3COM 5500 Switches, VLANs, QOS

Posted on 2010-11-29
Last Modified: 2012-05-24

We are moving our network from point to point to metro ethernet (MVLS).  My Internet provider allows for two vlans:  priority/real-time traffic, and all other traffic.  The real-time traffic would be items like ICA, DNS, LDAP, DS, and so on.  

Creating vlans is not a problem.  My issue is how to assign certain traffic (tcp ports) to particular vlans?  From what my ISP tells me, the ISP's systems read my vlans and will prioritize the vlans I tell them are real-time.  So do I use QOS to create traffic profiles for vlans?  Not having done this, I'd appreciate some guidance and recommendations.

All of my sites and HQ have 3com 5500 series switches.  

Question by:hnncsb
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LVL 29

Expert Comment

ID: 34249804
VLANs are just "networks",...that is all they are,...they make one physical cable act like two or more cables.  When you apply the TCP/IP config to them then they become two different subnets with two router IP#s (one for each virtual wire (aka VLAN)),....which become two alternate paths to a location.   The path taken is determined by the IP# used as the Gateway which will be the router virtual interface IP# of one of those two virtual cables (aka VLANs).

If it were me I would not even waste my time on it. All you are doing is creating all kinds of Protocol Overhead that in the end is going to slow it all down and make it excessively complicated to deal with. Use one IP segment (no VLANs) and run QoS to priortize the traffic.

All QoS does is prioritize, does not change bandwidth, does not give you more bandwidth,...all it does is give more preference to one type of traffic -vs- another type of traffic so that if two different types of traffic try to go at the same time it lets the one with the highest priority go first and makes the other wait.   If you have enough bandwidth in the first place to handle all the traffic then you don't need Qos in the first place, use QoS when the sufficiency of the bandwidth is in question.

The QoS would be performed by the ISP's routiung equipment were it enters and exists the MVLS.

LVL 29

Expert Comment

ID: 34250160
Here's a diagram of what I am talking about:

 MVLS with QoS

Author Comment

ID: 34250231
That makes sense.  You advise I tell my ISP what should be prioritized in a single vlan and let them do the QoS?  I guess doing QoS on my side wouldn't help since it may be ignored by my ISPs equipment?

I thought I can create vlans for traffic only, not creating a new subnet, but maybe I'm all wet.  Routing/switching is not my speciality.
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LVL 29

Expert Comment

ID: 34250458
There would not be any VLAN.  Yes, the ISP would configure the QoS on their environment.

Your QoS on your LAN would be completely separate.  The QoS on your Lan would "get it to the IPS's Router",...then the ISP's setup takes over from there and your system has "washed its hands of it"  at that point.

Your LAN is a highspeed, high bandwidth environment,...I personally would doubt you even need an QoS on the LAN.
LVL 29

Accepted Solution

pwindell earned 500 total points
ID: 34251192
I thought I can create vlans for traffic only, not creating a new subnet,

In my mind,  But hardware vendors may come up with creating ways to employ VLANing that I am unaware of,...I can't account for all of them  :-)

Author Closing Comment

ID: 34251374
Very detailed, very helpful.

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