Can I use 2 Gigabit Switches in "Series" - AVS Forum
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post #1 of 15 Old 08-19-2009, 06:48 AM - Thread Starter
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Would I lose anything in performance if I used one gigabit switch in one room to feed another gigabit switch remotely located? Without going into wiring details, locations of equipment, etc., I am thinking about using this configuration to feed two NMT's from a remotely located gigabit switch connected via cat5e to another gigabit switch which has a WHS and computer connected. I have a finshed home, so I don't want to pull any more cat5e cables. I have looked into converting telephone wiring to Ethernet, but I don't have any spares.
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post #2 of 15 Old 08-19-2009, 07:28 AM
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Quote:
Originally Posted by cappy1 View Post

Would I lose anything in performance if I used one gigabit switch in one room to feed another gigabit switch remotely located? Without going into wiring details, locations of equipment, etc., I am thinking about using this configuration to feed two NMT's from a remotely located gigabit switch connected via cat5e to another gigabit switch which has a WHS and computer connected. I have a finshed home, so I don't want to pull any more cat5e cables. I have looked into converting telephone wiring to Ethernet, but I don't have any spares.

You should be fine doing that.
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post #3 of 15 Old 08-19-2009, 07:43 AM
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Agreed. That's done all of the time.

CIAO!

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post #4 of 15 Old 08-19-2009, 08:12 AM - Thread Starter
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Thanks for the help...I'm off to Best Buy!
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post #5 of 15 Old 08-19-2009, 12:18 PM
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Without being too technical, in large networks, you use 1 switch that has each of the ports feeding another switch.
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post #6 of 15 Old 08-21-2009, 05:32 AM
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The variables are if the two devices communicating over the single GigE link between switches are sending traffic which maxes the GigE link AND there is other traffic not a part of this communication being carried between switches. This is why older 100 Mbit switches have GigE uplinks. The GigE uplinks provide more bandwidth/throughput to accommodate aggregate inter-switch traffic. With current GigE switches, you don't see many of them with faster uplink ports. The next step would be 10 Gbit which is costly and not many people have the physical wiring infrastructure to support 10 Gbit comms.

The other alternatives to help in preventing uplink bottlenecks are to use Etherchannels or QoS (quality of service.) Both of these features are strictly in the domain of managed switches. Etherchannel is a setup where you group physical connections into one virtual link. The maximum number of links which can be grouped into a single Etherchannel is 8 from the switches I've worked with. The switches at both ends of an Etherchannel must support this. QoS looks to enforce frame forwarding policies where particular traffic is singled out to be treated a special way. You can set up QoS to ensure traffic between the NMTs to always have the best bandwidth and priority.

In larger network setups, you see hub and spoke type topologies. Basically, the setup is broken down into core, distribution, and then access layer switches. Depending on the performance/redundancy requirements, you'll see combinations of etherchannels and faster port protocols...currently at 40 Gbps over data center ethernet.
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post #7 of 15 Old 09-14-2009, 08:52 PM
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i have a situation where i need to add a switch in another location. if one has a 4 port gigabit router, can i plug 1 24 port switch into port 1 on the router and then another 16 port switch into port 2 of the router? will this be a bottleneck in any way as described above?

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post #8 of 15 Old 09-14-2009, 08:58 PM
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WonHung, your responses remind one time (true story) someone asked an ex-Army Cook, "say, that's a great meal, can I have the recipe?" And the ex-Army Cook went on to list: 50 pound of flour, 5 dozens eggs...

Solution: FREE. Explanation: I will have to charge$ you.

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post #9 of 15 Old 09-14-2009, 09:21 PM
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Quote:
Originally Posted by Anthony A. View Post

i have a situation where i need to add a switch in another location. if one has a 4 port gigabit router, can i plug 1 24 port switch into port 1 on the router and then another 16 port switch into port 2 of the router? will this be a bottleneck in any way as described above?

Yes, technically it will be the bottleneck, but depending on the uplink speed of your 'remote' switches and the devices attached to it, you may never even notice...

But it will most certainly work. What devices are you attaching to these switches? If they're mainly accessing the Internet (assumed to be attached at the unlink of your 4-port Gb router), you'll be limited by the bandwidth of your Internet connection, which is most likely well below the 100Mb (likely) uplink of your 'remote' switches. Meaning that even if a PC connected to the remote switch had a 1Gb connection to the router, it wouldn't go any faster.

There are more scenarios, but that's probably the short answer...

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post #10 of 15 Old 09-14-2009, 10:09 PM
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thanks for the response. to be more specific, i have about 20 drops of cat6 that will be used solely for accessing the internet. these will go into the 24 port switch which, through some reasearch, looking into the netgear managed switches with jumbo packets, etc. (ie. GSM7224). the other 4 ports on the switch will be used for home automation panel and touchscreen panels throughout the house for music control. this is all located in the electrical room. i then have a media closet which houses all my audio components for whole-home control and home theater. since it is in another room (and i don't want to run 8 cat6 cables to the electrical room), i was hoping i could get away with a 8 or 16 port managed switch, again with jumbo packets, etc. in the media closet will be whole-house music controller, htpc's, network media streamers with HD/bluray content streaming to different tv's in the house. i am concerned that the HD stuff will stutter with this setup.

so im really wondering what i can do to get away with using 2 switches as outlined above. perhaps getting better switches? where will the bottle neck be.... at the 24 port switch or the 8 port in the media closet.... or will all ports be bogged down?

thanks for the help.

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post #11 of 15 Old 09-14-2009, 10:44 PM
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Quote:
Originally Posted by MrBobb View Post

WonHung, your responses remind one time (true story) someone asked an ex-Army Cook, "say, that's a great meal, can I have the recipe?" And the ex-Army Cook went on to list: 50 pound of flour, 5 dozens eggs...



Anyways....I recommend a Cisco Catalyst 6504 because a 6506 or 6509 would be a bit overkill.... j/k.
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post #12 of 15 Old 09-14-2009, 11:20 PM
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Quote:
Originally Posted by Anthony A. View Post

thanks for the response. to be more specific, i have about 20 drops of cat6 that will be used solely for accessing the internet. these will go into the 24 port switch which, through some reasearch, looking into the netgear managed switches with jumbo packets, etc. (ie. GSM7224). the other 4 ports on the switch will be used for home automation panel and touchscreen panels throughout the house for music control. this is all located in the electrical room. i then have a media closet which houses all my audio components for whole-home control and home theater. since it is in another room (and i don't want to run 8 cat6 cables to the electrical room), i was hoping i could get away with a 8 or 16 port managed switch, again with jumbo packets, etc. in the media closet will be whole-house music controller, htpc's, network media streamers with HD/bluray content streaming to different tv's in the house. i am concerned that the HD stuff will stutter with this setup.

so im really wondering what i can do to get away with using 2 switches as outlined above. perhaps getting better switches? where will the bottle neck be.... at the 24 port switch or the 8 port in the media closet.... or will all ports be bogged down?

thanks for the help.

So here's the problem with going with jumbo frames. Every device connected into a jumbo frame infrastructure has to support jumbo frames. If one device does not support jumbo frames, this device will not be able to talk over the network. So what can you do in a mixed mode environment? You can isolate components which can support jumbo frames by creating a specific VLAN for them. Other devices which don't support jumbo frames can then be put on a separate VLAN. Now the problem comes where you need the devices in the jumbo frame VLAN to talk to the devices in the non-jumbo frame VLAN. In this case, you'll need a router. Layer 3 switches can bridge this deficiency as they support routing. Otherwise, you'll have to add a separate router which will then route traffic between the VLANs. You will also have to run two different subnets to get routing to work. One subnet per VLAN. The assumption with doing VLAN segregation is if the managed switch in question supports isolation of jumbo frame enabled ports via VLANs. The last gotcha is with performance. When you have traffic crossing through areas of the network where there is a difference in MTU sizes, the device which has to either assemble frames or fragment them takes a performance hit. How huge depends on the amount of traffic we are talking about. In this case, the device would either be your switch (if you decide to go with a layer 3 switch which the GSM7224 is not) or the router you add to route traffic between the two VLANs.

As you can see, the use of jumbo frames is not trivial. It requires proper planning and many times just isn't worth the headache.

An alternative which you've alluded to is to run multiple uplink connections between switches. Since you are planning on using managed switches at both ends, you should have no problems getting this to work. You don't need to run 8 links. You can run 2, 3, or 4 links. It's really up to you. I personally haven't gone past 2 links between switches in my home environment. Once you have the physical drops pulled, you need to configure both switches to utilize the links as one virtual uplink. Doing this is called link aggregation. You will some times run into manufacturers who call this trunking. I prefer not to call it trunking as trunking in the Cisco world is used to describe a link which carries more than one VLAN traffic through it. Link aggregation supports up to 8 physical uplinks grouped into one virtual link. The IEEE standard for this is 802.3ad. At the basic level, a standard 802.3ad aggregated link operates in a static mode. The logic in choosing which link a frame is pushed down is very basic and takes on a round robin type behavior. The protocol enhancement to this is LACP (link aggregation control protocol.) LACP allows switches to pass loading information between each other to better determine which physical link in the link aggregation group to use. Cisco has their own proprietary protocol which they are phasing out called PAgP.

Notice I've been careful about not stating a link aggregated group operates at the sum of all the links participating in the aggregation. What this means is if I use 8 GigE links, the link aggregation does not operate at 8 Gig. All traffic going through a link aggregation is still limited to 1 Gig. But because there are multiple pipes, the chances of multiple sessions saturating a single GigE link is decreased. There are other reasons why link aggregation is used such as link redundancy. I have done tests where I've pulled links out of a aggregation group without dropping a single frame...same applies when I re-establish the link.

The above is probably more than you or anyone would care to know. But since we are discussing more advanced layer 2 switching, I felt it appropriate to talk about this to ensure that people understand there are some complexities and concepts that need to be understood.

So how does this fit in with your scenario? You have to determine how much traffic you think will traverse between switches. As I've said in other posts, it is always best to keep high bandwidth heavy traffic generating devices on the same physical switch. Having these type of devices on the same physical switches allows maximum performance as the communication never leaves the switch but stays within the backplane which always has a at a minimum the performance/throughput of all the physical puts added together. Many times the backplane will have more by a certain margin. Solid, well performing networks are always designed properly before any hardware gets thrown into the mix.

PS....Mr. Bobb is going to love this post......
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post #13 of 15 Old 09-15-2009, 08:05 AM
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Quote:
Originally Posted by Anthony A. View Post

thanks for the response. to be more specific, i have about 20 drops of cat6 that will be used solely for accessing the internet. these will go into the 24 port switch which, through some reasearch, looking into the netgear managed switches with jumbo packets, etc. (ie. GSM7224). the other 4 ports on the switch will be used for home automation panel and touchscreen panels throughout the house for music control. this is all located in the electrical room. i then have a media closet which houses all my audio components for whole-home control and home theater. since it is in another room (and i don't want to run 8 cat6 cables to the electrical room), i was hoping i could get away with a 8 or 16 port managed switch, again with jumbo packets, etc. in the media closet will be whole-house music controller, htpc's, network media streamers with HD/bluray content streaming to different tv's in the house. i am concerned that the HD stuff will stutter with this setup.

so im really wondering what i can do to get away with using 2 switches as outlined above. perhaps getting better switches? where will the bottle neck be.... at the 24 port switch or the 8 port in the media closet.... or will all ports be bogged down?

thanks for the help.

It sounds like you have all the PCs / servers / media streamers all located in the media closet, correct? And in the electrical closet is just the Internet access point and some links for touch panels?

If that's the case, you're probably fine with any decent switch at the media closet, as the bulk of your traffic is being routed around the media closet, and only Internet access (again limited to the bandwidth of your cable/dsl link) is going up to the electrical closet.

Do you really have the need for a 24 port switch there? Are there that many devices, or are you just hooking up every possible jack in the house? For PCs/servers/streamers that have Gbit support, you'd like to have those on Gbit ports mostly for better file copy performance. But a 24-port Gbit switch is going to be expensive relative to a readily available consumer 8-port variety...

Oh, and individually, any HD streaming device (server or client) will live perfectly happy on a 100Mb link, as they're consuming much less than half the bandwidth, probably much less...

Jeff

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post #14 of 15 Old 09-15-2009, 10:10 AM
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okay great. yes you pretty much nailed it out as to my setup. i won't be using 24 ports but would like to have all the inputs around the house connected directly to the switch so i never have to go down and connect stuff when i need to. just a cleaner setup imo, although more expensive.

the pc's connected to the 24 port switch in the electrical closet will mostly be accessing the internet but will also need to access the main server pc (located in the media closet) for file transfer, music and bluray collection, etc hence why im a bit uncertain as to whether or not the bottleneck will affect transfer times and streaming. both points are valid and im wondering if i should go the extra mile and do fully managed switches with uplink setup as mentioned by WonHung. either way, what you are saying is that most of the traffic will be in the media closet, so does that mean that the pc's accessing the internet (connected to the 24 port switch) in the electric closet will be the bottleneck or the other way around? and would it make sense to get the exact same switch for both areas to minimize this in any way?

one last question. will i gain anything by connecting a few inputs directly to the router as opposed to the switch (for pc's such as the server)?

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post #15 of 15 Old 09-15-2009, 10:55 AM
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Easiest way to understand this is to draw it out. In general, you want the links between switches to be as fast as possible, since those links are carrying the load of everything downstream. If you have 8 PCs connected at 100Mb to a switch with a 1Gb uplink, they will each get effectively 100Mb of bandwidth (since 8*100Mb < 1Gb). If that uplink is only 100Mb, each PC would only get 1/8th of that. But that's if they are all being used at the same time. One PC could still consume 100Mb if nothing else is going on. That's why it's best to draw out the usage - PCs on the same switch talking to each other don't consume any of the uplink bandwidth - hence the questions about Internet usage vs. streaming...

Fully managed switches won't do much for you - they don't overcome any bottlenecks, just allow you to manage the bandwidth. But for a residential setup where you own all the devices, you can just plan this out and know what to expect.

Ports on the router vs. the switch are all the same answer - it depends on who they're talking to. Just try to lay everything out to minimize traffic between switches when possible, and Ethernet will figure out the rest for you...

Jeff

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