Forum Discussion
- Kevin_StewartEmployee
The answer here depends on how you're doing the forward proxy. Are you doing SSL forward proxy, where you're decrypting, sending decrypted data to the Blue Coat devices, and the re-encrypting? Or simply load balancing encrypted traffic to the Blue Coat?
If the latter, then you're generally limited to destination addresses, though you could conceivably make the decision based on the ClientHello SNI value.
- minnkhank12_304Nimbostratus
- minnkhank12_304Nimbostratus
Dear Kevin Stewart,
Thank you for your support. As our diagram, all traffic pass through the blue coat proxy expect office 365 traffic. The green line is a bypass traffic directly to internet. Our solution want only O365 traffic go through from bypass to reduced the load on blue coat. Please can you help me as well as you can.
- Kevin_StewartEmployee
So minimally you'd have two pools:
- The pool of BC proxies
- The pool of routers on the other side of the BCs
Based on some criteria, you'd select the BC or router (bypass) pool. The question then becomes what criteria to use. If you know the destination IP addresses for O365 resources, then it's super easy to switch pools based on the destination IP. If you don't know the IPs, and because you're not decrypting at the F5, you may have to collect and use the ClientHello SNI value (for encrypted traffic) or the HTTP host header (for unencrypted traffic).
- Kevin_StewartEmployee
Since you're grabbing the ClientHello SNI without decrypting the packet, you'll be doing it at OSI layer 4. Here's what that iRule would look like.
when CLIENT_ACCEPTED priority 300 { set detect_handshake 1 TCP::collect } when CLIENT_DATA priority 200 { binary scan [TCP::payload] H* orig if { [binary scan [TCP::payload] cSS tls_xacttype tls_version tls_recordlen] < 3 } { reject return } 768 SSLv3.0 769 TLSv1.0 770 TLSv1.1 771 TLSv1.2 switch $tls_version { "769" - "770" - "771" { if { ($tls_xacttype == 22) } { binary scan [TCP::payload] @5c tls_action if { not (($tls_action == 1) && ([TCP::payload length] > $tls_recordlen)) } { set detect_handshake 0 } } } "768" { set detect_handshake 0 } default { set detect_handshake 0 } } if { ($detect_handshake) } { skip past the session id set record_offset 43 binary scan [TCP::payload] @${record_offset}c tls_sessidlen set record_offset [expr {$record_offset + 1 + $tls_sessidlen}] skip past the cipher list binary scan [TCP::payload] @${record_offset}S tls_ciphlen set record_offset [expr {$record_offset + 2 + $tls_ciphlen}] skip past the compression list binary scan [TCP::payload] @${record_offset}c tls_complen set record_offset [expr {$record_offset + 1 + $tls_complen}] check for the existence of ssl extensions if { ([TCP::payload length] > $record_offset) } { skip to the start of the first extension binary scan [TCP::payload] @${record_offset}S tls_extenlen set record_offset [expr {$record_offset + 2}] read all the extensions into a variable binary scan [TCP::payload] @${record_offset}a* tls_extensions for each extension for { set ext_offset 0 } { $ext_offset < $tls_extenlen } { incr ext_offset 4 } { binary scan $tls_extensions @${ext_offset}SS etype elen if { ($etype == 0) } { if it's a servername extension read the servername set grabstart [expr {$ext_offset + 9}] set grabend [expr {$elen - 5}] binary scan $tls_extensions @${grabstart}A${grabend} tls_servername_orig set tls_servername [string tolower ${tls_servername_orig}] set ext_offset [expr {$ext_offset + $elen}] break } else { skip over other extensions set ext_offset [expr {$ext_offset + $elen}] } } } } if { ![info exists tls_servername] } { This isn't TLS so we can't decrypt it anyway SSL::disable clientside SSL::disable serverside } else { log local0. "tls_servername = ${tls_servername}" This is where you'd check the SNI and do something useful So for example: if { ${tls_servername} contains "o365.com" } { pool outer_router_pool } else { pool bluecoat_pool } } TCP::release }
- Kevin_StewartEmployee
I'm a little confused. You started by describing a scenario where you don't decrypt the SSL and the F5 is simply load balancing to, or around a Blue Coat ProxySG. The iApp "airgap" template I believe you're referring to is designed to decrypt the SSL, send it to security services, and then re-encrypt. That's not what you were originally asking for.