I'm having a hard time understanding route scaling on the bigger M and
MX boxes.
You are not alone.
Official documentation is very sparse in this area.
In a CFEB based box maximum FIB is around 500k due to the limited SRAM
on the CFEB holding the FIB.
On a CFEB-E this is increased.
Now looking at the M320 or MX240 the FIB is present on all FPC boards
in each PFE, correct?
Yes
What is the architectural difference when using a
distributed setup, and how does it affect maximum FIB size? Eg. On an
FPC3-E2 in an M320 what can be expected to be the limit?
On M320 maximum FIB size is 1M ipv4 or 768k ipv6 routes.
Expected limit depends on many factors; around 700k ipv4 routes seems
feasible here.
The many factors include use of firewall filters, number of aggregated
interfaces ECMP.
Also use of features like LFA will influence FIB use somewhat.
http://www.juniper.net/us/en/local/pdf/whitepapers/2000345-en.pdf has
some info on LFA,
it also describes different types of FIB entries;
M320 FPC can accommodate different amount of them (has different jtree
memory use).
On E3 FPCs expected limit can be somewhat higher:
http://www.juniper.net/techpubs/en_US/junos10.4/topics/task/configuratio
n/junos-software-jtree-memory-repartitioning.html
On MX960 (MX240 should be same) maximum FIB size on Trio based PFE is 2M
ipv4 or ipv6 routes.
Expected limit should be much closer to maximum here.
-thomas
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