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72 Cards in this Set
- Front
- Back
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What are the 3 network types of OSPF? |
1. Broadcast 2. Point-to-point 3. Non-broadcast-multiaccess |
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What are the 5 OSPF modes for NBMA networks?
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RFC: Non-broadcast Point-to-multipoint Cisco Proprietary: Broadcast Point-to-multipoint non-broadcast point-to-point |
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What can't the ABR do before the intra-area is synchronized?
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An ABR cannot send LSUs outside of the network until the entire intra-area is fully synchronized. |
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What is the OSPF metric calculation? |
Cost of an interface is based off it's bandwidth divided by 100,000,000 (100Mbps) |
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What is the default metric for interfaces over 100Mbps? How do you change it to accept higher bandwidth interfaces? |
Default Metric: 1 You change the bandwidth that it divides by to something greater |
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Name the 5 OSPF packet types |
Hello: Discovers neighbors and builds adjacencies Database Description: Check for synchronization of the LSDB between routers. (Must be identical for convergence) Link-State Request: Requests specific records to get more information about an entry Link-State Update: Sends the specifically requested records, otherwise sent every 30 minutes. Link-State Acknowledgement: Acknowledges the other packet types |
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What are the 6 field required to establish a neighbor adjacency?
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Hello Interval Dead Interval Network Type Area ID Authentication password (optional) Stub area flag (optional) Subnet mask must match |
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What is the LSU timer? |
An LSU is sent every 30 minutes or when a change is percieved |
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How is the Router-Id chosen? |
1. Priority 2. Router-Id command 3. Highest loopback 4. Highest IP address on an active interface |
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What are the 6 OSPF states? |
Down Init: Hellos exchanged using 224.0.0.5 Two-way: Once a hello reply is sent Exstart: Election of the DR Exchange: DR starts sending LSDB Loading: Requests more information |
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When does the BDR become the DR? |
When the DR is not reachable after the dead timer exceeds it's limit. However if the DR is unreachable after a router is trying to send information the BDR becomes the DR. |
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What address does the DR send packets through |
224.0.0.5
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What is the least favorable number and the most favorable number in DR/BDR election? |
Least: 1 Most: 255 |
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If a better router is added is a new DR elected? |
No |
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What address do packets destined for the DR/BDR sent? |
224.0.0.6
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Type 1 LSA |
Router: Generated by all routers in an area Describes their directly attached links Floods within an area |
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Type 2 LSA |
Network:
Advertised by the DR of the network (only sent by the DR) Flooded within an area Notifies other router who is the DR LSID is the DR |
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Type 3 LSA? |
Summary:
Advertised by the ABR Summary for every subnet LSID is the Network or subnet advertised Sent to networks not in it's current area Summary LSAs don't contain summarized addresses says what networks have what subnets |
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Type 4 LSA? |
ASBR Summary:
Advertised by the ABR of the area to advertise ASBR to other areas in the AS Regenerated by all other ABRs to flood through the networksLSID is the ID of the ASBR |
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Type 5 LSA? |
External:
ASBR are advertised by the originating ASBR. Used to advertise an external networkABRs redistribute the ASBR LSA into their areas Summary LSAs do not actually contain summarized addresses |
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Type 7 LSA? |
Not-So-Stubby-Area LSA:
Generated by an ASBR inside a NSSA are to describe routed redistributed into the NSSA The NSSA area only allows type 7 LSAs to be distributed Type 7 LSAs are translated into Type 5 LSAs at it leaves the NSSA |
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Type 8 LSA? Specified protocol? |
Link: OSPFv3 A link local LSA for OSPFv3. Used to give info about link-local addresses and a list of IPv6 addresses on the link. |
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Type 8 LSA? Specified protocol? |
Intra-area prefix: OSPFv3
Link-local prefix summart for transit areas. Summary at the ABR for OSPFv3 |
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Calculate this: http://puu.sh/kU4s6/d357a3ad59.jpg |
Type 1: The directly connected links Type 2: Number of routers in the area (not including the router itself) Type 3: Routers not in the area (If router is an ABR do it for both instances of OSPF for each area) |
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Why is a sequence number important? |
A sequence number maintains the LSDB and it's updates and the reliability of it.
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When does a sequence number increment?
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It increments by 1 after an update is received |
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What is a Stub Area?
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Does not accept external summary routers (LSA 4 and 5) ABR injects a default route no matter how suboptimal paths are Default route 0.0.0.0 is propagated throughout the area to reach external Cannot be Area 0 Cannot be a virtual link area No ASBRs allowed All routers must be configured as stub |
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What is a Totally Stubby Area |
No type 3 LSAs allowed Cannot be area 0 Cannot be a virtual link No ASBR allowed All routers must be configured as stub ABR must be totally stubby |
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What is a Not-So-Stubby area? |
Used to usually connect to ISP Does not accept type 4 or type 5 LSA Allows importing of external routes as type 8 and translates them to type 5 on ABR |
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What is a Totally-Stubby-Not-So-Stubby-Area? |
Does not accept external routes or inter area routes (Type 3, type 4, type 5 LSA) Recognizes intra area routes only and default route |
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What does a default-route do in a normal area? |
Does not automatically generate default route Default information originate command must be used |
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What does a default-route do in a Stub and Totally Stubby area? |
ABR auto generates summary LSA |
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What does a default-route do in a NSSA area? |
ABR can generate default but not by default |
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What does a default-route do in a Totally Stubby NSSA? |
ABR automatically generates a default route |
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What is a passive interface? What does it prevent? |
Appears as a stub network OSPF routing information is neither sent nor received on interface Prevents from neighbor establishment |
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What is a virtual link? |
Used to connect discontinuous area to area 0 Not an optimal solution, should only be temporary Virtual link LSA have a DoNotAge option set, no sequence |
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Why are virtual links bad networking practice? |
Virtual links are a solution to a bad network topology. |
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What protocol does address families run on for OSPF and why? |
Address families only run on OSPFv3 because it supports both IPv4 and IPv6
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How are interfaces added to address families and what do you need to specify? |
OSPFv3 is activated per instance specifying which address family you are activating |
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How does OSPFv3 determine a Router-ID? |
1. Router ID2. Highest loopback IPv4 Address3. Highest active IPv4 Interface
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http://puu.sh/kUmRr/6f8267ddd9.jpg |
http://puu.sh/kUmRr/6f8267ddd9.jpg |
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What is contained in the Topology Table in EIGRP? |
Contains all destinations advertised by neighboring routers Contains addresses from the whole networkUsually is the same for every router |
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What is contained in the EIGRP Routing table? |
Containts EIGRP successor routes
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Advertised Distance |
Or reported distance is the cost between the next hop-router and the destination |
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Feasible Distance |
The cost between the source router + the next hop routers distance to the destination (total distance) |
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What is a successor? |
Neighboring router that has the least-cost path to the destination (low FD) that is not in a routing loop Are in the routing table and used to forward packets Multiple successors can exit if the FD is the same |
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What is a Feasible Successor? |
Neighbor that is closer to the destination but it is not the least-cost path Ensures a loop-free topology because the AD is less than the FD of the current route. This guarentees that there can be no loop since it does not pass through the current pathSelected as the backup at the same time as the successor Topology can maintain multiple feasible successors for a destination |
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What is the Feasibility Condition? |
Feasible successors must meed the feasibility condition Feasibility condition states that the next-hop router must have an AD less than the FD of the current successor route for the particular network. Ensures that FS cannot use route through local router, avoiding loops (Doesn't have a zero cost route or something that causes it to go back through the current successor) |
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What is an Active route? |
Route lost FS or FD and is undergoing recomputation A route goes active then it is sending out queries |
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What is Reliable Transport Protocol? (RTP) |
Cannot use services of UDP or TCP RTP is used to provide reliable packet delivery for Update Query and Reply Unreliable packets Hello and ACK do not use RTP |
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How are neighbors discovered in EIGRP? |
Adjacencies are established using small Hello PacketsHello's send every 5 seconds or 50 seconds Dead times are 15 and 180 |
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How are routes discovered in EIGRP? |
1. Hello 2. Hello, Update 3. Ack, Update 4. Ack |
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What are Protocol Dependent Modules? |
Various routed protocols are used with PDMProvides independence from other routed protocols Each PDM has its own Neighbor, Topology, and routing table |
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Explain DUAL |
Uses the neighbor and topology table to calculate information If a link fails DUAL looks for feasible successor in its Neighbor and topology table Compares all routes and composes a metric for each route Lowest cost is added |
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How does DUAL query? |
When know FS exists EIGRP begins diffusing Sets the route active 1. Sends query packets to all neighbors looking for another path 2. Waits for replies from all neighbors before choosing a new best path 3. The neghbors forward the queries and they also wait for replies 4. Updates topology routing and advertises new route |
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What part of the EIGRP packet says what type it is? |
The header |
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EIGRP Packet type 1? |
Hello:
EIGRP relies on this to discover, verify, and redistover neighbors Mutlicasted to 224.0.0.10 Always sent unreliable does not use RTPHello/Hold timers do not need to match High bandwidth: 5 seconds Low Bandwidth 60 seconds, tefault on T1 or less Holdtime is the max time allowed before neighbor is dead (any EIGRP packet resets timer) Hold time is 3x the Hello Timer |
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EIGRP Packet type 2? |
ACK: Are used to reply to any reliable packet They are sent as dataless hello packets and unicast Can also be sent to attached to other unicast messages like updates or hellos |
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EIGRP Packet type 3? |
Update: After neighbors are discovered, updates packets are sent to new neighbors Updates are also sent when a router detects change, multicast to all neighbors All update packets are sent reliably (RTP) |
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EIGRP Packet type 4? |
Multicasted to other EIGRP routers during re computation If link goes down queries are sent out neighbors are also send out queries Query packets are sent reliably (RTP) Sent only if there are no feasible successors |
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EIGRP Packet type 5? |
Used to reply to a query saying there is a feasible successor or there is not Replies are always unicasted |
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Summarized networks???? |
To be added |
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Describe Stuck In Active |
If a router does not receive a reply to queries withing 3 minutes (180) route goes to Stuck in Active (SIA) If a router becomes in SIA, it sends out SIA queries, other SIA routers will send SIA replies |
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Describe a Stub in EIGRP |
Commonly hub-and-spoke topology A stub router should be router connected core network but where core traffic does not need to flow Stub router should only have hub routers for neighbors Stub router sends special peer information to all routers saying it's a stub A neighbor will not query a stub router |
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Types of stubs? |
Receive only: Restricts router from sharing any of its routers with other routers Connected: Permits EIGRP stub to send connected routes Static: Permits EIGRP stub to send static routesSummary: Permits stub router to send summarizaed routes Redistributed: Permits stub to send redistributed routes |
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What are the 4 things EIGRP uses for Metric calculation? |
Bandwidth (Default): Uses slowest bandwidth in calculation Delay (Default): Measure of time it takes for a packet to traverse a route, uses a cumulative sum of outgoing interfrace, best way to manually change interface metric is to change delay not bandwidth Reliability: Measure of likelihood that a link will fail, determined dynamically as represented as a fraction, higher fraction = better reliabilityLoad: Reflects how much trafic is using the link, determined dynamically and represented as fraction, lower fraction = less load on the link |
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What is the metric formula |
Metric= K1*BW+K3*Delay EIGRP Neighbors must have the same metric K values MTU is included in the routing update but not in metric calculation |
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EIGRP for IPv6 |
Link-local addresses are used for neighborsConfigured on per-interface Starts in shutdown states Routes IPv6 Only Router ID is still IPv4. If there is no IPv4 running and no router ID configured, EIGRP will not run Must enter no shut command in EIGRP config mode to turn it on |
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Named Mode EIGRP |
Runs IPv4 and IPv6 on the same instance The name must be unique on the router but has to be the same for instances run on other routers Uses address families. One for IPv6 and one for IPv4 Once address family is made, EIGRP is running for that protocol AS number is required for address familiesUsing the af-interface, you go into the interface to add it to the processAuthentication, hello/hold interval can be edited there like a normal interface Topology based is used as the global EIGRP interface command center |
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Load Balancing |
Routes equal to the minimum metric are installed in the routing table as equal-cost load balancing The maximum paths that are equal allows up to 16 equal paths If AD and FD are equal they can equal balance The default is 4 Setting it to 1 disables |
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Unequal Load Balancing |
Only one protocol can do this The variance multiplier controls the unequal cost-load balancing A variance higher than 1 installs multiple loop-free routes with unequal cost in the tableVariance allows feasible successors as candidates routes to be installed in routing table Variance uses routes that have a FD less than the number specified times the FD of currenct successor Variance is propotional. It will only get a percentage of the packets (variance specifies how much) |
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Authentication |
Simple password Authentication 1. Router sends packet and key 2. Neighbor checks key received to own key and verifies 3. Not secure at all |
