SRX

Hello,
I have a SRX in packet mode acting as an internet gateway (basically BGP multihoming on the northbound interfaces and connected to a pair of firewalls  in the south.

fw1-----ge-0/0/0
                               |--- SRX ----  ISP (multihoming)
fw2-----ge-0/0/1

Both internal interfaces are in the same vlan as well as the irb (which is  exported via BGP to the ISP providers).

I am seeng a a very persistent flapping behavior  with messages like this:

Oct 16 10:00:20 cpe1.cambridge.grapeshot.co.uk /kernel: if_pfe_linfo: Sending ifl down reason tlv value (0x0) for ifl(ge-0/0/0.0)
Oct 16 10:00:20 cpe1.cambridge.grapeshot.co.uk /kernel: if_pfe_linfo: Sending ifl down reason tlv value (0x0) for ifl(ge-0/0/0.0)
Oct 16 10:05:24 cpe1.cambridge.grapeshot.co.uk /kernel: if_pfe_linfo: Sending ifl down reason tlv value (0x0) for ifl(ge-0/0/0.0)

I haven't modified any CoS or spanning tree setting and  cabling and neighbor devices have been chcked. Any ideas?

This messages are harmless (internal communication) and can be ignored. Ideally these will come only with traceoptions, can you check if you have enabled traces under ge-0/0/0 or interfaces hierarchy, if so please disable them and see if the logs continue occuring.