Where the election happens, and where it does not
The election belongs to a segment, not to the OSPF area or the routing domain. A router with three Ethernet interfaces takes part in three separate elections and can be DR on one segment and a DROTHER (neither DR nor BDR) on the next. Point-to-point links skip the election entirely, because two routers have nothing to coordinate (RFC 2328, section 9.4).
Priority is an interface setting from 0 to 255, default 1. An interface at priority 0 never stands. The router ID that breaks ties is chosen in a fixed order: a manually configured router-id, else the highest loopback IPv4 address, else the highest IPv4 address on an active interface. Changing it later takes an OSPF process reset.
This is v1.1 topic 3.4.c and v2.0 topic 3.3.c. Adjacency requirements, timers and cost are in the OSPF and first-hop redundancy study area.
How a segment settles its DR and BDR
Set aside the ineligible
Interfaces at priority 0 are excluded. They still form neighbor relationships, but never hold DR or BDR.
Compare priority
Among the candidates, the highest interface priority takes the role.
Break ties on router ID
Equal priorities fall to the highest router ID, compared as a dotted 32-bit number.
Keep the result
Once elected, a DR and BDR keep their roles until they go away. A new router, or a priority raised afterwards, changes nothing by itself.
The election as a neighbor table shows it
R3 (router ID 3.3.3.3, priority 1) on a four-router Ethernet segment.
R3# show ip ospf neighborNeighbor ID Pri State Dead Time Address Interface4.4.4.4 1 2WAY/DROTHER 00:00:33 10.40.0.4 GigabitEthernet0/02.2.2.2 50 FULL/BDR 00:00:35 10.40.0.2 GigabitEthernet0/01.1.1.1 50 FULL/DR 00:00:38 10.40.0.1 GigabitEthernet0/0R1 and R2 share priority 50, and R2 has the higher router ID, yet R1 is DR. R1 came up first and won an election with no rival; R2 joined later and could only take BDR. R3 and R4 stop at 2WAY with each other and go FULL only with the DR and BDR.
Which OSPF network types elect
| Network type | Elects a DR and BDR | Where you meet it |
|---|---|---|
| Broadcast | Yes | Default on Ethernet interfaces |
| Non-broadcast multi-access (NBMA) | Yes | Multi-access clouds without broadcast; neighbors are configured |
| Point-to-point | No | Two routers only; on Ethernet, set with ip ospf network point-to-point |
| Point-to-multipoint | No | Treated as a set of point-to-point links |
Frames on OSPF DR/BDR election
Track three things through each scenario: which interfaces are eligible, who was already elected, and whether the segment is broadcast at all.
Practice frames written by our editors for study, not Cisco items. The 200-301 exam itself mixes multiple choice, drag-and-drop and lab-style items.
Frame 001 of 008 · 0 answered · 0 ok
Keys
1–5 or A–E pick an option (on choose-N frames they toggle; then Check answer) · ← → previous / next frame · ↑ ↓ move in the frame list
- Frame 001 of 008
In a network running OSPF, what occurs when the Backup Designated Router (BDR) fails?
Pick an option. The verdict shows here; open the note under any option to see why.
Note on A
The network type does not change when a router fails; a broadcast segment stays broadcast and keeps a DR and BDR.
Note on B
Routers do not flush their tables; only routes through the failed router are recalculated.
Note on C
The DR keeps its role, because OSPF never demotes a working DR to fill an empty BDR slot.
Note on D
Correct: the DR stays in place, and the remaining routers hold an election (priority, then router ID) to choose a new BDR.
Best answer: D · why
On a broadcast segment, the DR and BDR both form full adjacencies with every other router. If the BDR fails, the DR keeps working and the DROTHER routers elect a new BDR: highest interface priority wins, then highest router ID. If the DR fails instead, the BDR is promoted to DR and a new BDR is elected. The network type never changes.
- Frame 002 of 008
What OSPF packet type is used to elect the Designated Router (DR) and Backup Designated Router (BDR)?
Pick an option. The verdict shows here; open the note under any option to see why.
Note on A
An LSR asks a neighbor for specific LSAs during database exchange, after the DR and BDR are already known.
Note on B
Correct: Hello packets carry each router’s priority and its view of the DR and BDR, and the election is based on them.
Note on C
DBD packets summarize the link-state database while neighbors synchronize, after the election.
Note on D
LSUs carry the full LSAs that update the database; they play no part in choosing the DR.
Best answer: B · why
OSPF has five packet types: Hello (1), Database Description (2), Link State Request (3), Link State Update (4) and Link State Acknowledgment (5). Hellos discover and keep neighbors and carry the router ID, area, timers, priority, DR and BDR fields, so the DR/BDR election runs on the information in Hellos. DBD, LSR and LSU packets come later, to synchronize the database.
- Frame 003 of 008
What happens to an OSPF network when the DR fails but the BDR is still operational?
Pick an option. The verdict shows here; open the note under any option to see why.
Note on A
Neighbors do not drop to 2-WAY to wait for an administrator; the election is automatic and needs no manual configuration.
Note on B
The network type stays broadcast; a failed router never turns a multi-access segment into point-to-point.
Note on C
OSPF does not run without a DR on a broadcast segment; the BDR exists precisely to take over at once.
Note on D
Correct: the BDR is promoted to DR right away, and the remaining routers elect a new BDR.
Best answer: D · why
The BDR keeps full adjacencies with every router on the segment, so it can take over immediately when the DR fails. The other routers then elect a new BDR by priority and router ID. Because OSPF elections are non-preemptive, the old DR does not take its role back when it returns; it becomes a DROTHER unless another failure promotes it.
- Frame 004 of 008
What command would you use to set the OSPF interface priority to 100 on interface GigabitEthernet0/0?
Pick an option. The verdict shows here; open the note under any option to see why.
Note on A
IOS has no ospf priority interface command; the keyword needs the ip prefix, as in ip ospf priority.
Note on B
Correct: OSPF priority is set per interface, so you enter the interface and use ip ospf priority 100.
Note on C
Router ospf mode has no command that sets a priority for one interface, because priority lives on the interface.
Note on D
Global configuration has no ip ospf interface command; show ip ospf interface exists only as a show command.
Best answer: B · why
OSPF interface priority (0 to 255, default 1) is an interface setting: interface GigabitEthernet0/0, then ip ospf priority 100. A higher value makes the router more likely to win the DR election on that segment, and 0 removes it from the election. Because the election is non-preemptive, the change only takes effect at the next election, for example after clear ip ospf process.
- Frame 005 of 008
What is the role of the Designated Router (DR) in an OSPF broadcast network?
Pick an option. The verdict shows here; open the note under any option to see why.
Note on A
OSPF routers do not exchange routing tables; the DR relays LSAs, and each router runs SPF to build its own table.
Note on B
Load balancing over equal-cost paths is a routing-table function and has nothing to do with the DR role.
Note on C
Correct: every router forms a full adjacency only with the DR and BDR, which cuts the number of adjacencies and LSA flooding on the segment.
Note on D
Filtering LSAs between areas is done at area border routers, not by the DR of a segment.
Best answer: C · why
On a broadcast segment with n routers, a full mesh of adjacencies would need n(n-1)/2 of them. With a DR, each router sends its updates to the DR and BDR (224.0.0.6), and the DR floods them to all OSPF routers (224.0.0.5). That reduces both adjacencies and flooding traffic. The DR also originates the network LSA (type 2) for the segment.
- Frame 006 of 008
Which command would you use to verify the current DR and BDR for an OSPF-enabled interface?
Pick an option. The verdict shows here; open the note under any option to see why.
Note on A
This lists neighbors with states such as FULL/DR, so it shows the roles of neighbors rather than a summary for your own interface.
Note on B
Correct: show ip ospf interface prints the DR and BDR router IDs and addresses for each OSPF interface, plus its own state and priority.
Note on C
This lists routes to ABRs and ASBRs and says nothing about the DR or BDR of a segment.
Note on D
The database shows LSAs, so DR details are buried in type 2 LSAs instead of being stated per interface.
Best answer: B · why
show ip ospf interface [type number] shows, per interface: area, network type, cost, the router’s own state (DR, BDR or DROTHER), its priority, the router IDs and addresses of the DR and BDR, timers and neighbor count. show ip ospf neighbor gives a partial view through each neighbor’s state, such as FULL/DR, but the interface command answers the question directly.
- Frame 007 of 008
What criterion is used to elect the OSPF Designated Router (DR) on a broadcast network?
Pick an option. The verdict shows here; open the note under any option to see why.
Note on A
Interface cost drives path selection, not which router becomes DR on a segment.
Note on B
The first router up often ends up DR because elections are non-preemptive, but the rule itself compares priority and router ID.
Note on C
OSPF knows nothing about a router’s CPU or memory; only priority and router ID enter the election.
Note on D
Correct: the highest interface priority wins (default 1, and 0 means never), and the highest router ID breaks a tie.
Best answer: D · why
On a broadcast or NBMA segment, OSPF elects a DR and BDR from Hello packets: highest interface priority first (0 to 255, default 1, 0 means never), then highest router ID. The election is non-preemptive, so a router that joins later with a better priority does not take over; in practice the first routers up often keep the roles until a reset or failure.
- Frame 008 of 008
What configuration command would prevent a router from becoming the Designated Router (DR) in an OSPF network?
Pick an option. The verdict shows here; open the note under any option to see why.
Note on A
There is no ip ospf dr-disable command; DR eligibility is controlled only through the priority value.
Note on B
IOS has no ip ospf role command; DROTHER is a resulting state, not something you configure.
Note on C
Correct: priority 0 makes the interface ineligible for both DR and BDR on that segment.
Note on D
ospf dr-ineligible is not an IOS command; the way to opt out is ip ospf priority 0.
Best answer: C · why
OSPF priority ranges from 0 to 255 and defaults to 1. A value of 0 removes the interface from the DR and BDR election, so the router stays a DROTHER on that segment. It is set in interface configuration mode with ip ospf priority 0, which is typical for spoke routers in hub-and-spoke designs or for devices with limited resources.
DR and BDR, briefly
Is the DR the router with the best path to anywhere?
No. The election uses priority and router ID only; interface cost and route quality play no part.
Why do two DROTHERs stay in 2WAY?
On a broadcast segment each router forms full adjacencies only with the DR and BDR. Two DROTHERs see each other’s hellos and stop at 2WAY, which is the normal, healthy state between them (RFC 2328, section 10.4).
Does a link between two routers on Ethernet need an election?
Only if it is left as the broadcast network type. Setting both ends to point-to-point removes the election and the wait that comes with it.
References
- [1]RFC 2328: OSPF Version 2
- [2]Cisco technote 13689: OSPF interface and DR/BDR statesChecked October 29, 2026.
- [3]Cisco Learning Network: CCNA v1.1 exam topicsChecked October 29, 2026.
- [4]Cisco Learning Network: CCNA v2.0 exam topicsChecked October 29, 2026.