Users report that some/few URLs are not accessible over SRX.

SRX has PPPoE (time fiber) dialup Internet Connection/uplink.

Few URLs wont load and the User receives "connection time out" on the Browser.

Where-in most of the URLs are accessible and working fine.

PPPoE header uses 6 bytes + the PPP protocol ID uses 2 bytes.

This restricts the MRU (Maximum Receive Unit) size on a PPPoE interface to 1492 bytes.

If any URL or host uses/requires MTU greater than or equal to 1492, those might face connectivity issue.

Check the affected URL MTU:

Linux:    ping -s 1480 -M do google.com
Mac:      ping -s 1480 -D google.com
Windows:  ping -l 1480 -f google.com

Confirm the exact MTU size and we can configure the same MTU for the flow.

To address this issue, we can adjust the flow TCP MSS:

root@SRX# set security flow tcp-mss 1400