can mpls support multicast?

[rachelhor]

Hi,

Can mpls support multicast packets?

Meaning, can multicast packets be sent to destinations over mpls network?

If so, how does it work?

I read in this forum somewhere that someone mentioned mpls and multicast can co-eixt.

What exactly does it mean?

Thanx!

[Harold Ritter]

Multicast traffic can not currently be forwarded down an LSP. By co-exist we mean that you can have an SP core network running both MPLS an Multicast but they run independently from each other.

Hope this helps,

[rachelhor]

hi hritter and romccallum,

I'm still confused

I read book that says "In LAN environment, labeled packets carrying multicast layer 3 packets use ethertype value 8848 hex. These ethertype values can be used directly on Ethernet media"

From the above sentence, does it mean that multicast packets still can be labelled and sent over mpls?

Another question, where is this ethertype value contained? Is it contained inside the layer 2 header or inside the shim header (label)?

thanx!

[Harold Ritter · Accepted solution]

Provisions are there for multicast to be transported by MPLS. Unfortunately it is not supported yet.

The ethertype value is part of the L2 header. The shim header is 32 bits long and comprises the following fields:

Label value: 20 bits

expirimental bits: 3 bits

bottom of stack bit: one bit

TTL: 8 bits

Hope this helps,

[rachelhor]

oh i see!

think i am clearer now

so all those technical documents/notes about multicast by mpls from ietf and other companies etc found on web-site, are just theory?

thanx a lot!

:)

[Harold Ritter]

I know thar there is work being done with IOS to support it. I don't know about other vendors implementation.

As far as IETF is concerned, there is currently no RFC for mcast over MPLS. The only thing I'm aware of is a the following draft to support mcast over TE tunnels:

http://www.simpleweb.org/ietf/internetdrafts/complete/draft-raggarwa-mpls-p2mp-te-02.txt

This draft is currently expired.

Hope this helps,

[rachelhor]

thank you very much

I have one "last" question

So, if I have a network of cisco routers with mpls configured (so this means mpls network right?), and my ingress edge LSR receives a multicast IP packet.

How does my ingress edge LSR sent this multicast IP packet to its destinations over this network where all the routers have mpls enabled?

Am I right to say that

- this multicast IP packet will not be tagged

- and this multicast IP packet will be sent over the network (routers with mpls enabled) using layer 3 routing protocol, eg OSPF ??

[Harold Ritter]

In the MPLS network you can either use native multicast or you could implement mVPN on the PE routers if you implement MPLS VPN. mVPN uses native multicast in the core to encapsulate the multicast messages coming from a CE router and to forward these messages to PEs containing the same VRF.

For more information on mVPN, see the following link:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t13/ftmltvpn.htm

Hope this helps,

[rachelhor]

thanx a lot!

:-)

[romccallum]

In other words Multicast within a VPN works absolutely fine. It just doesnt get label switched across the MPLS network and is just Native IP (multicast).