Multicast

= Multicasting =

224.0.0.0/4 - 224.0.0.0 -239.255.255.255
 * Ranges

Link local address - 224.0.0.0/24 Source specific multicast -232.0.0.0/24 Administratively scoped -239.0.0.0/8

Multicast control plane work differently than unicast routing ,it needs to know who is sender of mutlicast and to which group ,also the reciever of multicast.

Multicast Data plane -do RPF check ( was traffic received on correct interface and bulid multicast routing table ).

Multicast is source based routing.

IGMP -Host on LAN singanl the router to join the mutlicast group.

Two kind of request - (*,G)-Any source who is genrating the mutlicast stream for that group -Supported by IGMP V1 and V2                      (S,G)-want to join particular source sending the mutlicast group .-IGMP version 3 support both (s,g and (*,G)

IGMP get enabled when the IP PIM [ Dense mode,sparse mode,SParse-DENSE-mode) is enabled.

BY default IGMP version 2 is enabled.

IP IGMP join group address can be used for testing on routers to see weather muticast traffic is recieved on router for particular group.

ip igmp static group command can be used to mannually put the request for particular mutlicast group insteaed of reling on IGMP queriy messsage for particular group.

PIM- used to siganl routers to bulid muticast tree ,tree could be sender to receiver or sender to rendevpoint--- receiver.

PIM version 1 or 2 ,By default its PIM version 2, RP information is already encoded in PIM packet in version 2. PIM version 2 has field for BSR.

DENSE mode - Implicit join ,mutilcast traffic is send across entire network unless if some one report for not joing the particular stream.Flood and prune behiviour. Nighbor discovery on multiicast address 224.0.0.13 same for sparse mode as well.

Note if we have (*,G) entery then we know about reciver and if we have (S,G) entry then we know about sender as well.

Two ways to genrate mutlicast traffic either through pinging mutlicast address or through IP SLA. IN PIM dense -through RPF nei information is used to send unicast packet back to source ,message could pim prune or graft message .when the multicast source flood the traffic for particular multicast groups each multicast enable router will install (S,G entry) and (*,G) entries even if they are not intersted.

So in dense every router needle to install (*,G ) and (S,G) entry as we canot have (S,G) untill we have (*,G) entries.so if the source is active every router need to maintain the state table for mutlicasting.

Graft message for (S,G) entry is to unprune the mutlicast traffic as earlier it was set to prune.

State refresh to keep the link prune as its original state.

SParse mode -uses explict join unless it is asked by someone to join mutlicast traffic uses RP as reference point.In case we are using source specific mutlicast we don't need RP.for Group specfic joins we need RP.Traffic is not send anywhere unless it is requested .Sparse mode uses both source based trees and shortest path trees RP needs to know the recievers and senders. DR on lan segment send (S,G) register mess age to  and RP in turns reply regiester stop process and recievers on lan sengment send IGMP join and which will be converted to pim join(*,G) message to RP to form RPT tree.So pim join will traverse from receiver till RP every device will have (*,G) entry and from source till RP every device will have (S,G) entry.once RP knows about sender and reciver it will send (S,G) join request back to source and source would start sending the mutlicast traffic to RP then to receiver.then its up to the last hop reouter on reciever side for the optimation process weather it want to join directly to source using SPT bypassing RP.

Note -When we do debug only process switchd traffic is debug if we want to debug the data plane traffic then we need to disable cef (no ip route cache),if we change the unicast routing it will also change the mutlicasting routing,To change the unicast routing we can also use Ip mroute command.

Source based tree- tree is bulid based on shortest path from reciver till sender. shared tree -tree from sender to RP and then RP till receiver.

To check RP configured on each transient router -sh ip pim rp mapping RP can be assigned staticaly (ip pim rp address ) or dynamically ( auto RP and BSR)

Auto RP -uses two data plane mutlicast address (224.0.1.39) advertised by routers willing to become RP to mapping agents , 224.0.1.40- chooses the RP and advertised to rest of routers for RP information.

To stay on shared tree rather than SPT ( ip pm spt-threshold infinity)

Sparse-dense-mode -ANY group for which we have RP assigned used sparse mode for other uses dense mode.

RPF check is used for loop free path in mutlicast data plane ,AS per RPF check if the mutlicast packet is received on incoming interface router will check the unicast routing for source and that matches the incoming interface RPF check Passes else fail.

Once the mutlicast routing table is populated router always prefer (S,G) over (*,G) and in muticast routing table we have incoming interfaces and OIL for outgoing intefrcae list if the RPF check passes mutilcast traffic is send across all interfaces in OIL.

On multicast router -sh ip igmp group -- shows which multicast group is active on ethernet and which receiver has joined the group

To determine which router is IGMP querier router - sh ip igmp interface EO

We can manauly tune the query interval and query max response time - query interval - ip igmp query interval 120 (default 60 sec) respose time - ip igmp query-max-response-time 20 (default 10 sec)

IOS command to support which version of IGMP is - Ip igmp version 1/2

ip igmp join group ip igmp static group
 * Test commands for IGMP

for sparse mode we need to assgn RP - ip pim rp address x.x.x.x

inorder to check if there are any rp mapping - sh ip pim rp mappings

Inoder to check for mutlicating packet conuters- sh ip mroute counters

In sparse mode there is SPT switch over shorted path tree

for the SPT threshold we can set the threshold on DR muticast router that is receiving the IGMP join request in gloabl config mode ip pim spt threshold (vlaue)- Value is volume of multicast feed

if the Rpf check is failing we can still have interface to forward multicase by static mrouter ( ip mroute server mask next hop address )