Four Switches in a Circle... What can go wrong ?
That reminds me of some event that occured in my previous life in Telecoms...
My colleagues and me, at that time, wanted routers, and only routers as gateways to the systems we were integrating in the $TELCO networks... It lead to several fight with the pre-sales guy in charge of this product line, as he wanted to put L3 switches as they were cheaper than routers (with a switch card in some case)... we are talking of something like 300€ less overall on a whole thing that's being billed in hundreds thousands Kilo Euros or more....
Since we also were the guys doing the On Call Support, the game was skewed our way : if we said we weren't going to support it, it meant getting a new team, and that meant getting that new team up to speed on all the legacy stuff we were covering. It was a big No Way, so after much fight we always got our routers.
Then came the day where the last Legacy Stuff went the way of the dodo, and a brand new shiny thing was coming to replace even the not that old stuff... the Grumpy team got disbanded ( well technically we saw the writting on the wall and self disbanded each of us finding a nice little corner to tuck in ) and a new team was put on the new stuff... We tried to tell them about the Switch against router thing... but they didn't really have a clue, and the new shiny system offered the option to use L3 switches instead of routers.
And then one day, after they installed 2 new swtiches at a $TELCO, the backbone of said $TELCO went down, for 4 hours... That's the time it took to locate the tw new, unconfigured switches that were creating a loop and breaking everything. After that at $TELCO an order was given to put all the unconnected ports down.
The worst is that they did it again... at another $TELCO (this time it only took an hour to fix it)
now the technicallity of why we wanted routers and not switches :
- we didn't have that many switched ports to connect and a 8 port switch card in a router was more than enough most of the time.
- by default router ports comes unconfigured and are administratively shutdown, while by default switches ports are administratively up and put in a default VLAN.
- It was much easier to get routing going in a router, and all the external flows were routed
- we didn't have to bother with Spanning Trees (because obviously it's a story about spanning trees gone AWOL)
The most interesting bit of the story, if that following generations went full custom hardware, with routers (in card form) integrated in the rack as the front end of the system towards the external world.