German FTTH PPPoE Experience using a SRX (GlasfaserConnect Bochum)
[ Edited ]
2 weeks ago
I just want to share my experience with setting up a FTTH connection using a SRX300. Basically my ISP only provides a PPPoE username and password and that you have to use VLAN-tagging with VLAN-ID 7. In theory you are allowed to use any router but they provide no help whatsoever.
After setting up the connection with some default values, I found that the performance wasn't as expected so after some reading and sniffing with Wireshark I found that I had a big fragmentation Problem so I had to tweak the MTU
MTU, from the SRX: > ping 220.127.116.11 size 1412 do-not-fragment, so I changed the MTU to 1412+ 28= 1440 (from 1490 what is suggested for PPPoE.
This improved the performance somewhat.
Allowing ping ping on the internet (untrust) zone gave a little further improvement, this allows for Path MTU Discovery (PMTUD).
Only after changing the MSS value did I see good performance MSS= MTU-40=1400
This is the (relevant) configuration I ended up with: