I am currently installing a server rack for a customer, and they've asked a qauestion.

They want/need to optimise U space as to avoid paying overheads for U's that aren't needed.

The question they've asked, is whether or not they can use Static Routing with a L3 Switch.

This in their eyes would remove the need for 1 U, and would combine Switch/Router into 1 U.

It's a valid question, however I am not sure how to answer it as ARP came to mind.

So, can we replace the Router/Switch with a good L3 Switch?

And if so, can we statically route to each Server in the Rack without generating massive ARP cache?


The answer to this is yes, but depending on speed you need to spend a LOT of money. High end switches basically run a complete operating system and can handle OSPF, BGP and other things. Depending on speed and requirements, though, the client may decide that another rack (in price) is not worth it.

And if so, can we statically route to each Server in the Rack without generating massive ARP cache?

Yes, but what do you care? Because in the world of L3 switches those caches would not be "massive" but rather "tiny".

  • Okay. The switch they where thinking of broadbandbuyer.com/products/41437-zyxel-xs1930-10-zz0101f-cloud That is the one they liked the specification of, each server is capable of 1Gbs burst. – Charlotte Wells Apr 5 at 22:31
  • Neither giving product advice - as per site rules - nor following a link that requires me to fill out a crazy visual check whether I am a human. Looking at that one... from the manufacturer... whow. That thing is as low end as it gets. In that price area I would go with Mikrotik. I was thinking you talk of a real TOR switch, you know, 100gbit backbone or something like that. This is - something you can pick up in a retail shop for home use, pretty much. No higher functions. Like zero. Check Mikrotik, they at least can be used to run a full router with offloading. – TomTom Apr 5 at 22:48
  • Ah, okay my bad. They said their budget for this device is £600 - 750$. They don't want to spend more, sadly. Could you recommend a device? – Charlotte Wells Apr 5 at 22:50
  • Nope. At that price point you look either in the garbage bin or for a used device - from the garbage bin. Or Mikrotik (and no, they do extremely low cost but quite amazing for their price point stuff). For a L3 switch it is delusional to try to get something "proper" for a max. 750$. The market is not there. That is a router, but should reach those speeds: mikrotik.com/product/CCR1016-12G - you really need to try it out, but for those budget it is "buy and pray". – TomTom Apr 6 at 10:08
  • I would get a lower end switch and as I would run a virtual infrastructure anyway for most computers, just us a virtual router (Again, Mikrotik, 50 USD or so for the 1gb license) – TomTom Apr 6 at 10:09

ARP is a Layer 2 mechanism. ARP resolves ip addresses to MAC addresses.

The volume of ARP traffic on your network is immaterial to whether or not you use your Layer 3 switch as a router or use a "traditional" router.

If your servers are all in the same layer 3 network then no routing would be taking place to begin with as the traffic wouldn't be transitting the router in the first place. If your servers are in different layer 3 networks and you need to route traffic between these layer 3 networks then the amount of ARP traffic is neither greater or lesser based on your choice of routing device. It would be exactly the same.

The device you choose to use as a router has no bearing on the volume of ARP traffic.

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