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Possible port speed/duplex issue??

Tue Nov 27, 2012 6:25 pm

Hello All,

I have a number of RB-750G's deployed on a routed network with good success. I have run into one problem that eludes me....

I have a DLS Internet connection that uses a NetGear DSL modem. I have some traffic routed to that connection via an RB-750 that is simply NATing to one of my static IP's on the DSL circuit. This connection fails to pass traffic for periods of 2-45 minutes at random times. I have other devices connected to the DSL modem with no issue. One of them is a Cisco ASA that also NATs the devices behind it to a single public IP.

I have disconnected the RB-750 from the DSL modem and connected a laptop with the same IP etc as the RB-750 and it works fine.

I replaced the RB-750 with a new one and reconfigured from scratch. No change in symptoms.

I tried replacing the DSL modem (with a Motorola) and found that the RB-750 would not pass any traffic. I changed the Ethernet Port settings from auto to 10mbps full duplex and then I could pass traffic but not at all reliably.

I returned to the original hardware/config and things returned to the original behavior. I then changed the WAN IP to a static IP on the network behind my Cisco ASA and moved the WAN connection to the ASA.
It works perfectly...

In short: Placing the ASA between the DSL modem and the RB-750 resolved the dropped traffic issue.

Any thoughts on this? Changing the speed/duplex settings is the only thing that appears to have affected the issue. I was only able to change the settings on the RB-750 as niether of the DSL modems had this option. Could it be that the RB-750 and the DSL modems could not negotiate connection properly where the RB750-ASA-DSL combination can?????

What do you all think?

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Re: Possible port speed/duplex issue??

Wed Nov 28, 2012 12:55 am


yes it is coming from speed and duplex with the dsl modem
we experienced exactly same problem with RAD DSL modem
we had to enforce speed and duplex on the DSL modem and the RB

from our experience same problems exists with different cisco switchs like
C3550 - C2960 - C2970 - 48 ports linecards for C6500


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