AT&T OPT-E-MAN aka ASE aka EVC

Routing & Switching Quality of Service
1

I am working with an ATT link between two WAN sites.

Site 1 = JC, connected from 3750G-JC-CORE on interface GigabitEthernet1/0/3
Site 2 = CB, connected from 3750G-CB-CORE on interface GigabitEthernet1/0/28

Our switches are connected via fiber to a ATT’s Ciena hardware at both sites, 1Gb link speed.
However, we pay for a CIR of 100Mb. The rate limiting on my 3750Gs does not appear to be working correctly.

Symptom:
File transfer from a host at JC to a host at CB is very slow when the link speed is 1Gb end-to-end.
If I set the NIC on the host at CB to 100Mb, the file transfer is nearly 10 times faster.
I’m pretty sure I am doing something wrong with rate-limit / shaping / policing on our CPE interfaces that connect to the Ciena hardware.

Here is the relevant config on both interfaces:

S3750G-JC-CORE#sho run int g1/0/3
interface GigabitEthernet1/0/3
 description ATT OPT-E-MAN CKTID: XXXXXXXX
 no switchport
 ip address 10.254.20.1 255.255.255.248
 rate-limit input 100000000 18750000 37500000 conform-action transmit exceed-action drop
 rate-limit output 100000000 18750000 37500000 conform-action transmit exceed-action drop
 speed nonegotiate

S3750G-CB-CORE#sho run int g1/0/28
interface GigabitEthernet1/0/28
 description ATT OPT-E-MAN CKTID: XXXXXXX
 no switchport
 ip address 10.254.20.2 255.255.255.248
 rate-limit input 100000000 18750000 37500000 conform-action transmit exceed-action drop
 rate-limit output 100000000 18750000 37500000 conform-action transmit exceed-action drop
 speed nonegotiate

I am now going to read your lessons on shaping, policing, etc. - but I thought I would post this first.

Thank you!
Kris Jacobs, network admin @ Calhoun County, Michigan

2

I think I got it!

QoS on switches is indeed lots different than on routers - as you say in your lessons. =)

All I did was this on each of the two switches:

srr-queue bandwidth limit 10

I removed all of the rate-limit lines.

Transfers from JC to CB and back are much faster now.

What I believe was happening:

Our 3750Gs were trying to send data back and forth over the ATT cloud at line speed - 1Gbps.
Since we pay for a CIR of 100Mbps, ATT’s hardware was dropping our packets all over the place.
This accounts for a lot of mysterious reports from the users at CB - dropped packets because of incorrect QoS.

Thanks so much for this site - money well spent already. =)

-KJ

3

Hi Kris,

Good to hear you figured it out. Did you check if you saw any matches on your rate-limit commands? It’s an old command and I don’t think it even works on the 3750. Limiting traffic on the 3750 is best done with the srr-queue command like you did, a second option would be policing.

Depending on your traffic it’s likely that your provider dropped a lot of packets which resulted in poor performance.

Rene