Routing Question

Hi. I just wish to ask a question that may seem to be simple. If i have a router connected to a 100mb LAN link and a wan link with 1 mb bandwidth limit. If several workstations send out data through the Lan link to the router that reaches say 70 mb, will the router queue the 70 mb data until all has left the 1mb wan link? Or will it drop the packets? Is there a way to keep it from dropping the packets?

Thanks in advance.

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Comments

ColbyG

Look into QoS

kryolla

marcusaureliusbrutus wrote: »

Hi. I just wish to ask a question that may seem to be simple. If i have a router connected to a 100mb LAN link and a wan link with 1 mb bandwidth limit. If several workstations send out data through the Lan link to the router that reaches say 70 mb, will the router queue the 70 mb data until all has left the 1mb wan link? Or will it drop the packets? Is there a way to keep it from dropping the packets?

Thanks in advance.

Interface has buffers, once you exceed it it starts to tail drop all packets. So the question is how do I know when the interface buffers are full. This is not as simple as you think it is. A packet comes in and the router does a routing table look up and finds the outgoing interface. If the interface hardware que is full it puts it in software que. You can only have 1 software que outbound but there can be differenct types of que but only 1 can be applied. As Colby said it depends on your queuing method is how fast the software que fills but it also depends on the speed of the link called serialization delay and the speed of the router CPU called processing delay. So if money is no object you can just bump up the speed of the link and get a faster router. There is a lot of things you can do to solve that issue without buying new circuits or routers such as traffic shaping or re-mark lower priority traffic and drop it downstream when congestion occurs. There is also compression which eats up CPU. So as you can see QOS is a complicated technology thus you have ONT and QOS in CCIP.

networker050184

kryolla wrote: »

You can only have 1 software que outbound but there can be differenct types of que but only 1 can be applied.

This is not true. You can have multiple outbound software queues on an interface. You only have one hardware queue, which may have been what you were referring to.

kryolla

try applying MQC then CQ then PQ and see what happens. I wasnt talking about a queuing method and traffic shaping at the same time. So let me be more specific you can only have one queuing method on an interface i.e fifo, wfq, MQC, CQ, and PQ

Rack1R3#sh int s1/0
Queueing strategy: weighted fair
Rack1R3#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Rack1R3(config)#int s1/0
Rack1R3(config-if)#cu
Rack1R3(config-if)#custom-queue-list ?
<1-16> Custom queue list number

Rack1R3(config-if)#custom-queue-list 1
Rack1R3(config-if)#end

Rack1R3#sh int s1/0 | inc Queueing
Queueing strategy: custom-list 1
Rack1R3#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Rack1R3(config)#int s1/0
Rack1R3(config-if)#prio
Rack1R3(config-if)#priority-group 1
Must remove custom-queue configuration first.
Rack1R3(config-pmap-c)#int s1/0
Rack1R3(config-if)#service-policy output STUFF
Must remove custom-queue configuration first.
Rack1R3(config-if)#

as you can see only 1 type of queuing method can exist

mikearama

Not being a Windoze guy for years... I thought tcp windowing would allow the router to notify the clients that it has a small pipe (where have I heard that before!?!?!), so that outbound traffic limitations would be shared between the router and the PC's. No?

I prolly shoulda researched this (and by research, I mean Google) before posting... but I'm lazy today.

kryolla

mikearama wrote: »

Not being a Windoze guy for years... I thought tcp windowing would allow the router to notify the clients that it has a small pipe (where have I heard that before!?!?!), so that outbound traffic limitations would be shared between the router and the PC's. No?

I prolly shoulda researched this (and by research, I mean Google) before posting... but I'm lazy today.

it will drop the packets then the app will not get an ack back and it will reduce the window size and build it back up (tcp slow start) until it drops packets then it still start all over again. It will do this to all apps due to tail drop and is know as TCP synchronization because all apps will be in sync. It hasnt nothing to do with winblowz it is part of the tcp protocol

networker050184

You are correct that you can only use one queuing method, but a single method can form multiple software queues. If you could only have one software queue then what would the point be really?

Netwurk

The client, be it windows or linux or whatever, will hold onto the bulk of the data until the bandwidth it needs is available. Routers hold x amount of packets in their queue, not anything near the 70mb the original poster was theorizing about.

The most obvious example of QoS coming into play is with phones - which have to offload all their packets quickly (unlike PCs or servers, which can spend hours or even days uploading data if need be).

kryolla

networker050184 wrote: »

You are correct that you can only use one queuing method, but a single method can form multiple software queues. If you could only have one software queue then what would the point be really?

All a software que is needed is so the router can re-arrange the packets in a priority order before they get put on the tx ring so it doesnt matter if you have 1 que or multiple queues what matter is classification so the router can re-arrange them. If you want to be more specific there can only be 1 scheduler that picks between the different queus and puts it in a fifo order to tx ring. We all know the CQ has 16 queus on PQ has 4 and MQC can have multiples queues with each queu being FIFO except the class-default which can be WFQ. Oh wait CQ has 17 queues but 1 is for keepalives, routing protocols etc. My point is there is only 1 tx ring which is FIFO so it doesnt matter if there is 1 software que or multiple, anyways the OP isnt going to understand all this so I wanted to give him the gist of QOS with my original post but it looks like it didnt work ohh well

networker050184

kryolla wrote: »

All a software que is needed is so the router can re-arrange the packets in a priority order before they get put on the tx ring so it doesnt matter if you have 1 que or multiple queues what matter is classification so the router can re-arrange them.

Actually it does matter if you have more than one queue. If you only have one queue the packets can not be rearranged (see FIFO). Placing the packets in multiple queues then de-queuing from those queues and placing on the hardware queue is what rearranges the packets. So, like I said if you only have one software queue there really isn't much use except that it would give you a little more space for packets to be queued.