Looking for clarification on how switch chips and bridging work

RouterOS Beginner Basics
1

Hi All,

Id like clarification on what happens logically internally when a frame is forwarded. Not really attempting to troubleshoot something, just was curious as to what happens inside.

RB2011UAS-2HnD

In Winbox, Starting off without default config (System-> Reset Configuration-> check “Do not backup” and “No default configuration” boxes->Reset configuration)

After the reboot, I create a new bridge interface. Assign ports eth1 - eth3 to new bridge.

/interface bridge

add name=bridge1

/interface bridge port

add bridge=bridge1 interface=ether1

add bridge=bridge1 interface=ether2

add bridge=bridge1 interface=ether3



PC1 with ip 192.168.1.2/24 connected to ether 1

PC2 with ip 192.168.1.3/24 connected to ether 3

On a command prompt window on PC1, type in ping 192.168.1.3 and hit enter



Does the arp broadcast go from eth1 → AR8327 Switch → CPU → AR8327 Switch → Eth2 and Eth3?

Or does it go from eth1 → AR8327 Switch → Eth2, Eth3, and CPU?

If the arp broadcast follows eth1 → AR8327 Switch → Eth2, Eth3, and CPU , how does AR8327 Switch know to have all of these ports and bridge port on the same broadcast domain? Isn’t AR8327 Switch’s starting behavior to have all of the ports on a separate broadcast domain? What changed in the AR8327 Switch logic for it to recognize that these ports are all on the same broadcast domain?

Any help is appreciated. Thank you!
ARP Broadcast Path.png

2

Because you configured RouterOS to tell it so.

If you’re asking how switch chips work internally, you might be able to dig up a bootleg copy of the IC manual without signing an NDA, but it’ll be a slog to get through even so. These ASICs are quite complicated internally.

That may be enough of an answer right there: because the switching ASIC is highly programmable.