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# Blocking and Limiting Multicast Traffic

You can either block mroute creation, limit the multicast bandwidth admitted on an outgoing interface, or limit outgoing interface creation on a port.

## Blocking Mroutes

By default, when an interface receives multicast traffic, even when the scope of that traffic exceeds link-local, the virtual router creates an mroute. You can use the ipv6 block-multicast-sources command to block all multicast traffic with a scope larger than link-local (for example, global) and prevent mroute creation under these conditions.

| Note: Issuing this command does not affect reception of link-local multicast packets.

ipv6 block-multicast-sources

- Use to prevent mroute creation by blocking multicast traffic that has a scope larger than link-local (for example, global).
- Example
  `
  host1(config)#ipv6 block-multicast-sources
  `
- Use the no version to restore the default behavior of creating mroutes on receiving multicast packets.
- See ipv6 block-multicast-sources.

## Limiting Interface Admission Bandwidth

Interface-level multicast admission control is performed when an OIF on the interface is added to the mroute for a given (S,G) multicast data stream and the multicast bandwidth map contains a set admission-bandwidth action for that (S,G).

When enabled, the admission-bandwidth for a particular (S,G) is read from the multicast bandwidth map and recorded in the mroute when the (S,G) mroute is created. When an IOF is subsequently added to the mroute, the OIF is blocked from forwarding data if the additional bandwidth contributed by the (S,G) would exceed the admission-bandwidth limit for the interface.

| Caution: Before you can limit interface-level admission bandwidth, you must first create a bandwidth map. See Defining a Multicast Bandwidth Map for details.

### Enabling Interface Admission Bandwidth Limitation

You can use the ipv6 multicast admission-bandwidth-limit command to enable multicast admission control on interfaces (including dynamic IP interfaces) that are configured to run MLD. You can also use this command on a PIM (sparse-mode, dense-mode, or sparse-dense-mode) interface if MLD is configured on the interface (including the ipv6 mld version passive command).

ipv6 multicast admission-bandwidth-limit

- Use to limit bandwidth for an interface that accepts MLD groups.
- Use on any interface configured to run MLD.
- Can also configure on a PIM (sparse-mode, dense-mode, or sparse-dense-mode) interface if MLD (which you can configure using the ipv6 mld version passive command) is also configured on the interface.
- Example
  `
  host1:boston(config-if)#ipv6 multicast admission-bandwidth-limit 2000000
  `
- Use the no version to remove the bandwidth limitation for the interface.
- See ipv6 multicast admission-bandwidth-limit.

### OIF Interface Reevaluation Example

If you change the admission bandwidth for an interface, all mroutes with that interface as an OIF are reevaluated as follows:

- If the bandwidth limit is increased, blocked OIFs may become unblocked. If the interface is a blocked OIF on multiple mroutes, the order in which the mroutes are visited, and which (S,G) streams become unblocked, is not specified.
- If the bandwidth limit is decreased, no currently admitted OIFs are blocked. However, no new OIFs are admitted until the total admitted bandwidth for the interface drops below the new limit.
- If the bandwidth is increased to the point that the bandwidth limit for an interface is now exceeded, no currently admitted OIFs for the affected mroutes are blocked. However, no new OIFs are admitted until the total admitted bandwidth drops below the configured limit.

  | Note: If the multicast bandwidth map that includes the set admission-bandwidth command is changed, all affected mroutes are reevaluated in the same manner described previously.

As an example of this function, if the interface has accepted a total bandwidth of 2000000 bps, and you set a limit of 1000000 bps on the interface, the router does not disconnect any already connected OIFs but prevents the interfaces from accepting any more groups. Over time, some groups leave the interfaces and, eventually, the interface limit of 1000000 bps is reached and maintained by the router.

If you set limits for both a port and interfaces on that port, the router uses the lower of the two limits when determining whether or not an interface can accept any new MLD groups. For example, if you specify an admission bandwidth limit of 2000000 bps for the port and 3000000 bps groups for each interface, additional groups can only be accepted until the port limit of 2000000 bps is reached.

## Creating Mroute Port Limits

When a multicast forwarding entry (that is, an mroute) is added with an outgoing interface (OIF) on a port, the OIF count for that port is incremented. If you configure a port limit and the OIF count on the port count exceeds that limit, no OIFs on that port are added to mroutes (that is, new OIFs are blocked).

mroute port limit

- Use to configure a limit on the number of mroute OIFs that can be added across different virtual routers, on a port.
- Example
  `
  host1(config)#mroute port 3/0 limit 10
  `
- Use the no version to remove any OIF port limits.
- See mroute port limit.

## Limiting Port Admission Bandwidth

Port-level multicast admission control is performed when an OIF on that port is added to the mroute for a given (S,G) multicast data stream and the multicast bandwidth map contains a set admission-bandwidth action for that (S,G).

When enabled, the admission-bandwidth for a particular (S,G) is read from the multicast bandwidth map and recorded in the mroute when the (S,G) mroute is created. When an IOF is subsequently added to the mroute, the OIF is blocked from forwarding data if the additional bandwidth contributed by the (S,G) would exceed the admission-bandwidth limit for the port on which the interface resides.

| Caution: Before you can limit port-level admission bandwidth, you must first create a bandwidth map. See Defining a Multicast Bandwidth Map for details.

### Enabling Port Admission Bandwidth Control

You can use the mroute port admission-bandwidth-limit command to limit the total multicast bandwidth that can be admitted on a port. The admitted bandwidth is summed across all virtual routers with IPv4 and IPv6 mroutes that have OIFs on the port.

| Note: Admission bandwidth values for a given (S,G) mroute are determined from the bandwidth map. See Defining a Multicast Bandwidth Map for details.

mroute port admission-bandwidth-limit

- Use to configure a limit on the admission bandwidth of OIFs containing IPv4 or IPv6 mroutes, across different virtual routers, on a port.
- Example
  `
  host1(config)#mroute port admission-bandwidth-limit 3000000
  `
- Use the no version to remove any OIF admission bandwidth limits.
- See mroute port admission-bandwidth-limit.

### OIF Port Reevaluation Example

If you change the admission bandwidth for a port, all mroutes with an OIF on that port are reevaluated as follows:

- If the bandwidth limit is increased, blocked OIFs can become unblocked. However, the order in which the mroutes are visited, and which (S,G) streams become unblocked, is not specified.
- If the bandwidth limit of a port is decreased, no currently admitted OIFs are blocked. However, no new OIFs are admitted until the total admitted bandwidth for the port drops below the new limit.
- If the bandwidth is increased to the point that the bandwidth limit for an interface is now exceeded, no currently admitted OIFs for the affected mroutes are blocked. However, no new OIFs are admitted until the total admitted bandwidth drops below the configured limit.

  | Note: If the multicast bandwidth map that includes the set admission-bandwidth command is changed, all affected mroutes are reevaluated in the same manner described previously.

As an example of this function, if the port has accepted a total bandwidth of 3000000 bps, and you set a limit of 2000000 bps on the port, the router does not disconnect any already connected OIFs but prevents the interfaces from accepting any more groups. Over time, some groups leave the interfaces and, eventually, the port limit of 2000000 bps is reached and maintained by the router.

If you set limits for both a port and interfaces on that port, the router uses the lower of the two limits when determining whether or not an interface can accept any new MLD groups. For example, if you specify an admission bandwidth limit of 2000000 bps for the port and 3000000 bps groups for each interface, additional groups can only be accepted until the port limit of 2000000 bps is reached.

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