Network and Subnets and Loops Flashcards
CIDR
“Sidder” Classless Inner Domain Routing
CIDR tells us how many binardys are turned on in the subnet mask, EX: /24 or /8 or /30
VLSM
Variable Length Subnet Masking
Exactly the same as CIDR and subnetting
S
Static route in a routing table.
Gateway of Last Resort
The default route. “Where we will send all unknown traffic?” To the default route, or the Gateway of Last Resort
Routing Loops
An invalid route that causes traffic to be sent back in the direction it was received, causing a loop
When two routers are pointing to each other to get to a specific destination network. Traffic will not duplicate but it will go round and round the loop endlessly.
Loop
Infinity. Infinite hops. The loop is endless
Loop Causes
Slow routing protocol convergence (aka slow router)
Older routing protocols
Reverse route advertisement
Reverse Route Advertisment
Router B learned about a new netowrk and it advertised it to router A. And router A said “ Oh I learned about a network, let me advertise it out to all of my routers” and sends that update back to router B. Router B says “Oh, router A knows how to get there, let me update my routing table”. Now both routers are pointing to each other
When routers point to other routers for routes instead of routing to that location….?
Static Route Loops
Static routes can cause loops and can only be fixed by removing the bad static route
Loop Prevention
Maximum hop count
Split Horizon
Hold down timers
Modern router protocols
Maximum hop count
Setting a maximum number of hops before a failure
Split Horizon
Preventing us from advertising a route back to a router that we just learned that route from
Route Poisoning
Whenever we advertise a failed route with an infinite metric, meaning it’s unreachable
Poison Reverse
When we advertise an infinite metric for routes learned by neighboring routers
