LAN WAN Bandwidth etc

[avilt]

I have a query with the folliwng 2 scenarios.

1) Local LAN<----gbps ports----->ROUTER-------WAN link 10 mbps ----------->Remote LAN-gbps ports.

2) Local LAN<----gbps ports----->ROUTER-------WAN link 100 mbps --------->Remote LAN-gbps ports.

In either scenario, is there any possiblity of traffic burst at the router? Assuming that it's a high end router with gbps capability.

Let's say, 10 systems simultaneously sending files (FTP) to remote lan.

[Latchum Naidu]

Hi,

As per my knowledge there is no any burst at or done by Router.
There will be burst speed on the link which provided by your ISP provider.
Say for example you have 10 MB link and burst on that same link can be 12 or 14 MB, it depends on the provider give you.

Please rate the helpfull posts.
Regards,
Naidu.

[avilt]

Is there any possibility of receiving more than 100mbps traffic on the LAN interface of the router, if so what will happen as the WAN link is 1)10mbps 2)100mbps

[Latchum Naidu · Accepted solution]

Hi,

Yes, if you have a burst up to 110 MB on wan link (actual speed is 100 MB).
And of course it is completely depends on the interface type and speed, if it is FE interface with 100 MB speed and wan link speed is also 100 MB then no chance to go more than 100 MB.
If it is a gig interface with 1GB speed then Yes it can go morethan 100 MB.

Please rate the helpfull posts.
Regards,
Naidu.

[Joseph W. Doherty · Accepted solution]

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Posting

avilt wrote:
Is there any possibility of receiving more than 100mbps traffic on the LAN interface of the router, if so what will happen as the WAN link is 1)10mbps 2)100mbps

Yes, there is.

It would queue on the lower "speed" egress interface.  As queue fills, latency increases, if queue totally fills, packets are dropped.  (NB: depending on traffic type and host "stack" implementation, sender may slow transmission rate if drops and/or additional latency noticed.)

PS:

Some platforms, also often early drop options before egress queues totally fill.

[avilt]

Thank you for the precise explanation.

I have this scenarion with LAN = gbps, WAN = 100mbps. I cannot hard code the LAN speed to 100 mbps as I am using HWIC-1GE-SFP(GLC-T) for the LAN side. How can I prevent the packet drop scenario? I have to implement some sort of packet shaping on the LAN side. How do I define this?

[Joseph W. Doherty]

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.

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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

You would be unable to totally avoid packet drops if the ingress bandwidth can exceed egress bandwidth.

Depending on the nature of your traffic, not having any drops, even if possible, isn't always the best situation.

What you might try, assuming this is a software router with relatively recent IOS is something like.

policy-map CBWFQ

class class-default

fair-queue

interface fastethernet#

service policy CBWFQ output

[avilt]

It's a new 2901 ISR router. How can I make sure that the ingress traffic on LAN interface never exceeds more than 80 mbps?

[fasih2012]

You can use average shaping command under policy map.

Average shaping percent 80 ( on a 100 Mbps link)

Sent from Cisco Technical Support iPad App

[Kishore Chennupati]

fasih,

shaping can only be done outbound not inbound.

HTH

[Joseph W. Doherty]

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

You can not, unless you get regulate the other side's egress.

You can police the input so that no more than 80 Mbps will transit your router from the ingress interface, but the actual traffic hitting your interface could be much, much higher before it's dropped.  (e.g. ingress interface is gig.)  NB: policing can be very adverse to some traffic types.

What you can also do, if the LAN interface is a gig interface, run it at 100 Mbps.  Unfortunately, this may cause congestion on the other side of the LAN which often does not have QoS features as advanced as the ISR's.

[avilt]

I did not get any convincing answers. The whole problem is that I can not run the LAN interface which is HWIC-1GE-SFP(GLC-T) at 100mbps. It will run only in gbps mode.

In real life scenario's how is it controlled when your LAN  interface is gbps and wan is mbps?

[Kishore Chennupati]

Hi Avit,

The most widely accepted solution to your problem is to shape on the Egree( WAN interface). However, if you like to limit the ingress on LAN to 80Mbps then you can use policing on your LAN interface. However, policing has a downside that once traffic hits 80mbps per second it will kill the traffic anything beyond that and this will lead to excessive TCP re transmissions and latency etc. This is not good for critical applications like Citrix etc or VOIP. 

Remember, buffering is better than re - transmitting the whole packet. Hence, just shape on the egress.

Hope this helps,

Kishore

[Joseph W. Doherty · Accepted solution]

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

avilt wrote:
 I did not get any convincing answers. The whole problem is that I can not run the LAN interface which is HWIC-1GE-SFP(GLC-T) at 100mbps. It will run only in gbps mode.
In real life scenario's how is it controlled when your LAN  interface is gbps and wan is mbps?

Now it's gigE interface that can only run at gig - not a convincing question

Your router has more than one Ethernet port, doesn't it?  Can any of the others multi-speed?  If so, can you "juggle" which port is used for which connection?

In "real-life" you often have a large differences in LAN to WAN bandwidth.  For LAN to WAN, I've had gigE to T1s and 10 gig to gig, not unusual.

"Let's say, 10 systems simultaneously sending files (FTP) to remote lan."

Okay, let's say that. FTP runs on top of TCP which, by design, accommodates itself to available bandwidth.  Depending on which "flavor" of TCP is being used, a various number of packets might be dropped as TCP attempts to use all available bandwidth.  Dropped packets is something all flavors of TCP can use to slow their transmission rate.  On average, the 10 users would obtain about 1/10 the total bandwidth.  If 5 users stopped, the remaining 5 would ramp up and each get about 1/5 bandwidth.  If 10 more started transmitting FTP (in addition to the original 10), each would get about 1/20 the bandwidth.

Bandwidth differences aren't unique to just LAN to WAN.  Say you have a 48 FastE port switch.  What's you're uplink, another FastE?  Then you have 48:1 oversubscription.  Your uplink a gig?  Than you now only have about 5:1 oversubscription.

At this point, not really sure what will "convince" you, but WAN and LAN bandwidth differences are quite common in real world.  What specifically are you concerned about?

[avilt]

Thank you for the good explanation.