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New Member

Bandwidth slows through 2801 router

Hello all,

  Wanting to get some advice/help!  I have just received Time Warner Cable and get 16Mbps down from them directly through their modem (motorola DOCSIS 2.0 modem- SB5101) to my PC (using speedtest.net).  When I then connect TWC's modem through my 2801 router on fa0/0, the download rate I get is considerably slower (on the order of 3-4Mbps via same testing method).  What am I missing?

Here is how the passthrough interface is setup:

interface FastEthernet0/0

bandwidth receive inherit

ip address dhcp

ip nat outside

ip virtual-reassembly in

duplex auto

speed auto

I have attempted removing bandwidth command - nothing changed with it not there.  I have also hard coded the speed and duplex to 100/full to no avail....

Other possible relevant configs:

ip nat inside source list 1 interface FastEthernet0/0 overload

ip route 0.0.0.0 0.0.0.0 dhcp

access-list 1 permit 192.168.1.0 0.0.0.255

Basically this things is wide open... for testing but the download speed differential is perplexing to me.

Is it this?  Or some thing else?  Thanks in advance for your help!

tagman25

Everyone's tags (3)
1 ACCEPTED SOLUTION

Accepted Solutions

Bandwidth slows through 2801 router

Hi

virtual reasembly can be a problem for performance.

HTH Patrick

10 REPLIES
Super Bronze

Bandwidth slows through 2801 router

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

What's the router CPU usage look like during these speedtests?

New Member

Bandwidth slows through 2801 router

The cpu process does not go above 4% during the speed tests.  Confirmed that last night.  ANy other thoughts.  I cannot imagine that NAT would reduce the speed that much.  The reasoning behind that is because I just got rid of 5Mbps download speeds with another company, and the speedtests showed around the 3-4Mbps speed when I had that as well.

ANY other thoughts, advise, help would be appreciated.  Thank you.

Gold

Bandwidth slows through 2801 router

Here is a Cisco performance guide that covers the 2800 series

http://www.cisco.com/web/partners/downloads/765/tools/quickreference/routerperformance.pdf

As you can see, process switching is slow.

Super Bronze

Bandwidth slows through 2801 router

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

The only other thing that comes to mind, is speedtests often only run for a few seconds and the router's CPU might not accurately reflect the short term load.  However, assuming that's not the case, the only other thing that comes to mind, depending on the test, if the router is dropping any packets might degrade test performance.

I've never intentionally stressed tested a 2801 to its maximum but I have the next larger model in the series, the 2811.  On this model, I was able to push about 40 Mbps unidirectional UDP traffic.  If performance ratios are as I would expect, the 2801 should have enough performance to deal with 20 Mbps (aggregate up/down?) aggregate on your cable link.

New Member

Bandwidth slows through 2801 router

I will have a result on the cpu usage this evening, however if I remember correctly - it was never above 4%.  Confirmation coming this evening. 

Gold

Bandwidth slows through 2801 router

With NAT, you are process-switching the packets. Regardless of the router, thats the slowest method of all

here is a link to use for some tuning at the workstation:

http://cisconet.com/traffic-analysis/throughput/104-tcp-throughput-calculation-formula.html

Bandwidth slows through 2801 router

Hi

virtual reasembly can be a problem for performance.

HTH Patrick

New Member

Bandwidth slows through 2801 router

I took out the 'ip virtual reassembly in' in the interface and started receiving WAY faster download rates.  Thank you!

Super Bronze

Re: Bandwidth slows through 2801 router

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

The feature is documented as: (from http://www.cisco.com/en/US/docs/ios/12_3t/12_3t8/feature/guide/gt_vfrag.html)

Restrictions for Virtual Fragmentation Reassembly

Performance Impact

VFR will cause a performance impact on the basis of functions such as  packet copying, fragment validation, and fragment reorder. This  performance impact will vary depending on the number of concurrent IP  datagram that are being reassembled.

Automatically Enabling or Disabling VFR

VFR is designed to work with any feature that requires fragment  reassembly (such as Cisco IOS Firewall and NAT). Currently, NAT enables  and disables VFR internally; that is, when NAT is enabled on an  interface, VFR is automatically enabled on that interface.

However, surprised this doesn't show a difference for CPU usage, especially as it's noticeable impact to performance, as you've described.  Also surprising if you were NOT dealing with fragments, although the above does mention packet copying.  Glad Patrick noted this.

Re: Bandwidth slows through 2801 router

Thanks no Problem.

I noticed it some time ago on a 3640:-) router can do 80 - 100 Mbit routing over two FastEthers. With VirualReaembly it drops to 2 Mbit/s.

VPN encryption on them was also crappy..

Alway be carefull with Features.

2801 should do 40 Mbit/s plus. Bad Traffic Mix (64k Packts and Services drops performance)

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