350-401 Question #812: Real Exam Question with Answer & Explanation

Question

Lab Simulation 1 Guidelines This is a lab item in which tasks will be performed on virtual devices. - Refer to the Tasks tab to view the tasks for this lab item. - Refer to the Topology tab to access the device console(s) and perform the tasks. - Console access is available for all required devices by clicking the device icon or using the tab(s) above the console window. - All necessary preconfigurations have been applied. - Do not change the enable password or hostname for any device. - Save your configurations to NVRAM before moving to the next item. - Click Next at the bottom of the screen to submit this lab and move to the next question. - When Next is clicked, the lab closes and cannot be reopened. Topology Tasks BGP connectivity exists between Headquarters and both remote sites, however Remote Site 1 cannot communicate with Remote Site 2. Configure BGP according to the topology to achieve these goals: 1. Configure R2 under the BGP process to provide reachability between Remote Site 1 and Remote Site 2. No configuration changes are permitted on R1 or R3. 2. Ensure that the /32 networks at Remote Site 1 and Remote Site 2 can ping each other. Initial Configs (Note: Maybe there are two versions of this sim. In the first version, R2 cannot be accessible and unnecessary configs have been removed. We will solve this version first.) If we use the "show ip bgp" command on R3 then we will see the Loopback0 interface of R1 is not learned since it is coming from same AS number 123. Answer: In order to allow same AS prefix to be received from eBGP neighbor and installed in BGP table, R1 can use the "allowas-in" command will as below: R1(config)#router bgp 123 R1(config-router)#address-family ipv4 R1(config-router-af)#neighbor 10.0.0.2 allowas-in Same configuration should be applied to R3: R3(config)#router bgp 123 R3(config-router)#address-family ipv4 R3(config-router-af)#neighbor 192.168.1.2 allowas-in Note: In the second version of this sim, only R2 can be accessible so the above commands cannot be applied to R1 & R3. In that case we have to use "as-override" on R2 as follows: R2(config)#router bgp 456 R2(config-router)#address-family ipv4 R2(config-router-af)#neighbor 10.0.0.1 as-override R2(config-router-af)#neighbor 192.168.1.3 as-override With "as-override" configured, R3 would accept routes advertised from R1 (and vice versa) as the AS 123 was replaced by AS 456 in the AS_PATH. R3 will see the AS_PATH "456 456 i" (instead of "123 456 i"). Since the AS_PATH does not contain its own AS number so it accepts the advertised routes. You can practice this version (AS-Override) with our own simulator at BGP Configuration online simulator v2. This version does not work with EVE-NG as AS-Override feature requires a VRF so we did not create a lab file in EVE-NG. Verification R1,R3#show ip bgp -> see Loopback0 of remote routers. R1 must ping Loopback0 of R3 successfully. Save the configuration Don't forget to save the configuration on R1 & R3 R1, R3#copy running-config startup-config In the second version, only R2 was configured so save its configuration: R2#copy running-config startup-config