Switching

hi,

    i need to parse the output for show route command and following questions related to Multicast 

1. 

224.0.0.2/32 *[PIM/0] 33w6d 16:43:25
MultiRecv

I see this output under inet.0  but inet.0 is for Unicast routes . I did not get why this entry was present udner inet.0

2.  How do I interpret this entry .  I do not have much exp in Multicast. also if you could direct me to  a link which explains about the interpretation of following outout will be helpful.

239.255.250.250,130.126.163.230/32*[PIM/105] 15w1d 09:06:59
Multicast (IPv4)

can some one help me with these questions.

Hi Jiten,

1. The 224.0.0.2 destination is the AllRoutersMulticast address, which appears in the inet.0 table when you enable PIM on your router.  As the name implies, it is used to discover other multicast routers on a subnet - the router needs this route in inet.0 in order to send this traffic.  A multicast routing protocol like PIM is used to exchange multicast groups from other subnets (which are placed into inet.1 once qualified).  If you enable OSPF on your router, you will see 224.0.0.5/32 appear as well, and 224.0.0.9 for RIP, which are used in the same way.

2. I'm assuming that route is from inet.1?  What it is telling you is that the Multicast Group 239.255.250.250 has been learnt via PIM, and 130.126.163.230 is either an active source of traffic for that group.

thanks Ben.  Just was curious to know more about

1. So the AllRoutersMulticast address helps to get connected to other multicast routers, but  does this help further to learn about the different multicast groups on the subnets attached to other multicast routers and fill table inet.1

 2.  Also in this entry :

224.0.0.2/32 *[PIM/0] 33w6d 16:43:25
MultiRecv

what does "MultiRecv" mean ?

Hi Jiten,

No - PIM is the protocol that is used to learn other multicast routes.  The AllMulticastRouters entry in inet.0 loads an entry in the forwarding table that allows the local device to send traffic to all multicast routers on that destination address (224.0.0.2) - think of it as enabling this switch/router to *use* multicast in the local subnet rather than learning routes from other devices.

The MultiRecv option is Junos's way of telling you that there are multiple receivers for the 224.0.0.2 address and they could be out some or all of the attached interfaces.  For example - if this was a router with 3 interfaces in three different subnets, but you had PIM enabled on all three interfaces, the router would send traffic to 224.0.0.2 out all three interfaces attempting to find other multicast routers with which to form PIM adjacencies.