[PLUG] Network boot link died...

Mike Connors mconnors1 at gmail.com
Wed Mar 10 10:37:24 UTC 2010


Michael Robinson wrote:
> If I understand the spec correctly for 100BaseTX, I should be fine.
> The 90' cable is labeled as outdoor Cat 5e, though I wonder how 
> long is this cable going to last?
>   
100 Meters [300 ft] unshielded twisted-pair cable is the "standard" for 
*all* "baseband" runs.  YMMV slightly depending on on cable choice [5, 
5e, 6].
> I don't know what CX is and I'm not running a gigabit link, so the run
> doesn't have to work at those speeds anyways.
>   
CX = coaxial cable [cable tv]
> Interestingly, turning off duplex and dropping the link speed to 10 mbps
> stabilizes the link.  I noticed that duplex was set to full on the link
> and that the link was unstable with that setting.
>   
f 10 Mbps half-dup works, but you can't get a stable connection that 
supports auto-negotiation to a higher speed and full-dup then there are 
2 things to look at.

1. The cable run.

2. The NICs

You can check for problems at both of these points by looking at 
ethernet error stats w. ethtool

ethtool -S eth0
NIC statistics:
     rx_errors: 0             
     tx_errors: 0             
     tx_dropped: 0            
     collisions: 0            
     rx_length_errors: 0      
     rx_over_errors: 0        
     rx_crc_errors: 0         
     rx_frame_errors: 0       
     rx_missed_errors: 0      
     tx_aborted_errors: 0     
     tx_carrier_errors: 0     
     tx_fifo_errors: 0        
     tx_heartbeat_errors: 0   
     tx_window_errors: 0      
     tx_abort_late_coll: 0    
     tx_deferred_ok: 0
     tx_single_coll_ok: 0
     tx_multi_coll_ok: 0
     tx_timeout_count: 0
     tx_restart_queue: 0
     rx_long_length_errors: 0
     rx_short_length_errors: 0
     rx_align_errors: 0
     tx_tcp_seg_good: 0
     tx_tcp_seg_failed: 0
     rx_csum_offload_errors: 0
     alloc_rx_buff_failed: 0
     rx_dma_failed: 0
     tx_dma_failed: 0

You should be able to just ifdown then ifup the interface to clear the 
counters and then watch the counters while both NICs are set to 
auto-negotiation.

*The problem w. auto-neg is that not all vendors implement the standard 
correctly, so many times an Intel card and D-link card may not play well 
together.

If you see a lot of collisions that could mean you have a bad NIC that's 
jabbering away and causing the other NIC t back-off and retransmit.

If you see carrier errors that would be more indicative of a problem w. 
the cable. I don't know if this is a home-made or store bought cable. 
But the other thing you could try if you have the tools and skills and 
cut the ends of and re-crimp new connectors on them. *Especially if you 
see the protective sheath is not inside the connector, which means the 
hair-width copper wires can be easily bent and/or broken.










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