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Fiber connection between networks

I'm a fiber newbie.  I ran multimode fiber between two rooms and it was almost plug-n-play.  Worked beautifully.  I stupidly thought I could do the same between two buildings.  It didn't work out so seemlessly and I need help.

I ran single mode fiber between two buildings approx. 700 feet apart (maybe a little more).  I have the jumpers (reversed appropriately) plugged into each switch.  However, the two networks cannot see eachother, ping, etc.  The networks are two separate submasks.  Does this matter?  Is this the problem?  How do I fix this?  When I ping from one side to the other I get the message that the destination host is unreachable.  From the other side the ping simply times out.

Help pleeeease,
Carol
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carolinasgirl28
Asked:
carolinasgirl28
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2 Solutions
 
Garry GlendownConsulting and Network/Security SpecialistCommented:
Question 1: Do you even get a Layer 1 connection, is the actual link up?
But the main problem seems to be your different "submasks". I assume you mean you have something like 192.168.0.0/255.255.255.0 on one side, and maybe 192.168.4.0/255.255.252.0 on the other network? If so, this will NOT work without a router in between, and has nothing to do with the actual fiber link. If you connect two (LAN or other) networks to each other with a plain switch/hub/bridge, they need to be using the same IP range and subnet mask in order to talk to each other. Depending on the type of switches you have, they might have L3 abilities, acting as a router and therefore forwarding data from one subnet to another. As those switches a typically significantly more expensive than simple L2 switches, chances are you do not have that.
In that case, the only thing you can do is migrate one subnet to the IP range of the other, possibly extending the other if there aren't enough IP addresses available.

Please post more details on the IP configuration and possibly make/model of the switch ...
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mat1458Commented:
First of all you have to look at the hardware you are using. Are the interfaces that you have capable of using single mode or do you have special SPF/GBIC that are made for single mode usage? If you don't have the right hardware it is too early to look at subnetting and other stuff.
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carolinasgirl28Author Commented:
I actually should have said that I have different ip class addresses not submasks.  Sorry about that.  Same subnet but one side is 192.xx.x.x and the other is 172.  As for the hardware....I took the advice of a vendor.  I have sc/sc converter and jumpers.  Each end plugs into a cisco switch.
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mat1458Commented:
If you do a show cdp neighbor on the Cisco switch: do you see the other switch on the end of the fiber link? If this is the case we can focus on addressing stuff, if not we have to stay with the hardware troubleshooting.
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Garry GlendownConsulting and Network/Security SpecialistCommented:
As for the actual link, same as I stated earlier - if you see a link on the switch, L1 should be fine (you can do a "show int g0/1" or which ever interface it is to check the status of the link - interface and line protocol should be status "up", and hopefully no errors on the interface)
The subnet _size_ alone does not matter, the relevant part is which subnet is actually used - and here you already mentioned that you use different networks ... without a L3 router in between, you won't be able to ping from one side to the other ...
So either you set up L3 routing, or you migrate one network to use IPs from the other network ...
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carolinasgirl28Author Commented:
Thanks Garry-G,

I changed one of the computers to match the other side's domain and ip scheme.  It doesn't time out but I get the attached message and I am still unable to use the resources. Oh, and the message is returned from my computer's ip address. What else needs to happen?

ping reply
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carolinasgirl28Author Commented:
mat1458 - how do I test what you are suggesting?
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Garry GlendownConsulting and Network/Security SpecialistCommented:
Can you log on to your switches and do a "show int gigX/y" for the ports that you use to interconnect the two sites?
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mat1458Commented:
Do you have the possiblity to log into the switches or into one of them (do you know passwords or eventual usernames)? If so issue a "show cdp neighbor" command and post the output please. If not, is there somebody at your site that can log into the switches?
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carolinasgirl28Author Commented:
I can log into the switch but cannot find a place for either command.  Anyone familiar with cisco network asst.?
fiber-switch.jpg
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carolinasgirl28Author Commented:
Actually....check this out....
fiber-switch2.jpg
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Garry GlendownConsulting and Network/Security SpecialistCommented:
Ah, OK ... so you have the line connected to a fast ethernet port of the switch ... check under the "monitor" section of network for interface status ...
On the first screen shot, you listed Fa0/7 for the interconnect - on the second screen shot, the CDP output only lists Fa0/1 on either side, so I assume that's the connection to another switch ...
You mentioned earlier you used I converter ... what converter exactly are you using? Do you have a make/model info on it?
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mat1458Commented:
Can you also add the following commands:
show interface status
show version
show running-config
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Garry GlendownConsulting and Network/Security SpecialistCommented:
Just a hunch, but I'm suspecting you have a fiber-copper converter running with Gigabit, while you only have Fast Ethernet available on the switch ... FE-converters aren't really that usual anymore ...
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carolinasgirl28Author Commented:
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Garry GlendownConsulting and Network/Security SpecialistCommented:
ok, so the converter and patch cable should be fine (assuming the link fibre you're using is also single mode fibre).
Does the converter light up some link LED when you hook up the connection to the remote side? What about the FE side when you plug it in to the switch?
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mat1458Commented:
Sorry for that one, I forgot to mention that for the "show running-config" command you need to say "enable" first and then enter a password. Maybe you can find that out too.

It looks like the switch on this side does see the converter and is fine (speed and duplex are negotiated correctly). As Garry-G says you might check if the converters help you with some LEDs. Especially important is that you have to cross the fiber cables once between both converters.

Can you log into the other switch as well and issue:
show interface status
show version
enable
show running-config
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carolinasgirl28Author Commented:
This is one side.  Should both tx and fx be lit?  I haven't made it to the other building yet to see what is lit on that side.
fiber-lights.jpg
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Garry GlendownConsulting and Network/Security SpecialistCommented:
yes, you need both links... from what I can make out, you're missing the fibre link at the moment...
Try switching the two fibres one end and see if that gets the link up. If not, put the two converters back-to-back without the inter-building link ... if that gets the FX link up, check the actual fibre link - are you sure you have single mode fibre there, too?
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carolinasgirl28Author Commented:
So, plugging the units up back to back with one single jumper lights up all led's.


Putting everything back together, despite the fact that I have reversed rx/tx on each end...the other end of each cable reverses it back.  Could that be the problem?   For example, on one end at the converter I have plugged in A, B which then gets plugged in to the fiber box as B, A.  At the other building I have one end on the coverter plugged in as B,A and the fiber box is A,B.   Could this be the problem?  The cables are made so that there is only one way to plug them in.  There is a sort of notch on one side that won't allow a single jumper cable to not reverse.
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carolinasgirl28Author Commented:
Attached shows better what I have going on. Except I have singlemode sc/sc ends. Each end is reversed but then each end is reversed on both sides!  Kinda defeats the purpose I think.  I don't see a way to undo each end from the molded plastic to undo the reverse.....
fiber-jumpers.png
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carolinasgirl28Author Commented:
Actually....here is my cable.
fiber-jumpers.png
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carolinasgirl28Author Commented:
Got them unreversed!  Whoo hoo!  Going to test now :)
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Garry GlendownConsulting and Network/Security SpecialistCommented:
guess that should be working now ... once you have all links up, you should be fine...
And yes , those SC prefab plugs are tricky to get apart if you never did that before ;)
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carolinasgirl28Author Commented:
Didn't work.  Was I right to unreverse the cables so that they were only reversed one time?
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Garry GlendownConsulting and Network/Security SpecialistCommented:
Correct, check whether both sides' converters have both FX and TX link lights on ... then check with "show cdp neigh" if you can see the remote switch ...
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mat1458Commented:
The way you describe it you might need to test if the cable between the buildings is ok. The back2back thing seems to work, so your boxes work allright. You have to make sure that the cables are reversed once only between both converters (Tx needs to go to Rx on the ohter side and vice versa).

Checking the cable might be a bit tricky but as you have said that you are able to separate the two cables in the plug you possibly can do some testing. Use a sheet of paper that you put in front ot the plug (don't touch it) and see the small red light that comes out of the cable where the laser is sending. Don't try to look into the cable, your eyes could get hurt.

With that you know the sending side and can test both fibers to the other building, repeating the test with the paper. If this is not ok you might need to clean the ends of the fiber cables or one fiber is damaged.
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carolinasgirl28Author Commented:
OK....so you were both right in the beginning.  I had the fiber company come back out and recheck the line.  The fiber was ok but the termination in the box was bad.  Redid it and once again was plug and play.  

Thank you for all the help!
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