IP forward

The problem that I have posted elsewhere has been narrowed down: Apparently comcast changes the IP address for IP forwarded servers.

I had established IP forward for my come computer, found out what address it was, checked that I could log on from outside and went traveling.

Early July I could not log on to my home machine any more. Of course I thought first that it had crashed but when I returned late July it still ran fine.

Eventually I found out that the IP address that IP forwarding had been assigned to has changed without me being notified.

This is of course a disaster for anybody who would like to access his/her home computer while traveling

Responses

user_3kzzhb

12 Messages

3 months ago

Things got worse again:

I could with ssh -X log on to a remote Linux machine. Used "last" to find out the IP address from where the login came from.

Used "ssh" to to to log on to that IP address and got a "Connection timed out". It worked a few days ago....

XfinityBillie

Official Employee

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2.8K Messages

3 months ago

@user_3kzzhb Thank you for taking the time to reach out to us here on our Xfinity Forums. Xfinity residential accounts all have a dynamic IP address, which does occasionally change the IP address. The only way to prevent this is to have a static IP address, which we don't offer to residential customers. I hope this helps.

user_3kzzhb

12 Messages

@XfinityBillie It helps in the sense that I need to look for an alternative provider. It did *not* help to solve the above problem that I could not even ssh to the "dynamic" IP address.

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3 months ago

XfinityAngie

Official Employee

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1.4K Messages

user_3kzzhb, I am sorry about that. I wish we could have been of more assistance.

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3 months ago

user_3kzzhb

12 Messages

It would help if there was a way to find out what the "dynamic" IP number is without logging on to a remote machine. The way it is now, IP forward is completely useless.

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3 months ago

EG

Expert

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107.1K Messages

3 months ago

@user_3kzzhb

Have you considered trying to see if one of those dynamic DNS services will work for you ? YMMV. You can Goggle it for more info. Good luck !

user_3kzzhb

12 Messages

@EG As far as I can see that also requires that I have access to my home computer. There is a work-around for the stupid policy of assigning

dynamic IP numbers to residential customers which makes the whole concept of IP forwarding useless: Run a cron job every day to log in to a remote server which then lets me find out from which IP address the login came from. BUT none of this works if comcast randomly does

not even permit ssh access. I had none of these problems with Verizon.

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3 months ago

BruceW

Gold Problem Solver

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26K Messages

3 months ago

@user_3kzzhb wrote: "... As far as I can see that also requires that I have access to my home computer ..."

https://www.cloudflare.com/learning/dns/glossary/dynamic-dns says:

How does dynamic DNS work?

... One very common method of enabling dynamic DNS is by providing users with software which runs on their computer or router. This software communicates with the dynamic DNS service provider anytime the IP addresses provided by the ISP is updated, and the dynamic DNS provider in turn updates the DNS with those changes, providing almost instant updates.

Some routers have dynamic DNS clients built in.

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user_3kzzhb

12 Messages

3 months ago

I am not sure how this helps. "Intelligently" comcast assigns a host name based on the IP number and not for example on the customer name or account information. There is no way to reach the home computer if one is traveling and the IP number has changed. Personally I am lucky enough that I have access to another machine with a static IP address, so I can run a cron job that logs me in regularly to that machine and I can find out from where the login comes. Most people are not that lucky., and with "home-office" becoming more and more popular the problem for comcast will become worse.

BruceW

Gold Problem Solver

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26K Messages

3 months ago

You are welcome to use a dynamic DNS service, or to not use one. But it's inaccurate to say "There is no way to reach the home computer if one is traveling and the IP number has changed". Solving that problem is one of the main reasons dynamic DNS services exist. By all means take 5 minutes to read up on them and perhaps you will understand "how this helps".

When you Comment on a post (by scrolling down to "Comment on this post here...") I am notified of your response. But if you select Reply, I am NOT notified and may not be aware of your message.

user_3kzzhb

12 Messages

sorry.. comcast assigns a host name based on the IP number and not for example on the customer name or account information.

so say the IP number is a.b.c.d, then the assigned host name is c-a-b-c-d.hsd1.wa.comcast.net, i.e. the hostname changes with the IP number.

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3 months ago

BruceW

Gold Problem Solver

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26K Messages

3 months ago

... the hostname changes with the IP number.

Which is why the Dynamic DNS services don't use the Comcast/Xfinity name. They assign a separate hostname, or have you create one.

It's a mystery to me why you continue to poke holes in an idea that you clearly do not understand.

And, again:

If you select Reply, I am NOT notified and may not be aware of your message.

user_3kzzhb

12 Messages

OK I try to explain it to you for the third time and then give up:

.Take 5 second to read and understand this:

"Intelligently" comcast assigns a host name based on the IP number and not for example on the customer name or account information\

So, taking what is said here and translate it:

For example, if a web administrator is operating a small website with a domain name of www.example.com and an IP address of 192.0.2.0, anytime another user enters www.example.com into their browser, the DNS will direct them to the server at 192.0.2.0. If the admin's ISP dynamically changes the IP to 192.0.2.1, a dynamic DNS service can automatically update the admin's DNS records so that other users trying to visit www.example.com will now go to the correct IP address.

That would work if comcast had assinged the hostname to the customer name or account information.

BUT:

They assigns a host name based on the IP number, so if the IP number is

192.0.2.0 then the hostname becomes c-192-0-2-0.hds1.wa.comcast.net

and if they decide to change it to

192.0.2.1 then the hostname becomes c-192-0-2-1.hds1.wa.comcast.net

So if I don't know the IP number then I don't know the hostname either.

Otherwise user_3kzzhb would have been of more help and not just "I am sorry about that. I wish we could have been of more assistance."

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3 months ago

BruceW

Gold Problem Solver

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26K Messages

3 months ago

... They assigns a host name based on the IP number ...

Which is why, as stated above, "Dynamic DNS services don't use the Comcast/Xfinity name. They assign a separate hostname, or have you create one". Anyone who wants to access the server uses that alternate hostname, not the Comcast hostname. If the IP changes, software running on the server or one of its local network components notifies the DynDNS service, and the DNS for the the alternate hostname is updated. Quite simple really.

Using a dynamic DNS service YOU DON'T KNOW OR CARE WHAT NAME COMCAST ASSIGNS BECAUSE YOU DON'T USE IT!!!

And, yet again:

If you select Reply, I am NOT notified and may not be aware of your message.

(edited)

user_3kzzhb

12 Messages

That's why I would have expected that user_3kzzhb would not have ended his statement with "I wish we could have been of more assistance"

but rather "we have assigned a permanent host name such-and-such to your forwarded IP address" which would have been, of course,

a much more elegant solution and had made all of this discussion unnecessary. All I can do is a reverse DNS lookup which gave me the above

names c-192-0-2-0.hds1.wa.comcast.net.

It seems I cannot reply to user_3kzzhb any more -- if you read this, please comment.

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2 months ago

user_3kzzhb

12 Messages

sorry, user user_3kzzhb is of course me. I meant the

XfinityAngie

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2 months ago

Your Home Network

user_3kzzhb

IP forward

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user_3kzzhb

XfinityBillie

user_3kzzhb

XfinityAngie

user_3kzzhb

EG

user_3kzzhb

BruceW

How does dynamic DNS work?

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user_3kzzhb

BruceW

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user_3kzzhb

BruceW

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user_3kzzhb

BruceW

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user_3kzzhb

user_3kzzhb

XfinityAngie

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