How To Troubleshoot A Cisco Router
FACT GATHERING
While troubleshooting a Cisco router you must some of the prerequisite that
are very necessary while troubleshooting process. A Cisco router has very
complex and sophisticated structure and implementation. So before you start
troubleshooting you must study some the key points described below:
- First thing is to make sure that problem lies with the
router and nature of the problem. Either the problem is on layer 3 protocol or
it is a process error. Basically a router operates on layer 3 of the OSI
model. This is a bit confusing when it comes to Arp (Address Resolution
Protocol) that will cause you many problems on networks if you do not
understand the infrastructure. Actually ARP works on Layer 2 and resolves the
MAC address and routing issues.
- Check carefully that whether the problem lies in DNS or
switch or firewall is a major cause of the problem.
- Check the entire access pint to ensure that they are not
out of order.
- Spend more time on correct investigation. It will helps
you in solving the problem efficiently.
Start to Troubleshoot the CISCO Router
Following is the sample topology and now it will helps us for the realization
of the problem.
If some part or segment of the network gets off at router A and D then see if
you could reach the paths or not. The network might get slow because router C
faces the problem and the path or links are to re converge and hence it will
lower the network speed.
Another reason of the slow down is the 56 K link. Check by sending a ping
command to both directions. You can also use remote access to manage workstation
1 of router D’s network.
You can use various tools like Tracert on Windows and for Linux it is Netware
to test in both directions. Check that you must see the path from router A and
from router D.
If you want to ping just go to the Command Prompt and make a Ping from your
local computer to some place away from last router i.e. router D. Now ping the
host such with ip 10.1.4.10.
Routing Table Problems
To show the routing table on windows environment uses the command ROUTE
PRINT. It will verify whether routing is enabled or disabled. Following figure
shows the routing table:
You can clear the routing table as ROUTE DELETE to remove one and force the
routers to relearn the addresses. This is why sometimes rebooting the routers
solve the problem. Another method is to clear the logs stored at the router to
refresh the settings.
Routing table problems include the following.
- Inactive routes
- Unneeded routes
- Black hole routes
- Flapping links Invalid route tables
- Invalid ARP cache causing incorrect IP assignment
- Problems with administrative distance or any other
settings
