nonzero matches on at least one sequence
    • Zero hit counts mean the redistribution metric is misconfigured
    • show route-map counters only update once every 24 hours

20. A redistribute ospf 1 subnets route-map TAG-OSPF command feeds routes into EIGRP, and TAG-OSPF's single sequence is permit with set tag 10, but no match statement at all. Does this route-map sequence still apply the tag to every redistributed route?

    • No, a set-only sequence with no match clause never executes
    • Yes, a permit sequence with no match condition matches everything, so its set tag 10 action applies to all redistributed OSPF routes passing through
    • Only routes with an existing nonzero tag are affected
    • The set action is ignored unless combined with a deny action

21. An engineer wants PBR to route web traffic (destination TCP port 80) out a dedicated low-latency path while leaving all other traffic to normal routing. Which route-map match clause is the correct building block for identifying that traffic?

    • match tag 80
    • match ip address referencing an extended access list that matches TCP destination port 80
    • match community 80
    • match interface referencing the low-latency path's egress interface

22. A mutual redistribution design between EIGRP and OSPF uses distribute-list filtering with prefix lists instead of route tagging to block routes from looping back into their protocol of origin. Compared to tagging, what is a practical drawback of this filtering-by-prefix approach as the network grows?

    • Prefix-list filtering cannot be applied to redistribution at all
    • The prefix lists must be manually maintained and updated whenever the set of routes originating from each protocol changes, whereas a tag automatically travels with the route regardless of which specific prefixes exist
    • distribute-list filtering only works with EIGRP, never OSPF
    • Prefix lists silently ignore VLSM subnets