Junos: Configuring bootp helper for all interfaces

This article explains a caveat when configuring bootp helper to forward BOOTP requests received on a specific interface to one server while all other interfaces forward BOOTP requests to another server.

Take, for example, the following configuration:

MX@root> show configuration forwarding-options helpers bootp 
relay-agent-option;
interface {
    irb.3612 {
        server 1.1.1.1;
    }

    all {
        server 2.2.2.2;
    }
}

With the previous configuration, it will be observed that DHCP requests received on interface irb.3612 will be forwarded to server 2.2.2.2 rather than 1.1.1.1.

However, the behavior will not be seen when the configuration is as follows:

MX@root> show configuration forwarding-options helpers bootp 
relay-agent-option;
interface {
    all {
        server 2.2.2.2;
    }
    irb.3612 {
        server 1.1.1.1;
    }
}

The observed behavior is related to the manner in which the BOOTP code parses the configuration.

For such a scenario, it is recommended to eliminate the “interface all” configuration stanza and use a configuration similar to the one shown as follows. With the following configuration, the system will automatically forward BOOTP requests to the server configured directly under the helpers bootp configuration stanza, while all BOOTP requests received on the explicitly configured interface will be forwarded to another server:

MX@root> show configuration forwarding-options helpers bootp 
relay-agent-option;
server 2.2.2.2;

interface {
     irb.3612 {
        server 1.1.1.1;
    }
}

In above configuration, all DHCP requests received on irb.3612 will be forwarded to 1.1.1.1 and requests received on all other interfaces will be forwarded to 2.2.2.2.

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