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Community Member

Simple QoS for backup traffic only

Hello,

We have the follwing task:

Bunch of remote offices on Cisco routers 8XX/17XX running email, office applications etc. Speed to world is 1.5Mbps.

And here we have backup traffic which takes entire channel.

Task is to configure simple QoS which will match destination ip of backup server as lowest possible priority if channel is busy (say 10% of the link speed)

Thanks.

6 REPLIES
Super Bronze

Re: Simple QoS for backup traffic only

Not sure those routers support CBWFQ, but if they do, something like:

(NB: syntax might be incorrect)

class-map backuptraffic match-any

match (match an ACL that matches your backup traffic)

policy-map sample

class backuptraffic

bandwidth percent 1

class class-default

fair-queue

interface serial #

service-policy output sample

Backuptraffic class can still utilize 100% link bandwidth, but it will yield bandwidth to other traffic. Effectively, it will only obtain bandwidth otherwise being usused.

Community Member

Re: Simple QoS for backup traffic only

Thanks!

But I am in doubt about CBWFQ in this implementation as it will quarantee 1% of bandwidth for backup when I need to guarantee all other traffic rather then backup (last priority).

SO I add some shaping here. Please have a look if it is fine from your perspective

ip access-list extended MATCH_BACKUP

permit ip any host XXX

permit ip any host YYY

permit ip any host ZZZ

class-map backuptraffic match-any

match access-group MATCH_BACKUP

policy-map USAGE

class backuptraffic

bandwidth percent 1

shape average 100000

shape peak 1544000

class class-default

fair-queue

interface serial #

service-policy output USAGE

Any comments?

Super Bronze

Re: Simple QoS for backup traffic only

No, don't see the need for shaping. Shaping would preclude backup from using bandwidth that's otherwise not being used. If we only guarantee backup 1% it leaves all other traffic 99%. (Actually with FQ in class-default, it's more complex but doubt if we need to get into why.)

If you want, you could guarantee other traffic absolute priority over backup traffic but that's a good way to completely break backup flows if you totally starve them of bandwidth.

Community Member

Re: Simple QoS for backup traffic only

Shaping should limit backup traffic, isn't it?

I read here http://www.cisco.com/en/US/docs/ios/12_2/qos/configuration/guide/qcfcbshp.html#wpxref80464

So actually what I try to achieve is not to give priority to backup but rather find a simple way to limit it when other types of traffic are present.

I could think about setting priorities for all other traffic but... too different apps and different offices around.

So my question about initial config - if backup traffic will exceed 1% and wan link will be full say with Exchange - who will drop backup or how fighting for bandwidth will be looking like?

Super Bronze

Re: Simple QoS for backup traffic only

"Shaping should limit backup traffic, isn't it? "

Should it? No. Could it? Yes.

"So actually what I try to achieve is not to give priority to backup but rather find a simple way to limit it when other types of traffic are present."

Yes, correct. What I suggested deprioritzes backup traffic relative to other traffic.

"So my question about initial config - if backup traffic will exceed 1% and wan link will be full say with Exchange - who will drop backup or how fighting for bandwidth will be looking like?"

If backup exceeds 1% it's because the bandwidth wasn't otherwise being used. For example, Exchange could use 10% leaving backup 90% or Exchange could use 70% leaving backup 30%. If both backup wanted all 100% and Exchange wanted all 100%, backup would only get 1% and Exchange 99%.

Community Member

Re: Simple QoS for backup traffic only

Did you try such QoS implementation? It is interesting as I did tests and it is not working at all. Then I did some more research and found that QoS input should be applied to Eth interface using dscp.

So simple task requires so many time to spend doing reseach.

Cisco has documentation about CBWFQ, but it doesnt work in reality

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