MBGP – Why Is It Needed?

bgpmulticastpim

I've been working on some multicast protocols and I came across MBGP and I want to know why is it needed.
The way everyone uses MBGP is that they set up PIM in every routers, and for the inter domain protocol, they use MBGP.
I don't understand why can'g BGP forward these packets. It's not like multicast packets are different in forwarding than unicast. BGP is capable of forwarding every other packet, why not multicast? Why must we use MBGP?
Thanks

Best Answer

MBGP or Multiprotocol BGP extensions

The first BGP specification was published in 1989, well before IPv6 was created and only shortly after multicast was added to IPv4. Even BGP-4 doesn’t support IPv6, multicast or VPNs. Until 1998, that is, when RFC 2283 introduced the multiprotocol extensions. These allow BGP to handle routing information for arbitrary "address families". In practice, an address family is associated with a specific network layer protocol, such as IPv4, IPv6, IPX or AppleTalk. There are also Address Family Identifier (AFI) numbers for tunneling mechanisms such as VPNs and MPLS. A Subsequent Address Family Identifier (SAFI) further specifies unicast versus multicast or more tunneling options.

When routers make a BGP connection, they exchange the AFIs and SAFIs they’re prepared to exchange routing information for. If the two routers agree on those, they’ll send UPDATE messages containing the regular path attributes with the prefixes (also known as Network Layer Reachability Information, NLRI) and next hops encoded in an MP_REACH_NLRI attribute. Withdrawn routes are encoded in an MP_UNREACH_NLRI attribute.

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KEMP Load Balancers – UCARP (VRRP) Multicast MAC Address Issue

I was able to resolve the issue. On the Kemp (with HA pair) you have the option of using a "Virtual MAC Address". If this box isn't checked, then the MAC of a load balancer VIP is that of the physical interface of the active Kemp unit. If this box is checked, then the MAC address of the VIP is a VRRP MAC. As you mentioned above the VRRP RFC states that the MAC being "00:00"{blah} with the last octet being the Router ID. The default Kemp HA [router] ID is 01. On my Powerconnects using Firmware 5.1.x.x I'm not using VRRP but I ran some traces and determined that the Powerconnect will drop a VRRP frame if the router ID is the same as itself. They do this EVEN if VRRP isn't configured and in that mode they default to 01. So changing the Kemp HA router ID to something like 22 (0x16) resulted in everything working.

Vlan – Setting up PIM Sparse mode

My questions are:

Should we setup on our core network switch OSPF with a router ID of 1.1.1.1 and then not set any OSPF settings on any other switch?

OSPF is not necessary for this implementation.

Would PIM Sparse Mode only need to be enabled on the core switches or on all of the switches in the network?

Pim-SM needs to be enabled on each L3 interface on which you want to allow the multicast traffic. For example, if you wish to contain the traffic to Vlans 15 and 14, you would have to do the following on your core:

configure
ip multicast
ip igmp
ip pim sparse
interface vlan 14
ip igmp
ip pim
interface vlan 15
ip igmp
ip pim
exit

If you want the traffic to traverse all Vlans, then you will need the appropriate interface configuration under each Vlan. Your L2 switches will need IGMP snooping turned on (ideally on all interfaces via the global configuration).

configure
ip igmp snooping 
bridge multicast filtering

For a very basic multicast setup like this, these should be the only features that you would need.

Best Answer

Related Solutions

KEMP Load Balancers – UCARP (VRRP) Multicast MAC Address Issue

Vlan – Setting up PIM Sparse mode

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