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34 Cards in this Set

  • Front
  • Back
What is Path Control?
It is a class of tools and protocols that Layer 3 devices use to learn, manipulate and use IP routes.
Why would you use Route Redistribution?
Route redistribution is used when the domain is using more than one routing protocol. An example is in the event of a company merger. One company can be using OSPF and the other EIGRP. To share each others' routes, redistribution of the routing protocols in both directions would be necessary. Redistribution is needed when routes from both routing protocols need to be shared.
What is the concept and process of redistribution?
In redistribution, at least one router must:

* Use at least one working physical link with each routing domain
* A working routing protocol for each routing domain
* Additional redistribution configuration on each routing protocol, using the redistribute command.

The concept is that a router between two routing domains will use the redistribute command to take routes from each routing domain and include them in the other. The redistribute command takes the routes from the IP routing table, connected interfaces and passive interfaces and redistributes them into the other routing domain.
What command is used to redistribute EIGRP?
redistribute protocol [process-id | as-number] [metric bw delay reliability load mtu] [match {internal | nssa-external | external 1 | external 2}] [tag tag-value] [route-map name]
What are commonly used OSPF terms for redistribution?
What are some methods of setting EIGRP metrics when redistributing EIGRP?
What does a baseline configuration of EIGRP redistribution look like?
Example: redistributing EIGRP routes into OSPF and vice-versa. On the router between both routing domains:

RD1# config t
! Redistribute OSPF routes into EIGRP
RD1(config)# router eigrp 1
RD1(config-router)# redistribute ospf 2
RD1(config-router)# end

RD1# config t
! Redistribute EIGRP routes into OSPF
RD1(config)# router ospf 2
RD1(config-router)# redistribute eigrp 1
RD1(config-router)# end
How do you verify EIGRP redistribution?
Can use the following show commands:

* show ip eigrp topology
* show ip eigrp topology x.x.x.x/x
What does the redistribute command tell the router?
When referred to another IGP as the routing source, it tells the router to redistribute the following:

* All routes in the routing table learned by that routing protocol
* All connected routes of interfaces on which that routing protocol is enabled
What command is used to redistribute OSPF?
redistribute protocol [process-id | as-number] [metric metric-value] [metric-type type-value] [match {internal | external 1 | external 2 | nssa-external}] [tag tag-value] [route-map map-tag] [subnets]
What are the parameters for OSPF redistribution?
What are the defaults for OSPF redistribution?
The following are default to OSPF redistribution:

* When taking from BGP, use a default metric of 1
* When taking from another OSPF process, take the source route's metric
* When taking from all other sources, use a default metric of 20
* Create a Type 5 LSA for each redistributed route (external) if not inside an NSSA area; create a Type 7 LSA if inside an NSSA area
* Use external metric type 2
* Redistribute only routes of classful networks, and not routes for subnets
Why would you include keyword subnets in redistribute command?
If the subnets keyword is left out, OSPF will only redistribute routes for entire classful subnets and only if the route exists in the IP routing table. By including the subnets keyword, the subnets will be redistributed.
What OSPF metrics can be configured for OSPF redistribution?
What is included in the LSA for External Type 2 routes?
Aside from the defaults for OSPF redistribution, the LSA Type 5 includes the following fields:

* LSID: the subnet number
* Mask: the subnet mask
* Advertising router: the RID of the ASBR injecting the route
* Metric: the metric as set by the ASBR
* External Metric Type: the external metric type, either 1 or 2
How would you determine the next-hop for Type 2 External routes in an intra-area?
The router will select the router with the lowest metric. The following are the steps in a tie-break when multiple equal-cost E2 routes exist for a particular subnet:

1. Find advertising ASBR(s) listed in Type 5 LSA(s)
2. Calculate lowest cost route to reach any of the ASBR(s) based on the intra-area LSDB topology
3. Use the outgoing interface and next hop based on the best route to reach the ASBR, chosen at Step 2
4. The route's metric is unchanged-it is still simply the value listed in the Type 5 LSA
How would you determine the next-hop for Type 2 External routes in an interarea?
The calculation is very similar to the calculation for an intra-area route except the router must include another LSA (Type 4 which lists RID for ASBR and ABR). The router calculates the lowest cost route to reach an ASBR and then adds the cost to reach an ABR between the areas.
Why would you redistribute OSPF as an E1 route?
An E1 route would be used when you want to influence the choice of best route. E2 routes maintain the same metric throughout the area. E1 routes are calculated by each router giving the routers the choice of lowest-metric route. They add the internal cost to reach the ASBR to the external cost defined on the redistributing ASBR.
How do you redistribute OSPF as an E1 route?
RD1# conf t
RD1(config)# router ospf 2
RD1(config-router)# redistribute eigrp 1 subnets metric-type 1
What are the main differences between E1 and E2 routes?
E1 routes use the external cost and internal OSPF cost for the choice of best route. E2 routes use only the external cost for choice of best routes.
How do external routes work in NSSA areas?
Of all the stub settings, only the NSSA can accept injection of external routes, as Type 7 AS External LSAs. Type 7 replaces Type 5 only inside an NSSA.

1. ASBR attached to NSSA area 1 redistributes a route for a subnet, creating a Type 7 LSA.
2. ASBR floods the Type 7 LSA throughout the NSSA area.
3. ABR converts Type 7 LSA to a Type 5 LSA when forwarding into other areas.
4. Other ABRs connect to another normal area forwards the Type 5 LSA from the NSSA subnet into another normal area.
What are virtual links?
Method of connecting two discontiguous backbone areas through a non-backbone area.
Describe the concept of virtual links?
A virtual link connects two discontiguous backbone areas, through a transit area, to create a contiguous backbone area. Virtual link is connected by an ABR on each end which send unicast IP packets with OSPF information.
How do you configure virtual links w/ no authentication?
area area-transit-num virtual-link remote-RID
How do you verify an OSPF virtual link?
sh ip ospf virtual-links
sh ip ospf neighbor
How do you configure virtual link authentication?
No authentication: area num virtual-link RID authentication null

Clear-text: area num virtual-link RID authentication authentication-key key-value

MD5: area num virtual-link RID authentication message-digest message-digest-key key-name md5 key-value
What are some IP subnetting designs for Frame Relay?
Designs include one subnet for all PVCs or one subnet per PVC.
What are some challenges of OSPF over multipoint?
By default, OSPF needs more configuration for correct operation over Frame Relay. Issues include neighbor discovery, Designated Router selection and mapping. For neighbor discovery to work, actions must be taken based on the configurations:

If network type allows neighbor discovery & InARP, neighbors will be discovered.

If network type allows discovery and frame-relay map is used, configure with broadcast keyword.

If network type doesn't allow neighbor discovery, must statically define neighbors.
How are neighbors defined?
With the neighbor router subcommand.
What mapping issues occur with a partial mesh?
DR & BDR are chosen depending on network type. Issues will arise on partial mesh networks because of connectivity to DR or BDR. In conclusion, if requiring the use of a DR or BDR, ensure that both have a PVC connection to each router. Or configure the network type to avoid DR/BDR usage.

To resolve Partial Mesh mapping issues, ensure that a router lists each other routers' DLCI used to reach that router. Problem occurs when using InARP or static frame-relay maps. Those without a direct PVC need a static IP to DLCI mapping.
What and how is Point-to-Multipoint used?
Point-to-multipoint is opposite of non-broadcast. DR/BDR are not elected and neighbors are dynamically discovered. Routers are configured with a network type ip ospf network point-to-multipoint interface subcommand. Frame Relay maps are required if partial mesh exists.

Point-to-Multipoint configuration: neighbor next-hop-IP [cost cost-value] [priority priority-value]
How do you verify Frame Relay on OSPF?
With command: sh ip ospf interface
What is Point-to-Multipoint non-broadcast?
Doesn't elect a DR/BDR and doesn't dynamically discover neighbors. Therefore, frame relay map needs to be configured for partial mesh network and neighbors must be defined with a neighbor command.
How do you configure OSPF Frame Relay?
To configure OSPF over Frame Relay, you need to know if using more than two routers. If so, decide on physical or multipoint interfaces. Then decide if routers should elect a DR/BDR. This will determine the network type.