SRX

I would like to know if anyone has this option in newer SRX series. " window-scale "? I had an srx300 with it. The common srx300's have it. Other SRX models owners are welcome to comment, in fact high model numbers is desired to know. I dont know about newer srx300's.

Policies

           policy All_Internal {

                match {

                    source-address any;

                    destination-address any;

                    application any;

                }

                then {

                    permit {

                        tcp-options {

                            syn-check-required;

                            window-scale;

                        }

                    }

                }

           }

------------------------------
Adrian Aguinaga
B.S.C.M. I.T.T. Tech
(Construction Management)
A.A.S. I.T.T. Tech
(Drafting & Design)
------------------------------

you can modify the TCP window in flow options 64L to 1M,  this feature was introduced to fix a throughput issue when IDP or UTM is enabled...  otherwise the SRX proxy modifies the window size to 0 (64K) which is fine for low latency involvements, but comes an issue for private to internet ( higher latency a 64K  = low throughput).   personally I set it to max 1M but 512k 256k etc are also an option.. 

-------------------------------------------

I have always thought that the 1M size was a bit small. Windows OS says about 2M in quote, but 4G is attainable. This is why I think going with the policy option is possibly better. Syn and others are more local in their own way.

One thing I learned about windows tcp was that it can process security/authentication with use of its registry. A trick for users back in the day was using 655360, not 65536. This was because old OS's could not handle 2M, or 4G, like now.

------------------------------
Adrian Aguinaga
B.S.C.M. I.T.T. Tech
(Construction Management)
A.A.S. I.T.T. Tech
(Drafting & Design)
------------------------------

Original Message:
Sent: 09-15-2025 03:06
From: JosephOhare007
Subject: Policy window scale option

you can modify the TCP window in flow options 64L to 1M,  this feature was introduced to fix a throughput issue when IDP or UTM is enabled...  otherwise the SRX proxy modifies the window size to 0 (64K) which is fine for low latency involvements, but comes an issue for private to internet ( higher latency a 64K  = low throughput).   personally I set it to max 1M but 512k 256k etc are also an option.. 

This message was posted by a user wishing to remain anonymous

You can look-up on juniper cli-explorer the description for this command, it also provides information on what release it was added ..

"The window-scale statement is introduced in Junos OS Release 15.1X49-D70"

This is not a new feature.

Reviving post!!!

------------------------------
Adrian Aguinaga
B.S.C.M. I.T.T. Tech
(Construction Management)
A.A.S. I.T.T. Tech
(Drafting & Design)
------------------------------