Cisco CCNP / BCSI Test Tutorial: Broadcasts As well as the IP Helper-Address Command
Even though routers take and generate broadcasts, they don't ahead them. This may be really a challenge every time a broadcast has to reach a device like a DHCP or TFTP server that’s on 1 aspect of the router with other subnets on another side.
If a Laptop attempts to Identify a DNS server which has a broadcast, the published might be stopped from the router and won't ever get on the DNS server. By configuring the ip helper-deal with command over the router, UDP broadcasts for example this tends to be translated right into a unicast because of the router, building the conversation feasible. The command should be configured about the interface which will be obtaining the broadcasts.
R1(config)#int e0
R1(config-if)#ip helper-tackle ?
A.B.C.D IP vacation spot tackle
R1(config-if)#ip helper-handle one hundred.1.1.two
Now, you could be asking yourself if this command handles all UDP companies. Sorry, you’re not getting off that easy! The command does forward 8 common UDP support broadcasts, even though.
TIME, port 37
TACACS, port 49
DNS, port 53
BOOTP/DHCP Server, port 67
BOOTP/DHCP Shopper, port 68
TFTP, port http://www.bbc.co.uk/search?q=토토사이트 69
NetBIOS name services, port 137
NetBIOS datagram provider, port 138
That’s intending to include most situations wherever the ip helper-address command are going to be valuable, but How about These conditions where the printed you require forwarded will not be on this listing? You need to use the ip ahead-protocol command to incorporate any UDP port variety on the listing.
Also, to remove protocols through the default list, use the no ip ahead-protocol command. In the next illustration, we’ll insert the Network Time Protocol port for the forwarding list although removing the NetBIOS ports. Keep in mind, You should utilize IOS Help to acquire a list of typically filtered ports!
R1(config)#ip ahead-protocol udp ?
<0-65535> Port amount
biff Biff (mail notification, comsat, 512)
bootpc Bootstrap Protocol (BOOTP) consumer (68)
bootps Bootstrap Protocol (BOOTP) server (sixty seven)
discard Discard (9)
dnsix DNSIX protection protocol auditing (195)
domain Domain Name Company (DNS, fifty three)
echo Echo (seven)
isakmp Internet Security Association and Vital Administration Protocol (five hundred)
cellular-ip Mobile IP registration (434)
nameserver IEN116 identify provider (obsolete, forty two)
netbios-dgm NetBios datagram provider 사설사이트 (138)
netbios-ns NetBios title provider (137)
netbios-ss NetBios session support (139)
ntp Community Time Protocol (123)
pim-car-rp PIM Vehicle-RP (496)
rip Routing Data Protocol (router, in.routed, 520)
snmp Simple Community Management Protocol (161)
snmptrap SNMP Traps (162)
sunrpc Solar Remote Method Connect with (111)
syslog Procedure Logger (514)
tacacs TAC Access Handle Program (49)
communicate Discuss (517)
tftp Trivial File Transfer Protocol (69)
time Time (37)
who Who company (rwho, 513)
xdmcp X Show Supervisor Handle Protocol (177)