Scenario: ABC corporation and XYZ company has merged into one huge organization known as EFG. Your employer company – MTA has been engaged to come out a solution to merge the IT departments of both companies without changing the existing corporate IP addresses and existing softwares. Two departments reside on different network, so in order for data to traverse across each other layer 3 devices are required, EFG only accepts Cisco routers or Cisco MLS to be the layer3 devices. The above diagram is the rough logical diagram that described part of the network.
A problem arises, softwares reside in 192.168.100.0/24 are legacy softwares which could only do unicast and broadcast, by default broadcast will not be forwarded to another subnet by a router, you are tasked by your employer – MTA to come out a feasible solution to this problem, a proof of concept is required to demonstrate the feasibility.
R1’s configuration:
R1(config)#ip multicast-routing
R1(config)#int fa0/0
R1(config-if)#description Broadcast source interface
R1(config-if)#ip address 192.168.100.1 255.255.255.0
R1(config-if)#no shut
R1(config-if)#ip pim dense-mode
R1(config-if)#ip directed-broadcast
R1(config-if)#ip multicast helper-map broadcast 239.5.5.5 mcxlate
R1(config-if)#exit
R1(config)#ip forward-protocol udp 65000
R1(config)#ip access-list extended mcxlate
R1(config-ext-nacl)#permit udp 192.168.100.0 0.0.0.255 any eq 65000
R1(config-ext-nacl)#exit
R1(config)#ip dhcp pool bcs-pool
R1(dhcp-config)#network 192.168.100.0 /24
R1(dhcp-config)#default-router 192.168.100.1
R1(dhcp-config)#lease 0 5 0
R1(dhcp-config)#exit
R1(config)#ip dhcp excluded-address 192.168.100.1
R1(config)#ip route 172.16.0.0 255.255.255.0 172.30.100.2
R1(config)#int fa0/1
R1(config-if)#ip address 172.30.100.1 255.255.255.0
R1(config-if)#no shut
R1(config-if)#ip pim dense-mode
R2’s Configuration:
R2(config)#ip multicast-routing
R2(config)#ip forward-protocol udp 65000
R2(config)#ip access-list extended bcxlate
R2(config-ext-nacl)#permit udp 192.168.100.0 0.0.0.255 any eq 65000
R2(config-ext-nacl)#exit
R2(config)#int fa0/1
R2(config-if)#ip address 172.30.100.2 255.255.255.0
R2(config-if)#no shut
R2(config-if)#ip pim dense-mode
R2(config-if)#ip multicast helper-map 239.5.5.5 172.16.0.255 bcxlate
R2(config-if)#description Last hop router’s arrival interface
R2(config-if)#exit
R2(config)#int fa0/0
R2(config-if)#ip directed-broadcast
R2(config-if)#ip address 172.16.0.1 255.255.255.0
R2(config-if)#no shut
R2(config-if)#description Broadcast destination interface
R2(config-if)#exit
R2(config)#ip route 192.168.100.0 255.255.255.0 172.30.100.1
R2(config)#ip dhcp pool bcd-pool
R2(dhcp-config)#network 172.16.0.0 /24
R2(dhcp-config)#default-router 172.16.0.1
R2(dhcp-config)#lease 0 5 0
R2(dhcp-config)#exit
R2(config)#ip dhcp excluded-address 172.16.0.1
Credits: From learningnetwork.cisco.com – Brian and Jared.
From supportforums.cisco.com Peter Paluch
Reference (the best source): http://www.cisco.com/en/US/docs/ios/ipmulti/configuration/guide/imc_inter_mc_helper_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1056647
ip directed-broadcast command is necessary for the router to process the incoming broadcast packet, if this command is not included then the router will drop the incoming broadcast and hence broadcast will not be translated into multicast.
ip forward-protocol udp command is necessary for the router to process packet that is destined for udp <port number>
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