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Wassim Aouadi
Enthusiast

Total Output Drops

Hi,

Please take a look at the topology. Interface g0/1 has increasing Total Output Drop counter. HQRouter's fa0/1 has no error counters.

We changed the cable between devices. We manually set the speed and duplex (100, full).

any idea?

HQRouter interface config:

interface FastEthernet0/1

description Connexion vers Switch Fibre TT

bandwidth 10000

ip address 192.168.230.46 255.255.255.252

load-interval 30

duplex full

speed 100

end

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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.

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Posting

"What do you think?"

What you describe is not surprising.  Raising the link bandwidth to gig often will reduce or eliminate drops seen at 100 Mbps.

If you review my 1st post, I explictly noted "Running at 100 Mbps . . ." and at that bandwidth, you might be helped by increasing the hold queue limit on the router's interface showing the drops.

If you review my 2nd post, I explicitly noted ". . . or more bandwidth from the same provider.", as another possible way to eliminate the drops.

If you run you PC at 100 Mbps, instead of gig, you'll likely see the drops reappear.  Conversely, if you use a router with gig capable interfaces, you might also not see any drops.  (NB: there's a difference between routers that have gig interfaces and those that can really sustain gig performance.  I.e. be careful selecting a router beyond that it offers gig interfaces.)

View solution in original post

10 REPLIES 10
Joseph W. Doherty
Hall of Fame Expert

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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.

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Posting

Might be perfectly normal; much depends offered traffic loads.

Running at 100 Mbps, if you also dealing with MAN/WAN latencies, you might want to increase the output queue size (it looks that you're currently running with the default of 40).  Too small a queue size, relative to the bandwidth delay product can cause premature drops.

The fact is that our router is not experiencing drops. It's the Provider switch - on the other end of the Ethernet cable- that's showing output drops.

Suppose I modify queue values on my router's interface. Would it impact the output drop count on the Provider switch?

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


Suppose I modify queue values on my router's interface. Would it impact the output drop count on the Provider switch?

No, it wouldn't.

The fact is that our router is not experiencing drops. It's the Provider switch - on the other end of the Ethernet cable- that's showing output drops.

Yes, that's the one in your  ISP side - Switch ME3400.jpg, correct?  That's what I was referencing about the queue size of 40 possibly being too small.

If your provider won't modify, not much you can do unless you get a different provider or more bandwidth from the same provider.

Yes you're right, that's the service provider switch.

I was able to get the configuration of SP switch interfaces. Please see enclosed file.

any idea?

Thanks

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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.

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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

Unfortunately, none beyond what I've already described in my two prior posts.

BTW, 1.25% drops is just a little high, but often isn't too adverse to traffic.  TCP traffic, especially older flavors, relies on drops while determining available bandwidth.  Cisco, I believe, recommends not being concerned about drops until they exceed 1%.

I see.

We focused our investigation on Total Output Drops and on the fact that, between router and switch, there's 100Mbps in full Duplex. So, instead of having HQRouter, I put a PC with a 100/1000Mbps NIC (Service Provider configured the same settings as with the HQRouter).

The result is surprising. Service Provider told me that there was no Total Output Drops (please see screen capture). And my download speed improved.

Thus, we agreed that our next test will be with another router instead of the 2801, with an interface that supports 1000Mbps.

I'm not convinced, but testing result says so :/

What do you think?

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 do you think?"

What you describe is not surprising.  Raising the link bandwidth to gig often will reduce or eliminate drops seen at 100 Mbps.

If you review my 1st post, I explictly noted "Running at 100 Mbps . . ." and at that bandwidth, you might be helped by increasing the hold queue limit on the router's interface showing the drops.

If you review my 2nd post, I explicitly noted ". . . or more bandwidth from the same provider.", as another possible way to eliminate the drops.

If you run you PC at 100 Mbps, instead of gig, you'll likely see the drops reappear.  Conversely, if you use a router with gig capable interfaces, you might also not see any drops.  (NB: there's a difference between routers that have gig interfaces and those that can really sustain gig performance.  I.e. be careful selecting a router beyond that it offers gig interfaces.)

View solution in original post

Thanks Joseph for your time

For the continuity of the discussion, I replaced the 2800 router with a 2900 router. No more drops, and download speed has increased.

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

Using a gig interface at gig speed?