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Cisco CCNP/BCSI Exam Tutorial: Broadcasts And The IP Helper-Address Command

While switches acknowledge and create communicates, they don't advance them. This can be a significant issue when a transmission needs to get to a gadget, for example, a DHCP or TFTP worker that is on one side of a switch with different subnets on the opposite side.

In the event that a PC endeavors to find a DNS worker with a transmission, the transmission will be halted by the switch and will never get to the DNS worker. By designing the ip aide address order on the switch, UDP broadcasts, for example, this will be converted into a unicast by the switch, making the correspondence conceivable. The order ought to be designed on the interface that will get the transmissions.

R1(config)#int e0

R1(config-if)#ip aide address ?

A.B.C.D IP objective location

R1(config-if)#ip partner address 100.1.1.2

Presently, you might be contemplating whether this order covers all UDP administrations. Apologies, you're not getting off that simple! The order advances eight basic UDP administration communicates, however.

TIME, port 37

TACACS, port 49

DNS, port 53

BOOTP/DHCP Server, port 67

BOOTP/DHCP Client, port 68

TFTP, port 69

NetBIOS name administration, port 137

NetBIOS datagram administration, port 138

That will cover most situations where the ip assistant location order will be valuable, yet shouldn't something be said about those REET Notification 2021 circumstances where the transmission you need sent isn't on this rundown? You can utilize the ip forward-convention order to add any UDP port number to the rundown.

Also, to eliminate conventions from the default list, utilize the no ip forward-convention order. In the accompanying model, we'll add the Network Time Protocol port to the sending list while eliminating the NetBIOS ports. Keep in mind, you can utilize IOS Help to get a rundown of generally sifted ports!

R1(config)#ip forward-convention udp ?

Port number

biff (mail notice, comsat, 512)

bootpc Bootstrap Protocol (BOOTP) customer (68)

bootps Bootstrap Protocol (BOOTP) worker (67)

dispose of Discard (9)

DNSIX security convention evaluating (195)

space Domain Name Service (DNS, 53)

reverberation Echo (7)

isakmp Internet Security Association and Key Management Protocol (500)

portable ip Mobile IP enlistment (434)

nameserver IEN116 name administration (out of date, 42)

netbios-dgm NetBios datagram administration (138)

netbios-ns NetBios name administration (137)

netbios-ss NetBios meeting administration (139)

ntp Network Time Protocol (123)

pim-auto-rp PIM Auto-RP (496)

tear Routing Information Protocol (switch, in.routed, 520)

snmp Simple Network Management Protocol (161)

snmptrap SNMP Traps (162)

sunrpc Sun Remote Procedure Call (111)

syslog System Logger (514)

tacacs TAC Access Control System (49)

talk (517)

tftp Trivial File Transfer Protocol (69)

time (37)

who administration (rwho, 513)

xdmcp X Display Manager Control Protocol (177)

R1(config)#ip forward-convention udp 123

R1(config)#no ip forward-convention udp 137

R1(config)#no ip forward-convention udp 138

As should be obvious, the ip assistant location order helps work around the way that broadcasts aren't sent by switches as a matter of course, and on the off chance that you simply need to send a couple of transmission types, different sorts can be killed without any problem.


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