As a CCNA / CCNP candidate you might be anticipated to know the purpose and performance of the OSPF protocol. The CCNA / CCNP's examination will ask of you to determine the aim of the DR and BDR together with the election procedure.

OSPF Designated Router and Backup Designated Router elections

OSPF routing algorithm is CPU intensive. Each and every time the OSPF process runs the shortest path first algorithm it's going to have an impact on the router. In a point to point network OSPF events are restricted to the periodic Hiya packet (Default 10secs on a PPP, HDLC, 30sec Frame Relay NBMA), 30 minutes for each route entry within the Link state database and triggered events.

In a Multi-access broadcast network where routers are related to a typical broadcast phase i.e many routers in a single vlan) all routers would wish to create an adjacency with all different routers in the same broadcast domain. Additionally event which causes an LSA to be generated would require the promoting router to create one LSA to be multicasted to all neighbors. The more routers there are in the broadcast multicast community the extra adjacencies could be required. Two routers require the next number of adjacencies: 2(2-1) / 2 = 1

4 routers require the next variety of adjacencies: 4(4-1)/2=6

Ten routers require the next number of adjacencies: 10(10-1)/2=45

Note: DR's and BDR's should not elected on level-to-level links as a result of there might be only one adjacency and the purpose of electing the DR and BDR is for efficiency. The extra routers you have on a segment will improve the number of adjacencies consume extra bandwidth and use more processing power on the routers. We have to scale back the amount of labor which every router has to do on the next by electing one router as a Designated Router which all other routers with kind adjacencies with. Whenever you use a Designated Router in your Multiaccess broadcast community the variety of adjacencies is reduced along with the discount in processing and bandwidth. All routers will kind full adjacencies with the Designated router, while you run the command on a cisco router which is not the DR: R1show ip ospf neighbor

Neighbor ID Pri State Lifeless Time Address Interface

192.168.1.3 1 FULL/DR 00:00:39 192.168.1.3 Ethernet0/0

You will see that your router has formed a "FULL" neighbour adjacency with the DR and the output also defines which neighbor is the DR. The router ID of the neighbour within the output above is 192.168.1.three and that this neighbour is the DR

Any events which occur are marketed to the DR utilizing the Multicast tackle of 224.0.0.6

When the DR advertises any occasions to the Non-DR units it's completed using the sort out of 224.0.0.5

Designated and Backup Designated Router Election:

The DR is elected primarily based on the router with the best router priority. The default router priority is 1, the vary is 0 to 255. Setting the router precedence to 0 means the interface cannot participate in any DR or BDR election. In the event you seta current DR's r current BDR's router precedence to 0 it would relinquish the position immediately. Routers which aren't elected either as DR or BDR still kind neighbor adjacencies, although they will not change any routing information between each other, only hellos are exchanged and these are dispatched to multicast handle of 224.0.0.5

Regardless of the title "router precedence" it's the truth is a precedence which s set on an interface diploma as follows:

R1(conf)interface fastethernet zero/zero R1(conf-if)ip ospf precedence 1

In the event that two or more interfaces sharing a common broadcast area have the same router priority the 70-643 braindumps ID is used as a tie-breaker. The election process is as follows:

1. To participate inside the election any router with its OSPF precedence set between 1-255 can try to grow to be DR by putting its own Router ID into the DR topic of its dispatched hellos. You possibly can view the election process by working the command "debug ip ospf adj", the elections occurs all through the two-strategy process. 2. Each router inside the widespread broadcast domain look at the acquired Hellos, having a look at different routers' precedence settings 3. If a obtained Howdy from another router has a greater router precedence then that router stops claiming to be DR and asserts that the higher candidate ought to be the DR by placing the sscp ID of the DR into the DR discipline of it is Good day packets. On account of this reality the primary standards for better is a router with the best priority 4. If the Router Priorities are equal, the router with the higher RID is chosen as a result of the DR 5. The with the subsequent highest precedence or next highest Router ID in the case hat there's a tie within the value of the Router Priority turns into the BDR, (Backup Designated Router). 6. If a brand new router comes onto the group after the election of the pmp certification and/or BDR, or if any current router improves it is priority it won't be able to pre-empt the prevailing DR and even the BDR, remember that DR and BDR roles are non-preemptive. 7. If the DR fails the prevailing BDR will take over as DR and another election is held for the BDR. 8. If the previous DR comes once more on-line it won't be ableto resume it's earlier role.

When a router which is neither the DR or the BDR must promote an event to its neighbors on the common broadcast community it's going to send the LSA (Kind 1) to the DR utilizing the deal with of 224.0.0.6 (The BDR listens passively to this trade and maintains a relationship with all the routers), the testking network+ will then promote the event to all adjacent routers on the widespread broadcast network LSA (Kind 2) All routers will then acknowledge the receipt with an ACK packet ensures that each has a synchronized copy of the LSDB.

Details regarding the DR and BDR

1. These roles should not pre-emptive, once a device is a DR or BDR the only occasions that can trigger it to give up the roles are as follows:

a. Shut the interface down b. Set Priority to zero c. Restart the router d. Restart the OSPF router process (hp2-q01 braindump) e. Unplug the cable from the interface

2. The router which turns into the DR is the primary one which boots up, starts it's OSPF processes and can get previous the 40sec wait timer, earlier than it sees one other router sending it is personal up packet claiming the DR role. The wait timer may be seen inside the output beneath, 8th line down.

R1_xshow ip ospf interface

Fastethernet0/0 is up, line protocol is up Internet Deal with 192.168.x.1/24, Space zero Course of ID 1, Router ID 192.168.3.1, Network Type BROADCAST, Price: 10 Transmit Delay is 1 sec, State DR, Precedence 1 Designated Router (ID) 192.168.3.1, Interface deal with 192.168.3.1 Backup Designated router (ID) 192.168.3.2, Interface deal with 192.168.3.2 Timer intervals configured, Hi there 10, Lifeless 40, Wait 40, Retransmit 5

3. A router ought to solely be a DR for one LAN segment. 4. Set the testking 70-640 by setting it's Router priority to 255. 5. Set the BDR by setting it's Router Precedence to 250 6. Set all totally different routers Router Precedence to 1, by no means set them to 0 as a result of within the occasion that you just lose both the DR and BDR the routers with the Router Precedence of zero will never become totally adjoining neighbors and in flip will never change routing data