Layer-4 load balancer in dual-legged configuration. Based on BalanceNg software load balancer. Default gateway of web servers set to the load balancer. w inet h.dstmac == Mac(LB) AND h.dstip == Ip(LB) AND h.dstport == 80 NewFlow? w = SrvrSelect h1 = Dnat_fwd(h,w) h1 d inet h.dstmac == Mac(LB) AND h.dstip == Ip(LB) AND h.dstport == 80 ! NewFlow? h1 = Dnat_fwd(h,s) h1 d srvr h.srcmac == Mac(W) AND h.srcip == Ip(W) AND h.srcport == 80 h1 = Dnat_rev(h) h1 d Periodic Probe_srvr(W) inet ! ArpReq(Ip(s)) srvr p == ArpReply(ip,mac)