Performance problem with Multilink PPP on 7206VXR w/PA-MC-8T1

[oatinetworksupport]

I have a 7206VXR/NPE400 with a PA-MC-8T1 installed. I also have a T3 card in it for other connectivity.

I have 4 of the T1 ports used. 2 of those are in a Multilink PPP configuration to form one 3Mbps connection.

On the other side of the connection, I have a 2801 with 2 WIC-1DSU-T1-V2 modules in it.

The customer is complaining of slowness, and the bandwidth graphs from my NMS show that the Multilink interface isn't hitting 100% at any time.

So, I'm doing some bandwidth testing with an FTP site. I've move all other traffic off of the Multilink connection and I'm downloading/uploading a large file from an FTP site to one client plugged directly into the router.

The results are interesting. Traffic from the 2801 side, destined for the FTP server behind the 7206, reaches the full 3Mbps just fine. However, traffic in the other direction, from the FTP server behind the 7206 destined to the FTP client behind the 2801, only reaches about 1.8Mbps total.

I've taken each T1 down and run the test on either of them alone, and they both perform at full 1.5Mbps on their own. I've also torn down the Multilink PPP configuration and had then be simply HDLC with IP addresses, and they do 1.5Mbps on their own as well. I've also tried using 'ip load-sharing per-packet' instead of MLPPP, and that configuration only gets me to 1.6Mbps.

There are no errors on the T1s or any of the Ethernet ports along the way. I do FTP through this router's T3 interface to the same FTP site and it reaches 45Mbps just fine, so the FTP site/server isn't the issue.

CPU doesn't seem to be high (5-6%), and the memory on the router seems fine.

Any ideas from anybody? Has anyone actually used a PA-MC-8T1 to do Multilink PPP?

[Darren Ramsey]

Have 2 7206-G2 running 12.4(15)T1 connecting 6Mbps 4xT1 between them, and able to push nearly 6M. Also have a 2811 12.4(17) connected to the 7206 running 3Mbps 2xT1, and I see it peak at nearly 3Mbps. Have measured the throughput with Ixia Chariot and see similar results.

My cards are PA-MCX-4TE1, and not the 8 port version you are using. The MLPPP interface configuration is generic.

Hope that helps.

[oatinetworksupport]

So, since the last posting on this issue, I've test a bunch of stuff. I've replaced the 7206VXR with a 2621 with two WICs...and we get the same performance.

The strange thing is, we test speed with a single FTP download session. The download from the 7206 to the 2801 only hits 1.8Mbps, but the upload back hits 3Mbps no problem.

I've also put a PC into the same VLAN on the same switch that the 7206 router is on, and using the same FTP test, I get 50Mbps, which is fast enough to fill 2 T1s I would hope.

So, I'm pretty sure that the problem is not the 7206. I'm running 12.4(15)T1 on both devices, and that seems to have a lot of bugs. I'm going to attempt a software upgrade to T4 and see if it's causing the issues...

[Darren Ramsey]

Download Qcheck and test the throughput, a better tool than FTP.

http://www.ixiacom.com/solutions/display?skey=qcheck

Is there a differential delay between your two T1s? If one T1 has a 3ms delay and the other has a 25ms delay, then the packets fragmented on the 3ms T1 will have to wait for the 25ms T1 packets to arrive for the reassembly.

[oatinetworksupport]

The delay on the T1s is almost exactly the same, around 56ms.

[oatinetworksupport]

OK, I used a 'WAN KILLER' application from Solarwinds to generate 3Mbps of UDP discard packets, and the T1s do go to 3Mbps in both directions. However, the FTP still only does 1.8Mbps in one directiona nd 3Mbps in the other. A PC plugged into the switch on the 7206 side doing the same FTP interaction gets between 25Mbps and 50Mbps. Why won't the routers go to 3Mbps on a TCP FTP session?