pt to pt connection very slow

Posted on 2011-02-25
Last Modified: 2012-05-11
I have a pt to pt connection between two sites running a T1.  While pinging and browsing each others network is fast.  Accessing shares or doing installations or copy information from site A to Site B is very slow
Question by:ssuser1
LVL 24

Expert Comment

ID: 34985863
More than likely a congested T1 (Saturated), even an issue with the T1 taking errors causing packet loss. What type of routers do you have connecting to the T1?
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Accepted Solution

Scott Gorcester earned 500 total points
ID: 34986006
T1's are only 1.5Mb's of bandwidth and depending on what other traffic might be present will simply not be very fast for copy or installation.

Author Comment

ID: 34988906
We have cisco routers on both end. Even if only one machine is trying to access the other site it is slow and the router will show high utilization even with one user.  If the T1 is just between the two ports shouldn't it be enough.  
LVL 24

Expert Comment

ID: 34989129
please report the output of the show serial interfaces

show serial int0/0 (replce 0/0 with your interface numbers)
Provide both ends.

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LVL 38

Expert Comment

ID: 34990332
Also, try an MTU ping test:

Standard MTU sizes are 1500 bits. By tunneling through a VPN, you are adding 24 bits to the packets.

A typical ping is only a few bits, and a browsing of each others sites is only a few packets, enough to not notice smaller sizes.

I think by changing the MTU size of your tunneling routers, it will allow your typical 1500 bit packes to go through freely without fragmentation.

This problem is called Maximum Segment Size Exceded. By showing serial interfaces, as mentioned above, it should tell what the MTU size is on that interface.
LVL 24

Expert Comment

ID: 34990402
Well, the MTU size is typically 1500 Bytes, and the VPN overhead is variable depending on the mode and encryption being used; If using a GRE tunnel, yes, the overhead would be 24 bytes. At any rate, this is typically not an issue for TCP hosts as they utilize PMTUD which is a mechanism that (Path MTU Discovery), as the name suggests, allows a host or network device to dynamically discover the lowest MTU along a path to a destination. This of course assumes that the host is setting the DF Bit, no firewalls blocking ICMP, and the host has the ability to reduce the size of data to meet the requirements end to end.
LVL 38

Expert Comment

ID: 34990531
That's why I wanted to see ping tests, to see if ICMP echo is disabled between adapters. I have seen drastically reduced efficiency from an MSS exceded problem. I have also seen timed out web pages. So, with the browser not having problems, maybe things are good with the MTU sizes on the tunneling routers.
LVL 24

Expert Comment

ID: 34992162
Agreed, something to look at.

LVL 20

Expert Comment

by:Daniel McAllister
ID: 34999552
There is an inherant delay in connection over the Internet that is not there on a LAN. Trying to use NetBIOS or SMB (version 1) over a VPN or other Internet-based conenction medium will result in VERY poor performance (usually unacceptably poor).

The "fix" is to use SMB version 2. It is ONLY available on:
  - Windows Vista, 7, and Server 2008
  - Samba 3.5 and above (including the recent releases of Samba 4 beta)

You'll be VERY hard pressed to find any NAS or embedded CIFS devices capable of running SMB version 2, so you're looking at a Windows 2008 or Samba 3.5 server to provide file services -- but again, the CLIENTS need to be one of the above OSes to make use of SMB 2's upgrades!

Read more here:

Best Regards,


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