I have a friend who just received his Windows Home Server. Home Server allows you to access it remotely so you can share photos, Remote Desktop and backup documents. The provided documentation includes details on how to setup your router, open ports, and setup an external name like “myhomesrv. homeserver.com.” The problem was, when he went to test this out by typing the address in his web browser, he was shown his router's administrative web page instead of his Windows Home Server web page. Yet, I was able to access the web page fine from my work machine.
I told my friend to download Network Monitor and get a trace. I also asked that he clear his local DNS cache by typing "ipconfig /flushdns". This is important because if a name is already cached it won't try and resolve the name again. This step ensures the resolution traffic will be captured when we reproduce the problem. In just a few minutes he sent me the capture file, and I opened it up.
I start by opening the trace and looking for DNS traffic by applying the display filter "DNS". In this particular trace there's a bunch of DNS traffic, but by looking at the summary line I can see the name my friend was trying to resolve.
DNS:QueryId = 0x847E, QUERY (Standard query), Query for myhomesrv.homeserver.com of type Host Addr on class Internet
DNS:QueryId = 0x847E, QUERY (Standard query), Response - Success, Array[xxx.143.174.204,yyy.46.154.126]
I see the query for "myhomesrv.homeserver.com" and then look for the matching response. In this case it was the next frame, but if you had a lot of traffic you could do a search for a DNS frame with the matching Query ID. And if you didn't know how to create a filter for the QueryID, you could right click on it in the frame details and “add to display filter” to understand how it should look.
Without even having to dig into the frame, you can see the response has all IP address info bubbled to the summary line. (By the way, I've obscured the address with xxx and yyy, but normally these would show as real numbers.) The proof I was looking for was to make sure the name, myhomesrv.homeserver.com, was being resolved to the external IP address of the router. Indeed the IP addresses matched, so I know that the name is resolving properly.
Next, I looked for the TCP setup and HTTP request that should occur since we were trying to browse his personal page. This occurs right after the DNS traffic as well.
We see that the client attaches to myhomesrv.homeserver.com, which is the same resolved name we saw picked up by DNS in the traffic before. The Network Monitor parsers will automatically resolve names for you when it sees name resolution traffic, but you can always add different columns or simply dig into the frame to verify the IP address.
Now, we see that the traffic is going to the right address. It appears that the name resolution is working correctly and doing want we want. However, the response shows information that looks like my friend’s router’s web page.
Of course this isn't a surprise because this is what we see in the browser as well. Then what happened? Why did the web page from his router appear instead of his home server?
We've identified some strange behavior, what next? A trace from the ISP might give us more information. Personally, I can't even get my ISP to answer simple billing questions so asking for a trace would probably be fruitless. But maybe we can see if other people are experiencing the same problem. After doing some Bing searches, I came across this blog (http://www.myhomeserver.com/?page_id=67). In particular in Step 7 it mentions the "loopback issue".
It appears that some routers don't know what to do with an external address when sent from the inside. As we see, this matches the behavior in the trace. The DNS request returns the address we expect, and the following HTTP request is also sent to the right place. However, we see that the response from the router comes back with the router’s web page. Instead we should have seen the HTTP request get bounced to our Home Server’s internal address.
Well maybe that's extreme. I would suggest checking for a firmware upgrade first. A less expensive simple solution is to use the Home Server machine name in these circumstances. In any case my friend is now able to access his Home Server’s website internally by using http://myhomesrv and externally with the address http://myhomesrv.homeserver.com.
You're not alone. I have seen the same problem.
Small Business Server gets around this by putting a record in its DNS of the external name that points to the internal address of the server.
You could put a HOSTS file on each client pointing to the right name, but for a lot of clients...
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