Topic: Weird network/internet issue

[JonB]

Bear with me because this is rather long and convoluted.

I have a client site running SME6 in Gateway/Server mode accessing the internet via an ADSL router (PPPoA) with a static IP. The ADSL router has ports 22 (SSH), 25 (SMTP), 80 (HTTP), 110 (POP), 443 (HTTPS), 3389 & 3390 (Remote Desktop Protocol) forwarded to the SME6. The SME6 forwards the RDP ports to the appropriate XP Desktops.

On my Home Office network I have a SME7 in Server/Gateway mode with all updates. The Server access's the internet via an ADSL router (PPPoA) and the server hangs off the DMZ of the router. IP is static.

I use the same ISP as my client with the SME6

My network consists of several XP desktops and laptops.

Heres where the problem starts. For the past couple of days I have been unable to access my clients Desktops via RDP. I cannot telnet into his mail server or POP server nor can get into the SME6 via SSH (putty, winscp) from any of the desktops on my home office network. I can ping my clients URL.

This is where it gets weird. From my home SME7 server console I can ssh into my clients SME6 server. I can also telnet into the mail server and pop server. Just not from the desktops.

From my desktops I can ssh into any other server I administer. I can RDP into a Windows 2003 server I look after in the States. It is just that one client I cant access.
This would appear to take any firewall,network routing or desktop PC's  issues out of the equation.

From my Workshop network (different location, SME7 in Gateway/Server mode, different ISP) I can ssh, telnet and RDP into my clients site from my network desktop PC's.
This would indicate that the client site setup is fine.

When I try to access my clients site via ssh or telnet from my home office desktops I can see the SYN packets arrive on the external interface of the SME6 but thats as far as it gets. There appears to be no acknowledgement back to my desktop.

Just to take my SME7 server out of equation I connected the desktop directly to my ADSL router and I still can't putty, telnet or RDP to my clients network.

The only thing that has happened in the past couple of days is that the ISP that my home office and client uses has had several outages.

Both ADSL routers and SME servers (mine and clients) have been rebooted.

I dont believe that the SME servers are the problem but that our ISP has some strange routing or firewall issues.

I can't see why I can access my clients server via my SME7 server console but not via my desktop PC's but I can access other servers via my desktops or why I can access my client from other network PC's off other ISP's.

I have talked to my ISP until I am blue in the face but they see no problems. Unless I can come up with hard data they won't listen to me.

Any suggestions would be greatfully accepted.

Jon

[JonB]

Ok, got it sorted. It's definitely an ISP issue.

TCP packets arriving at my clients site are arriving with "bad TCP checksum" when trying from desktop and only 50% of the time when trying from SME server.

Jon

[p-jones]

Is your client by any chance on Xtra Go Large ?? I am having all sorts of hasles with PPTP since telescum switched me over to GoLarge.

[JonB]

p-jones,

My issue is within Ihug and only occurs on Ihug to Ihug connections. Mind you it did all start last week when Telecoms had problems at Mayoral Drive.

I spent around 4 hours today getting tcpdumps and traceroutes for Ihugs network engineers. I had visit to 3 of my clients that are on Ihug connections and try to telnet into my clients server smtp server while running tcpdump. I bet Ihug wont offer to pay me for this and I certainly can't bill my client for it.

The interesting thing is that when using windows to telnet into the server we get 100% bad TCP checksums but when telneting using Linux it is only around 30% bad TCP checksums, which makes it just usable.

Might all be a waste of time because if they don't have it sorted by tomorrow I will be moving my clients 4 Ihug adsl accounts, my Ihug adsl account and a couple of my other clients Ihug accounts to quicksilver.

Jon