SrikantRajeev
asked on
OSPF - Convergence & Downtime
I have the attached diagram.
ALL The L3 switches are configured with OSPF with hello timers as 10 s & Dead timers as 40 s
If the L3 switch as shown in the diagram fails or it gets rebooted (assuming the traffic from PC1 & PC2 is flowing through that switch) how much will be the downtime approximately.
OSPF_Diagram.png
ALL The L3 switches are configured with OSPF with hello timers as 10 s & Dead timers as 40 s
If the L3 switch as shown in the diagram fails or it gets rebooted (assuming the traffic from PC1 & PC2 is flowing through that switch) how much will be the downtime approximately.
OSPF_Diagram.png
Downtime length would depend on actual OSPF, interfaces configuration and type of error that caused downtime, but should not be longer than 40 seconds. The shortest downtime period could be 50 - 200ms (with BFD configured).
ASKER
What is BFD ?
Bidirectional Forwarding Detection
BFD is a detection protocol designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning will be easier, and reconvergence time will be consistent and predictable.
ASKER
I have a basic question. Assuming I have not enabled BFD.
As shown in the Diagram the L3 swtich fails.
The switches which are connected to the failed switch will first detect physical layer down.
Once the physical layer down is detected will the switches will stop sending the traffic to the failed switch & choose the available active redundant path or it will wait till the hello & dead timers gets converged.
In this scenario what will be the down time.
As shown in the Diagram the L3 swtich fails.
The switches which are connected to the failed switch will first detect physical layer down.
Once the physical layer down is detected will the switches will stop sending the traffic to the failed switch & choose the available active redundant path or it will wait till the hello & dead timers gets converged.
In this scenario what will be the down time.
ASKER
I have made the clear diagram in the attachment. OSPF is enabled in all the L3 switches & have equal cost.
OSPF is having active - active path since the OSPF Cost is same.
Assuming R3 switch fails & the traffic between the PCs are flowing through this R3 switch.
R3 switch fails the R5 & R6 detects that the physical layer L2 is down.
Q1 - Will R5 & R6 immediately stops sending the traffic to R3 on detecting physical L2 layer down & send all the traffic to R4
Q2 - Or will it wait for the Hello Packets & Hold down timer to expire before forwarding all the packets to R4
Q3 - When will the routing table entry from R5 & R6 will remove pointing to R3
Basically would like to understand how many packet drop is experienced in this scenario.
Diagram.png
OSPF is having active - active path since the OSPF Cost is same.
Assuming R3 switch fails & the traffic between the PCs are flowing through this R3 switch.
R3 switch fails the R5 & R6 detects that the physical layer L2 is down.
Q1 - Will R5 & R6 immediately stops sending the traffic to R3 on detecting physical L2 layer down & send all the traffic to R4
Q2 - Or will it wait for the Hello Packets & Hold down timer to expire before forwarding all the packets to R4
Q3 - When will the routing table entry from R5 & R6 will remove pointing to R3
Basically would like to understand how many packet drop is experienced in this scenario.
Diagram.png
OSPF manages Layer 3 i.e multiple paths to IP network with default gateway. It has zero impact on L2 switching
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ASKER
Thanx
You're welcome.