Hi,
I'm inquiring about the 4 10-Mbit/s ports on the uBR905 model, and if they support full duplex. Isn't that a function of the IOS, and not the hardware? Would there be a performance issue if half duplex was enabled?
thanks, Jeff snipped-for-privacy@gmail.com
No, no, no, and no. If you do force whatever is connected to the other side of that port to full duplex the performance is going to suck because it will be getting so many errors due to the mis-match. It is highly unlikely that your cable provider is given you enough bandwith to even max out a 10Mbit half duplex port anyway.
Since the UBR905 performs switching functions any, or all, of its LAN side ports can be full-duplex. As for the WAN side, the cable has a separate reverse channel and is naturally full duplex.
There can be LAN local traffic that could easily max out a 10/100/1000 full duplex port, regardless of the speed of the WAn side.
It's got a HUB built into it, not a switch and I think you will be hard pressed to find a 10Mbit hub with full duplex support. I have a UBR924 (same router basically) and not only did it not support full duplex there were times when excessive traffic caused the thing to get so many collisions it freaked out. Yes, you can exceed 10Mbit on your local network, but, it's highly unlikely that you will out the cable port so the smartest thing to do, if you insist on using this, is hang it off one port of a 10/100 switch (not just a hub) to isolate it. If you force the duplex of your network devices to full, you'll probably get about the performance of a 2400bps modem due to the CRC errors it causes.
If you don't believe me, have a look at the Cisco documentation (link below). Also, just for fun, I dusted off my router and booted it up and it clearly does not want to do full duplex (see below), a full duplex capable device negotiates to half when connected to it, and there are plenty of collisions when I generate traffic (which, will not happen on full duplex).
Router#sh version Cisco Internetwork Operating System Software IOS (tm) 920 Software (UBR920-K9O3V6Y5-M), Version 12.2(10d), RELEASE SOFTWARE (fc1) ...
Router#conf t Enter configuration commands, one per line. End with CNTL/Z. Router(config)#int eth0 Router(config-if)#duplex full This command is not supported for Ethernet0. ...
Router#sh int eth0 | inclu collisions Ethernet0 is up, line protocol is up 0 output errors, 8705 collisions, 2 interface resets 0 babbles, 0 late collision, 6555 deferred
My bad. I was mistaken about the switching capability.
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