Juniper Networks IDP SERIES IDP250 - Manual (Page 25)

is in a state in which it cannot inspect the traffic. With NICs Off configured, in the event
of failure or graceful shutdown, the interfaces are turned off and the IDP Series appliance
becomes a point of failure. If your network design includes redundant network paths, you
can configure your routers to detect the downed IDP Series interfaces and choose an
alternate path.
Peer Port Modulation
The peer port modulation (PPM) feature supports deployments where routers monitor
link state to make routing decisions. In these deployments, a router might be set to monitor
link state on only one side of the IDP Series appliance. Suppose, for example, the router
monitors only the inbound interface. Suppose the inbound interface remains up but the
outbound interface goes down. The router watching the inbound link would detect an
available link and forward traffic to the IDP Series appliance. Traffic would be dropped
at the point of failure—the outbound link. PPM propagates a link loss state for one traffic
interface to all interfaces in the IDP Series virtual router.
When PPM is enabled, a PPM daemon monitors the health of IDP Series traffic interfaces
belonging to the same virtual router. If a traffic interface loses link, the PPM process turns
off any associated network interfaces in the same virtual router so that other network
devices detect that the virtual router is down and route around it. For example, assume
you have enabled PPM and configured IDP Series virtual routers as shown in
Figure 8 on
page 13 .
Figure 8: Peer Port Modulation
Suppose there is a network problem and eth3 goes down. The PPM daemon detects this
and turns off the other interface in vr0: eth2. The interfaces in vr1, vr2, and vr3 are
unaffected. After the you fix the problem with eth3, the PPM daemon detects this, and
turns on eth2.
13 Copyright © 2012, Juniper Networks, Inc.
Chapter 1: Hardware Overview