SSH stops working

Discussion in 'Cisco' started by dt1649651, Jul 18, 2005.

  1. dt1649651

    dt1649651 Guest

    Sometimes I cannot ssh to my router, a c2811 with advanced enterprise
    12.4.1a, but if I restarts the router then it will work fine again.

    When this problem happens, all other functions of the router seems
    working fine. Workstations still be able to access the Internet, VPN
    Client still be able to connect to the router ... only I can not ssh to
    the router.

    Any idea where I can look at ?


    dt1649651, Jul 18, 2005
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  2. www.BradReese.Com, Jul 18, 2005
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  3. dt1649651

    AM Guest

    Which kind of problem (connection timeout, connection refused or simply the client exits without any error messages)
    Have you perhaps changed RSA keys? After having changed them it will never accept new connections.
    It happened to me with 12.4.1

    HTH Alex.
    AM, Jul 18, 2005
  4. dt1649651

    dt1649651 Guest

    Hi Brad, thanks for your reply. Yes I did use those URL when I set up
    SSH on my router. I may have to read it again.

    What I do not understand is after I restart the router, it works fine

    dt1649651, Jul 18, 2005
  5. dt1649651

    dt1649651 Guest

    Hi Alex, thanks for your reply.
    I get the error "Connection refused.". No I do not change the key.
    Currently my temporary fix is to restart the router ( if it happens
    during the weekend ) or to use my Linux box with the serial cable to
    the console.

    dt1649651, Jul 18, 2005
  6. dt1649651

    polio Guest

    Since you're on the console you could do some debug to find out what's
    going on.
    polio, Jul 18, 2005
  7. dt1649651

    dt1649651 Guest

    Hi Polio, thanks for your reply.

    Yes, that's what I am waiting for at this time :) because it only
    happens sometimes, and while waiting for it to happen again, I would
    like to know if anybody experiences it. :)

    dt1649651, Jul 18, 2005
  8. I used to see this happen when the router runs out of memory.
    Barry Margolin, Jul 19, 2005
  9. dt1649651

    AM Guest

    While it happens please have a look to the number of connections opened by the router for NAT ("sh ip nat tra") in case use

    ip nat translation max-entries <# of translations>

    AM, Jul 19, 2005
  10. dt1649651

    rave Guest

    it seems to be a ARP issue. if it occurs again just clear the ARP on
    your oruter and your ISP router. See if it works. After that.
    Rebooting the router clears all the tables that is the only diference.
    so may be you could clear the nat table as well.
    rave, Jul 20, 2005
  11. dt1649651

    dt1649651 Guest

    Barry, Alex, Rave,

    Thanks for your reply. It makes sense to check what you suggested (
    more memory, NAT table is full, or ARP table is corrupted ).

    This problem does not always happen . To be safe than sorry, I just
    ordered a 512Mb to put in the router which is in production right now.

    I have another same router in development. I am going to use some Linux
    boxes, each for simulating one internal network, they will run the
    script to change their ip, mac address, to issue some ftp/web access. I
    hope this will help finding out the culprit.

    Thanks again,

    dt1649651, Jul 20, 2005
  12. dt1649651

    dbn58 Guest

    Have you thought about this to be some kind of software bug? I mean, it
    looks like random unsolicited behaviour whenever it happens. May be its a
    bug. I think, may be you should try another release (e.g. 12.4.2T).

    Extra information:

    12.4.1a is a limited deployment IOS, while 12.4.2T is early deployment:

    "Early Deployment (ED) ---
    Software releases that provide new features and new platform support
    *** in addition to bug fixes. ***"

    "Limited Deployment (LD) ---
    A Major Release of Cisco IOS software is said to be in the "Limited
    Deployment" phase of its lifecycle during the period between initial FCS and
    the General Deployment (GD) milestones."
    dbn58, Jul 20, 2005
  13. dt1649651

    dt1649651 Guest

    This problem just happened again. And I just found out that I set the
    vtys only from 0 to 4, and I used all of them.

    After extending this number, I am able to ssh to the router again. :)

    dt1649651, Jul 28, 2005
  14. dt1649651


    Mar 14, 2012
    Likes Received:
    Similar issue, SSH fails, telnet works

    Hi all,

    I have a weird behavior on my Cisco router here. I had to restart it for password recovery. Post restart, the config was restored from backup and since then SSH to router comes back with "Connection refused". I can telnet however.

    I have several VTY lines, all with preferred transport mode as SSH:
    line vty 0 4
    exec-timeout 9 20
    transport preferred ssh
    transport input telnet ssh
    line vty 5 15
    exec-timeout 9 20
    transport preferred ssh
    transport input telnet ssh
    line vty 16
    exec-timeout 9 20
    password 7 0945401A0D041B1E
    transport preferred ssh
    transport input telnet ssh

    I have identical config on several other branch routers (2800) and it works fine. OS version is Version 15.1(4)M2
    adm123, Mar 15, 2012
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