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I have a topology like below, wherein 2 subnets with address 192.168.0.0/24 and 192.168.1.0/24 are connected to a single router, Router0.

enter image description here

Now i want to send a directed broadcast from PC0 on subnet 192.168.0.0/24 to subnet 192.168.1.0/24. When i try doing it, it does not work as expected.

When i ping 192.168.1.255 from PC0, below is reply i get. The packet is not going past Router0's interface gigabitethernet0/0 at all!

C:>ping 192.168.1.255

Pinging 192.168.1.255 with 32 bytes of data:

Reply from 192.168.0.1: bytes=32 time=1ms TTL=255
Reply from 192.168.0.1: bytes=32 time<1ms TTL=255
Reply from 192.168.0.1: bytes=32 time<1ms TTL=255
Reply from 192.168.0.1: bytes=32 time=1ms TTL=255

Ping statistics for 192.168.1.255: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds: Minimum = 0ms, Maximum = 1ms, Average = 0ms

I understand that by default directed broadcast is disable on most of the routers. I could confirm the same by executing the below command-

Router#show ip interface gigabitethernet0/0 | include broadcast
Directed broadcast forwarding is disabled

So it needs to be enabled.

I followed few links and understood that i need to execute the command

ip directed-broadcast

So i tried as below-

Router#config terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#interface gigabitethernet0/0
Router(config-if)#ip directed-broadcast

                 ^ % Invalid input detected at '^' marker.  

Router(config-if)#

Looks like the router is not recognizing the command itself.

If I execute the command ip ? to see the supported arguments for ip command, it lists as below-

Router(config-if)#ip ?
  access-group     Specify access control for packets
  address          Set the IP address of an interface
  authentication   authentication subcommands
  flow             NetFlow Related commands
  hello-interval   Configures IP-EIGRP hello interval
  helper-address   Specify a destination address for UDP broadcasts
  mtu              Set IP Maximum Transmission Unit
  nat              NAT interface commands
  ospf             OSPF interface commands
  proxy-arp        Enable proxy ARP
  split-horizon    Perform split horizon
  summary-address  Perform address summarization

And looks like there is no directed-broadcast argument support!

Could someone please help me, how should I go ahead in enabling directed broadcast feature in the router?

  • What IOS version are you running? – user36472 Mar 21 '18 at 7:48
  • What is your configuration on interface gigabitethernet0/0? Could you post a show running config? – user36472 Mar 21 '18 at 7:56
  • @Cown: IOS version info - Cisco IOS Software, C1900 Software (C1900-UNIVERSALK9-M), Version 15.1(4)M4, RELEASE SOFTWARE (fc2) – Darshan L Mar 21 '18 at 8:38
  • @Cown: interface GigabitEthernet0/0 ip address 192.168.0.1 255.255.255.0 duplex auto speed auto ! interface GigabitEthernet0/1 ip address 192.168.1.1 255.255.255.0 duplex auto speed auto ! – Darshan L Mar 21 '18 at 8:40
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    Packet Tracer only supports a subset of IOS (enough for CCNA). You will need something with real IOS to get all the features. Directed broadcast is a giant security hole that should be avoided, so it is not included in Packet Tracer. – Ron Maupin Mar 21 '18 at 14:22
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The command you mentioned above it is not supported by Packet Tracer. Packet Tracer will not provide you all the features of a Router. For Routing you can use GNS3 which is the best software for routing and you can download it, as freeware.

In real equipment, it enables a port to send traffic to a host address with all ones. This reaches all hosts on that subnet. For example we could have an interface with address 192.168.1.1/24. If we enable directed-broadcast and sent a packet to 192.168.1.255, it will be broadcasted to all hosts on that interface. It will use a destination Mac address of FF-FF-FF-FF-FF-FF.

  • Are u sure that packet tracer doesnt support directed broadcast? Or are you inferring from the results? – Darshan L Mar 21 '18 at 8:45
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    @DarshanL it is not supported, I checked Cisco Support forums. – user36472 Mar 21 '18 at 12:07
  • supportforums.cisco.com - Is this the forum, you used, and we need to use to get clarification on Cisco IOS? Would you mind sharing me the link where you got confirmation? Just for my reference, I'm not doubting. – Darshan L Mar 21 '18 at 14:35
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    @DarshanL sorry i forgot to post link: learningnetwork.cisco.com/thread/36443 – user36472 Mar 21 '18 at 16:54

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