Most enterprise firewalls block all traffic not explicitly allowed by a rule. Because of this, people often fail to make proper allowances for ICMP in their firewall rules. The IETF has a great set of guidelines on ICMP filtering here: http://tools.ietf.org/html/draft-ietf-opsec-icmp-filtering-04 Some network guys will say, “I don’t want this server to be pinged or […]