Overrun errors?

Answered Question
Apr 14th, 2009

How can I fix overrun errors on an interface? I have 6 serial interfaces and all of them have CRC errors, frame errors, and overruns.

Overruns are:

Number of times the serial receiver hardware was unable to hand received data to a hardware buffer because the input rate exceeded the receiver's ability to handle the data.

It sounds like queueing could help, but I can't put fair-queue on these interfaces. I could rate limit, but I'm not sure that would help. Should I shape all of my traffic out to my link speed, and am I even on the right track???

Thanks,

John

I have this problem too.
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Correct Answer by Edison Ortiz about 7 years 7 months ago

Ok, Google came to the rescue:

http://www.cisco.com/en/US/prod/collateral/routers/ps5854/prod_qas0900aecd8033e8f9.html

Q. How do you position the Cisco 2800 and 3800 integrated services router WAN optimization bundles in the branch office?

A. The Cisco 2800 integrated services router WAN optimization bundles should be positioned at medium-sized and larger branch offices of 20 to 50 end users with bandwidth requirements up to 4 Mbps (2 T1/E1). The Cisco 3800 integrated services router WAN optimization bundles should be positioned at large branch offices and small regional aggregation sites with 50 to 150 end users and bandwidth requirements up to 16 Mbps (8 T1/E1).

This article is also useful:

http://www.cisco.com/en/US/prod/collateral/routers/ps5854/ps5880/prod_brochure0900aecd80425258.pdf

HTH,

__

Edison.

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Edison Ortiz Tue, 04/14/2009 - 09:54

What type of router and WAN circuit?

Can you post the show interface output?

You are hitting a physical limitation on the amount of traffic the router is able to handle.

Either control the amount of traffic coming into the box before it gets there or upgrade to a more powerful router.

__

Edison.

John Blakley Tue, 04/14/2009 - 09:58

Edison,

It's an IPFR circuit. I've posted all of my configs in another post:

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=WAN%2C%20Routing%20and%20Switching&topicID=.ee71a06&fromOutline=&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.2cd2a2fa

It's a 2821 on a 9mb link (6 T1s). Is the 2821 really not able to handle the speed??

Thanks,

John

Edison Ortiz Tue, 04/14/2009 - 10:03

John,

2821 is positioned for 4 T1s

2851 is positioned for 6 T1s

3825 is positioned for half T3

3845 is positioned for full T3

While the 2821 can support 6 T1s, you are pushing over its limits.

___

Edison.

John Blakley Tue, 04/14/2009 - 10:06

We're switching to a DS3 on this router, will it be able to handle it without the T1s?

John Blakley Tue, 04/14/2009 - 10:20

Edison,

We're going to have a fractional (20mb). Is this Cisco's official stance on this? I was able to insert the card, and the card was seen in the unit with no problems. In fact, it shows in Cisco's documentation that it will support it. (I'm not challenging you, I just need to see if we need to upgrade our router.)

Cisco 2821 (revision 53.51) with 251904K/10240K bytes of memory.

Processor board ID FTX0951A0T0

2 Gigabit Ethernet interfaces

7 Serial interfaces

6 Channelized T1/PRI ports

1 Subrate T3/E3 port

DRAM configuration is 64 bits wide with parity enabled.

239K bytes of non-volatile configuration memory.

62720K bytes of ATA CompactFlash (Read/Write)

Thanks,

John

Edison Ortiz Tue, 04/14/2009 - 10:30

Is this Cisco's official stance on this?

Yes. I can't find public documents at the moment for you to read.

While the module is supported on the router, as you noticed in bold, it provides subrate services. In other words, you can have the ISP provide for a DS3 handoff but the router can only accept and process X amount of data.

Anything over 6Mbps serialized on a 2821, can be pushing its limits - as it is positioned as a 4 T1 router.

For 20Mbps, I wouldn't go lower than a 3825 - if you don't trust me - call your Cisco account team :)

__

Edison.

Giuseppe Larosa Tue, 04/14/2009 - 10:34

Hello John,

overruns are a sign of performance problem.

I think Edison's note is about full rate support with QoS or other features applied not that the module shouldn't be recognized at all by your router.

For example C7200 have a check that says if you are running an oversuscribed chassis (the bandwidth points) that would be useful also on other platforms I think.

Edit:

about the serial T1: are you using them as stand-alone links or are they bundled ?

the limits are usually provided for the bundled configuration.

Hope to help

Giuseppe

Correct Answer
Edison Ortiz Tue, 04/14/2009 - 10:37

Ok, Google came to the rescue:

http://www.cisco.com/en/US/prod/collateral/routers/ps5854/prod_qas0900aecd8033e8f9.html

Q. How do you position the Cisco 2800 and 3800 integrated services router WAN optimization bundles in the branch office?

A. The Cisco 2800 integrated services router WAN optimization bundles should be positioned at medium-sized and larger branch offices of 20 to 50 end users with bandwidth requirements up to 4 Mbps (2 T1/E1). The Cisco 3800 integrated services router WAN optimization bundles should be positioned at large branch offices and small regional aggregation sites with 50 to 150 end users and bandwidth requirements up to 16 Mbps (8 T1/E1).

This article is also useful:

http://www.cisco.com/en/US/prod/collateral/routers/ps5854/ps5880/prod_brochure0900aecd80425258.pdf

HTH,

__

Edison.

John Blakley Tue, 04/14/2009 - 10:43

Edison,

This document concerns me because it only shows up to 16mb. We also have about 300 users that come through this edge router for internet access. Is there another series that I should be looking at?

John

Edison Ortiz Tue, 04/14/2009 - 10:52

John,

The document's statistics are really in the safe side and it does not categorize the 2800s as 2811, 2821, 2851 - same as 3800s.

I have the internal document with its positioning and for 20Mbps DS3 handoff, you will be fine with a 3825. If you are planning to go with full DS3 in the future, then I recommend getting the 3845 now.

300 users or 100 users, it really does not matter much. You need to concentrate on how much bandwidth the router can transmit on the WAN side w/o hitting a hardware limitation.

If you have 300 users and they are consuming more than 20Mbps, then the fault does not lie on the router, it lies on the WAN pipe. As long as the router is able to support 20Mbps, then you should be fine.

__

Edison.

John Blakley Tue, 04/14/2009 - 10:56

Thanks Edison. What kind of QoS can I do now that would help with the overruns, if anything?

Edison Ortiz Tue, 04/14/2009 - 11:02

The QoS can't be done on this router as you need to prevent the traffic hitting the hardware limitation.

Hardware limitation takes precedence over software queueing on incoming traffic.

You need to QoS on the sending devices, not sure if it's doable for you.

Joseph W. Doherty Tue, 04/14/2009 - 15:44

Would this also be the same 6 interfaces you mentioned in an earlier post running MLPPP? If so, MLPPP will add some load to the box and might be a factor in the 2821 not keeping up with the offered interface load.

A 2821 is rated at 170 Kpps (about 87 Mbps @ 64 byte packets). This might just barely handle your 20 Mbps subrate T3. (I've seen a 2811 on a full T3 - which tends to top out at about 15 Mbps, actual traffic, duplex.)

PS:

I've found there seems to be more capacity within the 2800/3800 series than Cisco's recommendations, but by going by their recommendations, you're unlikely to run into performance related issues.

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