Cisco CCNP/ BCSI Exam Tutorial: Broadcasts And The
Cisco CCNP/ BCSI Examination Tutorial: Broadcasts And The IP Helper-Address Command
While routers approve and produce programs, they do not ahead them. This can be rather a trouble when a program needs to get to a gadget such as a DHCP or TFTP server that gets on one side of a router with various other subnets beyond.
If a PC tries to find a DNS server with a program, the broadcast will be come by the router and will never ever reach the DNS web server. By setting up the ip helper-address command on the router, UDP programs such as this will be translated right into a unicast by the router, making the communication possible. The command should be set up on the user interface that will be receiving the broadcasts.
R1( config) #int e0
R1( config-if) #ip helper-address?
A.B.C.D IP destination address
R1( config-if) #ip helper-address 100.1.1.2
Now, you might be wondering if this command covers all UDP services. Sorry, you're not leaving that very easy! The command does onward 8 usual UDP service broadcasts, though.
TIME, port 37
DNS, port 53
BOOTP/DHCP Server, port 67
BOOTP/DHCP Customer, port 68
TFTP, port 69
NetBIOS name service, port 137
NetBIOS datagram service, port 138
That's mosting likely to cover most situations where the ip helper-address command will be useful, however what regarding those scenarios where the program you need sent is not on this list? You can make use of the ip forward-protocol command to include any kind of UDP port number to the list.
Additionally, to get rid of procedures from the default list, make use of the no ip forward-protocol command. In the following example, we'll include the Network Time Method port to the forwarding checklist while getting rid of the NetBIOS ports. Bear in mind, you can use iphone Aid to get a list of commonly https://www.bakermckenzie.com/en/people/c/cullen-daniel-f filteringed system ports!
R1( config) #ip forward-protocol udp?
<0-65535> Port number
biff Biff (mail notification, comsat, 512)
bootpc Bootstrap Method (BOOTP) client (68 )
bootps Bootstrap Method (BOOTP) web server (67 )
discard Discard (9 )
dnsix DNSIX safety method auditing (195 )
domain Domain Name Solution (DNS, 53)
echo Mirror (7 )
isakmp Internet Safety and security Association and Key Monitoring Method (500 )
mobile-ip Mobile IP registration (434 )
nameserver IEN116 name service (out-of-date, 42)
netbios-dgm NetBios datagram solution (138 )
netbios-ns NetBios name solution (137 )
netbios-ss NetBios session service (139 )
ntp Network Time Method (123 )
pim-auto-rp PIM Auto-RP (496 )
tear Routing Info Method (router, in.routed, 520)
snmp Simple Network Monitoring Method (161 )
snmptrap SNMP Catches (162 )
sunrpc Sunlight Remote Procedure Phone Call (111 )
syslog System Logger (514 )
tacacs TAC Accessibility Control System (49 Daniel CULLEN )
talk Talk (517 )
tftp Unimportant Data Transfer Procedure (69 )
time Time (37 )
that Who solution (rwho, 513)
xdmcp X Show Supervisor Control Protocol (177 )