Figure 4-3 Three Times Of Handshaking - Zte ZXR10 5900E Series Configuration Manual

ZXR10 5900E Series Configuration Guide (IPv4 Routing)
shorted to N-SEL) is similar to the protocol ID in an IP address. Different transmission
protocols have different SELs. In an IP address, the SEL is 00.
IS-IS neighbor establishment
The IS-IS distinguishes networks as point-to-point networks and broadcast networks. The
neighbor establish processes are different on these two types of networks.
l
Establish neighbor on a point-to-point link
If the Intermediate System (IS) on the network is configured with the IS-IS routing
protocol and the interface is in UP state, the system sends IIH PDU packets. The other
neighboring intermediate systems perform the following operations after receiving the
packets:
When the IS receives a point-to-point IIH PDU packet, it compares the area addresses
of these two ISs to ensure that the neighbor can be established. If the two ISs have
the same area address, the neighbor can be established for all IS router combinations
(except the connection between one L1 IS and one L2 Only IS). However, if the area
addresses are different, the neighbor can only be established between two L2 ISs.
On a point-to-point network, if the area address is correct, the local intermediate
system matches the circuit type of the received IIH PDU packet with that in the local
intermediate system. If they match each other, neighbor relation can be established,
the neighbor information is added to the neighbor database, and the neighbor state is
set to UP. If the circuit types do not match each other, this packet is dropped.
The above neighbor establishment process is proposed in RFC1142, which is based
on the premise that the point-to-point network is absolutely reliable. However, the
network is not necessarily reliably. Therefore, the RFC3373 introduced the TLV.
Establish neighbor relation after three times of handshaking, see

Figure 4-3 Three Times of Handshaking

The IIH PDU sent by router RTA carries the type 240 TLV, in which, the neighbor's
three states are saved. When router RTB receives the packet, it confirms the next
neighbor state according to the state of its neighbor and the neighbor state in the TLV.
For the state changes, refer to
Table 4-1 Neighbor State Changes
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Down
SJ-20150114102049-003|2015-01-15 (R1.0)
Table 4-1.
Down Init
Init Up
4-4
Figure 4-3.
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