IS-IS
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The IS-iS Protocol
PDU(协议数据单元，7种PDU APDU PPDU SPDU SEG Packet Frame Bit) Level1:Build common topology of system IDs inlocal area and routes within area using lowest cost path. Level2:Exchanges prefixinformation (area addresses)betweenareas.Routers traffic to area using lowest-cost path.
Level 2 routers use ISPs to build topologybetween different areas. Level 1-2 routers act as border routersbetween Level 1 and Level 2 routing domains.
Integrated (or Dual) IS-IS Routing Integrated IS-IS is IS-IS for multipleprotocols: --For IP,CLNS,or both Uses Its own PDUs to transport IP routinginformation; updates not sent in IP packets Requires CLNS addresses,even if onlyrouting for IP.
Default narrow metrics are limited to 6-bit interface and 10-bitpath metric In Cisco IOS SoftwareRelase 12.0,wide metrics allow 24bit interface and 32-bit pathmetric.
Four OSI Routing Levels
Similarities Between IS-IS and OSPF Link-state representation,aging timers,and LSDBsynchronization SPFalgorlthms Update,decision,and flooding processes VLSMsupport
OSPF is based on a central backbone with allother areas attached to it. In OSPF the brother is inside rouers(ABRs). Each link belongs to one area.
Integrated IS-IS vs.OSPF:Area Design (Cont.)
Each IS-IS router belongs to exactly one area. IS-IS more flexible when extending the backbone. Advantages of IntegratedIS-IS
Has three area types:mormal,stub,and NSSA Defaults to scaled metric(IS-IS always 10) Level 1 is intra-area. Level 2 is interarea.
IDP(Initial Domain Part) AFI(Authority FormatID) [1Byte] 49(私有) IDI（Intial DomainID) [Variable-Length] 47.0005 47.0006 Area address:Variable-length field (1 to 13 octets) composed of the higher-order NSAP octets, excluding system ID andNSEL. SystemID: ES or IS identifier in an area;fixed length ofsix octets in Cisco IOS software. NSEL:One octet NSAP selecor,service identifier. --AFI set to 49 Locally administered;thus ,you can assign your own addresses. --Area ID The octets of the area address after the AFI ---Cisco routers require a 6-bytes system ID. ---Always set to 0 for a router.
All routers within an area must use the same area adress. An ES may bi adjacent to a router only if they share a common areaaddress. Area address is used in Level2 routing.
Identifying Systems in IS-IS :System ID
This may be MAC (for example,0000.0c12,3556) or IP address (forexample:1921.6800.0001)taken from an interface. Refers to the device itself(equivalent tothe Layer 3 OSI address of the devce) Used in routers because they implement the network layer only(basefor SPF calculation) Virtual circuit ID (DLCI on Frame Relay) MAC address on LAN interfaces On point -to-point interfaces,SNPA is used. On LANs,circuit ID concatenated with six-octet system ID of adesignated IS to form seven-octet LAN ID (forexample,1921.68000001.01) is used.
1.0.0.0/24 is subnetted, 1 subnets
iL1 1.1.1.0 [115/20] via 12.1.1.1,00:04:19, Serial2/0
2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 2.2.2.0/24 is directly connected, Loopback0
L 2.2.2.2/32 is directly connected, Loopback0
3.0.0.0/24 is subnetted, 1 subnets
iL2 3.3.3.0 [115/30] via 12.1.1.1,00:04:19, Serial2/0
12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 12.1.1.0/24 is directly connected, Serial2/0
L 12.1.1.2/32 is directly connected, Serial2/0
13.0.0.0/24 is subnetted, 1 subnets
iL1 13.1.1.0 [115/20] via 12.1.1.1,00:04:19, Serial2/0 intra-area routing enables ESs to communicate. Level 1 area is a collection of Level 1 and Level 1-2routers. Level 1 IS keeps copy of the Level 1 areaLSDB Intra-area and interarea routing. Level 1-2 IS keeps separate Level 1 and Level 2 LSDBs and advertises default route to Level 1 routers. Interarea routing. Level 2(backbone) area is a contiguous set of Level1-2 and Level 2 routers. Level 2 IS keeps a copy of the Level 2 area LSDB if not equal,pass to nearest Level 1-2 router. if wqual,use Level 1 database to route by system ID. if not equal,use Level 2 database to route by area address. if equal,use Level 1 database to route by system ID.
优化 R1#show clns neighbors
SystemId Interface SNPA State Holdtime TypeProtocol
R2 Se2/1 *HDLC* Up 23 L1 IS-IS
R3 Se2/0 *HDLC* Up 24 L2 IS-IS
R1向内部区域公告Level1, LSP的Attached置1
产生默认路由条件 1、R1连接多个区域 2、R1、必须是L1-L2 3、R2、必须是L1 1.0.0.0/24 is subnetted, 1 subnets
iL2 1.1.1.0 [115/20] via 13.1.1.1, 00:15:37,Serial2/1
2.0.0.0/24 is subnetted, 1 subnets
iL2 2.2.2.0 [115/30] via 13.1.1.1, 00:15:37, Serial2/1
3.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 3.3.3.0/24 is directly connected, Loopback0
L 3.3.3.3/32 is directly connected, Loopback0
12.0.0.0/24 is subnetted, 1 subnets
iL2 12.1.1.0 [115/20] via 13.1.1.1, 00:15:37, Serial2/1
13.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 13.1.1.0/24 is directly connected, Serial2/1
L 13.1.1.3/32 is directly connected, Serial2/1
Network PDU = datagram,packet Data-link PDU = frame Examples: Hello(ESH,ISH,IIH) LSP PSNP(partial sequence number PDU) CSNP(complete sequence number PDU) PDU type,length,LSP ID, sequence number, remaining lifttime IS neighbors ES neighbors Authenticaton information ...... Assists with synchronizaton. Sequence numbers begin at 1. Sequence numbers are increased to indicate the newest LSP. Allows synchronization. Decreasing timer. Point-to-poing,Permanent or dynamically established links Broadcast for LANs and multipoint WANs Point-to-point for all other topologies Only routers with adjacencies are eligible. Highest interface priority. Highest SNPA (MAC) breaks ties.
Introducing IS-IS and Integrated IS-IS Routing
IS-IS -----------------OSI
OSPF ----------------TCP/IP
Large ISPs
Stable protocol
Originally deployed by ISPs because U.S. government mandatedInternet support of OSI and IP
IS-IS Routing
IS = router
IS-IS was originally designed as the IGP for theConnectionless Netwrok Service(CLNS),part of the
OSI protocol sulte.
The OSI protocol sulte layer 3 protocol is the ConnectionlessNetwork Protocol(CLNP).
IS-IS uses CLNS address to identify routers and build theLSDB.
IS-IS Features
Link-state routing protocol
Supports VLSM
Uses DIJkstra's SPF algorithm; has fast covergence
Uses hellos to establish adjacencies and LSPs to exchange link-state Information
Efficient use of bandwidth,memory,and processor
Supports two routing levels:
IS-IS Link-State Operation
Routers are identified as Level 1,Level 2, or Level1-2:
Routers are identified as Level 1,Level 2, or Level1-2:
默认为Level1-2.
所有连续L2L1-2,路由器的集合，构成IS-IS主干区域,
Integrated (or Dual) IS-IS Routing
Integrated IS-IS Design Principles
Issues with Integrated IS-IS
Default narrow metrics are limited to 6-bit interface and 10-bitpath metric
Cisco IOS software has default metric of 10 on allinterfaces.
Metric：范围0-63 Metric:1024,
End System-to-Intermediate System
Four OSI Routing Levels
Similarities Between IS-IS and OSPF
Integrated IS-IS and OSPF are both open standard link-stateprotocols with the following simllar features:
Scalabillty of link-state protocols has been proven (used inISP backbones).
They both coverge quickly after changes.
周期更新
OSPF:30 60
IS-IS: 15 20
触发更新
Integrated IS-IS vs. OSPF:Area Design
Integrated IS-IS vs.OSPF:Area Design (Cont.)
In IS-IS the area borders lie on links
Advantages of OSPF
OSPF has more features,including:
OSPF is supported by many vendors.
Information,examples,and experienced engineers are easier tofind.
Summary
IS-IS is a popular routing propocol in the ISP industry.
IS-IS is a stable,fast-converging IGP that is positioned toroute IPv4,CLNS,or IPv6.
All IS-iS interfaces have a default metrin of 10.
ES-IS (for CLNS routing only) provides discovery between hostand routers using hello packets to from adjacencies.Hosts sendESHs,while routers send ISHs.
OSI defines routing levels 0 through 3.Level 0 is between ESand IS.Level1 and 2 are between IS and IS to support intradomainrouting .Level3 supports interdomain routing.
IS-IS and OSPF are both open-standard link-state routingprotocols that support VLSM,scalability,and quickconvergence.
OSIAddresses
Integrated IS-IS NSAP Address Structure
IDP(Initial Domain Part)
DSP(Domain Sepcific Part)
HODSP(Area) [Variable-Length]
SystemID [6Bytes]
NSAP-Selector (0x00) [1Byte]
202.1.3.10
202.001.003.010
2020.0100.3010
NSAP :49.0001.0001.0001.0001.00
The Cisco implementation of Integrated IS-IS distinguishesonly the following three fields in the NSAP address:
Total length of NSAP is from 8 (minimum) to 20 octets(maximum).
Typical NSAP Address Structure
The simplest NSAP format used by most companies
running IS-IS as their IGP is as follows:
Area address (must be at least 1 byte)
System ID
NSEL
Identifying Systems in IS-IS Areaaddress
The area address uniquely identifies the routing area,and thesystem ID identifies each node.
Identifying Systems in IS-IS :System ID
System ID in the address used to identify the IS: it si notjust an interface.Cisco supports only a 6-byte system ID.
System ID is used in Level 1 routing and has bo be uniquewithin an area.
System ID has to be unique within Level 2 routers that fromthe routing domain
General recommendation:use domain-wide unique system ID.
OSI Addressing:NET Addresses
NSAP address includes NSEl field(process or port number)
NET:NSAP with a NSEL field of 0
Subnetwork Point of Attachment(SNPA) and Circuit ID
SNAP is equivalent to Layer 2 address:for example:
Interfaces uniquely identified by circuit ID:
Cisco routers use hostname instead of system ID (forexample,R1.01).
配置例子
R1#show clns neighbors
SystemId Interface SNPA State Holdtime Type Protocol
R2 Se2/1 *HDLC* Up 26 L1L2 IS-IS
R3 Se2/0 *HDLC* Up 21 L2 IS-IS
SystemId
R2
R3
R1#show isis hostname
Level SystemID Dynamic Hostname (notag)
2 2222.2222.2222 R2
2 3333.3333.3333 R3
* 1111.1111.1111 R1
Level
提示邻居变化信息
R1(config-router)#log-adjacency-changes all
R1#show clns is-neighbors
SystemId Interface State Type Priority CircuitId Format
R2 Se2/1 Up L1L2 0/0 00 PhaseV
R3 Se2/0 Up L2 0 00 Phase V
SystemId
R2
R3
R1#show clns interface s2/1
Serial2/1 is up, line protocol is up
Checksums enabled, MTU 1500, EncapsulationHDLC
ERPDUs enabled, min. interval 10 msec.
CLNS fast switching disabled
CLNS SSE switching disabled
DEC compatibility mode OFF for thisinterface
Next ESH/ISH in 32 seconds
Routing Protocol: IS-IS
CircuitType: level-1-2
Interface number 0x2, local circuit ID 0x102
Neighbor System-ID: R2
Level-1Metric: 10, Priority: 64, Circuit ID:R2.01
Level-1 IPv6Metric: 10
Number ofactive level-1 adjacencies: 1
Level-2Metric: 10, Priority: 64, Circuit ID: R2.01
Level-2 IPv6Metric: 10
Number ofactive level-2 adjacencies: 1
Next IS-ISHello in 1 seconds
if stateUP
Serial2/1 is up, line protocol is up
R1#show clns interface s2/0
Serial2/0 is up, line protocol is up
Checksums enabled, MTU 1500, EncapsulationHDLC
ERPDUs enabled, min. interval 10 msec.
CLNS fast switching disabled
CLNS SSE switching disabled
DEC compatibility mode OFF for thisinterface
Next ESH/ISH in 12 seconds
Routing Protocol: IS-IS
CircuitType: level-1-2
Interfacenumber 0x1, local circuit ID 0x101
Neighbor System-ID: R3
Level-1Metric: 10, Priority: 64, Circuit ID: R3.01
Level-1 IPv6Metric: 10
Number ofactive level-1 adjacencies: 0
Level-2Metric: 10, Priority: 64, Circuit ID: R3.01
Level-2 IPv6Metric: 10
Number ofactive level-2 adjacencies: 1
Next IS-ISHello in 4 seconds
if stateUP
Serial2/0 is up, line protocol is up
R1#show clns interface l0
Loopback0 is up, line protocol is up
Checksums enabled, MTU 1514, EncapsulationLOOPBACK
ERPDUs enabled, min. interval 10 msec.
CLNS fast switching disabled
CLNS SSE switching disabled
DEC compatibility mode OFF for thisinterface
Next ESH/ISH in 46 seconds
Routing Protocol: IS-IS
CircuitType: level-1-2
Interfacenumber 0x0, local circuit ID 0x100
Level-1 Metric: 10, Priority: 64, Circuit ID: R1.00
Level-1 IPv6Metric: 10
Number ofactive level-1 adjacencies: 0
Level-2Metric: 10, Priority: 64, Circuit ID: R1.00
Level-2 IPv6Metric: 10
Number ofactive level-2 adjacencies: 0
Next IS-ISHello in 2 seconds
if stateDOWN
Loopback0 is up, line protocol is up
R1#show clns protocol
IS-IS Router:
System Id: 1111.1111.1111.00 IS-Type: level-1-2
Manual area address(es):
49.0001
Routing for area address(es):
49.0001
Interfaces supported by IS-IS:
Serial2/1 - IP
Serial2/0 - IP
Loopback0 - IP
Redistribute:
static (onby default)
Distance for L2 CLNS routes: 110
RRR level: none
Generate narrow metrics: level-1-2
Accept narrowmetrics: level-1-2
Generate widemetrics: none
Accept widemetrics: none
R2#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B- BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF interarea
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-ISlevel-2
ia - IS-IS inter area, * - candidate default, U - per-user staticroute
o - ODR, P - periodic downloaded static route, H - NHRP, l -LISP
a - application route
+ - replicated route, % - next hop override
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B- BGP
Gateway of last resort is not set
iL1
C
L
iL2
C
L
iL1
更改R2的S2/0接口metric值
R2(config)#interface s2/0
R2(config-if)#isis metric 5
R2(config-if)#isis metric 5
清邻居
R1#clear isis *
R1#clear clns neighbors
Level 1,Level2,and Level 1-2 Routers
Level1 (like OSPF internal nonbackbone routers):
Level 1-2 (like OSPF ABR):
Level2(like OSPF backbone routers);
Addressing and Routing
Area address is used to route between areas;system ID is notconsidered.
System ID is used to route within an area; area address is notconsidered.
OSI IS-IS Routing Logic
Level 1 router:For a destination address,compare
the area address to this area.
Level 1-2 router: For a destination address,compare
the area address to this area.
R2改为level-1,R3改成L2
R2(config-router)#is-type level-1
SystemId
R2
R3
增加了一条默认路由
R2#show ip route
Gateway of last resort is 12.1.1.1 to network0.0.0.0
i*L1 0.0.0.0/0[115/10] via 12.1.1.1, 00:03:10,Serial2/0
1.0.0.0/24 is subnetted, 1 subnets
iL1 1.1.1.0 [115/20] via 12.1.1.1, 00:07:10, Serial2/0
2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 2.2.2.0/24 is directly connected, Loopback0
L 2.2.2.2/32 is directly connected, Loopback0
12.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 12.1.1.0/24 is directly connected, Serial2/0
L 12.1.1.2/32 is directly connected, Serial2/0
13.0.0.0/24 is subnetted, 1 subnets
iL1 13.1.1.0 [115/20] via 12.1.1.1, 00:07:10, Serial2/0
iL1
C
L
C
L
iL1
R1向内部区域公告Level1, LSP的Attached置1
产生默认路由条件
R3#show ip route
Gateway of last resort is not set
Gateway of last resort is not set
iL2
iL2
C
L
iL2
C
L
Level-2路由器有全网路由。
根据接口配置路由器类型
R2(config-if)#isis circuit-type level-1
Route Leaking
Available since Cisco IOS Software Release 12.0
Helps reduce suboptimal routing by allowing Level2
information to be leaked into Level 1
Uses up/down bit in Type,Length,and Value(TLV)field
路由泄漏命令
R1(config-router)#isis ip level-2 intolevel-1 distribute-list 100
OSI PDUs
PDUs between peers:
IS-IS PDUs
IS-IS PDUs are encapsulated directly into a data-linkframe.
There is no CLNP or IP header in a PDU.
IS-IS PDUs are as follows:
A Link-State Packet Represents Router
Router describes itself with an LSP
LSP header contents
include:
TLV variable-length fields:
LSP Header
LSPs are sequenced to prevent duplicaation ofLSPs.
LSPs in LSDB have a remaining lifttime.
LSP TLV EXamples
Each set of information,called a "tuple," includes a typecode,
Length field,and value
IS-IS Network Representation
Generally,physical links can be placed in the followingtwo
groups:
------ addressingof a group of attached systems
Only two link-state representations are avilable inIS-IS:
IS-IS has no concept of NBMA netwroks.
Broadcast Mode
Used for LAN and multipoint WAN interfaces.
Adjacency is recognized throughhellos;separate
adjacencies for Level 1 and Level2.
Designated IS (DIS) creates a pseudonode and representsLAN.
DIS for Level 1 and Level 2 may bedifferent.
There is no backup DIS.
以太网优先级
R2#show clns is-neighbors
SystemId Interface State Type Priority CircuitId Format
R1 Et0/0 Up L1L264/64 R2.01 Phase V
R1 Se2/0 Up L1L2 0/0 02 Phase V
SystemId
R1
R1
R1#show clns is-neighbors
SystemId Interface State Type Priority CircuitId Format
R2 Et0/1 Up L1L264/64 R2.01 Phase V
R2 Se2/1 Up L1L2 0/0 01 Phase V
R3 Se2/0 Up L2 0 00 Phase V
SystemId
R2
R2
R3
R1(config-if)#isis priority 66
R2#show clns is-neighbors
SystemId Interface State Type Priority CircuitId Format
R1 Et0/0 Up L1L266/66 R1.01 Phase V
R1 Se2/0 Up L1L2 0/0 02 Phase V
SystemId
R1
R1
R1#show clns is-neighbors
SystemId Interface State Type Priority CircuitId Format
R2 Et0/1 Up L1L264/64 R1.01 Phase V
R2 Se2/1 Up L1L2 0/0 01 Phase V
R3 Se2/0 Up L2 0 00 Phase V
SystemId
R2
R2
R3
R1#show isis database
IS-IS Level-1 Link State Database:
LSPID LSP Seq Num LSP Checksum LSPHoldtime ATT/P/OL
R1.00-00 * 0x00000006 0xE0A0 562 1/0/0
R1.01-00 * 0x00000001 0xBFFC 562 0/0/0
R2.00-00 0x00000007 0xDD41 560 1/0/0
R2.01-00 0x00000001 0x939A 0(562) 0/0/0
IS-IS Level-2 Link State Database:
LSPID LSP Seq Num LSP Checksum LSPHoldtime ATT/P/OL
R1.00-00 * 0x00000006 0x62B5 562 0/0/0
R1.01-00 * 0x00000001 0x4FF5 562
LSPID
R1.00-00
R1.01-00
R2.00-00
R2.01-00
IS-IS Level-2 Link State Database:
LSPID
R1.00-00
R1.01-00