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48 Cards in this Set
- Front
- Back
Routers and Layer 3 switches learn about remote networks in one of two ways: |
Manually Dynamically |
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Manually - Remote networks are manually entered into the route table |
using static routes. |
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Manual routes must be reconfigured anytime the |
network topology changes. |
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Static routing has three primary uses: |
Ease of routing table maintenance Routing to and from stub networks. Using a single default route. |
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Dynamically - Remote routes are automatically learned using a |
dynamic routing protocol. |
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Dynamic routing protocols require less |
administrative overhead. |
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The expense of using dynamic routing protocols is dedicating part of a router’s resources for |
protocol operation. |
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Most networks use a combination of |
dynamic routing protocols and static routes. |
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OSPF its features include: |
Classless Efficient Fast convergence Scalable Secure |
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OSPF is classless and supports |
VLSM and CIDR. |
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Routing changes trigger |
routing updates. |
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It uses the SPF algorithm to choose the |
best path. |
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OSPF supports this type of authentication: |
(MD5) authentication. |
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OSPF defines five network types: |
Point-to-point Broadcast multiaccess Nonbroadcast multiaccess Point-to-multipoint Virtual links |
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Multiaccess networks can create two challenges for OSPF regarding the flooding of LSAs: |
Creation of multiple adjacencies Extensive flooding of LSAs |
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The solution to managing the number of adjacencies and the flooding of LSAs on a multiaccess network is the |
DR. |
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OSPF elects a DR to be the |
collection and distribution point for LSAs. |
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A BDR is also elected in case the |
DR fails. |
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If the DR stops producing Hello packets, the BDR |
promotes itself and assumes the role of DR. |
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All other non-DR or BDR routers become |
DROTHER. |
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Instead of flooding LSAs to all routers in the network, DROTHERs only send their LSAs to the |
DR and BDR using the multicast address 224.0.0.6. |
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The router with the highest router-id is |
elected DR. |
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The state of neighbors in multiaccess networks can be: |
FULL/DROTHER FULL/DR FULL/BDR 2-WAY/DROTHER |
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The normal state for an OSPF router is usually |
FULL. |
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If a router is stuck in another state, it is an indication that there are problems in |
forming adjacencies. |
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Default DR/BDR Election Process: |
highest interface priority > highest router ID > highest loopback IP address > highest active IPv4 address |
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The DR and BDR election process takes place as soon as the first router is |
powered on or when the OSPF network command is configured. |
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After the DR is elected, it remains the DR until one of the following events occurs: |
The DR fails. The OSPF process fails or is stopped. The multiaccess interface fails or is shutdown. |
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Instead of relying on the router ID, it is better to control the election by setting |
interface priorities. |
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If the interface priority is configured after OSPF is enabled, the administrator must either: |
Shut down and re-enablethe OSPF process on all routers. Shutdown and re-enable the router interfaces. |
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The router located between an OSPF routing domain and a non-OSPF network is also called the |
autonomous system boundary router (ASBR). |
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The (ASBR) router connected to the Internet is used to propagate a |
a default route to other routers. |
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The default-information originate command |
propagate the default static route in OSPF updates. |
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O*E2 signifies that a route was learned using |
OSPF and that is an external route. |
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A type 1 route is the |
externel and internal cost combined and is always prefered. |
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A type 2 route is the cost of the |
external route. |
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The OSPF Hello and Dead intervals are configurable on a |
per-interface basis. |
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The OSPF intervals must match or a |
neighbor adjacency does not occur. |
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OSPF Attacks: |
disrupting routing peers. falsifying information. |
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The consequences of falsifying routing information are: |
Redirecting traffic to create routing loops. Monitoring traffic. Discarding traffic. |
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To mitigate against routing protocol attacks, configure |
OSPF authentication. |
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When neighbor authentication has been configured on a router, the router authenticates the |
source of each routing update packet that it receives. |
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This is accomplished by the exchange of an |
authenticating key. |
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OSPF authentication can either be: |
none (or null) simple Message Digest 5 (MD5) |
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Simple authentication |
plaintext password exchanged between peers. |
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MD5 authentication |
password is calculated using the MD5 algorithm. |
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The routing message and preshared key are used to calculate a |
signature. |
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The recieving router combines the message and key to determine the |
signature. |