Hello, I am planning to purchase the CRS310-1G-5S-4S+IN (main switch) and CSS326-24G-2S+ to increase the bus throughput from 1GbE to 10GbE. How does the configuration look in the case of two different interfaces, 1GbE and 10GbE? Should two separate bridges be created due to the MTU 9000 recommended for 10GbE and 1500 for 1GbE? Can two different bridges operate in the same subnet?
Large MTU is overrated nowdays[*]. Specially so as single IP subnet must use single MTU value on all members. When routing between subnets with different MTU sizes fragmentation occurs (causing various more or less serious issues). CSS can’t route (so MTU issue doesn’t really apply), CRS can but I guess that if MTU on both involved interfaces are not equal, L3HW may not be possible and software routing by CRS310 is a no-no. Additionally: only singke bridge csn be (L2) HW offloaded oer switch chip (and CRS310 has one), so with two bridges you will end up switching in software (which is a no-no).
So in short: do yourself a favour and stick to standard MTU size of 1500 bytes unless you know much better.
And a word of caution: MT switches (including CRS series, they are essentially switches) are notorious for having problems with link speed decreasing (i.e. traffic from 10Gbps port towards 1Gbps port) due to buffer sizes (they are mostly too small for switching).
[*] jumbo frames were introduced with FDDI which offered a whooping 100Mbps back when ethernet was usually 10Mbps over coaxial cable while connected computers were in range of a 33MHz 80386 … which couldn’t process much more than a few kPPS (which with standard MTU translates into a few tens of Mbps). Increasing MTU by almost 3 times thus directly translated into 3-fold increase of throughput.