Here is brief information about ip-helper address. If your DHCP server is located remotely, your local DHCP client might not get IP address due to broadcasting traffic block by router.
By default, routers drop all broadcast packets sent through them. Because DHCP clients use BOOTP packets, which are broadcasted to all hosts (255.255.255.255), they will be dropped by router TK1. The “ip helper-address” command enables the router to forward these BOOTP broadcast packets to a specific host, as specified by the address following the “ip helper-address” command. Note that this command must be placed on the router’s interface that is receiving the broadcast packets from the hosts, which is E0 of the TK1 router.
Speed mismatching issues may result in no connectivity. However, issues withauto-negotiation of duplex generally do not result in link establishment issues. Instead, auto-negotiation issues mainly result in performance-related issues. The most common problems when investigating NIC(Network Interface Card) issues deal with speed and duplex configuration. The table below summarizes all possible settings of speed and duplex for FastEthernet NICs and switch ports.
LAN 
