The Firewall page allows you to configure options to protect or facilitate various types of network communications.
WAN interfaces respond to ping and traceroute: If enabled, this allows your device to reply to ICMP ping and traceroute request packets from Internet hosts. This is necessary for ping and traceroute to work from the Internet.
Enable TCP SYN cookies: Enabling this uses the “SYN cookies” technique to protect the router from SYN Flood attacks. This function encodes information from the SYN packet into the (SYN/ACK) response. This is a standard method for preventing SYN floods. However, it has certain limitations which may cause issues with some old TCP/IP stacks.
Enable DCSP Fix: Checking this enables a workaround for packet marking, a well-known issue related to DSCP when connected to Comcast.
Allow DHCP Spoofing:
Smart MTU black hole detection:
NAT loopback: This technique allows LAN devices to access each other via the router's WAN interface. Also known as “Hairpinning”, this is commonly used when connecting to the DDNS domain of your router from the LAN. These days, this legacy setting is almost never needed. It also can create speed bottlenecks.
NAT target - This defines the way NAT is implemented for use during loopback. Masquerade is the default, but involves an additional lookup. ad the mapping of done towards an interface. SNAT is minutely faster, as the NAT mapping points directly to the destination IP and so it bypasses the lookup stage. However, SNAT is less reliable than Masquerade.
Enable IGMP proxy - Checking this enables the IGMP (Internet Group Management Protocol) service.
LAN0 - LAN3 Specifies which bridges will participate in IGMP, with the router acting as a proxy between selected LANs. This allows IGMP to work between VLANs.
Enable quick leave - This is a feature of IGMP v2 and later. Enabling this allows the router to stop streaming multicast to an IP address as soon as that device sends a “quick leave” IGMP packet.
Custom Configuration - This option allows you to set advanced parameters for the IGMP proxy daemon. Consult official IGMP documentation before using this.
Enable Udpxy - Like IGMP proxy, Udpxy allows multicast communications between devices on different VLANs. Since their behavior is very similar, you are advised to use either Udpxy or IGMP proxy, but not both at once.
Upstream interface - Here, enter the stream source is expected to live. (Default: blank).
LAN0/LAN1/LAN2/LAN3 - This specifies the location the streaming clients are expected to be found.
Enable client statistics - Enabling this causes FreshTomato to collect statistics about Udpxy clients.
Max clients - This represents the maximum number of simultaneous Udpxy clients. Udpxy is is a lightweight protocol, and only works well for a limited number of clients. For this reason, you might want to impose a maximum limit.
Efficient Multicast Forwarding (IGMP Snooping) - IGMP snooping makes the router's switch facilitate discovery of Multicast IGMP clients. This will help to send multicast traffic only towards ports with at least one multicast subscriber, reducing overall multicast traffic.
However, caution is advised. IGMP Snooping can interfere with proper functioning of UPnP or DLNA. This can make Multicast configuration errors or deficiencies appear as UPnP issues. Enabling IGMP snooping on a router's/switch will interfere with UPnP/DLNA device discovery. Specifically, it can interfere with SSDP protocol transmissions. If IGMP snooping is incorrectly or incompletely configured (say, without an active querier or IGMP proxy), this make UPnP appear unreliable.
A common symptom of this is a network host (say, a Smart TV) which appears after it's powered on, but then “disappears” from the network after a few minutes. To be more precise, often this period is 30 minutes. This is because the default setting for when IGMP group membership will expire. Please be aware of the wireless multicast forwarding setting in the the Advanced/Wireless menu.
Force IGMPv2 - IGMPv2 enhances IGMP with additional messages/behavior to optimize end-to-end client-server communication. Perhaps the most important of these additional messages is the “Leave Group” message. When a host no longer wants to listen to a multicast group address, it will report to the router that it has stopped listening. In v1, the host simply stopped listening, without informing the router.
Other features of IGMPv2 include:
Group specific membership query. The router can now send a membership query for a specific group address. When the router receives a leave group message, it will use this query to check if there are still any hosts interested in receiving the multicast traffic.
MRT (Maximum Response Time) field. This new field in query messages specifies how much time hosts have to respond to the query.
Querier election process. When two routers are connected to the same subnet, only one of them should send query messages. Having an “election” process ensures only one router, the router with the lowest IP address, becomes the active querier.