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New Member

ATM/IMA - PVC Bandwidth

I'm setting up a WAN w/ 7200's with 3 sites so for. I've set up the links w/ IPSec and I have tunnels between each site. Everything seems to work fine, except I notice that the bandwidth available between sites isn't symmetric - for example if I send data from my site in Virginia to my site in Alabama I can pass ~4Mb/s (PVC is rated at 3M), but if I run the same test sending data from Alabama to Virginia I only get 1Mb/s. Same is true for the other site. Before I call AT&T and complain, has anyone seen this before? I've tried to look for alternate routes but don't believe there are any (at least my links). TIA.


Re: ATM/IMA - PVC Bandwidth

Are all the circuits from the same provider? Are any of them old circuits (versus recently installed)?

Are the routers at both ends the same? Same version of IOS / RAM / firmware Revs, etc ?

Do either of the routers have more tasks (i.e., also does Internet, firewall, IDS ...)

What kind of data are you sending, and how are you sending it? Does any of the data cross VLANs / ELANs / subnets from source to destination.

Have you checked and cleaned the Fiber ends and panel ports? Are the jumper cables used commercially produced or hand-made?

Are there any errors reported on any of the interfaces?

Have you checked the traffic-shapeing / policing parameters on the routers and circuits?

Is the slow link always to router "A," or for any given pair (AB, AC, BC), there is always one that is slower?

If you are sending / receiving from computers, are the computers comparable (CPU, OS, NICs, driver versions, etc)?

Try sending to one site from the other two concurrently.

Sorry for all the questions, there could be quite a few things that can cause one-way performance problems, I'm just trying to cover the bases.

Assuming clean media and comparable equipment, I'd toss a nickle on the carrier's policing policies.



New Member

Re: ATM/IMA - PVC Bandwidth

This WAN was setup in the last month or so. It's possible that this condition was there from the beginning and I just never check the bidirectional thruput. All the PVCs were provisioned by AT&T, although the T1s to the local offices were done by the local provider (Verizon, AT&T & Quest). The T1's are all copper since the IMA interface has built-in CSU/DSUs. Also, the routers are all 7200VXRs running 12.2(15)T.

It's still hard for me to understand why the thruput isn't equal in/out. PCs on both end are comparible servers, but I guess that really shouldn't matter since they work find with data going in one direction.

Per your note, I did notice when I was testing last week that trying to simultaneously send and receive to one of the sites affects the sending rate. If I send traffic from my eastern US site to the Western site, the throuput is indpendent (that is I can run 6M to it regardless whether I'm receiving data from it or not - which is only 1M). However, when I try to run data to and from my southern site the outgoing bw drops to abt 1M so that both in & out are only 1M. Once I stop the data coming from the southern site my output rate from eastern to southern site jumps back to 4M.

I'm going to put the call in (toss the nickle!) to see what they say. And I'll let you know. Thanks for the the assist!

New Member

Re: ATM/IMA - PVC Bandwidth

The answer is...

There is a 'feature' in 12.2 - CSCdr12395

(we're running 12.2 (15)T) for the PA-8T1IMA adapter where the ima active-links-minimum setting sets the maximum number of links instead of the minimum. I intentionally set active-links to 1 so that my site stays up even if I loose 3 of the 4 T1s, but this bug changed that. One way to find this bug is to do a show atm pvc command, it shows the Peak Kbs setting which should be the total BW (rather than the active-links * 1500). To make matters worse, int interface setting for atm active-links doesn't show up in a show running!

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