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MX DHCP relay - how to do a replacement for forwarding-options helpers bootp ?

  • 1.  MX DHCP relay - how to do a replacement for forwarding-options helpers bootp ?

    Posted 21 days ago

    Hi,

    I probably need to move from pefectly working, but legacy forwarding-options/helpers/bootp to modern forwarding-options/dhcp-relay on our MX104/MX204 router to support DHCP relay operation.

    I have a router with multiple routing instances and multiple separate DHCP servers and I am a little bit scared about DHCP relay implementation using forwarding-options/dhcp-relay.

    Here is my current working DHCP relay config:

    forwarding-options {
    helpers {
    	bootp {
    		relay-agent-option;
    		server 192.168.1.5 routing-instance RI_XXX;
    		server 192.168.1.6 routing-instance RI_XXX;
    
    		interface {
    			xe-0/1/2.799 {
    				server 192.168.99.95 routing-instance RI_YYY;
    				server 192.168.99.96 routing-instance RI_YYY;
    			} 
    ...
    etc.				
    }

    My interfaces and RE firewall filter looks like:

    interfaces {
        lo0 {
            unit 0 {
                family inet {
                    filter {
                        input fw_router_mgmt;
                    }
                    address 127.0.0.1/32;             
                }
            }
        }
    }	
    	
    firewall {
    	family {
    	inet {
    	
    	filter fw_router_mgmt {
    		...
    		term 3 {
    			from {
    				source-address {
    					0.0.0.0/32;
    				}
    				destination-address {
    					255.255.255.255/32;
    				}
    				protocol udp;
    				port 67;
    			}
    			then accept;
    		}
    		...			
    	}}}
    }

    Everything works fine and there is no problem in IPv4 world.

    Now, I need to switch  to forwarding-options/dhcp-relay to be able to add support for IPv6 in the future. I have found Minimum DHCP Relay Agent Configuration article, but this is for SRX platform, not for MX.

    Summary of my requirements:

    • MX Router with multiple routing instances and working bootp helper, fortunately no IRB interfaces
    • No DHCP traffic inspection, snooping, no engineering - just forward DHCP frame from client to the DHCP server and back like bootp helper does.

    I saw few pieces of puzzle to disable unwanted things that can make it even more complicated:

    • use option called forward-only that should be used to disable almost all of the inspection features
    • use forwarding-options dhcp-relay no-snoop
    • use forwarding-options dhcp-relay forward-snooped-clients all-interfaces to permit traffic, because otherwise it could be dropped

    Please, if you have a simillar setup, I'd be glad for sharing a working piece of your config, something like "Minimum DHCP Relay Agent" above,  but for MX platform.

    Thank you for any feedback and support how to do the transition in no-horror way.