Accton Technology ES4710BD manual Introduction to Dvmrp

ES4710BD 10 Slots L2/L3/L4 Chassis Switch

correctness must be ensured.

—PIM-SM protocol requires the support of RP and BSR. So “show ip pim bsr-router” command should be run first for BRS information, if no BSR exists, then the unicast route to BSR should be checked.

—Use the “show ip pim rp” command to verify RP information is correct. If no RP information is displayed, the unicast route should be checked, too.

If PIM-SM problems persist after the above-mentioned procedures, please run debugging commands such as “debug ip pim” / “debug ip pim bsr”, and copy the output debug information in 3 minute and send the information to Edge-Core technical service center.

19.5DVMRP

19.5.1Introduction to DVMRP

Distance Vector Multicast Routing Protocol (DVMRP) is a dense mode multicast routing protocol. It employs a RIP like route exchange mechanism to establish a forwarding broadcast tree for each source, then a truncated broadcast tree (short path tree to the source) will be created by dynamic pruning/grafting. Reverse path forwarding (RPF) is used to decide whether multicast packet should be forwarded to the downstream nodes.

The following are some important DVMRP features:

1.The route exchange process determining RPF information is based on distance vectors (in the way similar to RIP)

2.Route exchange occurs periodically (every 60 seconds by default)

3.Maximum TTL = 32 hops (rather than the 16 hops in RIP)

4.Mask included in route update packet, CIDR supported.

Comparing to unicast routing, the multicast routing is a reversed route (i.e., interest is in where the packet comes from instead of where it is going to). This is why the route table information in DVMRP is used to determine whether the incoming multicast packet is arriving at the correct interface. The packet is discarded if the interface is not correct to prevent multicast loop.

The test to determine whether a packet is arriving at the correct interface is called RPF check. When a multicast packet arrives at an interface, the DVMRP route table will be checked to decide the reverse path to the source network. If the interface at which the packet arrives is the interface to send unicast information to the source, then the RPF check is success and the packet is forwarded from all down stream interfaces. Otherwise, there may be something wrong, and the multicast packet is discarded.

Since not all switches support multicast, DVMRP provide support for tunneling multicast information. Tunneling is a method used between DVMRP switches separated by non-multicast routing switch(es). A tunnel acts as the virtual network between two DVMRP switches. The multicast packet is encapsulated in a unicast packet and destined to a multicast-enabled switch. DVMRP treats tunneling interface the same way as common physical interfaces.

If two or more switches are connected to a multi-egress network, multiple copies of a packet may be sent to the subnet. Therefore, a specific forwarder must be specified. DVMRP fulfills this by routing switch mechanism. When two switches in a multi-egress network are exchanging routing

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