Hello everyone,

I have a strange issue where traffic that is routed over a site to site VPN 
fails after approximately 70Mb of transfer. There are no lifesizes associated 
with the VPN, and the lifetimes are not close to being exceeded each time. 
There is nothing in the logs to indicate anything wrong, the VPN does not rekey 
etc.

I've tried various file transfer types and they all fail - SFTP, FTP, etc. They 
fail with the remote side closing the session - it looks like it has received a 
TCP RST but the sender still has the socket open - eventually it times out of 
course.

I've run the transfer to the same end points bypassing the VPN, and it works 
fine every time (this traffic does not traverse the SRXs). From packet captures 
from the sending side it looks like there are a ton of retransmissions and 
duplicate ACKs. Unfortunately I've not been able to perform a capture on the 
receiving side, though I hope to do that tomorrow.

I've got a few thoughts - one is all the interfaces are 1GB but the WAN link is 
10M. Possibly this is something to do with the buffers overflowing somewhere? 
I've tried tweaking the MSS on both SRXs to below 1300 in case its some MTU 
issue on the WAN, but again, it still happens.

Anyone got any ideas? I performed a debug to see if either Juniper was 
initiating the TCP RST and it doesn't look like they are. Just to fill you in a 
bit more, the topology looks a bit like this

Server --> ASA --> Core switch --> SRX --> WAN Firewall (ASA) --> WAN --> WAN 
Firewall (ASA) --> SRX --> Core Switch --> ASA --> Server

I  bypassed the SRXs for a test - they are only there for encryption, as there 
is a requirement that traffic over the WAN is encrypted.

I've tried disabling tcp-session-checking, and also wanted to try rate limiting 
the traffic but as this is an SRX240 cluster, you can't do this on clustered 
interfaces apparently.

Any ideas would be appreciated!

Thanks for your time

Harry

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