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IP-Helper

Oron Yaniv
Level 1
Level 1

Hi All,

i am asking my self how IP-helper work?

how IP helper differentiate between services?

 

for example, when a packet of DHCP request riching the helper, base on which packet`s field the helper deciding that this packet is DHCP? (base on ports/UDP, Payload or Layer 2 B.C etc.) 

 

 

Thanks,

Oron Yaniv

1 Accepted Solution

Accepted Solutions

luis_cordova
VIP Alumni
VIP Alumni

Hi @Oron Yaniv,

 

The DHCP discover packets are identified by the port number associated with the DHCP service (UDP: source port = 68; destination port = 67).

These packets are sent with the broadcast destination address, but if a DHCP server is not found in the local network, the ip helper-address command changes the destination ip broadcast by a unicast destination ip (the one you indicate after the command ).
With this, it is possible for the packet to reach a DHCP server outside the broadcast domain.

 

Regards

 

 

View solution in original post

1 Reply 1

luis_cordova
VIP Alumni
VIP Alumni

Hi @Oron Yaniv,

 

The DHCP discover packets are identified by the port number associated with the DHCP service (UDP: source port = 68; destination port = 67).

These packets are sent with the broadcast destination address, but if a DHCP server is not found in the local network, the ip helper-address command changes the destination ip broadcast by a unicast destination ip (the one you indicate after the command ).
With this, it is possible for the packet to reach a DHCP server outside the broadcast domain.

 

Regards