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Community Member

MTU values for EPC3925


Can someone tell me what MTU values I can enter for the EPC3925. The default value =0 (1500 bytes).

The manual does not show a listing of values and the associated nbr. of bytes.




Cisco Employee

Hello,Thank you for your


Thank you for your question.  However, this community is for Cisco Small Business Products and the EPC3925 is not a Cisco Small Business Product.

Your product is an internet service provider (ISP) supported product.  In other words you need to contact your ISP or technology reseller that you purchased this from to help you with your question.


Glenn Martin


Community Member

Hi Glenn,First thing I did

Hi Glenn,

First thing I did was contacting my ISP.

They had absolutely no clue, other than suggesting I should not change any setting of the router, and referred me to Cisco. Hence my question in this forum.



Community Member

This discussion has been

This discussion has been reposted to the CSC Content with No Valid Community to Post community

Cisco Employee

Hello Wesjo, The way to

Hello Wesjo,


The way to determine if you are using the correct MTU is to follow the steps below.

-open a command prompt (Windows+R, cmd, Enter)

-type 'ping -f -l 1472'

--You will receive one of two possible results;

---Reply from bytes 1472...


---Packet needs to be fragmented but DF set


If you get the first one then your MTU is good at 1500 .

If you get the second one then try lowering the value until you get a reply.  Then you will take the value that worked and add 28, that is your correct MTU.


OR you could use a tool like the one available at

Hope this resolves your issue.  Also, the EPC3925 is not technically a Cisco small business device.  The phone number for support on that unit is 855-858-1882.





Community Member

Hi Mike,Thanks for the reply.

Hi Mike,

Thanks for the reply. I know how to find the optimum MTU.
The manual of this router shows that the default MTU value 0 =1500 bytes. So I assumed that there must be a table that shows value 1 = x bytes, value 2 = y bytes etc. etc. I just read thatit is not the case and that just value 0=1500 bytes. Any other value you choose is the absolute MTU required (e.g. value 1200 = 1200 bytes)



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