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SNPA or SubNetwork Point of Attachment	data link layer address used to identify a connection to a subnetwork, such as an Ethernet address

Packet or PDUs Protocol Data Unit	Link
Type 1: IS-IS hello (IIH) PDUs	Broadcast to discover the identity of neighboring IS-IS systems and to determine whether the neighbors are Level 1 or Level 2 intermediate systems Priority ( for DIS election ) Area IDs L1 Hello packet and L2 Hello packet
	Level 1: 01:80:C2:00:00:14 Level 2: 01:80:C2:00:00:15
Link-state PDUs	Contain information about the state of adjacencies to neighboring IS-IS systems. Link-state PDUs are flooded periodically throughout an area. on PtP links ack by CSNPs
Complete sequence number PDUs (CSNPs)	Contain a complete list of all link-state PDUs in the IS-IS database.
Partial sequence number PDUs (PSNPs)

DIS Election

Sent multicast by a receiver when it detects that it is missing a link-state PDU (when its link-state PDU database is out of date)

DIS Election on Broadcast & multi-access	ptp the priority = 0
	router with the higher priority >> Tie Highest

SNA

Metric	Link
SNPA or Mac@ Default priority: 64 [ 0 to 127 ] Priority = 0 >> ineligible
Highest priority
priority tie >>> highest SNAP or Mac@
	No backup DIS in IS-IS
pseudo-node ( Bcst Network = router )	on Broadcast & multi-access
all router adv a single link ( not all the adj ) to the pseudo-node

	from 1 through 63, or from 1 through 16,777,215 (2²⁴ – 1)
Wide metric	https://www.juniper.net/documentation/en_US/junos/topics/concept/isis-wide-metrics.html
Reference bandwidth	https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/reference-bandwidth-edit-protocols-isis.html cost = reference-bandwidth/bandwidth if ref= 100G then for 100G link cost = 1 and for 10G cost = 10 and for 1G link cost =1

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