Cisco CCNP / BCSI Exam Tutorial: Broadcasts Plus the IP Helper-Tackle Command
When routers acknowledge and deliver broadcasts, they don't forward them. This can be pretty an issue each time a broadcast really should get to a device such as a DHCP or TFTP server that’s on one particular aspect of the router with other subnets on the other facet.
If a Computer system attempts to locate a DNS server using a broadcast, the published will be stopped via the router and will never get for the DNS server. By configuring the ip helper-tackle command within the router, UDP broadcasts for instance this may be translated right into a unicast by the router, producing the interaction probable. The command need to be configured within the interface which will be obtaining the broadcasts.
R1(config)#int e0
R1(config-if)#ip helper-deal with ?
A.B.C.D IP desired destination tackle
R1(config-if)#ip helper-address a hundred.one.1.two
Now, you might be wanting to know if this command addresses all UDP solutions. Sorry, you’re not obtaining off that straightforward! The command does forward eight common UDP company broadcasts, however.
TIME, port 37
TACACS, port forty nine
DNS, port 53
BOOTP/DHCP Server, port 67
BOOTP/DHCP Shopper, port sixty eight
TFTP, port sixty nine
NetBIOS name services, port 137
NetBIOS datagram assistance, port 138
That’s about to protect most scenarios where by the ip helper-deal with command will likely be handy, but what about All those scenarios where the broadcast you would like forwarded will not be on this list? You need to use the ip forward-protocol command so as to add any UDP port range on the list.
Furthermore, to eliminate protocols within the default listing, make use of the no ip ahead-protocol command. In the following example, we’ll increase the Network Time Protocol port to your forwarding checklist when eradicating the NetBIOS ports. Try to remember, You should utilize IOS Enable for getting an index of normally filtered ports!
R1(config)#ip forward-protocol udp ?
<0-65535> Port range
biff Biff (mail http://www.bbc.co.uk/search?q=토토사이트 notification, comsat, 512)
bootpc Bootstrap Protocol (BOOTP) customer (sixty eight)
bootps Bootstrap Protocol (BOOTP) server (67)
discard Discard (nine)
dnsix DNSIX safety protocol auditing (195)
domain Domain Title Assistance (DNS, 53)
echo Echo (seven)
isakmp Net Safety Affiliation and Key Management Protocol (five hundred)
cell-ip Cellular IP registration (434)
nameserver IEN116 name company (out of date, 42)
netbios-dgm NetBios datagram assistance (138)
netbios-ns NetBios name assistance (137)
netbios-ss NetBios session support (139)
ntp Community Time Protocol (123)
pim-automobile-rp PIM Auto-RP (496)
rip Routing Facts Protocol (router, in.routed, 520)
snmp Uncomplicated Community Administration Protocol (161)
snmptrap SNMP Traps (162)
sunrpc Sun Remote Process 토토사이트 Connect with (111)
syslog Method Logger (514)
tacacs TAC Access Management Method (forty nine)
speak Converse (517)
tftp Trivial File Transfer Protocol (69)
time Time (37)
who Who assistance (rwho, 513)
xdmcp X Display screen Supervisor Management Protocol (177)