IPv4 Routing Flashcards
What are two types of rounting protocols?
Link State and Distante Vector
What is the metric used by RIP routing protocol?
Hop Count
Why RIP is a poorly designed routing protocol? Think about the metric it uses.
It uses only hop count as the metric but it does not take into account other factors like bandwidth or delay
Which rounting protocol type (Link State vs Distance Vector) has higher visibility on the network? Why
Link State.
Routers using Link State protocols have the full visibility over the network whereas Distance Vector use so called ‘routing by rumour’ which means that they only know what they are told by the neighbouring routers but cannot verify information themselves.
What are the advantages and disadvantages for Link State routing protocols?
Advantages:
- Better visibility of the network. Rounters can make better forwrding decisions
Disadvantages:
- Difficult to configure
- Require more memory and processing power
What is Adminisrative Distance?
It’s an indicator of how ‘believable’ a given route/path is
The higher the administratie distance, the better or worse it is?
Worse
What are the Administratie Distance default values?
Connected Interface: 0 Static Route: 1 EIGRP: 90 OSPF: 110 RIP: 120 Unknown: 255
Why classless rounting protocols are preferred over classful rounting protocols?
Because classless protocols advertise network masks
What is VLSM
Variable Length Subnet Mask
When is Administrative Distance used as a tie breaker?
When two different routing protocols advertise different routes for the same destination IP address
If the same route is advertised twice on the same router, but with different outgoing interfaces, what will the tie breaker be?
Administrative distance
There is a message that Link State routing protocols flood the network with to build their topological databases.
How are those messages calles
LSA (Link State Advertisement)
List two examples of a LInk State routing protocol
OSPF - Open Shortest Path First
IS-IS - Intermediate System - Intermediate System
OSPF is able to split whole AS (autonomous systems) into smaller groupings. How are those groups called?
Areas
In OSPF, how do we call a router in between areas?
ABR (Area Border Router)
What is an ASBR?
Autonomous System Border Router. It connects AS to the Internet.
What is a rounting table?
List of networks that the router knows about and information how to link those networks.
Each entry contains a destination network (with subnet mask), out-going interface and the next hop router
What happens with an entry in the routing table if its outgoing interface goes down?
It’s removed from the routing table
What is a Default Route in a routing table?
It’s an optional route that is used when no explicit path to a destination is found
What is a Default Gateway?
It’s an IP address that devices send traffic to if they don’t have the destination IP address in their routing tables
How can you create a default route on a layer 3 device? [There’s a command for that]
IF ‘ip routing’ command is enabled use:
ip route 0.0.0.0 0.0.0.0 [ip address of the default gateway]
if it’s disabled, use:
ip default-gateway [ip address of the default gateway]
Can you have multiple default gateways on one Layer 3 device?
If not. why not?
If yes, what would the consequences be?
Yes.
The device will load-balance traffic among all default routes if the administrative distance is the same. If not, the route with lowest administrative distance wins.
Why would ‘show running-config’ command show 3 different routes to the same destination when ‘show ip route’ shows only 1 route to the given destination?
IP Routing Tables pull only the best route available with Administrative Distance being the tie breaker
What is VSLM?
Variable Length Subnet Mask
What is CIDR
Classless Inter Domain Routing
What are the advantages of VLSM?
- More efficient use of IP addresses
- Fewer updates
- Hide topology changes
- Hierarchical levels for better route sumarization
