Switching & Routing loops

Question 1

Switching LOOPS - When there is More than One Parth between Source and Destination Devices that Creat Broadcast storm

Answer 1

Soloutuin - STP

Question 2

What is a Routing Loop?

Answer 2

**** What is a Routing Loop?**
A routing loop occurs when Router A sends traffic to Router B, Router B sends it to Router C, and Router C sends it back to Router A (or some smaller cycle).
The packet never reaches the destination and keeps looping until it dies.

Why Routing Loops Happen
Common causes:
1. Slow convergence
Routers haven’t fully updated their routing tables yet.
2. Incorrect static routes
A static route points to the wrong next hop.
3. Misconfigured dynamic routing
Mistakes in OSPF, EIGRP, RIP, etc.
4. Route redistribution issues
Leaking routes between protocols incorrectly.
5. Split networks
When network segments break but routers don’t know yet.Redundancy & Fault tolerance***

What routing loops cause
High CPU on routers/High bandwidth usage/Packet loss/Network slowness/Application failure

A routing loop occurs when packets are forwarded around the network in a continuous circle because routers have incorrect or outdated routing information. The packet never reaches its destination and keeps looping until it is dropped. Routing loops waste bandwidth and cause network congestion.

Question 3

Vulnerability

Answer 3

weakness in the network that can be exploited

Question 4

Risk

Question 5

Threat

Answer 5

Any potential danger to your Network. it can be an attack or Natural disaster

Question 6

Define routing loop.

Answer 6

A situation where data packets circulate endlessly in a network.

Question 7

True or false: Routing loops can cause network congestion.

Answer 7

TRUE

They can lead to increased latency and packet loss.

Question 8

What is a common cause of routing loops?

Answer 8

Incorrect routing table updates or misconfigured routers.

Question 9

Fill in the blank: Split horizon is a technique to prevent _______ loops.

Answer 9

routing

Question 10

Define count to infinity.

Answer 10

A problem in distance-vector routing protocols that can cause routing loops.

Question 11

What protocol often suffers from routing loops?

Answer 11

RIP (Routing Information Protocol)

Question 12

True or false: Link-state protocols are immune to routing loops.

Answer 12

FALSE

While less prone, they can still experience loops under certain conditions.

Question 13

What is the purpose of route poisoning?

Answer 13

To prevent routing loops by marking a failed route as unreachable.

Question 14

What is the TTL in relation to routing loops?

Answer 14

Time To Live; it limits the lifespan of a packet to prevent loops.

Question 15

Whats Route poisoning

Answer 15

Route poisoning is a method used by distance-vector routing protocols to prevent routing loops by marking a failed route with an infinite metric (for example, 16 in RIP).
This tells all routers that the route is no longer reachable, so it should be removed from routing tables.

Why Route Poisoning Is Used

Why Route Poisoning Is Used
Quickly spreads information that a network is down
Prevents routers from mistakenly sending traffic to a dead path
Works together with poison reverse and split horizon

Question 16

What is Split Horizon

Answer 16

Split Horizon is a loop-prevention technique used in distance-vector routing protocols.
It prevents a router from advertising a route back out of the same interface where it originally learned that route.

By not sending route information back the same way it came, routers avoid creating routing loops.

Question 17

Difference between Split Horizon and Poison Reverse

Answer 17

Split Horizon
Rule:
A router does NOT advertise a route back out the same interface it learned it from.
Purpose:
Prevents loops by not sending the route in the reverse direction.
Simple Example:
Router A → Router B (route learned)
B will not send that route back to A.

Poison Reverse
Rule:
A router DOES advertise the route back, but marks it as unreachable (with an infinite metric).
Purpose:
Prevents loops by actively telling the neighbor:
“This route is dead — don’t use me for it.”
Simple Example:
Router A → Router B (route learned)
If the route becomes invalid, B sends it back to A with metric = infinite (e.g., 16 in RIP).

Easy Way to Remember

Split Horizon Don’t send the route back Staying silent
**Poison Reverse ** Send it back as “unreachable” Explicit warning

Question 18

All Loop-Prevention Methods (Network+ Summary)

Answer 18

Flashcard 1 — Split Horizon
Front: What is Split Horizon?
Back: Don’t advertise a route back out the interface it was learned from. Prevents loops.
📘 Flashcard 2 — Poison Reverse
Front: What is Poison Reverse?
Back: Advertise the route back to the neighbor but mark it unreachable (infinite metric).
📘 Flashcard 3 — Route Poisoning
Front: What is Route Poisoning?
Back: When a route fails, advertise it with an infinite metric so all routers know it’s down.
📘 Flashcard 4 — Hold-Down Timer
Front: What is a Hold-Down Timer?
Back: A waiting period before accepting new updates about a failed route to prevent flapping.
📘 Flashcard 5 — Triggered Updates
Front: What are Triggered Updates?
Back: Immediate routing updates sent when changes occur, improving convergence.
📘 Flashcard 6 — Maximum Hop Count
Front: What is Maximum Hop Count?
Back: A limit on how many hops a route can have; prevents packets from looping infinitely. RIP max = 15.

⭐ Quick Memory Trick

⭐ Quick Memory Trick
“SHRHTM” → Split, Poison Reverse, Route Poison, Hold-down, Triggered updates, Max hops