Attaching a simple unmanaged switch

Discussion in 'Tomato Firmware' started by CharlieSummers, Jun 1, 2018.

  1. CharlieSummers

    CharlieSummers Network Newbie Member

    Is there any reason a simple unmanaged Ethernet switch won't work out-of-the-box in Tomato?

    A while back, I plugged an old 4-port portable switch into the Asus RT-N16 thinking I could easily add a few ports. No go. Dug around in the basement, found an old 5-port switch, which I used to use on an old router. This one, too, wouldn't work.

    So I bought a cheap Chinese 8-port switch (with Vlan switch - turned off, since I don't have enough devices to worry about it). I can't get that one to work, either.

    So either I have to do something interesting in Tomato (Tomato Firmware v1.28.7511 MIPSR2Toastman-RT K26 USB VPN-NC Built on Fri, 20 Jan 2017 22:13:11 +0700), I've done something stupid, or that d*mned black cloud that follows me everywhere I go is raining on me again. Shouldn't this be as simple as running an Ethernet cable from an output on the RT-N16 into the uplink port on the switch?
  2. eibgrad

    eibgrad Network Guru Member

    Should work.

    Have to ask the obvious. You did try more than one ethernet cable, right?
  3. koitsu

    koitsu Network Guru Member

    As long as you aren't using VLANs on the RT-N16, then yes, a generic consumer switch should work just fine hooked up to the LAN1-4 ports.

    That said:

    You intentionally mention an "uplink port" on your switches. This port has a very specific purpose, and as a result -- but depends on vendor and implementation -- often requires use of a crossover Ethernet cable, not a straight-through ("standard" or "patch") Ethernet cable. If the uplink port lacks auto-MDIX***, then failure to use the right cable on this port will result in no link. Product documentation should disclose this; if it doesn't, then shame on the vendor. It's this exact reason that I suggest anyone working with switches have both standard/patch cables and a couple crossover cables laying around. Make sure you label the crossovers appropriately.

    If your switches DO NOT have real uplink ports, then you should be able to use a standard Ethernet cable from any port on the switch, to any LAN port on the RT-N16, and achieve what you need.

    Finally, just as a reminder: you may potentially lose MAC visibility on the RT-N16 for any clients/devices attached to the (new) switch, as no longer are the devices directly attached to the router's switch, but an intermediary switch which handles all layer 2 forwarding. In essence, the MAC seen by the Tomato router for traffic on that port (connected to the (new) switch) would only be that of the (new) switch itself. If you see otherwise, let me know. Layer 3-7 traffic would not be impacted.

    If you are using VLANs on the RT-N16, the situation becomes very different, specifically if you're using tagged VLANs. In this scenario, you need a switch that supports 802.1Q (VLANs), because 802.1Q Ethernet frames are larger than non-802.1Q frames. A non-VLAN-supporting switch would drop/throw away such traffic, citing the Ethernet frames were "giants" (too large) due to the extended header. My general recommendation here is that you buy a managed switch since you're going to need to decide what Ethernet ports are to receive which VIDs' traffic (and maybe those ports will even be untagged); even the (less expensive) web-only managed HP ProCurve switches have this capability.

    *** - I have seen on at least one occasion a consumer switch claiming support for auto-MDIX on all ports (incl. uplink), but found that the uplink port required a crossover cable (standard would not work).

    My general opinion of auto-MDIX is: assume it doesn't work and wire things up properly. When auto-MDIX does work, consider it a blessing.
    Last edited: Jun 1, 2018
  4. Monk E. Boy

    Monk E. Boy Network Guru Member

    Uplink ports are wired the opposite of normal ports. If the uplink port doesn't work, try a normal port. I used to carry around a crosslink cable in my bag but its been so long since I needed one it got stuffed into a box at home. Crimped them by hand back in the day.

    I have an 8 port GigE switch connected to my router (originally an N16, then an N66, now an AC68) and it was just plug and play. I picked up a $13 Monoprice 8 port GigE switch a while back in case the old HP switch finally kicks the bucket and it worked without any fuss with the N66. Half the size despite both being 8 ports. A tenth the price too.

    As already suggested, try a different cable. Some 100Mb cables only contain two pairs and may cause issues with the GigE switch in the N16. I've also taken to tossing out Cat5 (not Cat5e) cables as they're old and all the ones I've been encountering for years now are non-spec since they can't link at GigE.
  5. Yim Sonny

    Yim Sonny Serious Server Member

    When I am on a business network with 35 or 40 computers I can do an ARP lookup and see the MAC & IP addresses of the computers. Does a Tomato router behave differently than a Windows computer in relation to MAC recognition ? Isn't a layer two switch MAC transparent ? Did you momentarily confuse the effects of connecting another router versus connecting a network switch ?

    Attached Files:

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    koitsu likes this.
  6. koitsu

    koitsu Network Guru Member

    Thanks for commenting! Yes, it's very likely I got this wrong and you are correct. I believe I can explain how/why I get some of this wrong on occasion. I think this is the 2nd time it's come up, so it deserves explanation for everyone's benefit, and I believe in being transparent, esp. when I get something wrong:

    My switching experience consists of three backgrounds:

    * Juniper EX switches (managed), which handle both extensive layer 2 and layer 3 configuration, where the environments I was using them in involved limited use of VLANs,
    * HP ProCurve switches (managed), focused heavily on layer 2 configuration, especially extensive use of VLANs, with the sole goal of ensuring layer 2-7 traffic was not visible to certain ports using MAC access lists, and minor layer 3 support (mainly for switch administrative access) -- I was responsible for this professionally, so my experience here is quite extensive,
    * Generic consumer equipment (i.e. unmanaged switches from D-Link and Netgear), which also should include TomatoUSB on some level, as well as the more recent Ubiquiti ER-X-SF (which does provide hardware switching fabric; only a very specific list of Ubiquiti routers offer this)

    As I get older in age, I tend to intermix this knowledge, and start thinking "ah yes, that traffic would not flow", when in fact it WOULD flow (and didn't at the time because of MAC ACLs, or intermediary devices).

    This is one of many reasons I tell people: take what I say with seriousness, but never ever forget that I too am human, I make mistakes (regularly!), and to please call me out of them, especially publicly! I won't be "butthurt". :) It's important that people get the truth, as this is technology, not magic.

    I'm overdue for going back and revisiting my networking background anyway. Spent too much of it doing systems stuff in the past 15 years...
    Yim Sonny, Justio and Malakai like this.
  7. Yim Sonny

    Yim Sonny Serious Server Member

    No problem at all koitsu Don't feel bad about slipping at the edges on occasion. It took me an hour to decide to post a response because I did not want to seem obtuse. I kept thinking it was me that had skipped a track, but I thought there might be something here I was not aware of and I wanted to learn what it was. Thank you very much for your contribution to the project.
    koitsu likes this.
  8. Monk E. Boy

    Monk E. Boy Network Guru Member

    I understand the "device list" part of Tomato is kind of wacky in how it derives its list of devices, although I normally see all active devices on the network, anyone connected through another AP connected to the main router via ethernet will be listed as eth1 or eth0 or whatever the main router has assigned to the ethernet ports, because that's how it, the main router, sees the traffic. Even though they're connected wirelessly to the AP, to the main router they come in over ethernet so they're shown as being connected via ethernet. The same would hold true for anything wired to a switch that's cabled to the main router, although in that case it would seem less unusual since you know they're cabled in.
    koitsu likes this.
  9. koitsu

    koitsu Network Guru Member

    Yeah, TomatoUSB's Devices List feature is not as "linear" as it may appear, and can lead to a lot of confusion as to what all the router can "see". A post of mine in the past covered just a small tip of the iceberg of the things it pokes at. Post was mainly about the wireless information shown, but does outline some of the other sources it uses.
    Techie007 and Monk E. Boy like this.
  10. Monk E. Boy

    Monk E. Boy Network Guru Member

    That's actually the post that sprung to mind but I was multitasking while writing that post and couldn't risk something going wrong by I searching for it. My system tolerates multiple tasks but sometimes gets really fussy and stops responding, which would have created a headache for me.
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