[j-nsp] Netflow config for MX204

[Nick Schmalenberger]

On Sat, Apr 11, 2020 at 03:52:53PM +1200, Liam Farr wrote:
> Hi,
> 
> Got things working in the end, thanks everyone for their help and patience.
> 
> Also thanks @John Kristoff especially for the template at
> https://github.com/jtkristoff/junos/blob/master/flows.md it was
> very helpful.
> 
> As I suspected I was doing something dumb, or rather a combination of the
> dumb.
> 
> 1. I had initially tried to use fxp0 as my export interface, it seems this
> is not supported.
> 2. I then tried to use an interface in a VRF to export the flows, I think
> some additional config may be required for this (
> https://kb.juniper.net/InfoCenter/index?page=content&id=KB28958).
> 3. It's always MTU... I suspect in one of my various config attempts flow's
> were being sent, but dropped because of the 1500 MTU on the flow collector
> and a larger MTU on the MX204 interface generating them.
> 
> In the end I set up a new link-net on a new vlan interface attached to
> inet0 between the MX204 and netflow collector, set the inet mtu to 1500
> and 🍾 everything started working.
> 
> 
> Again thanks everyone for the help, I now have some really interesting flow
> stats to examine :)
> 
>
What are you using for flow analysis? I have elastiflow setup and
its showing me some pretty graphs but seems to severely
undercount. Like showing 5Mbps of traffic when SNMP tells me its
1-2Gbps. I'm not sure if its a performance problem on the router
or elastiflow side, but I'm glad to see someone else configuring
this on a MX204 :) Let me know if you run into that also.

I had the same issue with first trying to export over fxp0, then
trying with my routing instance, and I ended up making a static
route in inet6.0 with next-table over to the instance table where
the route into the LAN for my elastiflow collector is. Flow
export over IPv6 does also seem to work.
-Nick