Need help figuring out why packets are getting dropped

spfister336 · ‎02-08-2013

We have several remote sites connecting to a central location. Each remote site has its own file and print server hosted at the central location as virtual machines. Recently, we've been having problems pulling data from one of these servers (e.g., getting directory listing containing large amounts of files and folders), but only from machines at the central site. Users at the remote site who have been assigned this particular server have not reported any problems. All other servers have been behaving fine, and I can't see how this one server is different from the others.

Captures near the server show normal behavior until it comes time to actually send the directory contents, then there are repeated attempts to transmit the data, followed by a [RST,ACK]. Captures near the machine browsing the directory show just the [RST, ACK]. I've done captures in various points in the intervening network and I think I've found the spot where it's not sending data any further, even though all other connectivity to this machine is fine (I'm using my workstation for testing).

The last spot the retransmitted packets get to, the source and destination ips seem correct, and layer 2 info shows the source as being the switch at the remote site the packet came from, and the destination seems to be the MAC address associated with the vlan that the browsing machine is a part of. Packets seem to be dropped somewhere around this point. Captures at the interface where the packets should leave to head to the browsing machine show everything but the retransmitted packets. Again, the machine doing the browsing has normal connectivity for all other things.

How can I find out why the packets are getting dropped?

ALIAOF_ · ‎02-08-2013

So this server is sitting at a remote site and users from the central site are trying to access this server? If that is the case what kind of connection do you have between the two sites?

spfister336 · ‎02-08-2013

Sorry... that part wasn't very clear in my post. The server is a VM at the central site that normally users at the remote site access, and they're accessing it with no problems. When we try to access it from the central site, that's when the problems happen.

The central and remote sites are all connected via Opt-E-Man, a switched metro ethernet service from AT&T.

ALIAOF_ · ‎02-08-2013

Ok so it seems like the issue is only on the LAN side. Have you looked at the switches that users are connected to? Also if you do a continuous ping from the users PC's to the server do you see any dropped packets?

spfister336 · ‎02-08-2013

Continuous pings are fine, both from the users at the remote site and from us at the central site. Browsing folders from Windows seems normal up until the point where we open a folder with a large amount of files and folders.

spfister336 · ‎02-11-2013

I have more definite information about where packets get dropped. Packets get to the remote side and come back to the central side (in and out the same interface). Packets seem to go through fine if they're < 1514 bytes, but as soon as a 1514 byte packet is sent to the remote side, nothing comes back.

ALIAOF_ · ‎02-12-2013

Ok I thought you said users from the remote site can browse fine it is just the local users. But now you are saying the issue is with the Remote users and NOT the Local users sitting at the Central site?

spfister336 · ‎02-12-2013

No, no... the problem is with users browsing from the central site. Remote users are fine. My last message was about where packets get dropped for local users when they try to browse. It's kind of hard to explain without a diagram, maybe...