zNetLaB › Guided labs › Enterprise
BFD for OSPF — noticing a failure behind a switch
Enterprise Advanced 4 devices 4 checked tasks 100 points Plan lab
R1 and R2 meet on a switch, with a slower path through R3 as backup. If R2’s side fails, R1’s port stays up and OSPF waits out its dead interval while traffic black-holes. Run BFD under OSPF on the shared segment so the loss is seen in milliseconds. You build it in a browser, type real commands at each device, and every task below is
checked against the running configuration — so you find out it is wrong before anybody else does.
Open this lab in the simulator
The simulator runs in your browser with nothing to install. This lab is part of the full simulator: open it free for 7 days with a new account, then with a plan. It needs an account, which keeps your progress.
The scenario
R1 and R2 meet on a switch, with a slower path through R3 as backup. If R2’s side fails, R1’s port stays up and OSPF waits out its dead interval while traffic black-holes. Run BFD under OSPF on the shared segment so the loss is seen in milliseconds.
Your role: a network engineer on the enterprise team. Level: Advanced Done when: all 4 goals show as passed (100 points).
Network status
Devices: 3 routers, 1 switch, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. R1 starts with addresses (G0/0 10.0.0.1/24, G0/1 10.0.13.1/24) and OSPF 1 already configured. R2 starts with addresses (G0/0 10.0.0.2/24, G0/1 10.0.23.2/24, L0 2.2.2.2/32) and OSPF 1 already configured. R3 starts with addresses (G0/0 10.0.13.3/24, G0/1 10.0.23.3/24) and OSPF 1 already configured. SW starts with an empty configuration. Known problems
None: nothing is misconfigured. The network is simply not finished: what the goals list is what you have to build or secure. Goals
A BFD session is up from R1 to R2 (30 pts) And from R2 back to R1 (25 pts) R1 still has both OSPF neighbours (20 pts) R1 reaches R2’s loopback by the short path (25 pts) The activity, in order
A BFD session is up from R1 to R2 Why: Each goal is a state the lab can check on the running device. Verify with: show running-config And from R2 back to R1 Why: Each goal is a state the lab can check on the running device. Verify with: show running-config R1 still has both OSPF neighbours Why: OSPF routes only flow over a FULL adjacency. If a neighbour is stuck in INIT or EXSTART, compare the two ends’ settings. Verify with: show ip ospf neighbor R1 reaches R2’s loopback by the short path Why: A ping needs a route in BOTH directions. This is the end-to-end proof that everything before it worked. Verify with: ping 2.2.2.2 Tips
Work in the order given: later goals depend on the earlier ones. After every change, run the verify command before moving on; do not guess. Stuck? Read the verify output first. It names the interface, neighbour or route that is wrong. Why this matters
R1 and R2 meet on a switch, with a slower path through R3 as backup. If R2’s side fails, R1’s port stays up and OSPF waits out its dead interval while traffic black-holes. Run BFD under OSPF on the shared segment so the loss is seen in milliseconds.
What you will be able to do
A BFD session is up from R1 to R2
And from R2 back to R1
R1 still has both OSPF neighbours
R1 reaches R2’s loopback by the short path
The network
ISR 2911, Catalyst 2960-24TT — 4 devices in all, already cabled.
Gi0/0 10.0.0.1/24 Fa0/1 Gi0/0 10.0.0.2/24 Fa0/2 Gi0/1 10.0.13.1/24 Gi0/0 10.0.13.3/24 Gi0/1 10.0.23.3/24 Gi0/1 10.0.23.2/24 R1 R2 R3 SW Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
R1 ISR 2911 configure it R2 ISR 2911 configure it R3 ISR 2911 configure it SW Catalyst 2960-24TT configure it
Cabling
R1 Gi0/0 ↔ SW Fa0/1 R2 Gi0/0 ↔ SW Fa0/2 R1 Gi0/1 ↔ R3 Gi0/0 R3 Gi0/1 ↔ R2 Gi0/1
What is configured at the start
These are already configured when the lab opens — including, where this is a troubleshooting lab, the fault itself:
R1 interface g0/0
ip address 10.0.0.1 255.255.255.0
no shutdown
exit
interface g0/1
ip address 10.0.13.1 255.255.255.0
no shutdown
exit
interface g0/1
ip ospf cost 100
exit
router ospf 1
network 10.0.0.0 0.255.255.255 area 0 R2 interface g0/0
ip address 10.0.0.2 255.255.255.0
no shutdown
exit
interface g0/1
ip address 10.0.23.2 255.255.255.0
no shutdown
exit
interface lo0
ip address 2.2.2.2 255.255.255.255
no shutdown
exit
router ospf 1
network 10.0.0.0 0.255.255.255 area 0
network 2.2.2.2 0.0.0.0 area 0 R3 interface g0/0
ip address 10.0.13.3 255.255.255.0
no shutdown
exit
interface g0/1
ip address 10.0.23.3 255.255.255.0
no shutdown
exit
interface g0/0
ip ospf cost 100
exit
router ospf 1
network 10.0.0.0 0.255.255.255 area 0 Tasks, and how each one is checked
Every task is decided by reading the live network — a neighbour in FULL, a ping that succeeds, a line in the running configuration — not by looking for a keyword you typed. The same command shows you what the lab sees.
# Task Pts How to verify it yourself
1 A BFD session is up from R1 to R2 30 Checked automatically against the device’s live state (bfdUp). 2 And from R2 back to R1 25 Checked automatically against the device’s live state (bfdUp). 3 R1 still has both OSPF neighbours 20 On R1: show ip ospf neighbor shows at least 2 neighbour(s) in FULL. 4 R1 reaches R2’s loopback by the short path 25 On R1: ping 2.2.2.2 must succeed. and On R1: show ip route 2.2.2.2 shows next hop 10.0.0.2.
Stuck? Ask the coach
Tell the coach what you see or what you tried. It gives you a hint, not the answer, the way a senior engineer would. Included with a free trial or any plan.
Ask the coach
Reference solution
Try it yourself first — the lab checks your work either way. This is one configuration that makes every task pass, device by device:
R1 interface g0/0
bfd interval 50 min_rx 50 multiplier 3
ip ospf bfd
exit R2 interface g0/0
bfd interval 50 min_rx 50 multiplier 3
exit
router ospf 1
bfd all-interfaces Where this is examined
This lab practises these topics in the zNetLaB certification courses:
Related labs
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