The Candid Test On CCIE-r&s-bGP Quiz

iBGP (internal BGP) is a type of BGP (Border Gateway Protocol) connection that occurs between routers within the same Autonomous System (AS). In this case, the correct answer states that a neighbor is considered iBGP when it is in the same AS. This means that the routers are part of the same network and can exchange routing information within the AS.

The AS_PATH attribute is used to track the path that a BGP route has taken through different autonomous systems. It helps prevent routing loops and provides information about the route's history.

BGP communicates with its neighbors by using the unicast neighbor address to TCP port 179. This means that BGP establishes a direct one-to-one connection with its neighbors using the TCP protocol. The use of TCP ensures reliable and ordered delivery of BGP messages between routers. The communication is not done through multicast addresses or UDP ports, but rather through a specific unicast address and TCP port number.

NLRI stands for Network Layer Reachability Information. It is used in routing protocols to advertise and exchange information about IP prefixes and their associated prefix lengths. Therefore, an NLRI is indeed a combination of an IP prefix (the network address) and a prefix length (the number of bits in the network address). This information is crucial for routers to determine the best path for forwarding packets in a network. Hence, the given answer "True" is correct.

The TTL (Time to Live) value in an eBGP (external Border Gateway Protocol) packet determines the maximum number of hops the packet can traverse before being discarded. By default, the TTL value for eBGP packets is set to 1, which means that the packet can only travel to the immediate neighbor router. This is done to prevent eBGP packets from being forwarded beyond the directly connected routers, ensuring that they reach their intended destination without being unnecessarily propagated throughout the network. Therefore, the given answer, "True," is correct.

Confederation routers remove the confederation Autonomous System Number (ASN) from the AS_PATH attribute in updates that are sent outside the confederation. This means that when a router within a confederation sends an update to a router outside the confederation, it will strip off the confederation ASN from the AS_PATH. This is done to ensure that routers outside the confederation do not see the internal structure of the confederation and treat it as a single AS. Therefore, the statement "Confederation routers remove the confederation ASN from the AS_PATH in updates sent outside the confederation" is true.

BGP supports MD5 authentication method. MD5 is a widely used cryptographic hash function that provides a secure way to authenticate BGP peers. It ensures that the BGP messages exchanged between routers are not tampered with or modified by unauthorized parties. By using MD5 authentication, BGP peers can verify each other's identities and establish a trusted connection for exchanging routing information.

BGP uses the shortest AS Path to choose the best route. The AS Path is a list of autonomous systems that a route has to traverse in order to reach its destination. BGP prefers routes with shorter AS Paths because they indicate a more direct path to the destination. This helps to reduce the likelihood of loops and improves network efficiency. Therefore, BGP selects the route with the shortest AS Path as the best route.

BGP uses the Notification message type when errors occur, causing a reset to the neighbor relationship when sent. The Notification message is used to inform the neighbor that an error has occurred and includes information about the specific error. This message is crucial in maintaining the integrity of the BGP network by allowing routers to quickly respond to errors and reestablish the neighbor relationship if necessary.

KeepAlive messages are used to maintain a neighbor relationship in the BGP protocol. These messages are sent periodically between BGP neighbors to ensure that the connection is still active and functioning properly. By exchanging KeepAlive messages, BGP routers can confirm that their neighbors are reachable and responsive. If a router stops receiving KeepAlive messages from a neighbor, it may consider the neighbor as unreachable and take appropriate actions, such as marking the neighbor as down and removing its routes from the routing table.

The command "neighbor update-source" is used to determine the source IP address used to reach a neighbor. This command allows the router to specify a specific interface or IP address to use when establishing a connection with its neighbor. By setting the update-source, the router ensures that the correct source IP address is used for BGP updates and communication with the neighbor. This can be useful in scenarios where the router has multiple interfaces or IP addresses and needs to control which one is used for BGP communication.

BGP uses the "Update" message type to exchange Network Layer Reachability Information (NLRI). The Update message is used to advertise, withdraw, or modify routing information between BGP peers. It contains the NLRI, along with other attributes such as path information, to inform neighboring routers about the available network destinations and their reachability.

The command "bgp log-neighbor-changes" enables logging of BGP neighbor status changes (up or down) and resets. This command is useful for troubleshooting network connectivity problems and measuring network stability as it allows for tracking and monitoring the changes in BGP neighbor status, which can help identify any issues or instabilities in the network.

The given configuration allows the RTC router to advertise iBGP learned routes to the iBGP speakers 2.2.2.2 and 3.3.3.3. By configuring the "neighbor" command with the "route-reflector-client" option for both neighbors, RTC is able to act as a route reflector and distribute the routes it learns from other iBGP peers to these two iBGP speakers. This helps in propagating the routes throughout the network and ensuring reachability between different BGP speakers.

The command "BGP network 10.1.1.0 mask 255.255.255.0" instructs the BGP process to put the equivalent Network Layer Reachability Information (NLRI) in the local BGP topology table if there is an exact match for the subnet 10.1.1.0/24 in the current IP routing table. This means that if there is a route for 10.1.1.0/24 in the routing table, BGP will consider it as a valid network and include it in its routing updates.

The BGP network 10.1.1.0 mask 255.255.255.0 command instructs the BGP process to check if the network 10.1.1.0/24 matches an entry in the current IP routing table. If it does, the equivalent Network Layer Reachability Information (NLRI) is added to the local BGP topology table. This allows BGP to advertise this network to its neighbors and include it in the BGP routing updates.

When a router chooses the best routes based on the shortest AS_PATH, it does not consider Confederation Autonomous System Numbers (ASN) as part of the length of the AS_PATH. This means that even if a route includes Confederation ASNs, they are not counted towards the length calculation. Therefore, the statement "Confederation ASN are not considered part of the length of the AS_PATH when a router chooses the best routes based on the shortest AS_PATH" is true.

The correct answer is to configure two static routes to the other loopback addresses (10.1.34.0/24 and 10.1.134.0/24), and then configure the neighbor 3.3.3.3 update-source looback0 and neighbor 3.3.3.3 ebgp-multihop 2 commands on R4. This configuration allows R3 and R4 to establish a BGP neighbor relationship using the loopback interface as the source address and enables BGP to use multiple hops to reach the neighbor. By configuring static routes to the loopback addresses, the traffic can be load balanced between the redundant links between R3 and R4.

When BGP advertises routes to an eBGP neighbor, the default action is to change the NEXT_HOP to the update source IP address. This means that the NEXT_HOP attribute in the BGP update message will be modified to reflect the IP address of the router that is sending the update. This is done to ensure that the eBGP neighbor will use the correct path to reach the advertised routes.

Confederation routers remove the confederation ASN from the AS_PATH in updates sent outside the confederation. So others routers does not know that a confederation was used.

BGP verifies the reachability of the NEXT_HOP as the first attribute in its decision process to find the best route. This means that the router checks if it has a route in its routing table to reach the NEXT_HOP specified in the route. If the NEXT_HOP is not reachable, the route is considered invalid and will not be chosen as the best route.

The correct answer is "R1# clear ip bgp * soft". This command allows a soft reconfiguration of BGP by clearing the BGP table without closing the neighbor connections. This means that the BGP peer can reapply its routing policies without disrupting the established connections with its neighbors.

By default, keepalive messages are sent at an interval of 60 seconds. Keepalive messages are used to ensure that a connection between two devices remains active and to detect if the connection has been lost. By sending keepalive messages at regular intervals, devices can confirm that the connection is still alive and functioning properly. In this case, the correct answer indicates that the default interval for sending these messages is 60 seconds.

The destination IP address is determined by manually configuring it using the neighbor command. This means that the network administrator manually specifies the IP address of the neighbor to reach.

The keepalive timer default value is 180 seconds, which means that after 180 seconds of not receiving any response from a neighbor, the neighbor is considered to have failed.

When BGP advertises routes to an iBGP neighbor, the default action is that it does not change the NEXT_HOP. Instead, it uses the NEXT_HOP value that is already present in the routing table. This means that the iBGP neighbor will receive the routes with the same NEXT_HOP value that was originally determined by the routing table.

The Open message type is used in BGP to establish a neighbor relationship and exchange basic parameters. This message is sent by a BGP speaker to initiate a TCP connection with a neighboring BGP speaker. It contains information such as the BGP version number, the BGP router ID, and the autonomous system number. The Open message is an essential step in the BGP neighbor establishment process.

The BGP Routing Information Base (RIB) refers to the BGP topology table that holds the Network Layer Reachability Information (NLRI) learned by BGP. This table contains information about the available paths to reach different network destinations. It includes details such as the next hop, path attributes, and network prefixes. The RIB is used by BGP to make routing decisions and determine the best path for forwarding traffic.

With Auto-Summary, if any subnets of the classful network exists in the routing table, it is injected into BGP.

MED default value is 0 (best value). So if one uses MED in its network, it is better to use this command to avoid mistaken routes using the default value. BGP subcommand "bgp bestpath med missing-as-worst" reset the default value for MED to the largest/worst value possible (2^32)

The "aggregate-address" command is used in BGP to summarize multiple routes into a single route. In this case, the command "aggregate-address 10.2.0.0 255.255.0.0 summary-only" is entered, which means that the route 10.2.0.0/16 will be advertised to its neighbors. This is because the command specifies the network address 10.2.0.0 and the subnet mask 255.255.0.0, which covers the range of IP addresses from 10.2.0.0 to 10.2.255.255. Therefore, all the more specific routes within this range, such as 10.2.0.0/24 and 10.2.1.0/24, will be summarized into the larger route 10.2.0.0/16 and advertised to neighbors.

When the keepalive timer within the OPEN message of each BGP neighbor mismatch, they use the lower keepalive timer value. This means that both neighbors will agree to use the keepalive timer value that is lower between the two. This ensures that the BGP session remains stable and both neighbors can continue exchanging keepalive messages at the agreed upon interval.

With Cisco IOS 12.3 and later, BGP does not perform Auto-Summary by default. Auto-Summary is a feature that automatically summarizes the network prefixes at the classful network boundary. However, starting from IOS version 12.3, BGP does not perform this auto-summary feature by default. This means that BGP will not automatically summarize the network prefixes unless specifically configured to do so.

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The configuration includes the "neighbor 160.10.1.1 ebgp-multihop" command, which allows a neighbor connection between two external peers that do not have a direct connection. This is a workaround to achieve load balancing between two eBGP speakers over parallel links. The two static routes for the 160.10.0.0 network with different next hops also support this load balancing by distributing traffic between the two links.

The configuration includes a BGP neighbor statement with the "remote-as" command, indicating that the neighbor is in AS 200. The "send-community" command is used to send BGP community attributes to the neighbor. The "route-map" command is used to apply a route map named "set-community" to the neighbor, with the "out" keyword indicating that it will be applied to outbound routes. The route map includes a permit statement with a match condition using access list 1 and a set action to add the "no-export" community attribute to the routes. Therefore, the routes that match access list 1 will not be advertised by the BGP speaker 171.69.232.50 in AS 200.

The missing command to achieve the task is "ip as-path access-list 1 permit ^44_|_44_|_44$". This command allows routes with AS_PATH containing ASN 44 to match the route-map set_ospf_tag. The regular expression "^44_|_44_|_44$" matches any AS_PATH that starts with "44_", ends with "_44", or contains "_44_" in the middle. This ensures that routes with AS_PATH containing ASN 44 will be tagged when exporting into the main IP routing table.

The bgp default local-preference command sets the local preference on the updates out of the router that go to peers in the same AS.

The missing command to achieve the task is "ip as-path access-list 1 permit ^44_|_44_|_44$". This command allows routes with AS_PATH containing AS_SEQ 44 to be matched and exported with the route tag set as defined by RFC 1403.

None of the above properties define a neighbor in the state "Idle." In the Idle state, the router is not actively listening on any port (TCP 179) or initiating a TCP connection with the neighbor. It has not formed a TCP connection or sent/received any OPEN messages. The router has not established a BGP connection with the neighbor either. Therefore, none of the given properties apply to a neighbor in the Idle state.

The given configuration uses BGP to add the community values 200 200 to routes originating from autonomous system 70. This is achieved by applying a route map called "set-community" to the neighbor with IP address 171.69.232.90. The route map has a permit statement with a match condition of as-path 1, which matches routes with an AS_PATH ending in 70. The set action is used to add the community values to these routes. Routes originating from other autonomous systems are advertised as normal, without any modifications.

The given configuration removes the COMMUNITY PA from the routes advertised because the "set community none" statement in the route-map set-community removes any community attribute from the routes.

The command "R1# clear ip bgp *" allows to reset all BGP neighbor connections by clearing the BGP routing table. The command "R1 (router-config)# neighbor 172.16.8.8 shutdown" shuts down the specific BGP neighbor connection with the IP address 172.16.8.8. Both commands are valid ways to reset BGP neighbor connections.

With NO Auto-Summary, only EXACT match in the routing table, it is injected into BGP.

The correct answer explains that if the network 10.0.0.0 matches an entry in the current IP routing table, then the equivalent NLRI (Network Layer Reachability Information) will be placed in the local BGP (Border Gateway Protocol) topology table. This means that BGP will consider the network 10.0.0.0 as reachable and will include it in its routing decisions and advertisements to its neighbors.

The missing command to achieve the task is "ip as-path access-list 1 permit .*". This command is used to create an access list that permits any AS path. The "match as-path 1" statement in the route map is referencing this access list to match routes with any AS path. By using the regular expression ".*", it will match any AS path, allowing all routes to be tagged when exporting from BGP to the main IP routing table.

The correct answer is "R1(config-router)#neighbor 1.1.1.1 default-originate". This command will instruct the router to advertise a default route to its BGP neighbor 1.1.1.1. By using the "default-originate" keyword, the router will inject the default route (0.0.0.0/0) into BGP, even if there is no default static route present in the routing table.