 | Copyright © 2008, Juniper Networks, Inc. All rights reserved. Trademark Notice. | |
To discover LDP peers that are not directly connected, LSRs periodically send out LDP targeted hellos to potential peers. The targeted hellos are contained in UDP packets that are addressed to the well-known LDP discovery port, 646. The destination address for the ports is a specific targeted address. LDP sends targeted hellos when you configure one or more IP addresses in a targeted-hello send list. In a layer 2 Martini circuit, targeted hellos are automatically sent to the remote PE neighbor (the base tunnel endpoint). See Configuring Layer 2 Services over MPLS for information about layer 2 circuits.
The targeted hello includes the LDP identifier for the label space that the LSR intends to use. In the JUNOSe implementation, this is always the platform label space, so the LDP identifier specifies the LSR ID and a value of 0 for the label space. The targeted hello also includes other information, such as the targeted-hello hold time, which is configured globally. The targeted-hello hold time configures how long an LSR waits for another targeted hello from its peer before declaring the adjacency to be down.
Unlike basic discovery, where hellos are sent by all LSRs, extended discovery is initiated by one LSR that targets a specific LSR. The initiating LSR periodically sends targeted hellos to the targeted LSR. The targeted LSR then determines whether to respond to the targeted hello or to ignore it. If the targeted LSR responds to the sender, it does so by periodically sending targeted hellos to the initiating LSR. The exchange of targeted hellos constitutes a hello adjacency for the two LSRs.
Targeted hello values are configured globally with the mpls ldp targeted-hello holdtime, mpls ldp targeted-hello interval, mpls ldp targeted-hello receive list, and mpls ldp targeted hello send list commands.
| Copyright © 2008, Juniper Networks, Inc. All rights reserved. Trademark Notice. | |