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Lan Interface up on 1841 but down on 3825 with the same settings


I have a strange problem and I hope it may have a simple solution. I had configured a 1841 router for an internet leased line for the office - works perfectly even now.Then we got a new 3825 and I configured it exactly the same way, but it doesn't work. On both routers, the 0/1 is configured for lan and the 0/0 is for wan with the same IPs. But although everything works fine with the 1841, on the 3825 the lan interface shows protocol down, and the wan interface shows up. On the 3825, I cannot ping the router inside but through another internet connection I can ping my wan gateway outside. On the 1841 I can ping inside, outside no problem. I did no shutdown for the interfaces but didn't help. Is there a different setting for giga on the 3825? Media is rj-45. Am I missing something ? Thanks in advance.

Hi again

Well just to update what else I have done. I reset the 3825 to factory settings. Then I connected it to a pc and configured it with CP express together with some CLI. Now it is configured interface wise the reverse ie on the 1841 0/0 is WAN and 0/1 is LAN and on the 3825 0/0 is LAN and 0/1 is WAN. (Not that it made any difference) But here is the strange thing - when connected to the PC, both interface protocols were up, however the moment I disconnected the PC from the LAN interface (0/0) and connected it to the rest of the LAN network like on the 1841, the interface went down ! It is as if the 3825 is allergic to the rest of my network. By the way, I also changed the timezone to IST from UTC but that also didn't help. I read somewhere that encapsulation may be an irritant as it should be the same both sides, but I don't know what to do where that is concerned. One more thing, earlier I had set NAT inside and outside for the interfaces, like my 1841, but this time I couldn't do it with the CP Express (didn't open up), so after this update I will set it using CLI and check if it makes any difference to the 3825 allergy. The major difference between the interfaces in the two routers is that in the 1841 it is FastEthernet and in the 3825 it is GigaEthernet, but my local area network is all giga so it really shouldn't be so irritated with my network. So anyway guys, I really would appreciate some guidance. Thanks again in advance.


Message was edited by: Joshua Ferreira

New Member

Re: Lan Interface up on 1841 but down on 3825 with the same sett

Thank you for your question.  This community is for Cisco Small Business products and your question is in reference to a Cisco Elite/Classic product.  Please post your question in the Cisco NetPro forums located here:;jsessionid=E0EEC3D9CB4E5165ED16933737822748.SJ3A?page=Network_Infrastructure_discussion

This forum has subject matter experts on Cisco Elite/Classic products that may be able to answer your question.