Cisco routers stop working until reboot

Posted on 2003-11-03
Last Modified: 2012-05-04
We have about 300 cisco routers connecting our stores to a private network. These routers are a mixture of 1721's and 827's. I am not a cisco router expert, so I need some expert advice. Every once in a while these routers will stop working. You can still connect to the terminal on the external port. If we physically shut down the router and power it back up it works fine. Is there a way to reboot the router from the terminal. Is there another solution. This may be a very common problem.

These routers perform nat and on the dsl stores that use the internet there is 3des encryption.
Question by:mrconover
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
LVL 79

Accepted Solution

lrmoore earned 100 total points
ID: 9672191
This is not a common problem. If it happens routinely, there is a problem that needs to be investigated.
Common causes are CPU or Memory overload. Latest batch of virus/worms - specifically Welchia and MSBlast - cause these denial of service symptoms due to the extreme amount of icmp traffic looking for other hosts to infect. I would almost bet money that your network is infected.
If you can still connect to vty term (telnet), you can reboot with "reload" command.
Proceed with reload? [confirm] <enter>

Now just pray that you get connection back in a couple of minutes..

Another common cause is CPU overload caused by too much traffic for the CPU to handle (3DES encryption on a heavy-use VPN tunnel). If it is more common on the 827's than on the 1721's, they have a smaller CPU and less memory to work with.
Sometimes a Cisco engineer will turn on a debug and forget to disable it.
Before you reload, take a look and see if any debugs are turned on:
No debugs running:
Router#sho deb

Router#sho deb
Generic IP:
  IP NAT debugging is on
  UDP packet debugging is on

Turn off all debugging:
Router#u all  <short for "undebug all">
Make sure you are at the global router# prompt, and not in config mode:
Router(config)#u all
Now I've just created a username "all" with no password, and the debugs are still running..

Assisted Solution

sheahmed earned 100 total points
ID: 9676503

i guess u should try this command on your other router as well ...

router#sh ver

this will display you the very basic information of your router inclding the reason of last reboot ...

like ...
new-tdma uptime is 10 weeks, 2 days, 5 hours, 6 minutes
System returned to ROM by power-on
System image file is "flash:c2500-dos-l.122-16a.bin"  

you can get some error report instead of power on ...

Try this access-list on your core interfaces first and then monitor the traffic? are u satisfied with the current traffic load? ... it can certainly block blaster, nache, welchia ...

access-list 120 deny   tcp any any eq 445
access-list 120 deny   udp any any eq 445
access-list 120 deny   tcp any any eq 4444
access-list 120 deny   tcp any any range 135 139
access-list 120 deny   udp any any range 135 netbios-ss
access-list 120 deny   icmp any any
access-list 120 permit ip any any    

sheeraz ahmed

Expert Comment

ID: 9918777

its definetly not a commn prob  you should have alook at the buffers and cpu load on the routers which  stop processing
you could chek the ios versions and have the latest once ios upgraded,  have the buffers size fine tuned and have ur cahce timeout speicified.


Featured Post

MIM Survival Guide for Service Desk Managers

Major incidents can send mastered service desk processes into disorder. Systems and tools produce the data needed to resolve these incidents, but your challenge is getting that information to the right people fast. Check out the Survival Guide and begin bringing order to chaos.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Problem Description:   Couple of months ago we upgraded the ADSL line at our branch office from Home to Business line. The purpose of transforming the service to have static public IP’s. We were in need for public IP’s to publish our web resour…
In the world of WAN, QoS is a pretty important topic for most, if not all, networks. Some WAN technologies have QoS mechanisms built in, but others, such as some L2 WAN's, don't have QoS control in the provider cloud.
After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…

733 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question