igmp_snooping
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| igmp_snooping [2009/04/25 16:29] – created blade | igmp_snooping [2012/10/17 11:40] (current) – claudiu | ||
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| - | Port states: | + | ====== IGMP Snooping / Forwarding Behaviour ====== |
| + | |||
| + | ===== Port states | ||
| * mrouter (router port) | * mrouter (router port) | ||
| * subscriber (port belongs to established multicast group) | * subscriber (port belongs to established multicast group) | ||
| * none | * none | ||
| - | Forwarding cases (igmp snooping enabled on vlan): | + | ===== Forwarding cases (igmp snooping enabled on vlan) ===== |
| - | * multicast traffic received on " | + | |
| + | * multicast traffic received on " | ||
| * if no mrouter present, flood to all ports | * if no mrouter present, flood to all ports | ||
| * otherwise flood to mrouter ports | * otherwise flood to mrouter ports | ||
| - | * igmp received on " | + | * igmp received on " |
| - | * flood to mrouter ports only | + | * if no mrouter present, ignore frame (no group is created) |
| + | * otherwise | ||
| + | * creates multicast group | ||
| + | * forwards | ||
| + | * port becomes " | ||
| + | * multicast traffic received on " | ||
| + | * send to established group members only | ||
| + | * igmp received on " | ||
| + | * creates multicast group | ||
| + | * forwards to mrouter ports only | ||
| + | |||
| + | ===== Other notes ===== | ||
| - | Other notes: | ||
| * if igmp snooping is disabled, multicast traffic is flooded to all ports in vlan, regardless of frame nature (i.e. it is igmp or not); static multicast fdb entries are ignored; | * if igmp snooping is disabled, multicast traffic is flooded to all ports in vlan, regardless of frame nature (i.e. it is igmp or not); static multicast fdb entries are ignored; | ||
| + | * mrouters can be statically configured while igmp snooping is disabled on vlan, but they are ignored until igmp snooping is enabled; when igmp snooping is enabled, the rules listed above apply; | ||
| + | * mrouters are not activated until: interface is up AND interface has access to mrouter vlan (either access mode vlan or trunk allowed vlan) | ||
| + | |||
| + | When changing access vlan, with mrouter already configured (in new vlan): | ||
| + | < | ||
| + | 5w0d: IGMPSN: mgt: Vlan 15, port Fa0/5 port_id 7 in non-fwd mode | ||
| + | 5w0d: IGMPSN: mgt: received pmvlan_linkchange down event on vlan 15 | ||
| + | 5w0d: IGMPSN: Adding router port Fa0/5 to all GCEs in Vlan 18 | ||
| + | 5w0d: L2MM: added rport Fa0/5 on Vlan 18 | ||
| + | 5w0d: %SYS-5-CONFIG_I: | ||
| + | </ | ||
| + | |||
| + | ====== Implementation Approach ====== | ||
| + | |||
| + | Analyzing the forwarding cases, it turns out that when incoming packets are forwarded to more than one port at the same time, they are forwarded to either all ports in a specific igmp group or all mrouter ports (but not a mix of the two). In other words, depending on the igmp snooping logic, either an igmp group or a list of mrouter ports is sufficient to determine which ports to forward to. | ||
| + | |||
| + | ===== Forwarding to ports in an igmp group ===== | ||
| + | |||
| + | * igmp group membership is stored as special fdb entry | ||
| + | * is_static field in struct net_switch_fdb_entry is change to a bitwise field: | ||
| + | * b0 tells if entry is dynamic or static | ||
| + | * b1 tells if entry is regular fdb entry or igmp membership entry | ||
| + | * for igmp membership entries, a b0 value corresponding to " | ||
| + | * all igmp membership entries have a virtual MAC address formed as 01-00 plus the group address (4 bytes) | ||
| + | * when flooding to all ports in a group, the following actions are taken: | ||
| + | * first the virtual mac corresponding to the packet destination is build; | ||
| + | * the fdb bucket corresponding to the virtual mac is determined; | ||
| + | * the fdb bucket is walked to determine the ports to forward to: | ||
| + | * virtual mac must be equal (between fdb entry and packet) | ||
| + | * vlan must be equal (between fdb entry and packet) | ||
| + | * igmp group listing is done only on the slow path (upon user request) by walking the entire fdb and building the igmp group list: | ||
| + | * the kernel module is asked for a list of all igmp membership fdb entries (with the ability to filter by a specific group and/or vlan); | ||
| + | * userspace code walks the fdb entry list and builds a (temporary) list of groups and, for each group, a list of member ports | ||
| + | |||
| + | The following changes need to be made to existing code: | ||
| + | * fdb queries from userspace need to filter out igmp membership entries; | ||
| + | * standard (non-multicast) packet fdb lookup needs to ignore igmp membership entries; | ||
| + | |||
| + | ===== Forwarding to mrouter ports ===== | ||
| + | |||
| + | Whether a port is mrouter or not is a function of the port and vlan. In other words, mrouter can be stored as a flag (bit) depending on the port and vlan. Since vlan number is limited and relatively small (4096), mrouter information can be stored as a per-port vlan-indexed bitmap. The data structure would be similar to vlan membership for trunk ports. | ||
| + | |||
| + | Flooding to all mrouter ports in a specific vlan becomes very simple: | ||
| + | * use the VDB to iterate through all ports in the required vlan; | ||
| + | * for each port check if it's mrouter in the required vlan; | ||
| + | |||
| + | Algorithm can be easily cloned from sw_flood(). | ||
| + | |||
| + | ====== CLI Commands ====== | ||
| + | |||
| + | **exec#** | ||
| + | < | ||
| + | sh ip igmp snooping [vlan x] | ||
| + | sh ip igmp snooping groups [vlan x] [dynamic|user] [count] etc | ||
| + | sh ip igmp snooping mrouter [vlan x] | ||
| + | </ | ||
| + | |||
| + | **config#** | ||
| + | < | ||
| + | [no] ip igmp snooping vlan x mrouter interface y | ||
| + | [no] ip igmp snooping vlan x static a.b.c.d interface y | ||
| + | </ | ||
| + | ====== Useful links ====== | ||
| + | * [[http:// | ||
| + | * [[http:// | ||
| + | * [[http:// | ||
| + | * [[http:// | ||
| + | * [[http:// | ||
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