[j-nsp] Which Router

[Blake Willis]

Hi there,

 	A few performance evaluation papers on the J-Series are available from Iometrix:

http://www.iometrix.com/site/pdfs/CA-Iometrix-Juniper-J4350.pdf
http://www.iometrix.com/site/pdfs/CA-Iometrix-Juniper-J6350.pdf

 	In general it is as important to be as aware of performance limitations 
in packets/sec as bandwidth, and especially so with any centralised CPU-based 
forwarding platform as the same CPU is handling both forwarding and control 
plane functions.  The Iometrix papers have a note at the end on "IMIX and 
Stateful Traffic" that explains the packet size distribution used in their 
testing methodology that will be helpful in determining the real load that these 
routers can handle in a production environment.

 	A few things to be aware of with the J-Series that are not necessarily 
clear from the spec sheets:

  - Juniper doesn't recommend exceeding 40 BGP peers on the J2320, but in real 
life it all depends on the number of routes/peer and how much you're willing to 
let control plane processes use the CPU instead of forwarding packets with it. 
Several folks here seem to be running double that number without incident.  YMMV.

  - With a gig of RAM, these things are supposed to be good to 700K FIB routes 
and a million in the RIB.  I haven't tested a box with more than two full views 
on it, but I think it's safe to say that for the purposes you describe you're OK 
memory-wise for a good long while, esp. w/J4350 & 2 gigs.  It's worth pointing 
out that unlike an M/T/MX routing engine there's no hard drive, so if you run 
out of physical memory there's no swapping, only pain.

  - There are EPIM (PCI Express) slots on the J4350 (2) and J6350 (4) that allow 
for approx. 7x the bandwidth of the normal expansion slots.  When using a UPIM 
card (the new multi-GigE cards) in one of these slots I think it's safe to say 
that as traffic increases, the packet forwarding will kill the CPU before the 
bus runs out of bandwidth.  These slots are a good argument for springing for 
one of the beefier routers, and the presence of only 2 of them in the J4350 is a 
good argument for choosing the 16 port GigE card from the beginning if you need 
copper ports.

  - As of JunOS 8.5 there exists a version of JunOS called "JunOS ES" (enhanced 
services), which begins the integration of JunOS with ScreenOS (you'll notice 
that the many J-series and SSG products are identical).  This is useful if you 
indend to use the box as a stateful firewall or an application accelerator, but 
if you're primarily looking for a router, stick to normal JunOS.  JunOS ES has a 
stateful mode & a packet-based mode, and both are a compromise WRT which 
features are available.  Obviously the state tables use memory in stateful mode 
as well, leaving less room for routing.

  - A good part of the reason for the box's performance WRT certain other 
expensive blue CPU-based platforms is the scheduling & interrupt handling, which 
seems to have been extensively reworked for the J-Series.  The "downside" of 
this is that ICMP (ping & co.) will never get priority on the CPU, so if you're 
monitoring devices with ping & traceroute you should be prepared to not take the 
information you get back too seriously.

 	Best of luck.

  -Blake

---
  Blake Willis
  Network Engineering Consultant
  blake at 2112 dot net

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