OSPF3C.4 # HOW TO ELECTED THE DR AND BDR ON OSPF
Diagram:-
| Port | Status | Device |
|---|---|---|
| Router | ||
| Serial 0/0 | Routed link-port | Side_A |
| Serial 0/0 | Routed link-port | Side_B |
| Serial 0/1 | Routed link-port | Side_C |
| Serial 0/0 | Routed link-port | Side_D |
| FastEthernet 0/0 | Routed link-port | Side_E |
| FastEthernet 0/0 | Routed link-port | Side_F |
| Switch_Layer 2 | ||
| FastEthernet 0/1 | Trunk port | Switch0 |
| FastEthernet 0/1 | Trunk port | Switch1 |
| FastEthernet 0/1 | Trunk port | Switch2 |
| Broadcast n Collision domain status | ||
| Number of broadcast domain | Number of collision domain | |
| 8 | 14 |
# OSPF Configuration Lab : -
1) Configuration of Side_A
Router >enable
Router #configure terminal
Router (config)#hostname Side_A
!
Side_A (config)#interface FastEthernet0/0
Side_A (config-if)#ip address 192.168.1.1 255.255.255.0
Side_A (config-if)#no shutdown
Side_A (config-if)#exit
!
Side_A (config)#interface Serial0/0
Side_A (config-if)#ip address 10.10.10.1 255.0.0.0
Side_A (config-if)#encapsulation hdlc
Side_A (config-if)#clock rate 64000
Side_A (config-if)#no shutdown
Side_A (config-if)#exit
!
Side_A (config)# router ospf 760
Side_A (config-router)# network 10.0.0.0 0.0.0.255 area 0
Side_A (config-router)# network 192.168.1.0 0.0.0.255 area 0
Side_A (config-router# exit
!
2) Configuration of Side_B
Router >enable
Router #configure terminal
Router (config)#hostname Side_B
!
Side_ B (config)#interface FastEthernet0/0
Side_ B (config-if)#ip address 192.168.2.1 255.255.255.0
Side_ B (config-if)#no shutdown
Side_ B (config-if)#exit
!
Side_ B (config)#interface Serial0/0
Side_ B (config-if)#ip address 10.10.1.2 255.0.0.0
Side_ B (config-if)#no shutdown
Side_ B (config-if)#exit
!
Side_ B (config)#interface Serial0/0
Side_ B (config-if)#ip address 20.20.2.1 255.0.0.0
Side_ B (config-if)#encapsulation hdlc
Side_ B (config-if)#clock rate 64000
Side_ B (config-if)#no shutdown
Side_ B (config-if)#exit
!
Side_ B (config)# router ospf 760
Side_ B (config-router)# network 10.0.0.0 0.0.0.255 area 0
Side_ B (config-router)# network 20.0.0.0 0.0.0.255 area 0
Side_ B (config-router)# network 192.168.2.0 0.0.0.255 area 0
Side_ B (config-router# exit
!
3) Configuration of Side_C
Router >enable
Router #configure terminal
Router (config)#hostname Side_C
!
Side_C (config)#interface FastEthernet0/0
Side_C (config-if)#ip address 192.168.3.1 255.255.255.0
Side_C (config-if)#no shutdown
Side_C (config-if)#exit
!
Side_C (config)#interface Serial0/0
Side_C (config-if)#ip address 20.20.2.2 255.0.0.0
Side_C (config-if)#encapsulation hdlc
Side_C (config-if)#clock rate 64000
Side_C (config-if)#no shutdown
Side_C (config-if)#exit
!
Side_C (config)# router ospf 760
Side_C (config-router)# network 20.0.0.0 0.0.0.255 area 0
Side_C (config-router)# network 192.168.3.0 0.0.0.255 area 0
Side_C (config-router# exit
!
4) Configuration of Side_D
Router >enable
Router #configure terminal
Router (config) #no ip domain lookup
!
Router (config)#hostname RouterD
!
RouterD (config)#interface FastEthernet0/0
RouterD (config-if)#ip address 192.168.2.101 255.255.255.0
RouterE (config-if)#ip ospf priority 1
RouterD (config-if)#no shutdown
RouterD (config-if)#exit
!
RouterD (config)# router ospf 10
RouterD (config-router)# network 192.168.2.0 0.0.0.255 area 0
RouterD (config-router# exit
!
5) Configuration of Side_E
Router >enable
Router #configure terminal
Router (config) #no ip domain lookup
!
Router (config)#hostname RouterE
!
RouterE (config)#interface FastEthernet0/0
RouterE (config-if)#ip address 192.168.2.102 255.255.255.0
RouterE (config-if)#ip ospf priority 1
RouterE (config-if)#no shutdown
RouterE (config-if)#exit
!
RouterE (config)# router ospf 10
RouterE (config-router)# network 192.168.2.0 0.0.0.255 area 0
RouterE (config-router# exit
!
6) Configuration of Side_F
Router >enable
Router #configure terminal
Router (config) #no ip domain lookup
!
Router (config)#hostname RouterF
!
RouterF (config)#interface FastEthernet0/0
RouterF (config-if)#ip address 192.168.2.103 255.255.255.0
RouterE (config-if)#ip ospf priority 1
RouterF (config-if)#no shutdown
RouterF (config-if)#exit
!
RouterF (config)# router ospf 10
RouterF (config-router)# network 192.168.2.0 0.0.0.255 area 0
RouterF (config-router# exit
!
# Note: -
The range of the priority values that allow a router to be a candidate are 1 through 255. The priority settings of 0 means that the router does not participate in the election and can never become the DR or BDR.And the last one Routers (Router_B, D, E and Router_F) will have to decide in which, who one will become a DR & BDR after the configuration. You can see from the following commands.
| Neighbor ID | Pri | State | Dead Time | Address | Interface |
|---|---|---|---|---|---|
| 192.168.2.101 | 1 | FULL/BDR | 00:00:30 | 192.168.2.101 | Fa 0/0 |
| 192.168.2.102 | 1 | FULL/DR | 00:00:32 | 192.168.2.102 | Fa 0/0 |
| 192.168.2.103 | 1 | 2 WAY/DROTHER | 00:00:34 | 192.168.2.103 | Fa 0/0 |
RouterF# show ip ospf neighbor
| Neighbor ID | Pri | State | Dead Time | Address | Interface |
|---|---|---|---|---|---|
| 192.168.2.101 | 1 | FULL/BDR | 00:00:36 | 192.168.2.101 | Fa 0/0 |
| 192.168.2.102 | 1 | FULL/DR | 00:00:38 | 192.168.2.102 | Fa 0/0 |
Number of logical connection = N(N-1)/2
Number of logical connection = 10(10-1)/2 = 10(9)/2
Number of logical connection = 90/2 =45
# OSPF metrics
• It can be manually configured and value between 1 – 65,535
• It will be configure the cost based on bandwidth automatically before the configuration.
• IOS can calculate a value based on the generic formula.
Ref – Bw / Int Bw (Default to 100 Mbps)
Ref Bw is a reference of bandwidth.
Int Bw is a interface of bandwidth setting.
Simplify the formula:
=> 100 Mbps / Int – Bandwidth => 100000 / 1 intial Bandwidth
• OSPF calculates the metric for each possible route by adding up the outgoing interface OSPF costs.
• Less cost route is the best path for OSPF metrics.
Note: -
Bandwidth is considered of the exit interface – not on the ingress interface. Also it is sum from Source to Destination
# Debugging command for troubleshooting
• Router# debug ip ospf packet (Function: show hello packet being sent and received on your router)
• Router# debug ip ospf hello (Function: show hello packet being sent and received on your router)
• Router# debug ip ospf adj (Function: show DR and DBR elections on a broadcast and non-broadcast multi – access network)
# Administrative distancsand Metric of all protocols
| Routing Information | AD | Metric Table | Types |
|---|---|---|---|
| Default routing | 0 | N/A | Unknown |
| Static routing | 1 | N/A | Manually |
| BGP routing | 20 | Attributes | Distance Vector |
| IGRP routing | 100 | Bandwidth, Delay | Distance Vector |
| EIGRP routing | 90 | Bandwidth, Delay,Load | Dual |
| OSPF routing | 110 | Cost | Link state |
| IS – IS routing | 115 | Cost | Link state |
| RIP Version1/2 | 120 | Hop Count | Distance Vector |
| BGP External | 170 | Vector of attributes | Path Vector |
| BGP Iternal | 200 | Vector of attributes | Path Vector |
Note: -
To stop routing loops these are three major issues
1) Count – to – infinity (IGRP/RIP)
2) Split – horizon (OSPF)
3) Routs poisoning (EIGRP)
• IGP is used to communicate between AS i.e BGP
• EGP is used to communicate within a single AS.
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