Chapter 16: Dynamic Routing Protocols
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
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Three-Way Handshake — Previously, only a two-way handshaking mechanism was provided when establishing adjacencies
on point-to-point links. The basic mechanism for this operation is that each side declares the other side to be reachable if a
Hello packet is detected. Once this occurs, each side then sends a Complete Sequence Number PDU (CSNP) to trigger
database synchronization.
This mechanism is not reliable, and is alleviated with the implementation of three-way handshake for point-to-point
adjacency. This is accomplished by providing an optional mechanism (TLV 240) that allows each system to report its
adjacency three-way state, thus allowing a system to only declare an adjacency to be up if it knows that the other system is
receiving its IS-IS Hello (IIH) packets.
Point-to-Point Adjacencies for IS-IS Multi-Topology
Adjacencies on point-to-point interfaces are formed with IS-IS routers not implementing MT extensions. If a local router
does not participate in certain MTs, it will not advertise those MT IDs in its IIHs and thus will not include that neighbor
within its LSPs.
On the other hand, if an MT ID is not detected in the remote side's IIHs, the local router is not allowed to include that
neighbor within its LSPs. The local router is not allowed to form an adjacency if they don't have at least one common MT
over the interface.
Configuring IS-IS Point-to-Point
The following CLI commands are provided to configure a circuit as point-to-point:
configure interface gigabitethernet <WORD> isis network point-to-point [no]
configure interface tengigabitethernet <WORD> isis network point-to-point [no]
A user must shut down the IS-IS protocol on the circuit first before enabling or disabling IS-IS Point-to-Point.
Related MIB — The Point-to-Point command populates the
isisCircPtToPtOverLAN MIB of the IsisCircEntry MIB table with either TRUE (1) or FALSE (2).
Related Show Command — With this feature, the output of the
show isis interface
command has been updated, as
seen in the following output example:
tenGigabitEthernet 17/2.0 is Up, line protocol is Up
CLNS/IS-IS protocol processing enabled
MTU 1500
Circuit Type: level-1 point-to-point
Interface Number 0x1000012f (268435759), local circuit ID 0x0