Product Affected

All releases of JUNOS Internet Software released prior to February 12, 2003 are affected.
Medium

Problem

Packets are improperly forwarded when destined to the broadcast or network address of a nonbroadcast point-to-point interface. If the router at the far end of the link is also susceptible to this problem, it may forward the packets back onto the link, causing the packets to loop and to consume bandwidth until their TTLs expire.

Solution

JUNOS software can now optionally install two /32 static routes with a discard next hop on point-to-point links configured with a /30 prefix length. To enable this option, include the no-targeted-broadcast statement at the [edit interfaces unit <n> family inet] hierarchy level.

JUNOS Releases 5.5, 5.6, and later built on or after February 13, 2003 contain the new configuration option. Juniper Networks recommends that you either install an updated release and configure the no-targeted-broadcast statement, or that you implement one of the two workarounds as soon as possible.

An immediate workaround is to create two /32 discard static routes for the broadcast and network addresses on each point-to-point interface. For example, if the link IP subnet is 1.1.1.0/30, use the following configuration-mode commands: 

      set routing-options static route 1.1.1.3/32 discard
      set routing-options static route 1.1.1.0/32 discard
An alternate workaround is to reconfigure each point-to-point link. You can reconfigure each link to use a /31 prefix, or you can reconfigure each link to use a /32 prefix if you also configure the remote end's destination address

Severity Assessment

This condition presents an opportunity for an outsider to launch a denial-of-service (DoS) attack against the provider’s network. The attacker need only identify a vulnerable point-to-point link within the provider’s network; the traceroute utility can be used to easily identify such links.