Summary

Several IPv4 and IPv6 related kernel and system-wide parameters are configurable.

IPv4 Settings

Sub-menu: /ip settings

PropertyDescription
accept-redirects (yes | no; Default: no)Whether to accept ICMP redirect messages. Typically should be enabled on a host and disabled on routers.
accept-source-route (yes | no; Default: no)Whether to accept packets with the SRR option. Typically should be enabled on the router.
allow-fast-path (yes | no; Default: yes)Allows Fast Path.
arp-timeout (time interval; Default: 30s)Sets Linux base_reachable_time (base_reachable_time_ms) on all interfaces that use ARP. The initial validity of ARP entry is picked from the interval [timeout/2..3*timeout/2] (default from 15s to 45s) after the neighbor was found. Can use postfix ms, s, m, h, d for milliseconds, seconds, minutes, hours, or days. if no postfix is set then seconds (s) are used. Parameter DOES NOT represent a time when ARP entry is removed from ARP cache, ARP cache entries can be stored in the cache for up to 10minutes if the reference in a route cache is created.
icmp-rate-limit (integer [0..4294967295]; Default: 10)Limit the maximum rates for sending ICMP packets whose type matches icmp-rate-mask to specific targets. 0 to disable any limiting, otherwise the minimum space between responses in milliseconds.
icmp-rate-mask ([0..FFFFFFFF]; Default: 0x1818)Mask made of ICMP types for which rates are being limited. More info in linux man pages
ip-forward (yes | no; Default: yes)Enable/disable packet forwarding between interfaces. Resets all configuration parameters to defaults according to RFC1812 for routers.
rp-filter (loose | no | strict; Default: no)Disables or 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.
The 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 or VRRP, then the loose mode is recommended.

Warning: strict mode does not work with routing tables

secure-redirects (yes | no; Default: yes)Accept ICMP redirect messages only for gateways, listed in the 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 to 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.
max-neighbor-entries (integer [0..2147483647]; Default: )

A maximum number of allowed neighbors in the ARP table. Since RouterOS version 7.1, the default value depends on the installed amount of RAM. It is possible to set a higher value than the default, but it increases the risk of out of memory condition.

The default values for certain RAM sizes:

  • 2048 for 64 MB,
  • 4096 for 128 MB,
  • 8192 for 256 MB,
  • 16384 for 512 MB or higher.
route-cache (yes | no; Default: yes)Disable or enable Linux route cache. Note that by disabling the route cache, it will also disable the fast path.

Read-Only Properties

PropertyDescription
ipv4-fast-path-active (yes | no)Indicates whether fast-path is active
ipv4-fast-path-bytes (integer)Amount of fast-pathed bytes
ipv4-fast-path-packets (integer)Amount of fast-pathed packets
ipv4-fasttrack-active (yes | no)Indicates whether fasttrack is active
ipv4-fasttrack-bytes (integer)Amount of fasttracked bytes
ipv4-fasttrack-packets (integer)Amount of fasttracked packet.

IPv6 Settings

Sub-menu: /ipv6 settings

If changing settings the new configuration should not result with SLAAC address assigned to the router and old configuration had that address, the router have to be rebooted, or wait till SLAAC address times out


PropertyDescription
accept-redirects (no | yes-if-forwarding-disabled; Default: yes-if-forwarding-disabled)Whether to accept ICMP redirect messages. Typically should be enabled on host and disabled on routers
accept-router-advertisements (no | yes | yes-if-forwarding-disabled; Default: yes-if-forwarding-disabled)Accept router advertisement (RA) messages. If enabled router will be able to get address using stateless address configuration
disable-ipv6 (yes | no; Default: no)Enable/disable system wide IPv6 settings (prevents LL address generation)
forward (yes | no; Default: yes)Enable/disable packet forwarding between interfaces
max-neighbor-entries (integer; Default: 7168)A maximum number or IPv6 neighbors. Since RouterOS version 7.1, the default value depends on the installed amount of RAM. It is possible to set a higher value than the default, but it increases the risk of out of memory condition.

The default values for certain RAM sizes:

  • 1024 for 64 MB,
  • 2048 for 128 MB,
  • 4096 for 256 MB,
  • 8192 for 512 MB,
  • 16384 for 1024 MB or higher.
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