can't ssh from host to remote

Sat Jul 19 11:39:34 MST 2014

>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~(-:
>>>>>
>>>>   ---------------------------------------------------
>>>> PLUG-discuss mailing list - PLUG-discuss at lists.phxlinux.org
>>>> To subscribe, unsubscribe, or to change your mail settings:
>>>> http://lists.phxlinux.org/mailman/listinfo/plug-discuss
>>>>
>>>
>>>
>>
>>
>> ---------------------------------------------------
>> PLUG-discuss mailing list - PLUG-discuss at lists.phxlinux.org
>> To subscribe, unsubscribe, or to change your mail settings:http://lists.phxlinux.org/mailman/listinfo/plug-discuss
>>
>>
>>
>> ---------------------------------------------------
>> PLUG-discuss mailing list - PLUG-discuss at lists.phxlinux.org
>> To subscribe, unsubscribe, or to change your mail settings:
>> http://lists.phxlinux.org/mailman/listinfo/plug-discuss
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.phxlinux.org/pipermail/plug-discuss/attachments/20140719/0c82d0d8/attachment.html>