Cisco lab - fractional T1 interfaces
Hi all, I know this is not directly certification related but I have a burning question about hooking up Cisco fractional T1 interfaces back to back:
In my home BSCI lab, I'm trying to create an OSPF stub area by hooking up two Cisco 2611 routers both using fractional T1 CSU/DSU interfaces with a T1 x-over cable. All the configurations are correct on both sides (clocking, clock rate, DCE/DTE, b8zs, esf, frame-relay encapsulation, line build-out set to "none", etc, etc). Ok, no problem there.
I played around with this for a while trying to get the two interfaces to come up but still showed "down & down" status. I Googled for a while and found the solution: "use a longer T1 cross-over cable". This fixed the problem and two interfaces came right up. My question is: why would a 20ft T1 cross-over cable make any difference compared with the 2ft that I was using before??? Both are known good working cables. I don't get it, why would the longer cable make everything work. Do the interfaces sense if there's a slightly higher attenuation? Cisco layer1 voodoo?
Any explanations would be great.
thanks!
crtplague
In my home BSCI lab, I'm trying to create an OSPF stub area by hooking up two Cisco 2611 routers both using fractional T1 CSU/DSU interfaces with a T1 x-over cable. All the configurations are correct on both sides (clocking, clock rate, DCE/DTE, b8zs, esf, frame-relay encapsulation, line build-out set to "none", etc, etc). Ok, no problem there.
I played around with this for a while trying to get the two interfaces to come up but still showed "down & down" status. I Googled for a while and found the solution: "use a longer T1 cross-over cable". This fixed the problem and two interfaces came right up. My question is: why would a 20ft T1 cross-over cable make any difference compared with the 2ft that I was using before??? Both are known good working cables. I don't get it, why would the longer cable make everything work. Do the interfaces sense if there's a slightly higher attenuation? Cisco layer1 voodoo?
Any explanations would be great.
thanks!
crtplague
Comments
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dtlokee
Member Posts: 2,378 ■■■■□□□□□□
How do you know the original cable was good? I use 2-3 ft cables in my lab and don't have any issues. There is a setting to configure the cable length to short which may change things (lower output gain).The only easy day was yesterday! -
scheistermeister
Member Posts: 748 ■□□□□□□□□□
It works like a thermos... Magic!
Give a man fire and he'll be warm for a day. Set a man on fire and he'll be warm for the rest of his life. -
crtplague
Member Posts: 13 ■□□□□□□□□□
The original cable works fine when I use it between two T1 interfaces on a pair of old Netopia routers. Guess I'll trying playing around with the line build-out.
Thanks!