listing of the transmit password is not in the receive password database, the packet
is dropped. There are three types of transmit and receive passwords: domain, area,
and circuit.
A domain password provides security for L2 routing information. An area password
provides security for L1 routing information. A circuit password provides security for
IS-IS hello messages.
ESIS Protocol
The ES-IS protocol enables ESs and ISs attached to the same subnetwork to
dynamically discover each other’s existence and availability. This information also
permits ESs to obtain information about each other without an available IS.
Route redirection information enables an IS to inform an ES of a better route when
forwarding NPDUs to a particular destination. For example, a better route could be
another IS on the same subnetwork as the ES, or the destination ES located on the
same subnetwork.
Hello Message
Addressing information is passed on to ESs and ISs through hello messages.
A local configuration timer (CT) and a holding timer (HT) is present on each ES and
IS. Each time the CT expires, a hello message is multicast on the LAN. When the
hello message is received, the recipient sets its HT value according to the value
transmitted in the HT field of the message. The recipient is expected to retain this
information until the HT expires to ensure correct operation of the ES-IS protocol.
End System Hello (ESH) Message
The ESH message is multicast from the ES to all L1 ISs when its local CT expires.
The ES constructs this message to inform an IS of any NSAPs that it serves. Upon
receiving this message the IS extracts the NSAP and SNPA information and stores
the pair in its L1 routing table, replacing any other information currently stored
there.
Intermediate System Hello (ISH) Messages
The ISH message is multicast to all adjacent ESs when its local CT expires. The IS
constructs this message to inform the ES of its NET. Upon receiving of this
message, the ES extracts the NET and SNPA information and stores the pair in one
of its local routing tables, replacing any other information currently stored there.
X.25 Circuits for DECnet V/OSI
For X.25 networks, the router establishes X.25 switched virtual circuits (SVCs) on
routing circuits.
Note: To enable DECnet V/OSI for X.25, you must enter the DECnet IV process
and define your router to be a DEC-AREA or DEC-ROUTING-IV router. You
must do this (and restart the router!) to enable the commands to do the
DECnet V/OSI configuration. Use the define executor type command.
Using OSI/DECnet V
Chapter 9. Using OSI/DECnet V 299
