What Does DRother Mean?
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Quick Definition
An OSPF router that is neither the Designated Router (DR) nor the Backup DR (BDR) on a multi-access network segment.
Commonly Confused With
The DR is the router that has the central role on a multi-access network segment. It collects LSAs from all DROTHERs and floods them to the entire segment. In contrast, a DROTHER is a regular router that only sends its updates to the DR and BDR, and does not flood directly to other routers. The DR has a higher OSPF priority or Router ID than DROTHERs.
If R1 has priority 100 and becomes DR, and R2 has priority 1 and becomes DROTHER, then R2 sends its routes to R1, not to R3 (another DROTHER). R1 then sends the update to everyone.
The BDR is the standby for the DR. It forms a full adjacency with all routers on the segment, including all DROTHERs, and shadows the DR's database. A DROTHER does not have this standby role. The BDR takes over as DR if the DR fails, while a DROTHER does not become DR automatically unless it wins a new election. The BDR is elected along with the DR using the same priority/RID rules.
If the DR fails, the BDR immediately becomes the new DR to minimize disruption. A DROTHER would only become BDR if a new election is held and it has the second-highest priority or Router ID.
The 2-Way state is an OSPF neighbor state that indicates two routers have exchanged Hello packets and see each other, but have not formed a full adjacency. Between two DROTHERs, this is the final state. However, a DROTHER itself is a role (a router that is not DR or BDR), not a state. A router can be a DROTHER and have neighbors in various states, including 2-Way (with other DROTHERs) and Full (with the DR and BDR). Confusing the term "DROTHER" with the state "2-Way" is a common error.
R4 is a DROTHER. Its neighbor R5 (also a DROTHER) shows state 2-Way. Its neighbor R1 (the DR) shows state Full. R4's role is DROTHER, but its neighbor states vary.
Must Know for Exams
CCNA and CCNP exams regularly test DR/BDR election and DRother behaviour. Common exam questions: What state are DROthers in with each other? (2WAY). What multicast does DRother use? (224.0.0.6). How do you force a new DR election? (clear ip ospf process). A router with priority 0 can never become DR or BDR — it will always be DRother.
Simple Meaning
Think of a multi-access OSPF network like a committee. The DR is the chairperson, the BDR is the vice-chair, and DROthers are all the other members — they only communicate through the chair, not directly with each other.
Full Technical Definition
A DRother is an OSPF router on a multi-access (broadcast or NBMA) network that did not win the DR or BDR election. DROthers form FULL adjacencies only with the DR and BDR, maintaining a 2WAY state with other DROthers. They send routing updates to AllDRouters multicast 224.
0.0.6 (which only DR and BDR process) and receive updates via AllSPFRouters multicast 224.0.0.5.
Real-Life Example
In a Cisco data centre with 8 OSPF routers on a core VLAN, two routers are elected DR and BDR. The remaining 6 routers become DROthers. When a topology change occurs, DROthers send the LSA to 224.
0.0.6 (DR/BDR only). The DR reflods it to 224.0.0.5 so all 8 routers update their LSDB. This means only 2 adjacency relationships per DRother instead of 7.
Why This Term Matters
Understanding DROthers explains why show ip ospf neighbor shows 2WAY state between DROthers — this is correct behaviour, not an error. It also explains why changing OSPF priority requires clear ip ospf process to take effect.
How It Appears in Exam Questions
In CCNA and other OSPF-related exams, DROTHER questions typically fall into four patterns: state identification, multicast addressing, election outcomes, and troubleshooting.
The first pattern is state identification. A multiple-choice question shows the output of "show ip ospf neighbor" on a router. One neighbor shows state "2-WAY/DROTHER," another shows "FULL/DR," and another shows "FULL/BDR." The question asks: "What can be concluded about the router with the 2-WAY/DROTHER state?" The correct answer is that this router is a DROTHER and has formed a full adjacency only with the DR and BDR, not with other DROTHERs. Distractors might claim that the router has a problem or that the link is down.
The second pattern is multicast addressing. A question asks: "Which IP multicast address is used by OSPF DROTHER routers to send Link State Updates to the Designated Router?" The answer is 224.0.0.6. Another common variation asks: "Which multicast address does the DR use to flood LSAs to all routers on the segment?" That answer is 224.0.0.5. These questions are straightforward but require memorization of the assigned multicast addresses.
The third pattern is election outcome questions. A typical question presents a table of four routers with their interface priorities and Router IDs, then asks: "Which router will be elected as the DR?" The candidate must apply the election rules: highest priority wins, and if there is a tie, highest Router ID wins. A router with priority 0 is ineligible and becomes a DROTHER automatically. Some questions include a twist where a router has just joined the network and does not immediately become DR because the election is non-preemptive. The question might ask: "Router C has a priority of 100 and Router ID 3.3.3.3. It joins an OSPF segment that already has a DR with priority 50. What is the role of Router C?" The answer is DROTHER, because OSPF does not preempt the existing DR.
The fourth pattern is troubleshooting output. A question provides the output of "show ip ospf interface" and shows that the DR is 1.1.1.1 and the BDR is 2.2.2.2, but the local router has a priority of 255. The candidate is asked: "Why is this router not the DR?" The answer is either because the router just joined and the election is non-preemptive, or because the current DR has a higher Router ID (assuming equal priorities). Another troubleshooting scenario shows a router that is a DROTHER but has no Full adjacency with either DR or BDR. The candidate must identify that this indicates a problem, as DROTHERs must have Full adjacency with both DR and BDR.
Practise DRother Questions
Test your understanding with exam-style practice questions.
Example Scenario
A company has a network with four routers connected to a single Ethernet switch: R1, R2, R3, and R4. They are all running OSPF on the same subnet. The network administrator wants to ensure efficient OSPF operation.
Before any configuration, OSPF must elect a Designated Router and a Backup Designated Router. R1 has the highest OSPF interface priority, set to 100. R2 has a priority of 50. R3 and R4 both have the default priority of 1. Because the election looks at the highest priority first, R1 becomes the DR. R2, with the second-highest priority, becomes the BDR. R3 and R4 are the DROTHERs.
Now, OSPF neighbor relationships form. R3 and R4 each become fully adjacent (Full state) with the DR (R1) and the BDR (R2). However, between R3 and R4, the neighbor state is only 2-Way. They do not exchange LSAs directly; they just acknowledge each other's existence via Hello packets. This is normal and expected.
If R3 has a new route to advertise, it sends a Link State Update to the DR and BDR using the multicast address 224.0.0.6. The DR (R1) receives the update, records it, and then floods it to all routers on the segment, including R2, R3, and R4, using the multicast address 224.0.0.5. R4 learns about the new route from the DR, not from R3 directly. This keeps the network efficient.
If the DR (R1) fails, the BDR (R2) detects the loss because it stops receiving Hello packets from R1. After the DeadInterval, R2 takes over as the new DR. A new election is held among the remaining routers (R2, R3, R4) to select a new BDR. R2, now the DR, has priority 50, and R3 with priority 1 and R4 with priority 1 will compete. Since R3 and R4 have the same priority, the tiebreaker is the highest Router ID. Suppose R3 has a Router ID of 3.3.3.3 and R4 has 4.4.4.4. Then R4 becomes the new BDR. R3 remains a DROTHER. The network continues to function smoothly.
Common Mistakes
Thinking that DROTHER routers form full adjacencies with each other.
In OSPF, DROTHER routers only establish full OSPF adjacencies with the Designated Router (DR) and Backup Designated Router (BDR). Two DROTHERs remain in the 2-Way state and do not exchange LSAs directly. Expecting them to have Full adjacency is incorrect and indicates misunderstanding of the DR/BDR mechanism.
Remember that on a broadcast multi-access network, DROTHERs do not need to talk to each other directly. They only need to be fully adjacent to the DR and BDR. The neighbor state between two DROTHERs will always be 2-Way, not Full.
Assuming OSPF will automatically re-elect a new DR if a higher-priority router joins the network.
The OSPF DR/BDR election is non-preemptive. Once a DR and BDR are elected, they remain in their roles until they fail or the OSPF process on the interface is reset. A higher-priority router joining later will only become a DROTHER, not replace the existing DR. This is a common cause of confusion in real networks.
Understand that OSPF elects a DR and BDR when the network first comes up. If you want a newer, higher-priority router to become the DR, you must manually clear the OSPF process on the current DR interface or reload the router.
Confusing the multicast addresses used by DROTHERs vs. the DR.
DROTHERs send LSAs to the DR and BDR using 224.0.0.6 (AllDRouters). The DR sends LSAs to all routers (including DROTHERs) using 224.0.0.5 (AllSPFRouters). Mixing up these addresses leads to incorrect answers on exam questions about OSPF multicast behavior.
Use a simple memory trick: DROTHERs send to the DR (224.0.0.6 = All DRouters). The DR sends to everyone (224.0.0.5 = All SPF routers). Practice identifying which router uses which address in a given scenario.
Believing that a router with priority 0 can become a DROTHER in the same way as other routers.
A router with OSPF interface priority set to 0 is ineligible to become DR or BDR. However, it still functions as a DROTHER in the sense that it does not have a special role. The term DROTHER applies to any router that is not DR or BDR, including those with priority 0. The mistake is thinking priority 0 acts differently in terms of adjacency requirements-it still must form Full adjacencies with the DR and BDR.
Remember that priority 0 simply means the router will never be elected DR or BDR. It is still a DROTHER and behaves exactly like any other DROTHER in terms of adjacency rules. It will have 2-Way state with other DROTHERs and Full state with DR and BDR.
Exam Trap — Don't Get Fooled
{"trap":"On an OSPF broadcast network, a router shows a neighbor state of \"FULL/DROTHER\" in the output of \"show ip ospf neighbor.\"","why_learners_choose_it":"Learners assume that if the state is FULL, the neighbor must be a DR or BDR. They do not expect a DROTHER to have a Full adjacency with another router.
They might think the output is a typo or an error.","how_to_avoid_it":"Remember that the FULL state indicates a full OSPF adjacency, which is correctly formed between a DROTHER and the DR or BDR. A router can be a DROTHER (its own role) and still show FULL/DROTHER for a neighbor if that neighbor is the DR or BDR.
The key is to look at the neighbor's role column in the output. If the neighbor's role is DR or BDR, then it is normal to see FULL for that neighbor. The trap is focusing on the FULL state while ignoring the neighbor's role."
Practical Mini-Lesson
To work effectively with OSPF DROTHER routers in a production network, you need to understand both configuration and verification. First, decide which routers should be DR, BDR, and DROTHER. Typically, you want the most stable and powerful routers to be DR and BDR. For example, a core distribution switch should be DR, while access layer routers should be DROTHERs.
To influence the election, set the interface priority using the command 'ip ospf priority [0-255]' under the interface configuration. A higher number makes the router more likely to become DR or BDR. Setting priority to 0 ensures the router will never become DR or BDR and will always be a DROTHER. This is useful for routers that are not reliable enough to handle the DR workload. Keep in mind that the election only happens when the OSPF process starts or when the current DR or BDR goes down. If you change priorities on a running network, you must reset the OSPF process or reload interfaces to trigger a new election.
After configuration, verify the roles using 'show ip ospf neighbor'. Look at the state column: FULL/DR means the neighbor is the DR, FULL/BDR means BDR, and 2WAY/DROTHER means a DROTHER neighbor. Also use 'show ip ospf interface [interface]' to see the DR, BDR, and the router's own role. This command shows the priority, DR, BDR, and the neighbor count.
What can go wrong? If a router with high priority is added later, it remains a DROTHER until the current DR fails. This can lead to suboptimal DR placement if the current DR is a low-end router. Also, if you accidentally set priority to 0 on a router that should be DR, it will never become DR. Another issue is that if the DR goes down and the BDR becomes DR, the network is without a BDR until a new election completes. During that time, if the new DR also fails, the segment loses OSPF operation until another election.
In practice, monitor the DR and BDR. If the DR is a router that reboots often, consider changing priorities to make a more stable router the DR. Remember that DROTHERs are not passive; they still send Hellos and updates. They just do not form full adjacencies with each other. Understanding this distinction is key to diagnosing neighbor state issues correctly.
Memory Tip
DROther = 'DR Other' — it is the 'other' category of OSPF routers that are neither DR nor BDR. Like passengers on a bus — the driver (DR) and co-driver (BDR) run things; everyone else is 'other'.
Covered in These Exams
Current Exam Context
Current exam versions that test this topic — use these objectives when studying.
200-301Cisco CCNA →N10-009CompTIA Network+ →Related Glossary Terms
An Area Border Router is an OSPF router that connects multiple OSPF areas, including the backbone area, and exchanges routing information between them.
Area 0 is the backbone area in OSPF routing that connects all other OSPF areas to ensure a loop-free and efficient network routing topology.
The backbone area (area 0) is the central routing area in an OSPF network that all other areas must connect to for inter-area communication.
A Backup Designated Router (BDR) is a router in an OSPF network that waits to take over as the Designated Router if the current one fails, reducing network downtime.
Broadcast OSPF is a mode of OSPF operation used on multi-access broadcast networks (like Ethernet) where routers automatically discover neighbors and elect a Designated Router to reduce routing update traffic.
The Dead timer is the period an OSPF router waits to hear from a neighbor before declaring that neighbor as unreachable and removing it from the routing table.
Summary
DROTHER is a core concept in OSPF that describes any router on a multiaccess network that is not elected as the Designated Router (DR) or Backup Designated Router (BDR). Understanding DROTHER is essential for correctly interpreting OSPF neighbor states, DR/BDR elections, and multicast addressing. The key takeaway is that DROTHER routers form full adjacencies only with the DR and BDR, not with each other, resulting in the normal 2WAY neighbor state between DROTHERs.
In real-world networks, the DR/BDR election and DROTHER roles directly impact network stability and efficiency. Network engineers must carefully set interface priorities to ensure optimal DR/BDR placement. Misunderstanding DROTHER can lead to unnecessary troubleshooting and configuration errors.
For the CCNA exam, DROTHER appears in multiple question types, including neighbor state analysis, election scenarios, and multicast address identification. Mastering this concept helps you avoid exam traps and confidently answer questions about OSPF multiaccess network behavior. Remember the memory tip: DROTHER = Does Not Become DR Or BDR. They stay at 2WAY with each other.