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Ask the Expert: Switch and IOS Architecture and Unexpected Reboots on all Cisco Catalyst Switches

Community Manager
Community Manager

This session will provide an opportunity to learn and ask questions about Cisco Catalyst Switches IOS architecture, and how to troubleshoot any unexpected reboots and other errors on switches.


Ask questions from Monday, October 5 to Friday, October 16, 2015

Featured Experts

Ivan Shirshin is a customer support engineer in High-Touch Technical Services (HTTS). He is an expert on Routing, LAN Switching and Data Center products. His areas of expertise include Cisco Catalyst 2000, 3000, 4000, 6500,  Cisco Nexus 7000, ISRs, as well as Cisco routers ASR1000, 7600, 10000 and XR platforms. He has over 7 years of industry experience working with large Enterprise and Service Provider networks. Shirshin holds a CCNA, CCNP, CCDP, and CCIE (# 43481) in routing and swtiching, as well as XR specialist certifications. 


Naveen Venkateshaiah is a customer support engineer in High-Touch Technical Services (HTTS). He is an expert on Routing, LAN Switching and Data Center products. His areas of expertise include Cisco Catalyst 3000, 4000, 6500,  and Cisco Nexus 7000. He has over 7 years of industry experience working with large enterprise and Service Provider networks. Venkateshaiah holds a CCNA, CCNP, and  CCDP-ARCH, AWLANFE, LCSAWLAN Certification. He is currently working to obtain a CCIE in routing and switching.


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43 Replies 43

You are most welcome, Ajar!

Kind Regards,

Hi Naveen and Ivan

I lost my network connection and i have done troubleshoot. It says: the default gateway is not available. investigate router or broadband modem issues  not run.Could you help me please?

Hi Sara, 


Where are you seeing the message "default gateway is not available"? On Windows workstation? If yes, then you need to investigate what is the reason for this connectivity loss. The symptoms of connectivity loss are a wide scope and could be happening due to a number of issues.

It could be the router/modem you are connected to is having some problems, software or hardware. I suggest to access this device and verify if it is working fine. For Cisco devices you can use telnet/ssh terminal access or console connection.


Kind Regards, 


Kind Regards,

thank you very much!

Welcome, Sara.

Kind Regards,


I have a problem in my workplace. All computers are in a domain and before a week in two pc internet doesn't work. Now in two other computers interenet has problems two. Is this a router problem?

Hi Sara!


The answer is "possibly" but the issue may be something else as well. E.g. service provider issues. Or DHCP problem with IP address allocation to this 2 PCs. Or even NIC cards HW failures.


What you need to do is to check few things:

1. What is the router model?

2. Is PC NIC interface working fine?

3. Did PC get IP address properly?

4. Can PC ping the router IP address?

5. Does router have connection to internet?

6. Are other PCs connected to same router working fine?


Note that if PC is connected to router via switch or other device, then switch has to be checked as well.


I recommend to use step-by step approach and narrow down the problem point in the network - from physical (NIC, interface, cable, etc.) to layer 2 (switching, vlans, STP) to layer 3 (routing, etc.). 


Kind Regards, 


Kind Regards,

Router is connect to internet and the other computers are having the same issue in different days. 

What is the router model, Sara?

Kind Regards,

It is mikrotik router but i could not find other parameters.

I recommend to open a case with Mikrotik support team. They should be able to check if router is having some issue.

Kind Regards,

ok thank you!


Kind Regards,

Hello Sara,

If your question was resolved, kindly go ahead and rate it. Rating helps experts to be recognized and also help the community members to find good responses.


I appreciate it.

Kindest Regards,

Monica Lluis

Community Mgr

I hope you and your love ones are safe and healthy
Monica Lluis
Community Manager Lead

Level 1
Level 1

I had a WS-C2960+24PC-L reboot unexpectedly the other day. Sh ver says this...

System returned to ROM by power-on
Last reload reason: Unknown reason

Need to determine why the switch reloaded?



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