Cisco (300-410-ENARSI) Exam Questions And Answers page 4

The output of the command shows that Router C and Router B will fail to have all OSPF routes in their tables. In a hub and spoke configuration, as depicted in the diagram, the hub router (Router A) should be the designated router (DR) or the source of updates to the other routers. However, Router B is the DR, as evidenced by the output of the show ip ospf neighbor command executed on Router A.
This situation could be rectified by setting Routers B and C with a priority of 0, which would disqualify them from being the DR. After that, all routes could be distributed from the hub, which would have visibility of all routes.
All routing tables will be populated correctly until the hub router is made the DR.
Neither Router A nor C will be the DR, since it is indicated that Router B is the DR in the output of the command.
Objective:
Layer 3 Technologies
Sub-Objective:
Configure and verify OSPF operations
Cisco > Home > Support > Support Technology > Support > IP Routing > Configure > Configuration Examples and Technotes > Initial Configurations for OSPF over Frame Relay Subinterfaces
Cisco > Cisco IOS Wide-Area Networking Command Reference > frame-relay lapf n201 through fr-atm connect dlci > frame-relay map
Cisco > Cisco IOS IP Routing: OSPF Command Reference > ip ospf network

The neighbor with the IP address 10.2.1.1 has an established connection with RouterA. This is because the State/PfxRcd value for this neighbor is a number, 15, which indicates the number of prefixes received by RouterA from the neighbor. The prefixes are exchanged between BGP neighbors through the update message, which can be transmitted only if an established connection exists between the neighbors. An established connection exists between two neighbors if the local router is in Open Confirm state and it receives a KEEPALIVE or an UPDATE message.
The connection between RouterA and the neighbor with the IP address 10.1.1.1 is not established. This is because the State/PfxRcd value for this neighbor is OPENSENT. In this state, RouterA sends an OPEN message to a neighbor to determine the parameters for establishing a connection. The OPENSENT state occurs before the connection is established.
The connection between RouterA and the neighbor with the IP address 10.3.1.1 is not established. This is because the State/PfxRcd value for this neighbor is IDLE. In this state, RouterA does not accept any incoming connections from the neighbor.
The connection between RouterA and the neighbor with the IP address 10.4.1.1 is not established. This is because the State/PfxRcd value for this neighbor is ACTIVE. In this state, RouterA is attempting to establish a BGP peering session but it is not yet complete.
The connection between RouterA and the neighbor with the IP address 10.5.1.1 is not established. This is because the State/PfxRcd value for this neighbor is OPENCONFIRM. In this state, RouterA waits for a KEEPALIVE or NOTIFICATION message from the neighbor.
Objective:
Layer 3 Technologies
Sub-Objective:
Describe, configure, and verify BGP peer relationships and authentication
Cisco IOS IP Routing: BGP Command Reference > show ip bgp summary

The following statements are TRUE about the given output:
• The 10.62.7.0 route is learned by the router through an iBGP neighbor.
• All five routes have been originated by an IGP.
The show ip bgp command displays information about the BGP routing table, including origin type, metric, next-hop addresses for every route learned by BGP, router ID, local preference, and BGP path. In the output, the character i in the first entry of the 10.62.7.0 destination indicates that the route was learned by an iBGP neighbor. The * symbol at the beginning of the routes indicate that they are valid routes, while the > symbol indicate that the route is the current best route.
The i at the end of the entries under the Path column indicates that the routes have been originated by an interior gateway protocol (IGP). In the scenario output, all five routes have an i at the end of their respective entries. If the character e appears as the origin code, the routes are considered to have originated from an exterior gateway protocol (EGP). The origin code can also be the ? character, which implies that the origin of the route is unknown.
The output also displays the next-hop addresses for the routes. The 200.7.34.0 subnet is a local route, and hence has its next-hop address as 0.0.0.0.
The show ip bgp command also displays the local router's ID (RID), local preference, weight, and next-hop addresses for every route learned by BGP. In this case, the RID of RouterA is 200.17.34.15 and the local preference, weight, and next-hop address for the 10.62.7.0 network are 100, 0, and 10.62.7.78, respectively. The metric and the next-hop address for the BGP routes can also be viewed by using the show ip route bgp command, as follows:
RouterA# show ip route bgp
B 10.62.7.0 [200/0] via 10.62.7.78, 01:34:16
B 200.17.56.0 [200/0] via 10.62.7.78, 01:34:16
B 192.177.1.0 [20/100] via 10.62.7.115, 01:34:16

The BGP table version can also be displayed by using the show ip bgp neighbors and the show ip bgp summary commands. The show ip bgp neighbors command also displays the address, ASN, and RID of neighbors of the local router, as shown below:
RouterA# show ip bgp neighbors
BGP neighbor is 192.177.1.6, remote AS 200, external link
BGP version 17, remote router ID 200.17.34.15
BGP state = Established, table version = 16, up for 01:45:03

The show ip bgp summary command displays the RID and the BGP table version, as shown in the following output:
RouterA# show ip bgp summary
BGP router identifier 200.17.34.15, local AS number 100
BGP table version is 17, main routing table version 18

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
10.62.7.90 17 200 56 55 18 0 0 01:42:13 27
10.62.7.145 17 300 34 33 18 0 0 00:31:20 0

The router is not aware of the best path for the 61.80.3.0 route. The character h appears at the beginning of the entry for the 61.80.30 destination. This means that the route is in the history state currently and that the best route is not known.
There are not four AS between the router and the 192.177.1.0 subnet. In the output, the Path column for the 192.1771.1.0 subnet lists four AS numbers. The four AS numbers refer to the ASNs traversed by the route from RouterA to the 192.177.1.0 subnet. The first AS refers to the first neighbor of RouterA; the second AS refers to the neighbor of the first neighbor; and so on. The last AS in the column is the AS of the 192.177.1.0. This implies that there are three AS (1, 2, and 3) that exist between RouterA and the subnet.
Objective:
Layer 3 Technologies
Sub-Objective:
Configure and verify eBGP (IPv4 and IPv6 address families)
Cisco > Cisco IOS IP Routing: BGP Command Reference > show ip bgp
Cisco > Cisco IOS IP Routing: BGP Command Reference > show ip route bgp
Cisco > Cisco IOS IP Routing: BGP Command Reference > show ip bgp summary

The list is applied to the wrong interface. An access list that is designed to control remote access should be applied to the VTY lines, not to one of the physical interfaces. If the command were formatted correctly, the show run output would appear as follows:

The IPv6 address is formatted correctly. Although it has been shortened in format, it follows all of the shortening rules. It omits only leading zeros and it utilizes the double colon only once.
The access list does not require a deny statement. There is an implicit deny all at the end of the list.
The ipv6 access-group command should not be used to apply the list. This command is used when an access list is applied to a physical interface, not the VTY lines.
Objective:
Infrastructure Security
Sub-Objective:
Configure and verify router security features
Cisco > IPv6 Configuration Guide, Cisco IOS Release 15.0S > Implementing Traffic Filters and Firewalls for IPv6 Security > Access Control Lists for IPv6 Traffic Filtering
Cisco > Security Configuration Guide: Access Control Lists, Cisco IOS Release 15S > Controlling Access to a Virtual Terminal Line

The routes that will be present in Router R1 are 192.168.5.0 and 10.0.0.0. According to the output, only the route from EIGRP 55 will be redistributed to EIGRP 200. Therefore, the 10.0.0.0 network will be advertised to Router R1 from Router R2 and the 192.168.5.0 network, which is present in the routing table of Router R2, will be advertised to Router R1.
The 192.168.5.0 network alone would not be correct. The 10.0.0.0 network will be present as well.
The 172.50.0.0 network will not be present because Router 2 is not configured with a redistribution statement for that network. The required statement would be redistribute ospf 1.
Objective:
Layer 3 Technologies
Sub-Objective:
Configure and verify redistribution between any routing protocols or routing sources
Cisco > Home > Support > Technology Support > IP > IP Version 6 > Configure > Configuration Examples and Technotes > Redistributing Routing Protocols

Issuing the following commands will cause RTR2 to advertise the CIDR block 192.168.0.0/16 to the other routers by using BGP:
RTR2(config)# router bgp 65100
RTR2(config-router)# neighbor 172.16.1.2 remote-as 65101
RTR2(config-router)# neighbor 192.168.3.2 remote-as 65100
RTR2(config-router)# network 192.168.0.0 mask 255.255.0.0
RTR2(config-router)# ip route 192.168.0.0 255.255.0.0 null 0

The network command specifies the address that will be inserted into the BGP table. Without the mask keyword, the classful network will be assumed. Because 255.255.0.0, or /16, is not the natural mask for any Class C address, the mask keyword must also be specified. Thus, 192.168.0.0 and 255.255.0.0 identify the desired address and mask of the 192.168.0.0/16 network prefix.
The router checks the IP forwarding table for an exact match before it advertises the route. Without a matching entry in the IP forwarding table, that route will not be advertised. RTR2 must be able to advertise a CIDR block and not the individual subnets. A static route is required because BGP requires that a match of the network prefix be present in the forwarding table when using the network command with the mask keyword. Therefore, to ensure an exact match for the identified prefix exists in the IP forwarding table, and to ensure that the prefix will always be advertised, a static route for 192.168.0.0/16 to null 0 is also required.
The syntax for the network command is shown below:
network network-number [ mask network-mask ] [ route-map map-tag ]

The parameters are:
• mask - This parameter is optional and identifies the network or subnetwork to advertise.
• route-map - This parameter is optional and identifies a preconfigured route-map that will be used to filter specific addresses from being advertised.
The following command set is missing the mask keyword in the network command and the command to create a static route to null 0. The address used in the network command is also incorrect. It should 192.168.0.0:
router bgp 65100
neighbor 172.16.1.2 remote-as 65100
neighbor 192.168.3.2 remote-as 65100
network 192.168.3.0

The following command set is missing the mask keyword in the network command and the command to create a static route to null 0:
router bgp 65100
neighbor 172.16.1.2 remote-as 65101
neighbor 192.168.3.2 remote-as 65100
network 192.168.0.0

The following command set uses an incorrect mask (255.0.0.0) in the command that creates the static route to null 0. It should be 255.255.0.0:
router bgp 65100
neighbor 172.16.1.2 remote-as 65100
neighbor 192.168.3.2 remote-as 65100
network 192.168.0.0 mask 255.255.0.0
ip route 192.0.0.0 255.0.0.0 null 0

Objective:
Layer 3 Technologies
Sub-Objective:
Describe, configure, and verify BGP peer relationships and authentication
Internetworking Case Studies > Using the Border Gateway Protocol for Interdomain Routing > Controlling the Flow of BGP Updates > CIDR and Aggregate Addresses > Aggregation and Static Routes

At the area border router (ABR), router R2, the no-summary keyword is required with the area stub command to create a totally stubby area. All other routers in area 5 will require the stub command without the no summary keyword. The following commands are required to configure R2:
R2(config)# router ospf 5
R2(config-router)# area 5 stub no-summary
R2(config-router)# network 172.31.200.0 0.0.7.255 area 5

R1 will require:
R1(config)# router ospf 5
R1(config-router)# area 5 stub
R1(config-router)# network 172.31.200.0 0.0.7.255 area 5

All routers within a stub area must be configured as stub, or adjacencies will not form. Besides the command to enable OSPF and the command to identify the area, the only other required command identifies the area as a stub. A totally stubby area does not accept any external network LSAs (Type 5) or any inter-area summary LSAs (Types 3 and 4) from entering the area.
Use the area stub command with the no-summary keyword to configure a totally stubby area. The diagram below shows the commands that should be executed on R1 and R2.

The correct syntax for the area stub command is shown below:
Router(config-router)# area area-id stub [no-summary]

Note that the optional no-summary keyword is used only on area border routers (ABRs) to block summary link advertisements into the stub area. This option creates a totally stubby area. It is very important to configure the command consistently on all routers within the area. OSPF sends its stub status (on or off) in its hello packets. If two neighbors have conflicting stub status, they will not form an adjacency, and you end up with no OSPF communication over that link.
Objective:
Layer 3 Technologies
Sub-Objective:
Configure and verify network types, area types, and router types
Cisco > Home > Support > Technology Support > IP Routing > Design > Design Technotes > What Are OSPF Areas and Virtual Links? > What Are Areas, Stub Areas, and Not-So-Stubby Areas?
Cisco > Cisco IOS IP Routing: OSPF Command Reference > area stub

All routers within a stub area must be configured as stub, or adjacencies will not form. Besides the command to enable OSPF and the command to identify the area, the only other required command identifies the area as a stub. At the area border router (ABR), R2, the no-summary keyword is required. The following commands are required to configure R1:
R1(config)# router ospf 5
R1(config-router)# area 5 stub
R1(config-router)# network 192.168.5.0 0.0.0.255 area 5

A totally stubby area does not accept any external network LSAs (Type 5) or any inter-area summary LSAs (Types 3 and 4) from entering the area. Use the area stub command with the no-summary keyword on the ABR only to configure a totally stubby area.
The correct syntax for the area stub command is shown below:
Router(config-router)# area area-id stub [no-summary]

Note that the optional no-summary keyword is used only on ABRs to block summary link advertisements into the stub area. This option creates a totally stubby area. It is very important to configure the command consistently on all routers within the area. OSPF sends its stub status (on or off) in its hello packets.
If two neighbors have conflicting stub status, they will not form an adjacency, and you end up with no OSPF communication over that link.

Objective:
Layer 3 Technologies
Sub-Objective:
Configure and verify network types, area types, and router types
Cisco > Home > Support > Technology Support > IP Routing > Design > Design Technotes > What Are OSPF Areas and Virtual Links? > What Are Areas, Stub Areas, and Not-So-Stubby Areas?
Cisco IOS Master Command List, Release 12.4 > a through b > area stub

If either the clear ip arp or the clear adjacency commands were issued, the entry would temporarily be listed as incomplete in the adjacency table. The adjacency table is used by Cisco Express Forwarding (CEF) to maintain Layer 2 information about the next hop to remote networks. In CEF, an adjacency refers to a control structure that holds Layer 2 information for an IP address on a particular interface. When that information is not available the entry will be listed as incomplete, as shown in the example.
Layer 2 information normally comes from the ARP process. Therefore, if the ARP table is cleared with the clear ip arp command, the Layer 2 information will be temporarily unavailable until the ARP process re-learns it the next time a frame must be sent to that hop. Moreover, if the adjacency table is emptied with the clear adjacency command, the entry must be created again. This will also result in the entry being marked incomplete for a short period of time until the ARP table can be consulted and the Layer 2 information re-added.
The interface in the scenario is not a multipoint interface. A multipoint interface would include entries for multiple next hops, since a multipoint interface connects to multiple Layer 3 destinations. An example of this is shown below in sample output from a Frame Relay interface:

The layer 3 information of the next hop is present in the entry in the scenario example. It is 10.10.10.2.
Objective:
Network Principles
Sub-Objective:
Identify Cisco Express Forwarding concepts
Home > Support > Technology support > IP > IP switching > Troubleshoot and alerts > Troubleshooting Technotes > Troubleshooting Incomplete Adjacencies with CEF

It will drop the packet. The partial output of the show run command shows that the ip verify unicast source reachable via rx command has been executed on the Serial 0/0 interface. This enables the Unicast Reverse Path Forwarding (Unicast RPF) feature. This feature prevents IP spoofing by verifying from the routing table that there is a valid return path to the source IP address. If there is not valid return path, you can assume the IP address has been spoofed. When the command ends in the keyword rx, it means that there must be a return path through the interface where the command was executed. This is called strict mode.
The packet arrived on the Serial0/0 interface. The routing table shows that there is no routing entry for the 192.168.5.0/24 network that leads back through the entry interface of Serial0/0. In fact, in this instance there is no routing table entry for that network leading to any interface. When this occurs, the router will drop the packet.
The router will not send the packet to either the Ethernet0/0 or the Tunnel0 interfaces because the destination network, 10.11.11.0/24, is not a reachable destination on those interfaces. Even if it were reachable, the Unicast Reverse Path Forwarding (Unicast RPF) feature will drop the packet because it has been spoofed.
It will not send the packet to the Ethernet0/1 interface. The Unicast Reverse Path Forwarding (Unicast RPF) feature will drop the packet because it has been spoofed. If the packet were not spoofed, it would be sent to the Ethernet0/1 interface because that is the interface used by the default route. Because there is no route in the table to the 10.11.11.0/24 network, it would be sent to the default route.
Objective:
Infrastructure Security
Sub-Objective:
Configure and verify router security features
Cisco IOS Security Configuration Guide, Release 12.2 > Configuring Unicast Reverse Path Forwarding
Cisco > Configuring Unicast Reverse Path Forwarding