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Cisco CCNP / BCSI Test Tutorial: Broadcasts And TheCisco CCNP / BCSI Examination Tutorial: Broadcasts Along with the IP Helper-Tackle CommandWhile routers take and make broadcasts, they don't forward them. This can be rather a problem whenever a broadcast should get to a tool for instance a DHCP or TFTP server that’s on a single side of the router with other subnets on the other facet. If a Computer makes an Home page attempt to Identify a DNS server which has a broadcast, the printed might be stopped with the router and won't ever get into the DNS server. By configuring the ip helper-tackle command within the router, UDP broadcasts including this could be translated into a unicast because of the router, making the interaction probable. The command should be configured around the interface which will be getting the broadcasts.R1(config)#int e0R1(config-if)#ip helper-tackle ? A.B.C.D IP spot deal withR1(config-if)#ip helper-address one hundred.one.one.twoNow, you may well be asking yourself if this command handles all UDP providers. Sorry, you’re not having off that quick! The command does ahead eight common UDP service broadcasts, while. TIME, port 37TACACS, port 49DNS, port fifty threeBOOTP/DHCP Server, port 67BOOTP/DHCP Client, port 68TFTP, port 69NetBIOS name service, port 137NetBIOS datagram support, port 138That’s likely to address most situations wherever the ip helper-tackle command will be valuable, but How about All those scenarios in which the broadcast you need forwarded isn't on this listing? You should use the ip forward-protocol command to include any UDP port selection on the record.On top of that, to eliminate protocols from the default record, make use of the no ip ahead-protocol command. In the following case in point, we’ll include the Network Time Protocol port to the forwarding checklist though taking away the NetBIOS ports. Bear in mind, You need to use IOS Assist for getting a list of typically filtered ports!R1(config)#ip ahead-protocol udp ? <0-65535> Port variety biff Biff (mail notification, comsat, 512) bootpc Bootstrap Protocol (BOOTP) consumer (sixty eight) bootps Bootstrap Protocol (BOOTP) server (67) discard Discard (9) dnsix DNSIX security protocol auditing (195) area Domain Identify Service (DNS, fifty three) echo Echo (7) isakmp Online Stability Association and Essential Management Protocol (five hundred) mobile-ip Cell IP registration (434) nameserver IEN116 name provider (out of date, forty two) netbios-dgm NetBios datagram provider (138) netbios-ns NetBios identify provider (137) netbios-ss NetBios session services (139) ntp Community Time Protocol (123) pim-vehicle-rp PIM Vehicle-RP (496) rip Routing Facts Protocol (router, in.routed, 520) snmp Basic Community Management Protocol (161) snmptrap SNMP Traps (162) sunrpc Solar Distant Method Phone (111) syslog Program Logger (514) tacacs TAC Entry Command Program (forty nine) chat Chat (517) tftp Trivial File Transfer Protocol (sixty nine) time Time (37) who Who company (rwho, 513) xdmcp X Display Manager Handle Protocol (177