Hello, everyone! I Yibo East , is a Cisco background, focus on Huawei's network engineering; Well, did not talk much, we go directly to the topic.
Article Directory
1. Topology
Two, configuration and analysis
2.1 Handshake mechanism
The broadcast link implements a 3-way handshake to establish neighbors through IS NEI TLV.
The P2P link implements a 3-way handshake to establish neighbors through P2P ADJ Stata TLV.
A neighbor relationship can be established through a 2-way handshake on a P2P link.
The 3-way handshake mechanism is enabled on the isis ppp-negotiation 3-way P2P link, but the received hello packet is not required to carry p2p adj state tlv.
isis ppp-negotiation 3-way only P2P link only uses 3-way handshake to establish neighbors, and is not compatible with 2-way handshake.
The isis ppp-negotiation 2-way P2P link only uses the 2-way handshake to establish neighbors, and ignores the p2p adj state tlv.
AR1
[Huawei]sysname AR1
[AR1]int g0/0/0
[AR1-GigabitEthernet0/0/0]ip address 10.1.12.1 24
[AR1-GigabitEthernet0/0/0]q
[AR1]isis
[AR1-isis-1]network-entity 49.0001.0000.0000.0001.00
[AR1-isis-1]is-level level-2
[AR1-isis-1]int g0/0/0
[AR1-GigabitEthernet0/0/0]isis enable
[AR1-GigabitEthernet0/0/0]isis circuit-type p2p
AR2
[Huawei]sysname AR2
[AR2]int g0/0/0
[AR2-GigabitEthernet0/0/0]ip address 10.1.12.2 24
[AR2-GigabitEthernet0/0/0]q
[AR2]isis
[AR2-isis-1]network-entity 49.0001.0000.0000.0002.00
[AR2-isis-1]is-level level-2
[AR2-isis-1]int g0/0/0
[AR2-GigabitEthernet0/0/0]isis enable
[AR2-GigabitEthernet0/0/0]isis circuit-type p2p
2.2 P2P
2.2.1 P2P 3-way (default) neighbor establishment process
The P2P link establishes neighbors through the Point-to-point Adjacency state.
Capture packets on G0/0/0 interface of AR1
Both ends send ISIS HELLO messages in DOWN state
P2P: R1 sends an ISIS HELLO message (DOWN state)
with its own systemID: 0000.0000.0001,
TLV240, and local link ID.
P2P: R2 sends an ISIS HELLO message (DOWN state)
with its own systemID: 0000.0000.0002,
TLV240, and local link ID.
R2 receives the first ISIS HELLO message and enters Initializing.
R1 received the ISIS HELLO message (systemID: 0000.0000.0002) of R2, and the neighbors in TLV240 contained its own systemID: 0000.0000.0001, and the status entered up.
R2 received the ISIS HELLO message (systemID: 0000.0000.0001) from R1, and the neighbors in TLV240 contained its own systemID: 0000.0000.0002, and the status went up.
2.2.2 P2P 2-way neighbor establishment process
As long as ISIS HELLO messages are received, neighbors will be established in one direction.
ISIS HELLO packets do not carry TLV.
P2P 3-way is backward compatible with 2-way (neighbors can be established).
[AR1]dis isis peer
P2P 3-way only is not compatible with 2-way and cannot establish neighbors.
AR1 has neighbors (one-way neighbors), and AR2 has no neighbors.
2.3 MA
After receiving the first ISIS HELLO message, the status changes to init;
If you receive your own MAC address in TLV6, the state enters UP.
10.1.12.1 00e0-fc48-15a2
10.1.12.2 00e0-fc65-4e39
R1 receives the ISIS HELLO message from R2 and finds that TLV6 contains its own MAC address 00e0-fc48-15a2, so the status becomes UP.
R2 receives the ISIS HELLO message from R1 and finds that TLV6 contains its own MAC address 00e0-fc65-4e39, so the status becomes UP.
2.4 Common TLV
TLV1: Area ID
TLV132: Interface IP address
TLV129: Protocol support, if IPv6 is supported, the value of NLPID is equal to 142
TLV240: Describes the neighbor status
TLV229: Multi-topology
TLV8: padding
TLV6: The MA network describes the MAC address of the neighbor
Three, a brief overview
3.1 IS-IS protocol background
ISIS--------OSI 7-layer model------Used to support CLNP network environment----Intermediate system----End System
OSPF------TCP/ IP-------------Network environment for IP-----router-----------------terminal
CLNP (Unconnected Network Layer Protocol) is the network layer protocol in the OSI model. ISIS was originally developed to support CLNP.
Since CLNP was not popular, ISIS developed slowly and quietly in the early stage. Later, because ISIS is more flexible, it is a network layer protocol that works above the link layer, and its scalability is relatively strong.
The ISIS engineering team subsequently extended the ISIS protocol to enable it to support IPv4, IPv6, and CLNP, so the ISIS protocol is now called the integrated ISIS protocol. Because of its strong scalability, fast convergence, and simple working mechanism, it has been widely deployed by ISPs.
3.2 OSPF protocol and IS-IS protocol
The OSPF protocol determines the network type according to the link layer encapsulation protocol of the interface by default.
ISIS is similar. If it is an Ethernet interface, it is regarded as a broadcast type by default. If it is PPP, HDLC is a P2P by default, and it does not support NBMA and P2NP network types.
DIS: designated intermediate system
3.3 IP protocol, CLNP protocol
The IP protocol uses IP addresses to address interfaces.
The CLNP protocol uses NSAP (Network Service Access Point) addresses to address devices.
3.4 NET address
The NET (Network Entity Identifier) address is a special NSAP address, that is, the NSAP address with SEL=0. In the ISIS protocol, the NET address identifies a router.
SEL network service discriminator, 1 byte length, similar to the protocol number in the IP packet, used to distinguish the upper layer protocol type.
It consists of three parts: Area ID, System ID, SEL;
-------Area ID--------System ID------SEL
----- （1-13B） ------- （6B） ---------- （1B）
So the minimum is 8B and the maximum is 20B.
3.5 Message
The purpose of HELLO is to establish and maintain neighbor relationships.
L1 Hello is used to establish L1 neighbors
on broadcast links ; L2 Hello is used to establish L2 neighbors on broadcast links;
P2P hello is used to establish ISIS neighbors on P2P links.
LSP is used to describe and carry LSA information
L1 LSP describes the link status of the non-backbone area, which corresponds to the type 1 or type 2 LSA in the non-backbone area of the OSPF protocol;
L2 LSP describes the link status of the backbone area, which corresponds to the type 1 and type 2 LSA in the OSPF protocol backbone area LSA.
SNP sequence number PDU
CSNP complete sequence number PDU, similar to OSPF DD packet, is divided into L1 CSNP, L2 CSNP;
PSNP partial sequence number PDU, similar to OSPF LSR/LSACK, divided into L1 PSNP, L2 PSNP.
3.6 ISIS defines router level
The backbone area and non-backbone area of the ISIS protocol are determined by the neighbor level of the router.
ISIS defines three router levels:
level-1
level-2
level-1-2
Huawei/Cisco routers are default L1/2 routers
3.7 ISIS neighbor level
There are two types of
L1 neighbors at the ISIS neighbor level : Neighbors that require the same area number and
L2 neighbors: Do not require the same area number.
L1 routers can only establish L1 neighbors,
L2 routers can only establish L2 neighbors
L1/2 router: Establish L1 neighbors with L1 routers in the same area,
and L2 neighbors with L2 routers.
L1/2 routers in the same area establish L1 neighbors and L2 neighbors.
Routers in areas different from L1/2 can only establish L2 neighbors.
3.8 Backbone area, non-backbone area
The ISIS backbone area is the logical area composed of L2 neighbors. The
ISIS non-backbone area is the logical area composed of L1 neighbors.
The boundary between backbone and non-backbone is on the L1/2 router.
Four, summary
4.1 ISIS neighbor status
(1) Down did not receive the neighbor's hello
(2) Init received the neighbor's hello packet, but did not find its own mac address, also known as one-way
(3) Up received the neighbor's hello packet, and found its own Interface mac address
4.2 DMAC address
The DMAC address used by all L1 ISIS messages on the broadcast link is: 01:80:C2:00:00:14
The DMAC address used by all L2 ISIS messages on the broadcast link is: 01:80:C2 :00:00:15
On the Ethernet link, if the link type is changed to the P2P type, the P2P HELLO packet will be sent, LSP, CSNP, PSNP are still divided into L1/L2, and the DMAC address is 09:00:2b:00: 00:05.
4.3 Broadcast link
By default, the router of L1/2 sends L1 hello and L2 hello on the broadcast link.
The level at which the L1/2 router sends hello packets on the broadcast link is related to the level of the interface, and is the intersection of the interface level. isis circuit-level sets the level of the link.
L1 routers only send L1 hellos on broadcast links, regardless of the link level.
L2 routers only send L2 hellos on broadcast links, regardless of the link level.
4.4 DIS
isis.hello.priority is
used for DIS election. The value range is 0-127. The larger the priority, the higher the priority. 0 can also participate in the DIS election. If the priorities are the same, compare the MAC addresses of the interfaces, the larger the priority, the more preferred.
4.5 DIS election
(1) The greater the interface priority, the better.
(2) The same priority, the greater the mac address, the better.
(3) The default priority is 64.
(4) DIS is preemptive
(5) DIS is classified, L1 neighbor election L1_DIS , L2 neighbor election L2 DIS
(6) The router with DIS priority equal to e can also perform DIS election
(7) No backup DIS
The main reason why OSPF DR and BDR do not grab is because the neighbor status of the broadcast link is inconsistent. If the DR can be snatched, it will cause large-scale changes in neighbor status, which will affect many devices.
ISIS snatching will not lead to changes in neighbor status, and the stability is higher. But the pseudo-node LSP will change, which will have a certain impact on the SPF algorithm. This problem can be ignored in a stable network.
4.6 TLV
The ISIS protocol is based on the TLV mechanism to negotiate various attributes.
T: attribute type
L: length value
V: value
The TLV mechanism runs the routing protocol to only carry the required attributes, and the attributes are not required. The scalability is strong. If the protocol needs to support new features, it only needs to develop new TLV attributes to support it.
OSPFv2 is not a routing protocol based on the TLV mechanism, and the message fields are fixed, so the scalability is relatively poor.
4.7 LSP-ID
0000.0000.0004.00-00 LSP-ID 8 bytes in length
Consists of 3 parts
LSP-ID = system id (6 bytes). Pseudo node identifier (1 byte)-fragment identifier (1 byte)
The system id identifies the system id of the router that generated the LSP.
The pseudo-node identifier is 0 or non-zero.
If it is equal to 0, it means that the LSP is a solid-node LSP.
If non-zero, it means that the LSP is a pseudo-node LSP, and the system id is the system id of DIS.
Fragment identifier, used to describe different LSPs generated by the same router.
PSNP, the summary information of the LSP carried by the CSNP, including LSP ID, remaning lifetimer, seq, and checksum.
If the sequence number of the LSP ID carried in the PSNP packet is not 0, then PSNP is the confirmed function
. If the sequence number of the LSP ID carried in the PSNP packet is 0, then PSNP is the requested function.
The L1 router only describes the direct link information through the L1 LSP, which has nothing to do with the link level.
The L2 router only describes the direct link information through the L2 LSP, and has nothing to do with the link level.
L1/2 routers describe their L1/2 direct links through L1 LSPs and L2 LSPs;
L1/2 routers describe their L2 direct links only through L2 LSPs;
L1/2 routers pass L1's LSP and L2's LSP describe the direct link of its own L1.
How does the backbone area access the non-backbone area? The
L1/2 router describes the L1 route as its directly connected leaf and carries the backbone through the L2 LSP.
OK
famous aphorism moment:
Don't be eager to express yourself, nor eager to correct others, listen again, take a look again, and then think> ponder.
Welcome to my ebaina technical community article "Notes on Huawei IS-IS Protocol Summary"
https://www.ebaina.com/articles/140000005422
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