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What is a layer 3 lite Switch?

Discussion in 'Switches, NICs and cabling' started by coxhaus, Aug 21, 2018.

  1. coxhaus

    coxhaus Part of the Furniture

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    People are recommending layer 3 lite switches. What is a layer 3 lite switch? What is it's layer 3 capabilities?

    I would like to put a definition to this.

    My original thinking was no protocol routing only static routing.
     
    Last edited: Aug 21, 2018
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  3. ColinTaylor

    ColinTaylor Part of the Furniture

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  4. Trip

    Trip Very Senior Member

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    Using HPE hardware examples, an "L3 Lite" switch would be a 1920S, whereas a full L3 model would be a 2540. Compare their feature sets in-depth and I think you'll ascertain the differences along the lines of @ColinTaylor's links.
     
  5. System Error Message

    System Error Message Part of the Furniture

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    I explained in another thread, that was related to an enterprise LAN in a home article somewhere here in SNB.

    A layer 3 switch is simply a switch that can route on the IP layer. The best way to test this is not only about applying static routes into the switch but also some switches can learn L3 as well and some have routing protocols like BGP in them, the only difference between a L3 switch and router is that a router can do NAT while a L3 switch cant. To test this on the network level, you can define a static route on the switch, 2 different clients with different IPs and networks, but using some arbitrary device as the gateway (needed or clients may default to layer 2). Set the static route on the switch so that the packets can go between both clients, if both clients can talk to each other (or just ping) then it is a layer 3 switch.

    Typically a layer 2 switch keeps a list of addresses, and what ports they are on, so when a packet is destined for a mac, it just looks up a table and sends it to the right port. On the layer 3 however learning can be expensive and bad (in the case of mikrotik CRS switches, they are good switches, just the L3 learning can mean if you plug the router into another port, clients wont get internet back), so usually static routes or protocols (like BGP) help here. By using layer 3, you can do all sorts of static routing at wirespeeds that routers may not be able to do (except ones like the CCR), and by not having it go through the router, which is typically connected at only 1Gb/s for consumers, you could transfer files from one to another and not cut off internet for others. On the more advanced level other than segmentation is that you can use this to custom route with VPN if you want to route a set of IPs through one place, and the rest with another. Its not a great thing to do because of the internet being dynamic, but its also something you can do.

    Layer 3 switches dont see much use at homes but for any business, it is a must as part of segmentation and security apart from functionality. Cisco SG switches are layer 3 as well. If you do layer 3 segmentation, consider using one, and especially if it is managed means you can apply some cool layer 2 security as well that you cant normally do with semi managed layer 2 switches. Note that many switches will say layer 3 when they are actually layer 2 except that they recognise IPs but dont route them.
     
  6. coxhaus

    coxhaus Part of the Furniture

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    So I am thinking my original thinking is correct. A layer 3 switch routes at layer 3 and supports IP routing protocols. A layer 3 switch light routes at layer 3 and only supports static based routing. But either layer 3 switch can fully function without a router.

    I am thinking my Cisco SG300-28 is a layer 3 light switch since it only has static routing. It has full blown ACL support.

    My Cisco SG-500X-24 is a layer 3 switch which has 10 gig support and full blown ACL support. The big thing is the SG-500x-28 switch supports IP routing protocols. It generates a lot more heat and noise.
     
    Last edited: Sep 5, 2018
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  7. ColinTaylor

    ColinTaylor Part of the Furniture

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    "layer 3 light switch" :D:D:D

    [​IMG]
     
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  8. sfx2000

    sfx2000 Part of the Furniture

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    At the 10,000 foot view...

    Hubs, Switches, and Routers...

    Hubs work at layer 1 - all the ports are basically physical layer - the ethernet ports and wires - they're cool in their own way, and most network hackers have at least one hub in their toolbox... but the performance issues once we get to higher ethernet rates makes them less than useful.

    Switches work at layer 2 - the ethernet layer - or what some call the MAC layer, which is ok, since we're all ethernet - switches maintain MAC tables (yes, even unmanaged layer 2) as traffic from the uplink is directed only to the destination MAC address of the machine those ethernet packets are addressed to - unlike the hub above, which just broadcasts things across all ports - e.g. layer one

    Routers work at layer 3 - the network layer - IP - both TCP and UDP - layer 3 switches work at the network layer, routing packets across different networks/subnetworks...

    Should note that Routers can do Layer 4 and above - including even firewalls at Layer 3 and above, even to the application layer (layer 7)

    Here's where it get's interesting - there's a lot of Layer 2 switches that can do some managed traffic at Layer 2 - e.g. we get some VLAN action there, maybe even LAG's, since this is Layer 2 at the ethernet level.

    Some call those Layer 2 switches "smart switches" because of the VLAN and perhaps QoS at the ethernet level - yes, VLAN's, some QoS treatment perhaps, but all layer 2.

    Then there's what we call Layer 3 switches - and there's different degrees, depending on treatment at Layer 2 (the ethernet layer) and Layer 3 (the network layer)

    There's Layer 3 - which tends to keep things inside one network domain - e.g. provide treatment to packets for the main network, and any subnetworks below it - that includes everything that a layer 2 "smart switch" can do, plus do some network layer treatment.

    Some Layer 3 switches have a little capability, and some have much, depends on the vendor and target market... and that's where you get the terms Layer 3, and Layer 3-Lite.

    Routers are typically also Layer 3 - but the key difference is they can router across different networks - e.g. for many here, between the WAN (which is one network) and the LAN (which is another network).

    Without picking on, or endorsing Netgear... but their product line card on the ProSafe line makes it easy...

    • GS-108 - this is an unmanaged Layer 2 switch - it's a good switch for layer 2
    • GS-108e - this is a light Layer 2 managed switch - yes, it can do VLAN's, some QoS at the ethernet level - they offer this as a "smart switch"
    • GS-108t - it can do everything that the others can do, plus it can also manage traffic across different sub-networks on the same LAN, including some light duty routing for Layer 3 and the upper layers across different subnetworks
     
    Last edited: Sep 6, 2018
  9. sfx2000

    sfx2000 Part of the Furniture

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    What layers do they work at - as far as I know, both are layer 3, and good ones.

    It's really down to treatment of the Layer 3 traffic - like I mentioned, the Netgear GS-108T does do treatment there, but not to the same level of a Cisco SG series. Some would consider the SG's to have some routing capability, and there I would agree, but I wouldn't use one in that context...
     
  10. coxhaus

    coxhaus Part of the Furniture

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    This switch does not fit our definition of a light layer 3 switch. A light layer 3 switch needs to do everything that a layer 3 switch can do except not support IP protocol routing. A light layer 3 switch should handle DHCP, ACLs and static routing. It should be able to route IP traffic by it self without any help. You should be able to turn off your router and your layer 3 switch should still fully function. So GS-108T is a layer 2 switch unless it can perform all the above.

    They light layer 3 switch should be able to be a router without NAT.
     
    Last edited: Sep 6, 2018
  11. System Error Message

    System Error Message Part of the Furniture

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    doesnt have to be static routes only, as i mentioned, dynamic routing protocols like BGP can be supported too, plenty of things but at the minimum supports static routing.
     
  12. coxhaus

    coxhaus Part of the Furniture

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    What I am saying if the layer 3 switch supports routing dynamic protocols then it is a layer 3 switch. It does not matter which routing protocols. Some routing protocols are Cisco proprietary so will not be in other vendors switches.

    If a layer 3 switch does not support dynamic routing protocols then it is a light layer 3 switch.
     
  13. umarmung

    umarmung Regular Contributor

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    This is not a Layer 3 switch by any definition, including your own. It does not even have static routing support, cannot be used as a gateway, has no SVI, barely has ACL support and has no other features specific to Layer 3 switches. Even Netgear do not refer to it as a Layer 3 switch anywhere. It is just an L2 managed switch with slightly more features than the other even less featureful L2 desktop switches that Netgear sells. The only thing notable about it, other than its security failings, is that I believe it is the cheapest Netgear switch that supports Management VLAN.
     
    Last edited: Sep 6, 2018
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  14. sfx2000

    sfx2000 Part of the Furniture

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    I just figured I would yank some chains here - as this is a bit of a sensitive topic...

    @System Error Message @coxhaus @umarmung

    The GS-108T is a fine Layer 2 switch with the WebGUI usage - it does have some layer 3 oriented features, and is a great managed switch for most LAN's that SNB would be focused on. It's does some nice VLAN routing at L2, can do groups and ACL, and of course, stats - nice that it has some layer 3 with IGMP stuff out of the box.

    Get under the hood and into eCos you'll find it's very capable firmware - there is actually full Layer 3 functionality there, but this isn't exposed without a fair amount of hacking - this is why it's never a good idea to put one on to the internet directly...
     
  15. sfx2000

    sfx2000 Part of the Furniture

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    Most folks probably don't "need" a layer 3 switch in the home network - it's overkill for the most part.

    I do worry a bit about the Lightly Managed "Smart Switches" - many do not have a webgui, and are dependent on applications running on a PC on the LAN...

    I have a 24 port fast ethernet switch that does just that* - it requires an App on the desktop (and it requires Adobe Air just to add) - it's purely Layer 2 and very limited management - for items like that, best to lock it down with a password other than default, and run it as a dumb switch.

    * I didn't buy it, it was a 'gift' after a network upgrade - hey, 24 ports is 24 ports...
     
  16. System Error Message

    System Error Message Part of the Furniture

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    A layer 3 switch and a light (in terms of features and duty) are 2 very very different things. One is network layers and protocols, the other being featureset and duty (performance, etc). For instance, you could have a heavy duty switch that features a massive heatsink and fan that can operate in direct sunlight in the desert without any additional cooling, you could have a switch made for homes with features that are more towards basic use, excluding ACLs, some routing stuff and so on. A layer 3 switch with static or dynamic routing is still a layer 3 switch. So i would not say a light layer 3 switch, rather you can say a light duty layer 3 switch, or a semi managed layer 3 switch :p .
    The problem is that the features of the firmware are locked, so i dont know how one would argue whether it be false advertising or not. Firmware is one thing but the switch fabric and hardware also must support it or you could expect some very poor performance.
     
  17. sfx2000

    sfx2000 Part of the Furniture

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    Remarkably, it's not - the GS-108T line is non-blocking, and the SoC inside has a fair amount of horsepower - Netgear pulls back on the capabilities for business reasons and product line, not technical/engineering.
     
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