IP Routing Flashcards
What is a router on a stick consisted of
A layer 2 switch which cannot route information with separate vlans out of different ports, so it is connected to a router via a trunk port to be able to route between vlans
What is a SVI & routed port
With a layer 3 switch, you have a virtual interface (with ip address) for each VLAN, which represents all ports that belong to the VLAN so internal routing is possible, OR if you want a routed port, you assign a port on the switch to a router port and connect the switch to a router (assign an IP to the port)
What does SVI stand for
Switch Virtual Interface
What does OSPF stand for
Open shortest path first
What versions of OSPF are for IPv4 and IPv6
OSPFv2 only covers IPv4 while OSPFv3 covers IPv6
What is OSPF’s Admin Distance
110
What type of routing protocol is OSPF
Link State
What is characteristic of OSPF
Establishes adjacencies with other routers by sending Link State Advertisements to routers in an area, Constructs a link state database from link state advertisements
What does OSPF find the best path based on?
Cost, which is a function of bandwidth
How does a router send a packet down the right path
It attempts to inject the best path into an IP routing table (populates routing information table) to be injected into IP table
What is a neighbor
A neighbor is a router that reside on the same network link, exchange hello messages with one another BUT NOT NECESSARY Link State Advertisements
What is an adjacency
An adjacency are routers that are neighbors, have exchanged Link State Updates and Data Description Packets; Only adjacencies construct a link state database
What does each OSPF topology have?
Area 0, a backbone area, or 0.0.0.0
What’s the requirement for having multiple areas in the OSPF model?
Each non-backbone area should connect to the backbone area.
What are routers with interfaces in more than one area called
Area Border Router (ABR)
What is one way that Cisco does not recommend but can allow you to directly connect any non-backbone area to a backbone area
Establish a virtual link between the two areas
What is one way that Cisco does not recommend but can allow you to directly connect any non-backbone area to a backbone area
Establish a virtual link between the two Area Border Routers
How do you calculate cost of an OSPF route?
Cost = reference bandwidth / interface bandwidth
What is the default reference bandwidth?
100 Mbps
What happens if your OSPF cost is a decimal?
You round up to the next nearest number
What is the command to set a higher reference bandwidth for OSPF
auto-cost reference-bandwidth value
What’s the solution to not having a full adjacency for all routers in a network
Elect a DR and a BDR
What are the addresses for OSPF config
224.0.0.5 for All OSPF router multicast and 224.0.0.6 for All designated routers (top 2) FF02::5 and FF02::6 for IPv6 respectively
How is a DR elected?
DR election goes first then BDR, router with highest OSPF priority wins 0 = don’t run 1 = default up to 255 (can be statically set), Router with highest id becomes DR if that’s not enough (highest IP of router loopback or non-loopback = router id)
What does it mean that DR system is non-preemptive
If you add a router with a higher ID and OSPF priority to an existing configuration, the new router will not become the DR
Tell me about a OSPF Broadcast network (DR, Default Hello Interval, static neighbors?)
Will elect a DR and BDR, Default Hello Interval of 10 sec, Can use multicast to dynamically discover neighbors (ie 6 routers connected to a broadcast median such as a switch)
Tell me about a Point To Point Network
A Router connected to another router over a WAN
No need to elect a DR and BDR as there’s only one other router to discover, Default Hello 10 sec, Can discover other router so no need for static assignment
Tell me about a Non-Broadcast (NBMA)
Elects a DR& sometimes BDR but you have to make sure the DR is openly adjacent to the rest of the routers
Statically configure neighbors
Hello Interval is 30 seconds
Tell me about a point to multipoint network
Topologically looks like a non-broadcast type with a router connected to frame relay and 3 other routers connected via WAN
No DR and BDR needed since each dashed line is a point to point connection Hello Interval of 30 seconds no need for static neighbors
What is the default OSPF type for ethernet networks
broadcast
What is the default OSPF type for frame relay and point to point sub-interfaces
Point to Point
What is the default OSPF type on frame replay physical interfaces and multiple sub-interfaces
Non-Broadcast
How do you change the OSPF type of a network
in a specific interface, type: ip ospf network
What happens when you change a timer to align with a neighbor but both are set to different OSPF connections
showing a neighbor would be possible but routes from the network will not be received
What is the administrative distance of EIGRP
90
What is the administrative distance of RIP
120
What are some benefits of EIGRP
fast convergence time (that is if one path fails, you can find a new route quickly)
Load balance over unequal cost links
Supports variable length subnet masks
Used to be proprietary to Cisco
What is the multicast address that EIGRP communicates over
224.0.0.10 or FF02::A
What are 4 components of EIGRP
Neighbor discovery (automatic), Reliable Transport Protocol (EIGRP packets get there and in the right order), packets only sent when needed, Protocol Dependent Modules (can handle multiple protocols) including IPv4 IPv6 AppleTalk IPX, etc.
What is DUAL
DUAL Diffusing Update Algorithm, figures out which neighbor is the most efficient, next hop router successor, successor route
What is a feasible successor
A neighbor that can still get to the destination but not the most efficient one (which is known as the successor)
What are the 3 data structures of EIGRP and what do they do
Neighbor Table - holds info about the router’s adjacent EIGRP neighbors show ip eigrp neighbors
Interface Table - show info about interfaces participating in EIGRP
show ip eigrp interfaces
Topology Table - shows routes known to EIGRP
show ip eigrp topology
What’s the default hello interval and hold time for a EIGRP timer
5 and 15, hold time tells the other router how long to count down before assuming the neighbor is no longer available
Do timers have to match between EIGRP neighbors?
No
How do you access the timers of a router running EIGRP
show ip eigrp interfaces
What is the requirement to be a feasible successor
The reported distance must be < the feasible distance to become a feasible successor
What is the reported distance
How far a particular router is from its destination
What is the feasible distance
The Neighbor Distance + Reported Distance
How is the successor route determined (EIGRP)
The path with the feasible distance is considered the successor route
Variance
a feature that allows EIGRP to load-balance across a network’s successor route and one or more feasible successor routes.
Unequal Cost Load Balancing
When routes have different metrics and costs, you can set the variance which says to include all routes smaller than n times the successor route’s metric where n is the variance (n = 1 = equal cost load balancing)