Cisco Cisco Aironet 350 Mini-PCI Wireless LAN Client Adapter Guide De Conception
6-9
Enterprise Mobility 4.1 Design Guide
OL-14435-01
Chapter 6 Cisco Unified Wireless Multicast Design
How Controller Placement Impacts Multicast Traffic and Roaming
How Controller Placement Impacts Multicast Traffic and
Roaming
Roaming
Note
The multicast stream in either deployment, distributed or collocated, is not rate-limited and there is no
way to put ACLs on it. Once enabled, all multicast traffic is forwarded to the wireless including HSRP,
EIGRP, OSPF, and PIM packets
way to put ACLs on it. Once enabled, all multicast traffic is forwarded to the wireless including HSRP,
EIGRP, OSPF, and PIM packets
We look at two different deployments (distributed and centralized) and how they impact roaming with
multicast clients. In a centralized deployment, WLC WLAN interfaces are attached to the same VLANs/
subnets, the multicast streams is uninterrupted when a multicast client roams from APs on one WLC to
an AP on another WLC. The centralized deployment creates a flat WLC client multicast network. The
reason centralized WLCs do not affect multicast roaming is because once the multicast stream is
requested from a single multicast client on a WLAN, it streams out all APs on that WLAN, on all radios
(802.11g and 802.11a), on all WLCs, even if that access point WLAN has no clients associated with it
that have requested the multicast traffic. If you have more than one WLAN associated to the VLAN, the
AP transmits the multicast packet over each WLAN. Both the unicast mode LWAPP packet and the
multicast mode LWAPP packet contain a WLAN bitmap that tells the receiving AP which WLAN it must
forward the packet over.
multicast clients. In a centralized deployment, WLC WLAN interfaces are attached to the same VLANs/
subnets, the multicast streams is uninterrupted when a multicast client roams from APs on one WLC to
an AP on another WLC. The centralized deployment creates a flat WLC client multicast network. The
reason centralized WLCs do not affect multicast roaming is because once the multicast stream is
requested from a single multicast client on a WLAN, it streams out all APs on that WLAN, on all radios
(802.11g and 802.11a), on all WLCs, even if that access point WLAN has no clients associated with it
that have requested the multicast traffic. If you have more than one WLAN associated to the VLAN, the
AP transmits the multicast packet over each WLAN. Both the unicast mode LWAPP packet and the
multicast mode LWAPP packet contain a WLAN bitmap that tells the receiving AP which WLAN it must
forward the packet over.
The distributed deployment does not have this problem because while the WLANs are the same, the
WLCs are attached to different VLANs. This means that when the multicast client roams to a new WLC,
the WLC will first query the client for its multicast group memberships. At this point the client responds
with its group membership report and the WLC forwards this message to the appropriate multicast group
address through the VLAN associated with its local VLAN. This allows the client to resume its multicast
session through the foreign WLC.
WLCs are attached to different VLANs. This means that when the multicast client roams to a new WLC,
the WLC will first query the client for its multicast group memberships. At this point the client responds
with its group membership report and the WLC forwards this message to the appropriate multicast group
address through the VLAN associated with its local VLAN. This allows the client to resume its multicast
session through the foreign WLC.
The distributed deployment reduces the amount of multicast traffic on the APs because, although the
WLAN SSIDs are the same, the WLCs are attached to different VLANs. WLAN multicast traffic
depends on a client request on the VLAN of that WLC.
lists the advantages and
disadvantages
of distributed and collocated deployments.
Table 6-2
Pros and Cons of Centralized WLCs and Distributed WLCs
PROS
CONS
All centralized WLC
WLANs connected to the
same VLANs (subnets)
WLANs connected to the
same VLANs (subnets)
Multicast traffic started
on any client VLAN will
be transmitted to all APs
so clients roaming to any
AP will receive multicast
stream
on any client VLAN will
be transmitted to all APs
so clients roaming to any
AP will receive multicast
stream
If only one client requests multicast traffic, all
APs attached to all controllers will receive the
stream and transmit it if they have any clients
associated even if those clients did not request
the multicast stream
APs attached to all controllers will receive the
stream and transmit it if they have any clients
associated even if those clients did not request
the multicast stream
Distributed WLCs on
different VLANs and
subnet
different VLANs and
subnet
Multicast streams are
isolated to APs attached
to controller
isolated to APs attached
to controller
Disruptions caused by multicast stream
establishments after client roam
establishments after client roam