can't ssh from host to remote

[Michael Havens]

I think I should give you the models of my devices:
the router is a wrt54g and the modem is a pk5000. I did a little more
searching and read that I can change the firmware on the router but if
memory is correct if I screw up it becomes a brick so I need to ask what
the benefits are and if there is another way to do it. I just looked
closely at the router and it is labled as a wireless router and a 4 port
switch.

:-)~MIKE~(-:


On Sat, Jul 19, 2014 at 11:39 AM, Michael Havens <bmike1 at gmail.com> wrote:

> >Why were rules written for the second router but not the first?
> >Is it because it was connected first? Could we write the rules we need?
>
> What I meant was the second was connected to the first.
>
>
> :-)~MIKE~(-:
>
>
> On Sat, Jul 19, 2014 at 11:31 AM, Michael Havens <bmike1 at gmail.com> wrote:
>
>> > Going the other way, you have no rules to pass
>> > the communication through.
>>
>> Why were rules written for the second router but not the first? Is it
>> because it was connected first? Could we write the rules we need?
>>
>>
>> :-)~MIKE~(-:
>>
>>
>> On Fri, Jul 18, 2014 at 3:34 PM, Gilbert T. Gutierrez, Jr. <
>> mailing-lists at phoenixinternet.net> wrote:
>>
>>>  NAT is the reason. The ping is being translated from one network to
>>> another as well as telnet. Going the other way, you have no rules to pass
>>> the communication through.
>>>
>>> Gilbert
>>>
>>>
>>> On 7/18/2014 2:44 PM, Michael Havens wrote:
>>>
>>> so according to your tutorial 192.168.0.x is not on the same subnet as
>>> 192.168.1.x. If that is correct why can I ssh (and ping and telnet....)
>>> from client to host but not host to client?
>>>
>>> :-)~MIKE~(-:
>>>
>>>
>>> On Fri, Jul 18, 2014 at 12:30 PM, Michael Havens <bmike1 at gmail.com>
>>> wrote:
>>>
>>>>  telnet localhost 22 from the server received no answer from the client
>>>> telnet 192.168.1.101 22 from the client received no answer from the
>>>> server
>>>>
>>>>  I'll get back to you about the research project
>>>>   (and as a private message)
>>>>
>>>> :-)~MIKE~(-:
>>>>
>>>>
>>>> On Fri, Jul 18, 2014 at 6:41 AM, <kitepilot at kitepilot.com> wrote:
>>>>
>>>>> Hello Michael:
>>>>> the 'Net' is a hodgepodge of protocols, all abiding to the 'OSI Layer
>>>>> Model' to work properly (http://en.wikipedia.org/wiki/OSI_model).
>>>>> Troubleshooting your SSH connection should be a fairly simple
>>>>> proposition, because there are only so many moving parts (Three!).
>>>>> As anything under the OSI model, nothing on an upper layer will work
>>>>> unless the necessary components of the lower layer are working.
>>>>> AND you *HAVE* to troubleshoot each layer separately.
>>>>> So how does this go?
>>>>> Well, lets take a look at your SSH problem...
>>>>> 1.- In order for the SSH connection to work you need 3 things:
>>>>> 1.1.- a SSH server,
>>>>> 1.2.- a SSH client and,
>>>>> 1.3.- a TCP/IP connection.
>>>>> *EACH* one of the lines above is a separate project and *HAS* to be
>>>>> addressed as such.
>>>>> Lets cover the basics first, the TCP/IP connection:
>>>>> You *HAVE* to *KNOW* The Mantra:
>>>>> "In order for any 2 devices to establish a TCP connection they have to
>>>>> share a physical link and they need addresses in the same subnet".
>>>>> The statement above is a pretty dense one, and has several
>>>>> implications, number one being: What does "subnet" mean?
>>>>> Another is: what about IPs in different subnets?
>>>>> We'll get there...
>>>>> As there are already several books written (and to be written) about
>>>>> the few lines above, I'll water it down to the bare minimum:
>>>>> The subnet is defined via the netmask, and implies that "ON" parts of
>>>>> the netmask are always equal in all the addresses on a network segment, so:
>>>>> Network:
>>>>> 192.168.0.0/24 or
>>>>> 192.168.0.0 with netmask 255.255.255.0 means that
>>>>> *ALL* the addresses in *THIS* network are going to look like
>>>>> 192.168.0.${SOMETHING_ELSE}
>>>>> '192.168.0' is the "Network", and "${SOMETHING_ELSE}" is the "Host".
>>>>> You can not use "Host 0" (because that defines the network) and you
>>>>> can not use the highest number (255) because that's the 'broadcast address'.
>>>>> Which means that any '/24" (slash 24) network can address 254 'hosts'.
>>>>> Network:
>>>>> 192.168.0.0/16 or
>>>>> 192.168.0.0 with netmask 255.255.0.0 means that
>>>>> *ALL* the addresses in *THIS* network are going to look like
>>>>> 192.168.${SOMETHING_ELSE}.${SOMETHING_ELSE}
>>>>> '192.168' is the "Network", and "${SOMETHING_ELSE}.${SOMETHING_ELSE}"
>>>>> is the "Host".
>>>>> You can not use "Host 0.0" (because that defines the network) and you
>>>>> can not use the highest number (255.255) because that's the 'broadcast
>>>>> address'.
>>>>> Which means that any '/16" (slash 16) network can address 65534
>>>>> 'hosts'.
>>>>> The reason why '255' is the highest number is because IPv4 addresses
>>>>> (and netmasks) are represented in memory in 4 bytes, each number one byte.
>>>>> Bytes are 8 bits, but that's a different book that you need to read
>>>>> too, lets move on with the network.
>>>>> Things get pretty interesting (and math pretty convoluted) when you
>>>>> define networks like 192.168.127.0/25
>>>>> If yo want to see all variations, you can be lazy (like me) and run:
>>>>> ipcalc 192.168.0.127/25
>>>>> Finally, "Netmasks" are a patch to the first defined (and
>>>>> shortsighted) 'Address Type' as class A,B,C or D, but I'll let you research
>>>>> that yourself.
>>>>>
>>>>> Well, that's all good, but how do you talk to other addresses?, I talk
>>>>> to google.com...
>>>>> That's a valid question, but
>>>>> 1.- it is not part of *THIS* SSH problem and
>>>>> 2.- you don't 'talk to google'.
>>>>> We'll talk more about how devices find each other in a network down
>>>>> below, but in order to talk to devices outside your network you need the
>>>>> 'Routing Protocol' (implemented at [SURPRISE!] 'the router') which is
>>>>> nothing else than a table of rules stating 'this IP goes that way'.  In
>>>>> your case, all addresses go the same place (the router) so the router
>>>>> becomes the 'Default Gateway'.  As to resolve google, you need the DNS, but
>>>>> you knew that...   :)
>>>>>
>>>>> Now that we know what an IP address is, lets move on to the "Physical
>>>>> Link".
>>>>> Well, a cable will do...
>>>>> In the wireless world, the "Association" is the link.
>>>>> And how do you validate that?
>>>>> iwconfig will tell you what (if anything) you are associated to.  No
>>>>> association, no link, no connection, no SSH.
>>>>> ifconfig will tell you what (if anything) you are wired to.  No wire,
>>>>> no link, no connection, no SSH.
>>>>> Ain't that simple?   ;-)
>>>>> So we have a link...
>>>>> And we have IP addresses in the same subnet.
>>>>> So we are connected!!!   8-)
>>>>> Not so fast Armando!!!
>>>>> The fact that your addresses match is not necessarily a validation,
>>>>> because each computer may be connected to a different router providing the
>>>>> same NAT(ed) address!
>>>>> NAT?
>>>>> Yes NAT (Network Address Translation protocol), but that's yet another
>>>>> book, so lets water it down:
>>>>> NAT is the protocol that allows you to have an 'outside visible
>>>>> address' and an 'inside invisible network' in a router.
>>>>> NAT (as Netmask) was implemented mainly to alleviate the IPv4 shortage
>>>>> address because of the 'class A,B,C or D' mistake, but as a byproduct, you
>>>>> can 'hide' behind it, which provides some level of security.  How you hide
>>>>> is yet another bookshelf and essentially means that you cannot access
>>>>> devices 'behind the router' unless the device initiates the connection
>>>>> first, and that's how you raise a WEB site from 'behind the router' and why
>>>>> you can SSH from 'inside to outside the router' but not the other way
>>>>> around, so lets move on...
>>>>> So, how do we know that we are connected to the same router?
>>>>> Ah, glad you asked:
>>>>> ARP!
>>>>> Or Address Resolution Protocol.
>>>>> *ALL* data transmission is done at OSI layer 2.
>>>>> Quick implementation manual:
>>>>> OSI layer 1: Cable or association.
>>>>> OSI layer 2: MAC address.
>>>>> OSI layer 3: IP address.
>>>>> Your network doesn't know (and doesn't care) about IP addresses.  The
>>>>> IP address is there to resolve the MAC address.
>>>>> When you say:
>>>>> ping 192.168.0.1
>>>>> that generates a 'who has' request from the ARP protocol.
>>>>> That request is broadcasted to anyone on the physical link (OSI layer
>>>>> 1)
>>>>> The device with the IP address interrogated by 'who has' answers with
>>>>> its MAC address.
>>>>> This IP/MAC address pair is then saved to the ARP table.
>>>>> >From there on (and even though the IP address goes along in the
>>>>> TCP/IP header) all transmissions are sent to the MAC address.
>>>>> But then again, how do you know that your 2 boxes are talking to the
>>>>> same router?
>>>>> arp -n|grep 192.168.1.1
>>>>> Same MAC?
>>>>> Same box.
>>>>> Different MAC?
>>>>> Same Michael...   ;-)
>>>>> What do we know so far?
>>>>> Well, we know something about line 3 of the very first paragraph.
>>>>> What about line 2?
>>>>> Type
>>>>> which ssh
>>>>> You have it or not, and you know what to do, so lets move to line 1.
>>>>> We now need to troubleshoot the SSH server.
>>>>> Well, that boils down to 2 things, it is working or not...
>>>>> You *KNOW* that the SSH server is 'listening' (although not
>>>>> necessarily working) when you can connect to the 'port'
>>>>> Port?
>>>>> Yeah, port...
>>>>> Lets move on up in the OSI model to the application layer.
>>>>> In order to establish a TCP connection you need an IP connection and a
>>>>> port (or a socket and a port)
>>>>> The port is to the application what the IP address is to the MAC.
>>>>> So if the port is listening, the application is awake.
>>>>> And how do we know?
>>>>> There are only 975143684 possible ways to validate a 'port is open'
>>>>> (or listening) but I am a simple boring guy, so I do:
>>>>> telnet localhost 22
>>>>> I either get an answer or not.
>>>>> If I get an answer, then we are most likely all good, but if I don't
>>>>> get an answer then the ramifications are staggering and I'm not even going
>>>>> to think about it.
>>>>> In order to check that the other port listens then you:
>>>>> telnet ${REMOTE} 22
>>>>> Again, we either get an answer or not.  And the 'not' means another
>>>>> Sunday drive to the library...
>>>>> Finally, why 22?
>>>>> Because that's the SSH port and it is defined in the configuration
>>>>> file, which you can change to further complicate your (or someone else's)
>>>>> life.
>>>>> But who and where defined 22 as the SSH port?
>>>>> grep -i ssh /etc/services
>>>>> And who wrote /etc/services?
>>>>> http://www.iana.org/
>>>>> And how do I know all this crap?
>>>>> Because I finished LFS!!!!    ;-)
>>>>> I hope you see everything now as clear as mud.
>>>>> Keep this message handy, you'll need to read it several times...
>>>>> Keep in mind that what I have written here is a GROSS
>>>>> oversimplification of several bookshelves contained in several buildings
>>>>> and written along several decades all over the World, it's free advice, you
>>>>> can't sue me...   :)
>>>>> And always remember:
>>>>> For every question there exists a simple, direct and wrong answer.
>>>>> if you have any question,
>>>>> you will get any answer...
>>>>> ET
>>>>> PS: Research project:
>>>>> Why doesn't 'ping' use a port?
>>>>> Why is 'ping' 'setuid(ed)'
>>>>> What are 'routable' networks?
>>>>> What are 'non-routable' networks?
>>>>> What does it mean if you get and IP address like 169.254.0.0/16
>>>>> Why do you always have a 127.0.0.1 address in your boxes?
>>>>> Who defines (and where are the documents that define) all these
>>>>> protocols? (RFC anyone?)
>>>>>
>>>>>
>>>>> Michael Havens writes:
>>>>>
>>>>>> okay, so I bought a used computer to do Linux from scratch on. Well,
>>>>>> I'm
>>>>>> going to ssh from my primary computer to the new computer but got a
>>>>>> 'Connection timed out' error. After googling for a bit I discovered
>>>>>> ufw was
>>>>>> to blame.
>>>>>> after I disabled the firewall I could ssh from 192.168.1.101
>>>>>> <parasite> to
>>>>>> 192.168.0.4 <host>
>>>>>> the error I got going the other way was the connection timed out
>>>>>> error:
>>>>>> ssh mike at 192.168.1.101
>>>>>> ssh: connect to host 192.168.1.101 port 22: Connection timed out
>>>>>> After googling some more I thought perhaps openssh-server wasn't
>>>>>> installed... but it is. So please.... what is the problem? I verifed
>>>>>> openssh-client is installed but I don't know what it could be. Could
>>>>>> you
>>>>>> help me out?
>>>>>> :-)~MIKE~(-:
>>>>>>
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>>>>
>>>>
>>>
>>>
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