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requesting that the missing link-state PDU be transmitted. That routing device, in turn,

forwards the missing link-state PDU to the requesting routing device.

A PSNP is used by an IS-IS router to request link-state PDU information from a

neighboring router. A PSNP can also explicitly acknowledge the receipt of a link-state

PDU on a point-to-point link. On a broadcast link, a CSNP is used as implicit knowledge.

Like hello PDUs and CSNPs, the PSNP also has two types: Level 1 and Level 2.

When a device compares a CSNP to its local database and determines that a link-state

PDU is missing, the router issues a PSNP for the missing link-state PDU, which is returned

in a link-state PDU from the router sending the CSNP. The received link-state PDU is

then stored in the local database, and an acknowledgment is sent back to the originating

router.

Persistent Route Reachability

IPv4 and IPv6 route reachability information in IS-IS link-state PDUs is preserved when

you commit a configuration. IP prefixes are preserved with their original packet fragment

upon link-state PDU regeneration.

IS-IS Support for Multipoint Network Clouds

IS-IS does not support multipoint configurations. Therefore, when configuring Frame

Relay or Asynchronous Transfer Mode (ATM) networks, you must configure them as

collections of point-to-point links, not as multipoint clouds.

Installing a Default Route to the Nearest Routing Device That Operates at Both IS-IS Levels

When a routing device that operates as both a Level 1 and Level 2 router (Router B)

determines that it can reach at least one area other than its own (for example, in Area

Y), it sets the ATTACHED bit in its Level 1 link-state PDU. Thereafter, the Level 1 router

(Router A) introduces a default route pointing to the nearest attached routing device

that operates as both a Level 1 and Level 2 router (Router B). See Figure 26 on page 540.

Figure 26: Install Default Route to Nearest Routing Device That Operates

at Both Level 1 and Level 2

ACX Series Universal Access Router Configuration Guide

Juniper ACX2000 Configuration Guide

Other manuals for Juniper ACX2000