Lab Objective:
The focus of this lab is to hone your trouble isolation and resolution skills. This lab will include Layer 2 and Layer 3 technologies which fall within the scope of the current CCNP curriculum.
Lab Topology:
The lab network topology is illustrated below:
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IMPORTANT NOTE If you are using the www.howtonetwork.net racks, please download and paste the troubleshooting lab configurations. If you are using your own rack or lab, please modify this configuration to reflect the actual interface types, etc, that you have on your devices. Prior to beginning all labs, apply the pre-lab configuration for each individual device. When completing these labs, it is important to resolve the trouble tickets in the order in which they are listed because they build on each other. For example, if you begin with Trouble Ticket # 3, you might not get the expected resolution or result if you have not completed Trouble Ticket # 1 and Trouble Ticket # 2. It is very important to follow the order listed. |
Trouble Ticket # 1
You have configured BGP on R1 and R2 and notice that the adjacency is not established. Troubleshoot and resolve this issue.
Trouble Ticket # 2
You have received a call from the NOC stating that they are unable to reach the 198.1.1.0/24 subnet from the 150.3.3.0/24 subnet. Troubleshoot and resolve this issue.
Trouble Ticket # 3
You have received complaints stating that users connected to the 150.3.3.0/24 subnet are not able to communicate with users on the 150.2.2.0/24 subnet. Troubleshoot and resolve this.
Trouble Ticket # 4
The NOC has called you to advise that the 150.4.4.0/24 subnet is only able to reach devices on the 150.3.3.0/24 subnet, but nothing else. Troubleshoot and resolve this issue.
Lab Solutions
Solution # 1
When configuring indirectly connected external BGP peers, you need to modify the IP TTL of the BGP packets using the neighbor <address> ebgp-multihop <1-254> command:
| R1#show running-config | section bgp router bgp 254 no synchronization bgp router-id 1.1.1.1 bgp log-neighbor-changes network 198.1.1.0 neighbor 2.2.2.2 remote-as 65500 neighbor 2.2.2.2 update-source Loopback0 no auto-summary |
| R2#show running-config | section bgp router bgp 65500 no synchronization bgp router-id 2.2.2.2 bgp log-neighbor-changes network 150.0.2.0 mask 255.255.255.0 neighbor 1.1.1.1 remote-as 254 neighbor 1.1.1.1 update-source Loopback0 neighbor 10.0.0.10 remote-as 65500 neighbor 10.0.0.10 route-map NEXT_HOP out no auto-summary |
To resolve this issue, implement the following configuration on R1 and R2:
| R1(config)#router bgp 254 R1(config-router)#neighbor 2.2.2.2 ebgp-multihop 2 |
| R2(config)#router bgp 65500 R2(config-router)#neighbor 1.1.1.1 ebgp-multihop 2 |
NOTE: You do NOT have to specify a value of ‘2’ with this command to resolve this issue.
Solution # 2
The issue is that the outbound route-map configured on R2 is incorrect as it specifies a NEXT_HOP address of R3 instead of R2 for all advertised BGP prefixes:
| R2#show route-map route-map NEXT_HOP, permit, sequence 10 Match clauses: Set clauses: ip next-hop 10.0.0.10 Policy routing matches: 0 packets, 0 bytes |
To resolve this issue, implement the following configuration on R2:
| R2(config)#route-map NEXT_HOP permit 10 R2(config-route-map)#no set ip next-hop 10.0.0.10 R2(config-route-map)#set ip next-hop 10.0.0.9 |
Solution # 3
The issue is that the FastEthernet0/0 interface on R2 is shut down, which prevents this subnet from being advertised by R2 via BGP:
| R2#show interfaces fastethernet 0/0 FastEthernet0/0 is administratively down, line protocol is down Hardware is AmdFE, address is 000d.289e.f940 (bia 000d.289e.f940) Internet address is 150.0.2.2/24 MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) Auto-duplex, Auto Speed, 100BaseTX/FX [Truncated Output] |
To resolve this issue, simply bring up the FastEthernet0/0 interface:
| R2(config)#interface fastethernet 0/0 R2(config-if)#no shutdown |
Solution # 4
The issue arises from the fact that R3 is not configured as a route reflector for R2 and R4:
| R3#show running-config | section bgp router bgp 65500 no synchronization bgp router-id 3.3.3.3 bgp log-neighbor-changes network 150.0.3.0 mask 255.255.255.0 neighbor 10.0.0.9 remote-as 65500 neighbor 10.0.0.9 route-map R2-NEXT-HOP out neighbor 10.0.0.14 remote-as 65500 neighbor 10.0.0.14 route-map R4-NEXT-HOP out no auto-summary |
To resolve this issue, configure R3 as a route reflector for R2 and R4:
| R3(config)#router bgp 65500 R3(config-router)#neighbor 10.0.0.9 route-reflector-client R3(config-router)#neighbor 10.0.0.14 route-reflector-client |
Final Working Router Configurations
R1
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R1#term len 0 Current configuration : 1146 bytes R1# |
R2
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R2#term len 0 Current configuration : 1293 bytes R2# |
R3
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R3#term len 0 Current configuration : 1657 bytes R3# |
R4
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R4#term len 0 Current configuration : 972 bytes R4# |