On the network shown in the figure, EBGP peer relationships are established between neighboring routers through directly connected interfaces. The router ID of each router is 10.0.X.X, and the AS number is 6500X, where X is the number of the router. Both R1 and R4 have static routes to 192.168.1.0/24, which are imported to BGP through the import-route command. R3 is configured with the peer y.y.y.y as-path-filter 1 import command for all peers. Which of the following sets of commands enables R3 to select the route with the longest AS_Path to 192.168.1.0/24?
Answer(s): B
This command denies the paths starting with AS 65002 (R2) and AS 65005 (R5), thus preventing R3 from selecting these shorter AS paths. The permit .* command allows all other paths, including those with longer AS paths. This configuration will cause R3 to choose the longest remaining AS path to 192.168.1.0/24.
On the network shown in the figure, EBGP peer relationships are established between neighboring routers through directly connected interfaces. The AS number is 6500X, where X is the number of the router. Both R1 and R4 have static routes to 192.168.1.0/24, which are imported to BGP through the import-route command. By default, in the routing table of R3, which of the following is the AS_Path attribute carried in the route to 192.168.1.0/24?
Answer(s): C
Given the network: R1 and R4 have static routes to 192.168.1.0/24, which are imported into BGP. EBGP peer relationships are established between neighboring routers through directly connected interfaces. The AS number for each router is 6500X, where X represents the router number.Let's trace the route from R1 to R3: The route from R1 (AS 65001) is advertised to R2 (AS 65002). R2 passes the route to R5 (AS 65005). R5 then passes the route to R6 (AS 65006). Finally, R6 advertises the route to R3.So, in the routing table of R3, the AS_Path attribute for the route to 192.168.1.0/24 will show the sequence of AS numbers that the route has passed through, which would be: 65006 (R6) 65005 (R5) 65004 (R4) (if R4 advertises the route, but based on direct propagation from R1, this may not appear directly)
On the network shown in the figure, IS-IS runs on R1, R2, R4, and R5, and the area ID is 49.0001. IS-IS runs on R3 and R6, and the area ID is 49.0002. In AS 65000, R1, R3, R4, and R6 each establish IBGP peer relationships with R2 and R5. R2 and R5 are RRs, and R1, R4, R3, and R6 are clients. The IBGP peer relationships are established using Loopback0. The IP address of Loopback0 on each router is 10.0.X.X/32, and the router ID is 10.0.X.X, where X is the number of the router. R1 and R4 import the external route 192.168.1.0/24 to BGP through the import-route command, and R3 and R6 import the external route 192.168.2.0/24 to BGP through the import-route command. Which of the following statements are true? (Choose all that apply.)
Answer(s): A,B,C,D
For 192.168.2.0/24, R2 preferentially selects the BGP route received from R3. Correct: R2 is in area 49.0001 and acts as a route reflector. R3 is in area 49.0002 and has the 192.168.2.0/24 route. Since R2 and R3 have IBGP sessions established, R2 would receive the BGP route from R3 and select it, provided there is no other better option (e.g., no other shorter path or AS path).For 192.168.1.0/24, R3 preferentially selects the BGP route received from R2. Correct: R2, being a route reflector for R1 and R4 in area 49.0001, will reflect the route to 192.168.1.0/24 to R3. Since the IBGP session is established over Loopback0, R3 will receive this route from R2, and it would be the preferred route for 192.168.1.0/24.For 192.168.2.0/24, R5 preferentially selects the BGP route received from R3. Correct: R5, like R2, is a route reflector and would receive the route for 192.168.2.0/24 from R3. Since R3 is the origin of this route, R5 would prefer the route received from R3 over any other possible path.For 192.168.1.0/24, R6 preferentially selects the BGP route received from R2. Correct: R2 is the route reflector for area 49.0001, where 192.168.1.0/24 originates. R2 will reflect this route to its IBGP peer, R6. Since R6 is in area 49.0002, it will receive this route and prefer it, assuming no better alternative exists.
BGP allows you to use the filter-policy acl-number import command to filter received routes. The value of acl-number ranges from 2000 to 3999.
In BGP, the filter-policy command is used to filter routes, but it typically uses an ACL (access control list) or prefix list. However, the range of ACL numbers that can be used is not from 2000 to 3999. Standard ACL numbers range from 2000 to 2999 for numbered ACLs, but extended ACLs, which can also be used for filtering routes, have different ranges.The correct ACL number range for filtering is 2000 to 2999, not 3999.
To protect a device against the attacks of forged BGP messages, you can configure GTSM to check whether the TTL value in the IP message header is within the specified range. If the peer x.x.x.x valid-ttl-hops 100 command is configured on a device, the valid TTL value range of the detected message is [155, 255].
GTSM (Generalized TTL Security Mechanism) is used to protect against attacks by ensuring that BGP packets are only accepted if the TTL (Time to Live) value is within a certain range, which is close to the maximum TTL. The idea is that only directly connected peers should be able to send BGP messages with a high TTL value, making it difficult for an attacker from a distant location to spoof BGP messages.If the command peer x.x.x.x valid-ttl-hops 100 is configured, it means that the BGP packets sent by the peer must have a TTL value within a range calculated as [256 - 100, 255], which results in a valid TTL range of [156, 255], not [155, 255].
On the network shown in the figure, IS-IS runs on R1, R2, R4, and R5, and the area ID is 49.0001. IS-IS runs on R3 and R6, and the area ID is 49.0002. In AS 65000, R1, R3, R4, and R6 each establish IBGP peer relationships with R2 and R5. R2 and R5 are RRs, and R1, R4, R3, and R6 are clients. The IBGP peer relationships are established using Loopback0. The IP address of Loopback0 on each router is 10.0.X.X/32, and the router ID is 10.0.X.X, where X is the number of the router. R1and R4 import the external route 192.168.1.0/24 to BGP through the import-route command, and R3 and R6 import the external route 192.168.2.0/24 to BGP through the import-route command. Which of the following statements are true? (Choose all that apply.)
Answer(s): B,C
The route 192.168.2.0/24 in the routing table of R4 has two different outbound interfaces. True: R4 may learn the route to 192.168.2.0/24 through both R2 and R5, as they are route reflectors (RRs). This would result in two different paths for R4 to reach 192.168.2.0/24, each with a different outbound interface, assuming equal costs from the route reflectors.The routing table of R1 contains the route 192.168.2.0/24. True: R1 is a BGP client of the route reflectors (R2 and R5), and R3/R6 are injecting the 192.168.2.0/24 route into BGP. Since R1 is part of the same AS and has IBGP sessions with R2 and R5, it would receive the 192.168.2.0/24 route from its RRs (R2 and R5).
The figure shows the Router-LSA generated by a router. Which of the following statements are true based on the LSA? (Choose all that apply.)
The Link State ID of the Router-LSA is 0.0.0.0, which indicates that the router is generating this LSA for area 0 (the backbone area). Therefore, at least one interface of this router is in area 0.
On the OSPFv3 network shown in the figure, OSPFv3 is enabled on the interfaces connecting R1, R2, and R3. The router ID of each router is 10.0.X.X, where X is the number of the router. If you check detailed information about an LSA on R3, the command output shows that the LSA is generated by R2 and describes the IPv6 prefix address associated with the Router-LSA.
Answer(s): A
In the figure, the LSA shown is an Intra-Area-Prefix LSA generated by R2 (Originating Router: 10.0.2.2). This LSA type in OSPFv3 is used to advertise the IPv6 prefixes associated with the router's interfaces. The LSA describes the IPv6 prefix (2000::2/128) associated with R2. The fact that this LSA is related to the Router-LSA and includes the IPv6 prefix supports the claim that it is generated by R2 and refers to its connected prefixes.This output would be visible on R3, as R3 is in the same area (Area 0), and R3 would receive this LSA from R2.
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