Question : TTL Expired periodically on a ping to another subnet.

Hi folks,

I got a strange problem here.  I'll start by explaining the network layout...

I have two subnets in our office - lets call them A and B.  B is a small subnet holding four servers that were moved in from another office and because of configuration issues on the servers we simply created the subnet locally.  Subnet A is the main subnet for the office containing the majority of the servers and all client devices.  On subnet A we have 3 external lines - a line for internet, a line for VPN and a leased line to our head office in Germany.  Subnet A talks to subnet B via an old Windows 2000 Server with RRAS installed and 2 NICs (which has always worked fine).  We'll call this server Server1.

We recently upgraded our internet line to ADSL2+ and due to this had to replace the router.  We installed a Draytek 2820 - everything has been working fine for a few weeks now.

Now, all of a sudden we have this problem where by connectivity from subnet A to B drops.  Doing a constant ping is successful for a while and then you get TTL expired for like 20 seconds or so, and then back to replies.  All traffic on subnet A has the default gateway of the German Router which in turn forwards any traffic not destined for Germany onto our Internet router.  If the traffic is for subnet B our internet router has a static route that forwards it to Server1.

When this sudden loss in connectivity occurs I have gathered the following information:

1.  A tracert from a client on subnet A to a device on subnet B goes to the German router and then to our internet router 'pauses' and goes back to the German router again.  This continues back and forth until connectivity suddenly comes back and it carries on to Server1 and onto subnet B.

2.  I can ping the internal interface of our internet router from a client in subnet A.

3.  I can ping Server1's interface on subnet A from a device on subnet A.

4.  I cannot ping Server1's interface on subnet B from a device on subnet A.

5.  I cannot ping Server1's interface on subnet B from our internet router.

6.  I can ping Server1's interface on subnet A from our internet router.

Now, if this was it I would think great - the problem is with Server1.  However, some clients on subnet A need to access a server on subnet B.  I added static routes to the PC's to direct them to Server1 for any traffic going to subnet B.

So now I am confused - is it the internet router, or is it Server1 and what might it be?

I have come to the conclusion that it's possibly one of the following:

1.  A faulty NIC on Server1
2.  A corrupt TCP/IP stack on Server1.
3.  A dodgy internet router.

Last night I backed up the config on our internet router and reset the device to factory defaults.  I then loaded the config back on again - no change.

Any help/ideas would be greatly appreciated.

Thanks guys.

Answer : TTL Expired periodically on a ping to another subnet.

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