Title

SMTP Maximum Hop Count is not 30. (Cat III impact)

Discussion

E-mail system availability depends in part on best practices strategies for setting tuning configurations. This setting controls the maximum number of hops (E-mail servers traversed) a message may take as it travels to its destination. Part of the original Internet protocol implementation, the hop count limit prevents a message being passed in a routing loop indefinitely. Messages exceeding the maximum hop count are discarded undelivered. Recent studies indicate that virtually all messages can be delivered in fewer than 25 hops, well within the current default of 30. If the hop count is set too low, messages may expire before they reach their destinations. If set too high, an undeliverable message may cycle between servers, raising the risk of network congestion.

Check Content

Access the SMTP Maximum Hop Count configuration. Procedure: Exchange System Manager >> Administrative Groups >> [administrative group] >> Servers >> [Server] >> Protocols >> SMTP >> [specific SMTP server] >> properties >> Delivery tab >> Advanced button The “Enter maximum hop count” value should be 30. Criteria: If the “Enter maximum hop count” value is 30, this is not a finding.

Fix Text

Set the maximum hop count value. Procedure: Exchange System Manager >> administrative groups >> [administrative group] >> Servers >> [Server] >> Protocols >> SMTP >> [specific SMTP server] >> properties >> Delivery tab >> advanced button. For "Enter maximum hop count", enter 30.

Additional Identifiers

Rule ID: SV-20316r1_rule

Vulnerability ID: V-18688

Group Title:

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.