--- name: "ng_bridge" section: "4" platform: "linux" package: "freebsd-manpages" version: "6.0-5" release: "Debian 4.0 (Etch)" platforms: ["linux", "freebsd"] url: "https://new.carta.tech/ng_bridge" --- # ng\_bridge(4) Ethernet bridging netgraph node type ## NAME **ng\_bridge** – Ethernet bridging netgraph node type ## SYNOPSIS **#include \** **#include \** ## DESCRIPTION The **bridge** node type performs Ethernet bridging over one or more links. Each link (represented by a connected hook) is used to transmit and receive raw Ethernet frames. As packets are received, the node learns which link each host resides on. Packets unicast to a known host are directed out the appropriate link only, and other links are spared the traffic. This behavior is in contrast to a hub, which always forwards every received packet to every other link. ## LOOP DETECTION The **bridge** node incorporates a simple loop detection algorithm. A loop is when two ports are connected to the same physical medium. Loops are important to avoid because of packet storms, which severely degrade performance. A packet storm results when the same packet is sent and received over and over again. If a host is detected on link A, and is then detected on link B within a certain time period after first being detected on link A, then link B is considered to be a looped back link. The time period is called the minimum stable time. A looped back link will be temporarily muted, i.e., all traffic received on that link is ignored. ## IPFW PROCESSING Processing of IP packets via the [ipfirewall(4)](/ipfirewall/4.md) mechanism on a per-link basis is not yet implemented. ## HOOKS This node type supports up to NG\_BRIDGE\_MAX\_LINKS hooks. Each connected hook represents a bridged link. The hooks are named link0, link1, etc. Typically these hooks are connected to the lower hooks of one or more [ng\_ether(4)](/ng_ether/4.md) nodes. To connect the host machine to a bridged network, simply connect the upper hook of an [ng\_ether(4)](/ng_ether/4.md) node to the bridge node. ## CONTROL MESSAGES This node type supports the generic control messages, plus the following: - NGM\_BRIDGE\_SET\_CONFIG Set the node configuration. This command takes a struct ng\_bridge\_config as an argument: ``` /* Node configuration structure */ struct ng_bridge_config { u_char ipfw[NG_BRIDGE_MAX_LINKS]; /* enable ipfw */ u_char debugLevel; /* debug level */ u_int32_t loopTimeout; /* link loopback mute time */ u_int32_t maxStaleness; /* max host age before nuking */ u_int32_t minStableAge; /* min time for a stable host */ }; ``` The ipfw array enables [ipfirewall(4)](/ipfirewall/4.md) processing of IP packets received on the corresponding links. The debugLevel field sets the debug level on the node. At level of 2 or greater, detected loops are logged. The default level is 1. The loopTimeout determines how long (in seconds) a looped link is muted. The default is 60 seconds. The maxStaleness parameter determines how long a period of inactivity before a host's entry is forgotten. The default is 15 minutes. The minStableAge determines how quickly a host must jump from one link to another before we declare a loopback condition. The default is one second. - NGM\_BRIDGE\_GET\_CONFIG Returns the current configuration as a struct ng\_bridge\_config. - NGM\_BRIDGE\_RESET Causes the node to forget all hosts and unmute all links. The node configuration is not changed. - NGM\_BRIDGE\_GET\_STATS This command takes a four byte link number as an argument and returns a struct ng\_bridge\_link\_stats containing statistics for the corresponding link, which must be currently connected: ``` /* Statistics structure (one for each link) */ struct ng_bridge_link_stats { u_int64_t recvOctets; /* total octets rec'd on link */ u_int64_t recvPackets; /* total pkts rec'd on link */ u_int64_t recvMulticasts; /* multicast pkts rec'd on link */ u_int64_t recvBroadcasts; /* broadcast pkts rec'd on link */ u_int64_t recvUnknown; /* pkts rec'd with unknown dest addr */ u_int64_t recvRunts; /* pkts rec'd less than 14 bytes */ u_int64_t recvInvalid; /* pkts rec'd with bogus source addr */ u_int64_t xmitOctets; /* total octets xmit'd on link */ u_int64_t xmitPackets; /* total pkts xmit'd on link */ u_int64_t xmitMulticasts; /* multicast pkts xmit'd on link */ u_int64_t xmitBroadcasts; /* broadcast pkts xmit'd on link */ u_int64_t loopDrops; /* pkts dropped due to loopback */ u_int64_t loopDetects; /* number of loop detections */ u_int64_t memoryFailures; /* times couldn't get mem or mbuf */ }; ``` - NGM\_BRIDGE\_CLR\_STATS This command takes a four byte link number as an argument and clears the statistics for that link. - NGM\_BRIDGE\_GETCLR\_STATS Same as NGM\_BRIDGE\_GET\_STATS, but also atomically clears the statistics as well. - NGM\_BRIDGE\_GET\_TABLE Returns the current host mapping table used to direct packets, in a struct ng\_bridge\_host\_ary. ## SHUTDOWN This node shuts down upon receipt of a NGM\_SHUTDOWN control message, or when all hooks have been disconnected. ## FILES - */usr/share/examples/netgraph/ether.bridge* Example script showing how to set up a bridging network ## SEE ALSO [bridge(4)](/bridge/4.md), [netgraph(4)](/netgraph/4.md), [ng\_ether(4)](/ng_ether/4.md), [ng\_hub(4)](/ng_hub/4.md), [ng\_one2many(4)](/ng_one2many/4.md), [ngctl(8)](/ngctl/8.md) ## HISTORY The **ng\_bridge** node type was implemented in FreeBSD 4.2. ## AUTHORS Archie Cobbs ⟨archie@FreeBSD.org⟩