Keepalive v TCP Idle timeout

just in case you are asking about tcp keep-alive and tcp idle timeout.

Does one relate to client > F5 whilst the other to F5 > Server?

you can apply different tcp profile to each side of stack.

e.g.

//config

root@(B6900-R69-S40)(cfg-sync Standalone)(Active)(/Common)(tmos) list ltm virtual bar
ltm virtual bar {
    destination 100.100.100.41:23
    ip-protocol tcp
    mask 255.255.255.255
    pool foo
    profiles {
        tcp-5s {
            context serverside
        }
        tcp-10s {
            context clientside
        }
    }
    source 0.0.0.0/0
    source-address-translation {
        type automap
    }
    vs-index 4
}
root@(B6900-R69-S40)(cfg-sync Standalone)(Active)(/Common)(tmos) list ltm pool foo
ltm pool foo {
    members {
        200.200.200.101:23 {
            address 200.200.200.101
        }
    }
}
root@(B6900-R69-S40)(cfg-sync Standalone)(Active)(/Common)(tmos) list ltm profile tcp tcp-10s
ltm profile tcp tcp-10s {
    app-service none
    keep-alive-interval 10
}
root@(B6900-R69-S40)(cfg-sync Standalone)(Active)(/Common)(tmos) list ltm profile tcp tcp-5s
ltm profile tcp tcp-5s {
    app-service none
    keep-alive-interval 5
}

// clientside (client ip is 100.100.100.3)

[root@B6900-R69-S40:Active:Standalone] config  tcpdump -nni 0.0 host 100.100.100.41 and port 23
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on 0.0, link-type EN10MB (Ethernet), capture size 96 bytes

16:17:06.920322 IP 100.100.100.41.23 > 100.100.100.3.40419: . ack 146546235 win 65535
16:17:06.923296 IP 100.100.100.3.40419 > 100.100.100.41.23: . ack 1 win 5840 

16:17:16.923562 IP 100.100.100.41.23 > 100.100.100.3.40419: . ack 1 win 65535
16:17:16.923912 IP 100.100.100.3.40419 > 100.100.100.41.23: . ack 1 win 5840 

16:17:26.923624 IP 100.100.100.41.23 > 100.100.100.3.40419: . ack 1 win 65535
16:17:26.924216 IP 100.100.100.3.40419 > 100.100.100.41.23: . ack 1 win 5840 

// serverside (snat automap ip is 200.200.200.40)

[root@B6900-R69-S40:Active:Standalone] config  tcpdump -nni 0.0 -s0 host 200.200.200.101 and port 23
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on 0.0, link-type EN10MB (Ethernet), capture size 65535 bytes

16:17:01.920128 IP 200.200.200.40.40419 > 200.200.200.101.23: . ack 1911632262 win 65535 out slot1/tmm2 lis=/Common/bar
16:17:01.920542 IP 200.200.200.101.23 > 200.200.200.40.40419: . ack 1 win 5792  in slot1/tmm2 lis=/Common/bar

16:17:06.920311 IP 200.200.200.40.40419 > 200.200.200.101.23: . ack 1 win 65535 out slot1/tmm2 lis=/Common/bar
16:17:06.921807 IP 200.200.200.101.23 > 200.200.200.40.40419: . ack 1 win 5792  in slot1/tmm2 lis=/Common/bar

16:17:11.921239 IP 200.200.200.40.40419 > 200.200.200.101.23: . ack 1 win 65535 out slot1/tmm2 lis=/Common/bar
16:17:11.922911 IP 200.200.200.101.23 > 200.200.200.40.40419: . ack 1 win 5792  in slot1/tmm2 lis=/Common/bar

16:17:16.922554 IP 200.200.200.40.40419 > 200.200.200.101.23: . ack 1 win 65535 out slot1/tmm2 lis=/Common/bar
16:17:16.922970 IP 200.200.200.101.23 > 200.200.200.40.40419: . ack 1 win 5792  in slot1/tmm2 lis=/Common/bar

16:17:21.922125 IP 200.200.200.40.40419 > 200.200.200.101.23: . ack 1 win 65535 out slot1/tmm2 lis=/Common/bar
16:17:21.923134 IP 200.200.200.101.23 > 200.200.200.40.40419: . ack 1 win 5792  in slot1/tmm2 lis=/Common/bar

16:17:26.923613 IP 200.200.200.40.40419 > 200.200.200.101.23: . ack 1 win 65535 out slot1/tmm2 lis=/Common/bar
16:17:26.923952 IP 200.200.200.101.23 > 200.200.200.40.40419: . ack 1 win 5792  in slot1/tmm2 lis=/Common/bar