Newbie TTL Expired in Transit question

Discussion in 'Cisco' started by The Other Mike, Dec 14, 2006.

  1. I know this has to be something simple but I'm not sure what. We have
    a simple config on our Internet router supplied by our ISP. We had 2
    sets of IP's assigned to us...for example, 65.65.65.65/30 (router
    serial interface IP) and 75.75.75.75/27 for hosts. We have static
    nats for the 75.75.75.x ip's and a single IP Route command pointing
    everything out the Serial interface. When we ping the serial
    interface, it responds fine. When we ping any of the 75 addresses, we
    get the "TTL Expired in Transit" reply...tracert shows a continuous
    loop between our serial interface and the next hop to our ISP.
    But...we can still access whatever is running on the hosts (webserver,
    VPN, email...etc). What am I missing here? Shouldn't the pings be
    either timing out or replying depending on our firewall config? And
    why does the ping expire but port 80, 25..etc. are fine? It's not
    hurting anything...more of a curiosity question.
     
    The Other Mike, Dec 14, 2006
    #1
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  2. The Other Mike

    Guest

    The Other Mike wrote:
    > I know this has to be something simple but I'm not sure what. We have
    > a simple config on our Internet router supplied by our ISP. We had 2
    > sets of IP's assigned to us...for example, 65.65.65.65/30 (router
    > serial interface IP) and 75.75.75.75/27 for hosts. We have static
    > nats for the 75.75.75.x ip's and a single IP Route command pointing
    > everything out the Serial interface. When we ping the serial
    > interface, it responds fine. When we ping any of the 75 addresses, we
    > get the "TTL Expired in Transit" reply...tracert shows a continuous
    > loop between our serial interface and the next hop to our ISP.
    > But...we can still access whatever is running on the hosts (webserver,
    > VPN, email...etc). What am I missing here? Shouldn't the pings be
    > either timing out or replying depending on our firewall config? And
    > why does the ping expire but port 80, 25..etc. are fine? It's not
    > hurting anything...more of a curiosity question.


    what device is doing NAT - your ISP router or your firewall behind the
    router?
    take a look at http://www.dnsstuff.com/tools/tracert.ch?ip=75.75.75.x
    you will see how it jumps from outside to you

    the answer to your question is another question "how it's configured to
    travel from the INSIDE?"

    Roman Nakhmanson
     
    , Dec 14, 2006
    #2
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