2901 to ASA 5510 via leased line poor throughput

[kyle.heath]

I have two sites connected via 2901 routers to a head end with an ASA 5510, the WAN circuits are LES running at 100MB and at the head end we have a 100MB leased line.  All WAN circuits are provided wires onlyby another supplier.  I have setup the two 2901 routers with inside IP addresses on GE0/0 and a /30 subnet for the GE0/1 interfaces to the ASA over the LES circuit.

The LES circuits are set to 100MB but the problem I am having is that one of the 2901s will only negotiate at 10MBps Half Duplex with the ASA at 100MB Half Duplex, the other will negotiate at 100MBps Full Duplex at both ends.  My WAN provider tells me both LES circuits are the same so I cannot work out why one will negotiate at 100MB Full and the other at only 10Mb Half.

At the head end I have and ASA 5510 connected to the WAN providers 100MB circuit but testing from my end sites I can only get 6MB download and 0.5MB upload on an Internet Speedtest.

I used Wireshark when downloading from my end sites and I can see lots of TCP retries and duplicates so I think this is a duplexing issue, my question is, my WAN provider is stating the issue is nothing to do with them and it is my 2901 and ASA that is at fault, they state if they connect a laptop to the LES circuit and then their leased line they get 100MB up and down.

I am getting pressure from my client now that it is our fault.  Can anyone help guide me in the right direction?

Cheers

Kyle

[jyoung]

why don't you set the speed duplex manually?

Sent from Cisco Technical Support iPhone App

[kyle.heath]

If I set the duplex manually to full for example then the link protocol goes to down, the only option that will bring the link protocol up is for auto negotiation or I set 10MB half duplex on the 2901 and 100MB half duplex on the ASA.  I have had this on a LES circuit before between two 2950 switches and it was a duplexing issue that caused slow traffic until I changed the duplex settings but this time I cannot seem to work it out. 

[Mr_Helpful · Accepted solution]

If speed- and duplex-settings are auto/auto then this is what happens (at both sides) when the interface is connected:

1. First there is an auto-sensing for the speed. It doesn't matter if the other end of the link is set to auto, or if the speed is configured... this sensing will always be correct. So if your device ends up with 10Mbps, the other end will be set for 10Mbps. If the other end was set to auto (or fixed at 100Mbps), they would both have sensed they could do 100Mps.

2. After auto-sensing for speed is done, the auto-negotiating for duplex is initiated. If the other end is not configured for speed auto-negotiation, your end will not get a reply, and (as specified in RFC-somenumberhere) it will default to half-duplex. And it seems that is just what your end is doing.

3. If you want to do auto-sensing, auto-negotiation is mandatory. You can do auto-negotiation on an interface where the speed is fixed.

The conclusions I draw from your observations (combined with 'my' rules outlined above) :

1. The links where your device negotiates to 100/full, the provider-device is configured for auto/auto.

Because auto-negotiation has resulted in the non-defaut value 'full', and therefore auto-detection had to be enabled too.

2. The link that negotiated to 10/Half definitely has the provider-device configured for 10Mbps.

The speed is probably set for full-duplex at the provider-device, since half-duplex is not quite common to configure.

That would result in the duplex-negotiations to fail, and your end to default to half-duplex.

3. The link that negotiated to 100/Half has the provider-device configured for 100Mbps or auto for speed.

And again, the speed is probably set for full-duplex at the provider-device, since configuring half-duplex would be silly.

4. The fact your link goes down when you configure the speed/duplex manually on your end, is probably caused by the fact you are using [crossed/straight] cables where you should use [straight/cross] cables. That beautiful little feature auto-MDI/MDIX only works when the interface is not configured for fixed speed/duplex settings.

In all, your provider seems to have managed to supply you with three different interface-configurations on ther equipment.

[kyle.heath]

Thanks John, I was thinking it has to be the provider equipment that I do not control that is the issue.  I have straight through cables at present and that is due to previous configs in the uk on LES circuits, so I should have thought cross!  So my plan is visit site and change to cross cables and then find the right duplex on each device.  Let's say the wan provider is not helpful a d does not know the duplex for their equipment, they really don't, so this has made this job much more trying.  Thanks for a great explanation John