The following commands can be used to display information on hardware/software and to verify/debug:
Troubleshooting OSPF and EIGRP can be found in the two following links:
Listed below is a quick list of tools that can be used to troubleshoot connectivity issue.
Ping
Ping can be used to verify connectivity between end devices. Note – A device such as a firewall may block the ICMP packet.
Tracert
Shows routing paths from source to destination on a PC.
Telnet
Telnet can be used to connect to a router/switch although data is sent in plain text
SSH
Same as Telnet, but data is encrypted.
Ipconfig /all
Display IP information that can be verified against network documentation. IP/Subnet mask/Default gateway information can be seen. DNS/WINS is also provided.
arp -a
Shows the MAC address table from a PC.
show ip arp
Shows the MAC address table from a router/switch.
Next routing protocol up is configure, verify and troubleshoot EIGRP.
Using the same layout from OSPF, we will re-configure for EIGRP.
First turn off ospf on the routers
configure terminal no router ospf 1
Configuring EIGRP is similar to that of OSPF.
RouterA
configure terminal router eigrp 1 network 10.0.3.68 0.0.0.3 network 10.0.3.72 0.0.0.3 network 10.0.3.32 0.0.0.31 network 10.0.0.0 0.0.0.255 no auto-summary
RouterB
configure terminal router eigrp 1 network 10.0.1.0 0.0.0.255 network 10.0.3.64 0.0.0.3 network 10.0.3.0 0.0.0.31 network 10.0.3.68 0.0.0.3 no auto-summary
RouterC
configure terminal router eigrp 1 network 10.0.2.0 0.0.0.255 network 10.0.3.64 0.0.0.3 network 10.0.3.72 0.0.0.3 no auto-summary
Verify EIGRP
Router A routing table:
Router B routing table:
Router C routing table:
Troubleshoot EIGRP
In this topic we will configure OSPF, verify and troubleshoot using show commands and what kinds of problems we can expect and how we can resolve these.
I have made some changes to our switch diagrams and added a couple of routers and re-jigged things around:
To enable OSPF we first need to enable the routing protocol:
configure terminal router ospf 1
The value 1 is the instance number, this can be anything between 1 and 65535. Next we need to let the routing process know which networks we want to advertise, for example:
network 192.168.0.1 0.0.0.255 area 0
OSPF uses inverse (wildcard) subnet mask. The 0’s mean we want this part of the IP to exactly match (192.168.0.) and the last octet 255 means it can be any value. Area 0 is the backbone area for OSPF. I have kept this simple.
We can stop OSPF hellos being sent out of an interface using the passive-interface command. This can be useful on FastEthernet links that are connected to a switch network that do not need to receive routing updates. Sending routing updates to unnecessarily links can waste bandwidth and CPU resources also enhances security.
configure terminal router ospf 1 passive-interface FastEthernet0/0
Below are the outputs of the commands for each device needed to make the diagram above fully functional:
RouterA:
configure terminal interface FastEthernet 0/0 no shutdown interface FastEthernet0/0.10 encapsulation dot1Q 10 ip address 10.0.0.1 255.255.255.0 interface FastEthernet1/0 no shutdown interface FastEthernet1/0.50 encapsulation dot1Q 50 ip address 10.0.3.33 255.255.255.224 interface Serial0/0 ip address 10.0.3.73 255.255.255.252 interface Serial0/1 ip address 10.0.3.70 255.255.255.252 router ospf 1 network 10.0.3.68 0.0.0.3 area 0 network 10.0.3.0 0.0.0.127 area 0 network 10.0.3.72 0.0.0.3 area 0 network 10.0.0.0 0.0.0.255 area 0 passive-interface FastEthernet 0/0 passive-interface FastEthernet 1/0
RouterB:
configure terminal interface FastEthernet0/0 no shutdown interface FastEthernet0/0.20 encapsulation dot1Q 20 ip address 10.0.1.1 255.255.255.0 interface FastEthernet1/0 no shutdown interface FastEthernet1/0.40 encapsulation dot1Q 40 ip address 10.0.3.1 255.255.255.224 interface Serial0/0 ip address 10.0.3.66 255.255.255.252 interface Serial0/1 ip address 10.0.3.69 255.255.255.252 clock rate 64000 router ospf 1 network 10.0.1.0 0.0.0.255 area 0 network 10.0.3.64 0.0.0.3 area 0 network 10.0.3.0 0.0.0.127 area 0 network 10.0.3.68 0.0.0.3 area 0 passive-interface FastEthernet 0/0 passive-interface FastEthernet 1/0
RouterC:
configure terminal interface FastEthernet0/0 no shutdown interface FastEthernet0/0.30 encapsulation dot1Q 30 ip address 10.0.2.1 255.255.255.0 interface Serial0/0 ip address 10.0.3.74 255.255.255.252 clock rate 64000 interface Serial0/1 ip address 10.0.3.65 255.255.255.252 clock rate 64000 router ospf 1 network 10.0.2.0 0.0.0.255 area 0 network 10.0.3.72 0.0.0.3 area 0 network 10.0.3.64 0.0.0.3 area 0 passive-interface FastEthernet0/0
SwitchA:
configure terminal spanning-tree mode rapid-pvst interface FastEthernet0/1 switchport mode trunk interface FastEthernet0/2 switchport access vlan 10 switchport mode access spanning-tree portfast interface range FastEthernet0/3-24 switchport mode access spanning-tree portfast
SwitchB:
configure terminal spanning-tree mode rapid-pvst interface FastEthernet0/1 switchport mode trunk interface FastEthernet0/2 switchport access vlan 20 switchport mode access spanning-tree portfast interface range FastEthernet0/3-24 switchport mode access spanning-tree portfast
SwitchC:
configure terminal spanning-tree mode rapid-pvst interface FastEthernet0/1 switchport mode trunk interface FastEthernet0/2 switchport access vlan 30 switchport mode access spanning-tree portfast interface range FastEthernet0/3-24 switchport mode access spanning-tree portfast
SwitchD:
configure terminal spanning-tree mode rapid-pvst interface FastEthernet0/1 switchport mode trunk interface FastEthernet0/2 switchport access vlan 50 switchport mode access spanning-tree portfast interface Range FastEthernet0/3-24 switchport mode access spanning-tree portfast
SwitchE:
configure terminal spanning-tree mode rapid-pvst interface FastEthernet0/1 switchport mode trunk interface FastEthernet0/2 switchport access vlan 40 switchport mode access spanning-tree portfast interface Range FastEthernet0/3-24 switchport mode access spanning-tree portfast
OSPF by default uses the highest IP address for its routing process ID. The routing process ID is used to elect DR and BDR as well as advertise routes. For this reason, it may be a good idea to create a loopback interface to override this to ensure that becomes RID, Cisco even suggests using loopbacks.
Configuring a loopback is easy, lets do this on RouterC:
configre terminal interface loopback 1 ip address 192.168.0.1 255.255.255.0
This doesn’t automatically make the RID become 192.168.0.1 we must either reload the router – Which could be inconvenient in a live environment or we can using the command router-id 192.168.0.1 to force the change.
configure terminal router ospf 1 router-id 192.168.0.1
We can advertise default routes via the default-information originate command under the OSPF configuration. We can also use default-information originate always (not supported in Packet Tracer) – This advertises a default route even if one doesn’t exist, it will generate one and advertise this. To create a default route:
configure terminal ip route 0.0.0.0 0.0.0.0 s0/1
Verify OSPF
Lets first begin by checking the RID of RouterC – We can verify this by using the show ip ospf command on RouterC:
We can check OSPF routes via the show ip route command:
We can verify WAN connectivity by pinging each PC from each other. I’m going to demonstrate PC3 pinging PC1:
show ip osfneighbor will show information about all neighbors:
show ip ospf interface s0/0 will display information about the interface state whether it is up and OSPF information such as timers, what area the interface is in and network type.
Troubleshoot OSPF
You can download the Packet Tracer file here:
Download Packet Tracer OSPF configuration
Routing protocols are used to dynamically learn advertised routes from nearby routers. Imagine having to enter every possible route onto each router – nightmare.
Key information about some routing protocols covered by the ICND2:
EIGRP (Enhanced Interior Gateway Routing Protocol)
OSPF (Open Shortest Path First)
Troubleshooting local network issues:
First, from the computer ping the local loopback 127.0.0.1 this will ensure the NIC is functioning correctly.
Second, ping the Default Gateway for example 192.168.0.1 if this fails try and ping another PC on the same network.
To find the default gateway that is set (normally via DHCP) on a Windows machine Start > Run > Type cmd and enter – in the black box type “ipconfig /all” followed by enter. This will display information relating to IP, DNS, Default Gateway and Subnet mask.
If both pinging the default gateway and another PC fail and you have a working PC – verify the PC that isn’t working is in the same subnet by running an ipconfig /all and compare the IP, subnet mask and default gateway.
Tracert can be handy to see where the packets drop off and may help identify where the fault lies.
Try and ping (if have access) from router to router to test connectivity.
Most issues are configured with an incorrect IP, Subnet mask or default gateway. A good example of this is one I encountered recently. There was a PC that could talk to a printer offsite but not on site on inspecting further the printer had the wrong subnet mask, meaning when the PC was on site, the printer was in a totally different subnet to that of the PC – a quick amendment of the mask and boom it worked. Easily missed.
Always consult with network documentation to ensure IP addressing is correct with VLSM networks. As as last resort use a Subnet calculator such as Bitcricket beware you’re not allowed a calculator on the exam.
Summary: