IP Routing Flashcards by Daniel Zhu

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

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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)

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What does SVI stand for

Switch Virtual Interface

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What does OSPF stand for

Open shortest path first

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What versions of OSPF are for IPv4 and IPv6

OSPFv2 only covers IPv4 while OSPFv3 covers IPv6

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What is OSPF’s Admin Distance

110

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What type of routing protocol is OSPF

Link State

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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

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What does OSPF find the best path based on?

Cost, which is a function of bandwidth

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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

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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

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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

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What does each OSPF topology have?

Area 0, a backbone area, or 0.0.0.0

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What’s the requirement for having multiple areas in the OSPF model?

Each non-backbone area should connect to the backbone area.

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What are routers with interfaces in more than one area called

Area Border Router (ABR)

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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

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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

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How do you calculate cost of an OSPF route?

Cost = reference bandwidth / interface bandwidth

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What is the default reference bandwidth?

100 Mbps

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What happens if your OSPF cost is a decimal?

You round up to the next nearest number

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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

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?

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)