Routing

Question 1

What are the 3 methods of finding routes?

Answer 1

• Directly Connected Routes (Learned through a physical connection between routers)
• Static Route (manually set by an Administrator)
• Dynamic Routing (Learned by exchanging info between routers)

Question 2

How does Split Horizon works?

Answer 2

Its for preventing Routing Loops like STP for switching. It prevents a route learned on one interface from being advertised back out of that same interface or in simple terms:
Dont advertise a route into the same direction / to the same router you learned it from.

Question 3

How does Poison Reverse works?

Answer 3

Its similar to Split Horizon but instead of forbidding advertising a route in the same direction / to the router it has been learned from. Its advertised in that direction with infinite cost, so it will never be used.

Question 4

What are the 3 factors used to evaluate the quickest route?

Answer 4

• Distance Vectors (Based on Hop Count)
• Link State (Based on Link Speed)
• Hybrid of both of them

Question 5

What are popular Link-State protocols? (2)

Answer 5

• Open Shortest Path First (OSPF)
• Intermediate System to Intermediate System (IS-IS)

Both calculate cost based on Link speed, OSPF is more popular.

Question 6

What are popular Distance Vector protocols? (2)

Answer 6

• Routing Information Protocol (RIP): Oldest, relies on Hops, UDP)
• IGRP

Question 7

What are popular Hybrid protocols? (1)

Answer 7

• Enhanced Interior Gateway Routing Protocol (EIGRP): Cisco only, relies on combination of bandwith and hops/delay for cost

Question 8

What makes the BGP Protocol special?

Answer 8

The Border Gateway Protocol (BGP) is a Path Vector Protocol. It uses the number of autonomous system hops instead of router hops for cost.
It also is the only real exterior gateway protocol and thus is basically the backbone of the internet.

Question 9

What is AD?

Answer 9

Administrative Distance (AD) is a value that classifies how believable a route is to a router. The lower the number, the better.
1. Directly connected network: 0 AD
2. Statically connected network: 1 AD
3. EIGRP: 90 AD
4. OSPF: 110 AD
5. RIP: 120 AD
6. External EIGRP: 170 AD
7. Unknown/Unbelievable: 255 AD (unreachable)

Question 9

What Address Translation methods exist?

Answer 9

• Dynamic NAT (DNAT): One-to-One translation on a “on demand” basis
• Static NAT (SNAT): One-to-One translation, 1 public IP assigned to 1 private IP statically
• Port Address Translation (PAT): Many-to-One translation, 1 public IP is used for multiple private IPs

Question 10

What are FHRPs and what are the key benefits and what is needed for them to function?

Answer 10

First Hop Redundancy Protocols (FHRPs) are a set of protocols that allow to automatically switch to a backup router in case the first one fails. They require Virtual IPs & Subinterfaces to function.

The key benefits are: Reliability, Load Balancing & Seamless Transitions

Question 11

What are the 3 main FHRPs?

Answer 11

• Hot Standby Router Protocol (HSRP): By Cisco, connects 2+ routers as one virtual router, if the active router fails, the standby router takes over
• Virtual Router Redundancy Protocol (VRRP): Like HSRP but open standard, simple automatic election scheme
• Gateway Load Balancing Protocol (GLBP): By Cisco, like the other two, but it adds load balancing into the focus & allows all routers in the group to work at the same time

Question 12

What are the 2 protocols for multicasting?

Answer 12

• Internet Group Management Protocol (IGMP)
• Protocol Independent Multicast (PIM)

Question 13

What are the 2 PIM modes?

Answer 13

1. PIM-DM: Dense Mode: Flood & Prune to get optimal path, faster but uses alot of bandwith
2. PIM-DM: Sparse Mode: Shared Distribution Tree which is optimized over time until you have a shortest path tree (SPT)

Question 14

What is GRE?

Answer 14

Generic Routing Encapsulation (GRE): Used to create a tunnel to encapsulate a wide range of network layer protocols and send them over a virtual P2P link.
Benefits:
- Versatility and integration
- Universal translation (of otherwise incompatible protocols)