Week 5: DVP (RIPv2) Flashcards
What does a Routing Protocol Specify?
How routers communicate to distribute reachability information and network status
Path Determination
What must Routing Algorithms have procedures for?
Passing & receiving Reachability Information
Determining Optimal Routes
Reacting to Topology changes
List the common routing metrics
Hop Count Bandwidth Load Delay Reliability Cost
What is Administrative Distance?
Tells us how reliable the route information is. the lower the value the better
What work are DVP algorithms based on?
Bellman, Ford, & Fulkerson
What are DVP Algorithms oftern referred to as?
Bellman-Ford or Ford-Fulkerson Algorithms
What is the style of routing that DVP can be summarized by?
routing by rumor
List the common characteristics of DVPs
Periodic Updates
Neighbours
Broadcast Updates
Full Routing Table Updates
What is a limitation that is inherent to all routers?
Routers can only see the directly connected links/routers, nothing beyond
What are Routers vulnerable to?
Accidental or intentional misdirection
What are some refinements that can be added to routers to cover their limitations and vulnerabilities?
Route Invalidation Timers Split Horizon Counting to Infinity Triggered Updates Holddown Timers Asynchronous Updates
What is the typical timeout range for Route Invalidation Timers?
3-6 update periods
What must accompany every entry in a routing table?
A Route Invalidation Timer
What is a Route Invalidation Timer?
A mechanism used by a router to mark whether or not a specific route is valid and reachable
What is Split Horizon?
A technique for prevent reverse routes between two routers (prevents routing loop problems)
What is a Reverse Route?
A router pointing back to the router from which it received its packets
What are the two types of Split Horizon?
Simple Split Horizon
Split Horizon with Poisoned Reverse
How does Simple Split Horizon Updating work?
Simple Split Horizon does not advertise routes back to the neighbors from whom the routes were learned
Why is Split Horizon with Poisoned Reverse safer than Simple Split Horizon?
It helps remove corrupted routing information
How does Split Horizon with Poisoned Reverse work?
Advertises reverse routes but with an unreachable (infinite) metric
How is Infinity Defined?
A maximum set of hops
What Hop Count solves the Counting-to-Infinity Problem?
15 Hops, but convergence will be very slow as a result
How long would a network take to reconverge given an update period of 30 seconds?
7.5 minutes
What is a Triggered Update?
An update that is automatically sent out by a router whenever a metric changes (for better or worse) without waiting for its update timer to expire
What is a benefit of Triggered Updates?
Reconvergence will occur quicker
Regular updates may still occur along with triggered updates
What do Holddown Timers introduce in order to reduce?
A certain amount of skepticism to reduce the acceptance of bad routing information
When is a Holddown Timer set?
If the distance to a destination increases
When will the router begin accepting updates for a route with a Holddown Timer?
Once the timer expires
What factor contributes to System Delays?
routers becoming synchronized and causing collisions
What are the two methods by which Asynchronous Updates can be maintained?
Router’s update timer is made independent of the routing process
Add timing jitter to each update period as an offset
What 4 timers does RIP use?
Update Timer
Invalid Timer
Holddown Timer
Flush Timer
What are the properties of an Update Timer?
Represents the period of update
Usually 30 sec.
Real value may be a random value that is a little more or less than 30 sec.
What are the properties of an Invalid Timer?
If an update has not been received after 180 seconds (default), the route is marked as invalid by setting the metric to 16
The route is retained in the routing table until the flush timer expires
What are the properties of a Holddown Timer?
Stabilizes routing information and helps prevent routing loops during topology convergence
By default, the holddown timer is set to 180 sec.
What are the properties of a Flush Timer?
Flush Timer is set to 240 seconds (60 seconds longer than the Invalid Timer)
When the Flush Timer expires, the route is removed from the routing table
What are the properties of RIP?
it is a Distance-Vector Routing Protocol
The easiest Interior Gateway Protocol (IGP) to configure is RIPv1
Broadcasts entire routing tables to neighbours
RIP uses hop count as its sole metric
Administrative Distance is 120
How does RIP select its path?
via Hop Count (16 is unreachable)
What type of Subnetting does RIPv2 support?
VLSM
What type of network does RIPv2 support?
Discontiguous Networks
What is the downside to RIP?
It is susceptible to all the problems normally associated with Distance-Vector routing protocols
What are the characteristics of RIPv1?
Distance Vector Protocol Max Hop Count of 15 Classfull Broadcast-Based No VLSM Support No Authentication No Discontiguous Networks
What are the characteristics of RIPv2?
Distance Vector Max Hop Count of 15 Classless Multicast 224.0.0.9 Supports VLSM MD5 Authentication Supports Discontiguous Networks
What is the Cisco IOS command for RIP configuration?
#router rip
#network {IP}
#version {#}What is the Cisco IOS command to advertise each network?
network {IP}
What two modes must be entered before RIP can be configured on your router?
- Privileged Mode
2. Global Configuration Mode
What is the Cisco IOS command for checking the currently running routing protocols?
show ip protocol
What is the Cisco IOS command for checking the Routing Table?
show ip route
