First, let’s take a look at how the election process works with a basic OSPF configuration.
We can identify pretty quickly how the OSPF network is working by showing OSPF status on the eth0 interface of R2: [email protected]:~$ show ip ospf interface eth0 eth0 is up ifindex 2, MTU 1500 bytes, BW 0 Kbit < UP, BROADCAST, RUNNING, MULTICAST> Internet Address 10.1.1.1/24, Broadcast 10.1.1.255, Area 0.0.0.0 MTU mismatch detection:enabled Router ID 0.0.0.1, Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State DROther, Priority 1 Designated Router (ID) 0.0.0.5, Interface Address 10.1.1.5 Backup Designated Router (ID) 0.0.0.4, Interface Address 10.1.1.4 Multicast group memberships: OSPFAll Routers Timer intervals configured, Hello 10s, Dead 40s, Wait 40s, Retransmit 5 Hello due in 0.257s Neighbor Count is 4, Adjacent neighbor count is 2 [email protected]:~$ As you can see, R1 has detected the DR is R5, shown not only by the router-id that I configured (0.0.0.5) but also by the detected interface IP address 10.1.1.5.
Once neighbor relationships have been established, routing information must be distributed via Link State Advertisements, or LSAs.
In a shared-media environment, this can be problematic.
Observe the following diagram: In this network, all five routers are connected to the same layer 2 segment via a central switch.
If one of these routers were to experience an outage of some kind, perhaps a link to a network outside of this diagram were to go down, it would immediately send an update to all other OSPF routers, notifying them of the change.
Besides the blog, we have our security auditing tool Lynis.
I was inspired by a (relatively) recent post by Jeremy Stretch at that explained OSPF designated router configuration in Cisco IOS.
This means updates are only shared with the DR and BDR. This stands for Priority, and it is a key factor in the DR/BDR election process.
Since they’re all set to a priority of 1, the Router ID is used to break the tie, and the highest Router ID is elected the DR, and the second highest the BDR. Make up whatever reason you want, but my made-up reason is that R1 and R2 are far more reliable routers than the others - maybe they’re newer equipment.
To understand the purpose of a Designated Router in OSPF, you need to know how OSPF distributes routing information around the network.Tags: Adult Dating, affair dating, sex dating