|desc=Send out syncookies when the syn backlog queue of a socket overflows. This is to prevent against the common 'SYN flood attack'.
syncookies seriously violate TCP protocol, do not allow o use TCP extensions, can result in serious degradation of some services (f.e. SMTP relaying), visible not by you, but your clients and relays, contacting you.
IP Settings allows to configure several IP related kernel parameters.
Properties
Property
Description
accept-redirects (yes | no; Default: no)
Whether to accept ICMP redirect messages.
Typically should be enabled on host and disabled on routers.
accept-source-route (yes | no; Default: no)
Whether to accept packets with SRR option.
Typically should be enabled on router.
ip-forwarding (yes | no; Default: yes)
Emable/disable packet forwarding between interfaces. Resets all configuration parameters to defaults according to RFC1812 for routers.
rp_filter (loose | no | strict; Default: no)
Disables enables source validation.
no - No source validation.
strict - Strict mode as defined in RFC3704 Strict Reverse Path. Each incoming packet is tested against the FIB and if the interface is not the best reverse path the packet check will fail. By default failed packets are discarded.
loose - Loose mode as defined in RFC3704 Loose Reverse Path. Each incoming packet's source address is also tested against the FIB and if the source address is not reachable via any interface the packet check will fail.
Current recommended practice in RFC3704 is to enable strict mode to prevent IP spoofing from DDos attacks. If using asymmetric routing or other complicated routing, then loose mode is recommended.
secure-redirects (yes | no; Default: yes)
Accept ICMP redirect messages only for gateways, listed in default gateway list.
send-redirects (yes | no; Default: yes)
Whether to send ICMP redirects. Recommended to be enabled on routers.
tcp_syncookies (yes | no; Default: no)
Send out syncookies when the syn backlog queue of a socket overflows. This is to prevent against the common 'SYN flood attack'.
syncookies seriously violate TCP protocol, do not allow o use TCP extensions, can result in serious degradation of some services (f.e. SMTP relaying), visible not by you, but your clients and relays, contacting you.
