Category Archives: F5

F5 iRule Class Match Crash

Problem: F5 iRules with “class match” crash sometimes with this message: /Common/UA_DETECT – ambiguous option “-“: must be -all, -index, -element, -name, or -value while executing “class match [string tolower [HTTP::header User-Agent]] contains UA_STRINGS” Discussion: the class match command has … Continue reading

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Configure F5 TLS (SSL) Cipher String

The list of TLS ciphers is changing quite rapidly, old ciphers are considered insecure, and new ciphers are added. When you configure a virtual server on an F5 you can add a TLS client profile, which means F5 is doing TLS … Continue reading

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Annoyances while updating F5

I had to upgrade several F5 load balancers from 11.5 to 12.1 in the last weeks. Usually updating F5 is quiet easy, but there are bugs or annoyances you should know: Sometimes F5 asks for re-activating after the first boot into … Continue reading

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F5 Drops WebSockets

Problem: F5 LTM is used als load balancer for multiple web servers. When the client opens a websocket connection to the web server, the connection is closed. Discussion: F5 LTM version before 11.6.0 has a bug in the request_log module (profile). The … Continue reading

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F5 sending packets to wrong destination?

Problem: You have a network with two upstream routers and an F5 LTM loadbalancer. Even though the default gateway points to router R1 the F5 LTM sends packets to the mac address of R2. Discussion: “This is a feature not a … Continue reading

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