Руководство По Проектированию для Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter
6-6
Enterprise Mobility 4.1 Design Guide
OL-14435-01
Chapter 6 Cisco Unified Wireless Multicast Design
Multicast Deployment Considerations
Multicast Deployment Considerations
Recommendations for Choosing an LWAPP Multicast Address
Caution
Although not recommended, any multicast address can be assigned to the LWAPP multicast group
including the reserved link local multicast addresses used by OSPF, EIGRP, PIM, HSRP, and other
multicast protocols.
including the reserved link local multicast addresses used by OSPF, EIGRP, PIM, HSRP, and other
multicast protocols.
Cisco recommends that multicast addresses be assigned from the administratively scoped block 239/8.
IANA has reserved the range of 239.0.0.0-239.255.255.255 as administratively scoped addresses for use
in private multicast domains (see the note below for additional restrictions). These addresses are similar
in nature to the reserved private IP unicast ranges (such as 10.0.0.0/8) defined in RFC 1918. Network
administrators are free to use the multicast addresses in this range inside of their domain without fear of
conflicting with others elsewhere in the Internet. This administrative or private address space should be
used within the enterprise and blocked from leaving or entering the autonomous domain (AS).
IANA has reserved the range of 239.0.0.0-239.255.255.255 as administratively scoped addresses for use
in private multicast domains (see the note below for additional restrictions). These addresses are similar
in nature to the reserved private IP unicast ranges (such as 10.0.0.0/8) defined in RFC 1918. Network
administrators are free to use the multicast addresses in this range inside of their domain without fear of
conflicting with others elsewhere in the Internet. This administrative or private address space should be
used within the enterprise and blocked from leaving or entering the autonomous domain (AS).
Note
Do not use the 239.0.0.X address range or the 239.128.0.X address range. Addresses in these ranges
overlap with the link local MAC addresses and will flood out all switch ports even with IGMP snooping
turned on. For more information on overlapping multicast MAC addresses, refer to the following URL:
overlap with the link local MAC addresses and will flood out all switch ports even with IGMP snooping
turned on. For more information on overlapping multicast MAC addresses, refer to the following URL:
Cisco recommends that enterprise network administrators further subdivide this address range into
smaller geographical administrative scopes within the enterprise network to limit the “scope” of
particular multicast applications. This is used to prevent high-rate multicast traffic from leaving a
campus (where bandwidth is plentiful) and congesting the WAN links. It also allows for efficient
filtering of the high bandwidth multicast from reaching the controller and the wireless network.
smaller geographical administrative scopes within the enterprise network to limit the “scope” of
particular multicast applications. This is used to prevent high-rate multicast traffic from leaving a
campus (where bandwidth is plentiful) and congesting the WAN links. It also allows for efficient
filtering of the high bandwidth multicast from reaching the controller and the wireless network.
For more information on multicast address guidelines, refer to the document at the following URL:
http://www.cisco.com/application/pdf/en/us/guest/products/ps6592/c1244/cdccont_0900aecd80310d68
.pdf.
.pdf.
Fragmentation and LWAPP Multicast Packets
When a controller receives a multicast packet, it encapsulates it inside of LWAPP using the LWAPP
multicast group as a destination address and forward it to the APs via the management interface (source
address). If the packet exceeds the MTU of the link, the controller fragments the packet and send out
both packets to the LWAPP multicast group. If another controller were to receive this LWAPP
encapsulated multicast packet via the wired network, it would re-encapsulate it again, treating it as a
normal multicast packet and forward it to its APs.
multicast group as a destination address and forward it to the APs via the management interface (source
address). If the packet exceeds the MTU of the link, the controller fragments the packet and send out
both packets to the LWAPP multicast group. If another controller were to receive this LWAPP
encapsulated multicast packet via the wired network, it would re-encapsulate it again, treating it as a
normal multicast packet and forward it to its APs.
There are two different options to prevent this from happening, either of which is effective by itself. One,
you may assign all controllers to the same LWAPP multicast group address. Or two, you can apply
standard multicast filtering techniques to ensure that LWAPP encapsulated multicast packets do not
reach any other controller.
you may assign all controllers to the same LWAPP multicast group address. Or two, you can apply
standard multicast filtering techniques to ensure that LWAPP encapsulated multicast packets do not
reach any other controller.
lists the pros and cons of these two techniques.