Cisco CCNP / BCSI Test Tutorial: Broadcasts And The IP Helper-Tackle Command
Even though routers take and deliver broadcasts, they don't ahead them. This can be quite an issue any time a broadcast must reach a device for instance a DHCP or TFTP server that’s on 1 facet of the router with other subnets on the other aspect.
If a Laptop tries to Identify a DNS server which has a broadcast, the broadcast will likely be stopped from the router and won't ever get to the DNS server. By configuring the ip helper-address command about the router, UDP broadcasts for example this can be translated right into a unicast by the router, producing the conversation possible. The command should be configured over the 메이저사이트 interface that could be obtaining the broadcasts.
R1(config)#int e0
R1(config-if)#ip helper-address ?
A.B.C.D IP place tackle
R1(config-if)#ip helper-deal with one hundred.1.one.2
Now, you may be wondering if this command addresses all UDP companies. Sorry, you’re not obtaining off that easy! The command does ahead 8 typical UDP provider broadcasts, while.
TIME, port 37
TACACS, port forty nine
DNS, port fifty three
BOOTP/DHCP Server, port sixty seven
BOOTP/DHCP Shopper, port 68
TFTP, port sixty nine
NetBIOS identify service, port 137
NetBIOS datagram services, port 138
That’s about to deal with most situations exactly where the ip helper-handle command will be practical, but what about These cases wherever the broadcast you'll need forwarded will not be on this record? You can utilize the ip forward-protocol command so as to add any UDP port range to the listing.
Also, to eliminate protocols from your default list, utilize the no ip ahead-protocol command. In the following case in point, we’ll include the Network Time Protocol port on the forwarding list whilst eliminating the NetBIOS ports. Bear in mind, You can utilize IOS Assist to receive a list of commonly filtered ports!
R1(config)#ip ahead-protocol udp ?
<0-65535> Port amount
biff Biff (mail notification, comsat, 512)
bootpc Bootstrap Protocol (BOOTP) consumer (sixty eight)
bootps Bootstrap Protocol (BOOTP) server (sixty seven)
discard Discard (nine)
dnsix DNSIX security protocol auditing (195)
domain Domain Name Service (DNS, 53)
echo Echo (seven)
isakmp Net Security Affiliation and Important Administration Protocol (500)
cellular-ip Cell IP registration (434)
nameserver IEN116 name company (obsolete, 42)
netbios-dgm NetBios datagram service (138)
netbios-ns NetBios name service (137)
netbios-ss NetBios session provider (139)
ntp Network Time Protocol (123)
pim-vehicle-rp https://en.wikipedia.org/wiki/?search=토토사이트 PIM Auto-RP (496)
rip Routing Facts Protocol (router, in.routed, 520)
snmp Very simple Network Management Protocol (161)
snmptrap SNMP Traps (162)
sunrpc Sunlight Distant Technique Contact (111)
syslog Program Logger (514)
tacacs TAC Obtain Management Method (49)
speak Talk (517)
tftp Trivial File Transfer Protocol (sixty nine)
time Time (37)
who Who support (rwho, 513)
xdmcp X Screen Manager Manage Protocol (177)