Netmanias 기술문서: IS-IS(Intermediate System-to-Intermediate System) 상세동작원리

2010년12월5일
NMC Consulting Group(tech@netmanias.com)

2
목차
.Routing과Forwarding
.Link-State Routing Algorithm
.IS-IS에서사용되는용어들
.IS-IS에서의계층적Routing : Area & Level
.OSI Addressing
.IS-IS가알고있는Interface Type
.IS-IS PDU Encapsulation
.Basic IS-IS Operations
.LAN IIH, Point-to-point IIH
.Hello 메시지와Adjacency
.Link State PDU
.Broadcast LAN과Pseudo-node
.Flooding of LSP
.CSNP/LSP Throttling
.LSP Purging
.Route Summary
.Route Leaking
.Overloading
.Sub-TLV
.Extended IS Neighbor TLV
.Extended IP Reachability TLV

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.forwarding:라우터의인터페이스로들어온패킷을, 적젃핚출력인터페이스를찾아내보내는일.
.routing:패킷의출발지(source)에서부터목적지(destination)까지의젂달경로를결정하는일
.Routing algorithms에의해경로결정
비유하자면:
.routing:여행의출발지에서부터목적지까지의과정을계획하는일에해당함.
.forwarding:각Interchange를통과하는행위에해당함.
Network-Layer 기능: Routing, Forwarding

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Graph: G = (N,E)N = set of routers = { u, v, w, x, y, z }E = set of links ={ (u,v), (u,x), (v,x), (v,w), (x,w), (x,y), (w,y), (w,z), (y,z) }
Link-State Routing Algorithm: (1) Graph abstraction
Graph 표현법은, Network 연결을수학적으로표현하기위해흔히사용됨

5
.c(x,x’) = cost of link (x,x’)
.e.g., c(w,z) = 5
.cost는편의상1로가정핛수도있고, 대역폭의크기에반비례하게정하기도함.
.e.g., 10GbE .cost 1,1GbE .cost 10,100M .cost 100, …
Cost of path (x1, x2, x3,…, xp) = c(x1,x2) + c(x2,x3) + … + c(xp-1,xp)  
질문: u와z 사이의가장최단경로는?
Routing algorithm: 가장cost가적게드는경로를찾는알고리즘
Link-state Routing Algorithm: (2) Graph abstraction -costs

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Link-State Routing Algorithm: (3) Dijkstra’s SPF Algorithm
Dijkstra’s“Shortest Path First” Algorithm
.Network topology와모든Node 갂의link cost값을, 모든Node(라우터)들이알게함.
.위“Link-state”정보를Broadcast (flooding)함으로써모든라우터에게젂달함.
.모든라우터들이동일핚정보를갖게됨.
.각노드를source로해서, 모든노드로의최단경로를계산함.
.각노드(라우터)가각자의forwarding table을갖게됨.
.반복적계산방식: k개의destination에대해최단경로를얻으려면, 각노드로의경로의cost 값을k번반복계산함.
.핚번의계산당하나의목적지node로의최단경로가찾아지며,
.K번의계산을마치면k개의목적지node로의최단경로가모두찾아지게됨.

7
Dijsktra’s Algorithm & Example
Step
N’
D(v)/p(v)
D(w)/p(w)
D(x)/p(x)
D(y)/p(y)
D(z)/p(z)

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Example
Notation:
.c(x,y):node x와y 갂의link cost;  직접연결되어있지않으면∞.
.D(v):source로부터목적지v까지의경로의cost값.
.p(v):source로부터목적지v까지의경로에서, 목적지v의직젂node.
.N\':최단경로가결정된node들의집합
2
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5
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경로u.x: u-x, cost 1,  경로u.y: u-x-y, cost 2,경로u.v: u-v, cost 2,  경로u.w: u-x-y-w cost 3,경로u.z: u-x-y-z, cost 4
1  Initialization:2    N\'= {u} 3    for all nodes v 4      if v adjacent to u 5          then D(v) = c(u,v) 6      else D(v) = ∞ 7 8   Loop9     find q not in N\' such that D(q) is a minimum 10    add q to N\' 11    update D(v) for all v adjacent to q and not in N\' : 12       D(v) = min( D(v), D(q) + c(q,v) ) 13    /* new cost to v is either old cost to v or known 14     shortest path cost to q plus cost from q to v */ 15  until all nodes in N\'

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.ISO 10589 1990 Edition (RFC1142.ps로재출갂)
.ISO 10589 2002 Edition (부분수정, 일부Message Format 수정)
.http://standards.iso.org/ittf/PubliclyAvailableStandards/c030932_ISO_IEC_10589_2002(E).zip
.“Use of OSI IS-IS for Routing in TCP/IP and Dual Environment” (RFC1195)
.IS-IS를OSI protocol 환경과IP 환경의두가지모드(“Dual”)에서동시에사용핛수있도록규정함.
OSI IS-IS Intra-domain Routing Protocol

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IS-IS에서사용되는용어들
.Intermediate System (IS)
.Router
.End-system (ES)
.Network Host
.Designated Intermediate System (DIS)
.Designated Router : 하나의LAN에연결되어있는Router 중, 해당LAN을대표해선정되는하나의Router (선출방식은Priority 및System-ID 값비교)
.Pseudo-node
.Link-state 정보에LAN을표현하기위해, DIS에의해만들어지는, LAN을나타내는가상의Node.
.Network Service Access Point (NSAP)
.Network Layer Address : IP주소, OSI CLNP 주소, …
.Subnetwork Point of Attachment (SNPA)
.Datalink Interface : Ethernet Port, POS Interface, …
.Link State PDU
.Routing Information packet used in IS-IS

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IS-IS에서의계층적Routing : Area와Level
Level-1 Routing (L1 Routing)
Area 내부의망갂의Routing.

Level -2 Routing (L2 Routing)
다른Area에속핚망으로의Routing. 혹은, area 갂의Routing.

L1 IS
Level-1 Routing을수행하는라우터(= L1 Router)
L1 라우터는자기area 내부의network 경로만알고있다.
자싞이모르는경로로의라우팅이요구되면자싞에게가장가까운L2 라우터에게패킷을젂달핚다.

L2 IS
Level-2 Routing을수행하는라우터(= L2 Router)
L2 라우터는각area에속핚주소들을알고, 각area의border에위치핚L2 라우터에게패킷을forwarding핚다.

L1/L2 IS
L1 라우팅과L2 라우팅을모두수행하는라우터(= L1/L2 Router)
L2 라우터의각인터페이스는특정area에소속될수있으며, 그경우해당area내에서는L1 라우터로서의역핛도핚다.


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Area & Level in IS-IS: (1) Level-2로만구성된Area가없는경우
.Level과Area는Interface별로설정된다.
.Area의경계는라우터갂링크가될수도있고, 라우터자체가될수도있다.
.각인터페이스마다Level별로Neighbor가있다.
.각Level별로Link-state PDU가별도로돌아다닌다.
.Route Calculation도Level별로따로수행된다.
각Circuit (인터페이스)별Area 및Level 설정은?

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Area & Level in IS-IS: (2) Level-2로만구성된Backbone Area가있는경우
.L2 IS로만구성된Backbone Area를명시적으로구성핚경우이다.
각Circuit (인터페이스)별Area 및Level 설정은?

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Level 간Routing 정보교환
.L1 Routing을통해얻어짂모든Network Prefix는L2 IS 갂에모두젂달된다..모든L2 IS는IS-IS domain 내의모든IP Network을알고있다.
.L2 Router는L2 Routing을통해얻은Network 정보를Area 내에젂달하지않는다.
.대싞, LSP 내의Attach bit을1로줌으로써외부Area와연결되어있음을Area 내의모든L1 Router에게알린다.
.L1 Router는ATT bit 을보고L2 Router의존재를알게된다..Default Route를생성함.
.Area에둘이상의L2 Router가있는경우, 가장가까운L2 Router쪽으로Default Gateway를잡는다.(Note : LSP는Area 내에Flooding되므로, 모든L2 Router의ATT 정보는모든L1 Router에게젂달된다.)
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OSI Addressing
.모든IS는하나의OSI Address를갖는다.
.여러Area에속핚경우, 각Area별Address를가짐
.Interface별OSI Address는필요없다.
(하나를가지고여러인터페이스에서사용)
.Example 1) MAC주소를System ID로사용
.49.0005.0000.9833.c5de.00
.Example 2) IP주소(172.16.10.1)를System ID로사용(1앆)
.49.0005.1720.1601.0001.00
.Example 2) IP주소(172.16.10.1)를System ID로사용(2앆)
.49.0005.0172.0016.1001.00
Field
Description

IDP
.Initial Domain Part

DSP
.Domain Specific Part

AFI
.Authority and Format Indicator
-0x47 = Internet Domain
-0x49 = Local(Private) Use

IDI
.Initial Domain Identifier

HO-DSP
.High Order part of DSP

ID
.A System Identifier

SEL
.NSAP Selector

NET
.Network Entity Title


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IS-IS가알고있는Interface Type
.Broadcast Media (ISO 10589 “Broadcast subnetwork” or “Broadcast circuit”)
.Point-to-point Media (ISO 10589 “General topology” subnetwork, “point-to-point circuit”)

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Encapsulation of IS-IS PDUs: (1) IEEE802.3 (802.2 LLC) Encapsulation
.Destination MAC
.All-L1-IS-Group : 0180.c200.0014
.All-L2-IS-Group : 0180.c200.0015
.DSAP/SSAP : Dest./Source Service Attachment Point
.0xFE : OSI Protocol
.IS-IS는IP packet, ISO CLNP packet을이용하지않음.
.Layer2 format에바로encapsulation 된다.
.IS-IS 메시지위에각3계층프로토콜의Routing 정보를담을수있다. .유연하고, 새로운프로토콜(IPv6)에적용하기가쉽다.

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Encapsulation of IS-IS PDUs: (2) PPP Encapsulation
.PPP LCP (Link Control Protocol)에의해Link layer 연결, 인증및parameter setup이이루어짐.
.LCP 연결성공후각3계층Protocol별Control Protocol(CP)에의해메시지젂달
.IPCP, IPv6CP, IPXCP, OSINLCP, …
.OSINLCP 매우갂단(Capability advertisement만으로끝남-“Hey, 내가OSI를알거든. 너두나핚테OSI메시지보낼수있거든”)

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Basic IS-IS Operations
.PSNP-Interval: 2초(with jitter, 1.5~2초). 보낼PSNP가있으면모아두었다가보낸다.
.Minimum-LSP-Transmission-Interval: 5초(with jitter, 3.75~5초). Point-to-point circuit에적용되는timer값으로서, 보낼LSP가있으면모아두었다가보낸다

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Basic IS-IS Operations: Example

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Basic IS-IS Operations: Example -한참있다가

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Basic IS-IS Operations: Example .Topology 변경

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IS-IS PDU 종류
.Hello (IIH .“IS-IS Hello”)
.Neighbor를발 하기위해서, 또계속“살아있음”을서로확인하기위해주기적으로발생됨.
.LSP (Link-state PDU)
.Routing 정보를실어나르는패킷
.어떤Neighbor와연결되어있는지, 어떤IP Network와연결되어있는지등을나타내는, 가장중요핚Routing Information들을담고있음.
.CSNP (Complete Sequence Number PDU)
.각Router가가지고있는LSP(Routing 정보)들의목록을담고있는패킷.
.“목록”에는구체적인Routing 정보는들어있지않고, {LSP-ID, LSP-lifetime, Sequence Number, Checksum}등의LSP를식별핛수있는정보만들어있다.
.CSNP를수싞핚라우터는, 이식별정보만을가지고, 그LSP가자싞이알고있는것인지아닌지를판단핚다. (자싞이모르고있는LSP에대해서만Request핚다.)
.PSNP (Partial Sequence Number PDU)
.CSNP와마찬가지로LSP의요약정보만을담고있으며, 젂체LSP 목록이아닌, 일부의LSP 정보만을담는다.
.다른라우터에게LSP를요청핛때, 원하는LSP의목록만담아보내기위해사용됨.
.다른라우터로부터수싞핚LSP에대핚ACK의용도로도사용됨.

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Neighbor Discovery: (1) LAN IS-IS Hello (IIH)
Field
Description

Header Length
.TLV 이젂까지의총헤더길이
(8 byte 고정header 포함)

ID Length
.0 = 6 byte

PDU Type
.15 = Level 1 LAN Hello
.16 = Level 2 LAN Hello

Max Area Address
.0 = 3개
(이Hello를보낸IS가가질수있는최대Area 주소개수. “Area Address” TLV (Code 1)에실제Area Address가수록됨)

Circuit Type
.1 = L1-only, 2 = L2-only, 3 = L1/L2
(L1 LAN IIH에는“L2-only”는쓸수없음)

Source ID
.이Hello 메시지를보낸IS의시스템ID

Holding Time
.Hello timeout 값(Hello Interval x Hello Multiplier)
-IOS10589: 1s x 10 = 10s for LAN DIS,
3s x 10 = 30s for LAN non-DIS
-Cisco: 10s x 3 = 30s
-Juniper: 9s x 3 = 27s

PDU Length
.Header 포함젂체PDU 길이

DIS Priority
.LAN Designated IS를선출하는데필요핚Priority 값(0 ~ 127)
#NAME?
-0이면DIS가될수없음

LAN-ID
.DIS에의해정해짂이LAN의Pseudo-node ID 값


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LAN IIH와함께쓰이는TLV
TLV #1 .Area Address
TLV #6 .LAN IS Neighbors
TLV #8 .Padding
L1 IIH의경우, Hello를주고 는Neighbor들중Area Address가일치하는것이있어야서로Adjacency가형성됨.
LAN IIH에서만사용되며, Hello를보낸Neighbor들의목록임.“LAN Address”는, Neighbor로부터 은Hello메시지의Source MAC address임.하나의Circuit에여러Neighbor가있을수있으므로, 이들복수의IS갂Adjacency를파악하기위해사용핚다.
Hello 메시지의길이를MTU 또는Maximum-LSP-Buffer-Size값(1492 bytes)과같게만들기위해사용됨. (둘중큰값사용)Adjacency가맺어짂후에는Padding 필요없음.
TLV #10 .Authentication Information
Auth Type : 1 = Plain Text Password,
17 = HMAC-MD5 Password

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LAN IIH와함께쓰이는TLV
TLV #132 .IP Interface Address
이PDU의송싞측인터페이스의IP주소(들)
TLV #129 .Protocol Supported
NLPID(Network Layer Protocol ID) : ISO/TR9577에서핛당된3계층프로토콜코드

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.기타Field들은LAN IIH와같음.
.DIS Priority 및LAN ID는없음. (LAN Circuit이아니니까!)
.함께사용되는TLVTLV #1 .“Area Address”, TLV #8 .“Padding”,TLV #10 .“Authentication”, TLV #129 .“Protocol Supported”,TLV #132 .“IP Interface Address”
Neighbor Discovery: (2) Point-to-point IS-IS Hello (IIH)
Field
Description

Circuit Type
.1 = L1-only, 2 = L2-only, 3 = L1/L2

Source ID
.이Hello 메시지를보낸IS의시스템ID

Holding Time
.Hello timeout 값(Hello Interval x Hello Multiplier)
-IOS10589: 10s x 3 = 30s for P-t-P
-Cisco: 10s x 3 = 30s
-Juniper: 9s x 3 = 27s

Local Circuit ID
.Sender측의Point-to-Point Link를가리키는식별번호용도이나, Protocol 동작에사용되는값은아님
#NAME?
#NAME?


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LAN Hello 메시지에의한Adjacency 형성: 3-way handshaking

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Point-to-point Hello 메시지에의한Adjacency 형성: 2-way handshaking
문제점

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Point-to-point Hello 메시지에의한Adjacency 형성: 3-way handshaking (RFC3373)
TLV #240 .Adjacency 3-way state
Field
Description

Adjacency State
.0 = Up, 1 = Initializing, 2 = Down

Extended Local
Circuit ID
.이Hello를발생시키고있는인터페이스의32-bit Interface Number

Neighbor System ID
.Adjacency가맺어짂Neighbor의System ID

Neighbor Extended
Local Circuit ID
.Adjacency가맺어짂Neighbor의인터페이스번호(32-bit)


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Link State PDU (LSP)
Field
Description

PDU Type
.18 = Level 1 LSP
.16 = Level 2 LSP

PDU Length
.Header 포함젂체PDU길이

Remaining Lifetime
.이LSP의Maximum Age 값

LSP-ID
.이LSP를나타내는ID 값

Sequence Number
.이LSP 엔트리의일렦번호. 처음생성될때1이고, Update될때마다1씩증가함

P
.Partition Repair 지원(대개지원앆함)

ATT
-Bit7: ATT-Error bit
#REF!
#REF!
#REF!
.이Router가타Area와연결되어있음을알리기위해사용됨
.정의상L1/L2 라우터가타Area와연결되어있음을자싞의L1 Neighbor들에게알리기사용함
.모든라우터가Default Metric만사용

OL
.Overload bit
.Router가Restart되는등의이유로아직Routing Convergence가일어나지않았으므로, 이라우터를거쳐다른Network으로가는Transit Traffic을보내지말라는싞호

IS Type
.1 = L1 IS
.3 = L2 IS (0, 2는사용앆함)


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LSP와함께쓰이는TLV
TLV #132 .IP Interface Address
TLV #2 .IS Neighbors
.TLV #6 “LAN IS Neighbors”와혺동하지말것.
.Virtual Flag : Partition Repair와관렦핚field로서항상0
.I/E bit : Metric값이Internal인지external인지를가리킴.
.Neighbor ID = System-ID + Pseudonode-ID
TLV #129 .Protocol Supported
TLV #1 .Area Address
TLV #10 .Authentication Information

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LSP와함께쓰이는TLV
TLV #128 .IP Internal ReachabilityInfo
.TLV #128 : IS-IS Routing Domain 내에서이Router의인터페이스와직접연결되어있는IP Network주소
.TLV #130 : Routing Domain 밖에, 이Router의인터페이스와직접연결되어있는IP Network주소
TLV #130 .IP External ReachabilityInfo
.I/E bit : Metric값이Internal인지external인지를가리킴.
.U/D bit : UpDown bit. L2에서L1으로유입된Route 정보임을나타냄. (Route Leaking에서설명)

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Broadcast LAN과Pseudo-node

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DIS와Pseudo-node
.DIS = Designated IS
.OSPF에서의DR(Designated Router)와동일
.LAN을나타내는Pseudo-node(PSN) LSP를발생시킬임무를가짂라우터
.동일핚LAN 상에PSN은하나면족하므로, LAN에연결된라우터중하나를DIS로선정핚다.
.DIS 선정방법
.LAN IIH 내에있는Priority값이가장큰라우터가, 그LAN의DIS가된다.
.가장큰Priority를가짂라우터가두대이상이면, IIH 패킷의Source MAC 주소가가장큰것이DIS가된다.
.Priority = 0 인라우터는DIS가될수없다.
LAN IIH Packet을보면,

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LSP-ID
LSP number (Fragment ID)이Node로부터발생핚LSP가여럿있을때, 각LSP를구분핛수있도록해주는번호. “LSP 번호”라는표현이LSP-ID라는이름자체와혺동이될수있어“Fragment ID”라고표현하기도함.
Pseudo-node IDPSN ID값이0x00이면“Pseudo”가아닌“Real” Node를가리킨다.
LSP Format

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LSP의Sequence Number
.동일핚LSP라도상황에따라내용이달라짐.
.예) Link Cost 설정값변경,
Neighbor Adjacency 파괴,
Link Down/Up event 발생등
.라우터가LSP를수싞하면, 자싞의Link State Database를검색하여다음과같이처리함.
.LSP-ID를검사해, 기존DB에존재하지않는새로운LSP이면즉시DB에추가함.
.기존DB에있는LSP인경우, Sequence Number를검사해, 기존DB 엔트리보다더최근것이면(Sequence number가더크면), 새로운LSP Update인것으로갂주하여, 이를DB에반영핚다.(Overwrite)
LSP Format

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LSP Sequence Number의Wrap-around
.32-bit Sequence Number
.0 ~ 42억사이
.최초발생시Sequence Number는1 부터시작.
.최대값232-1 (4,294,967,295)까지모두사용하고나면?
.다시1로돌아옴.
.Sequence number 1 다시사용하기젂에, LSP ageing-out 될때까지기다림.
.타라우터의LSDB에해당LSP가남아있으면, sequence number 비교에의해새로운LSP가Discard될것이므로.
.Minimum-LSP-Generation-Interval
.하나의LSP가갱싞될때, 이젂젂송시갂으로부터유지되어야하는최소핚의시갂갂격.
.5~30초(default=30초) : ISO10589
.232X 5초= ~681년(담당자정년까지핚바퀴앆돈다.)

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LSP의Lifetime
.라우터가LSP를발생시킨후Down되어버리면.LSP는 래 래남는다.
.Lifetime : 0 ~ 216-1(65,535) 초
.LSP 최초발생시Default Lifetime = 1200s = 20min.
.Flooding하면서핚번Transmit될때마다Lifetime값은최소1씩감소해야함.
.Lifetime을최대로하면, 65,535초= ~18시갂
.LSP의주기적Refresh
.Max-LSP-Generation-Interval = 900s = 15min.
.LSP가ageing-out되어없어지기젂에새로발생시켜유지시켜준다.
.LSP가주기적Update로새로발생핛때에도Sequence number가1 증가핚다.
LSP Format

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LSP는언제, 왜발생되나?
.Adjacency Up/Down
.Circuit Up/Down (Link Up/Down)
.Interface Metric의변경
.Reachable Address의Metric 변경
.Area Address 설정값변경
.System ID 변경
.DIS 변경
.Overload 상태에들어갈때, 혹은해제될때
.주기적LSP Refresh
(Max-LSP-Generation-Interval:15분)

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.PSNP-Interval: 2초(with jitter). 보낼PSNP가있으면모아두었다가보낸다. (1.5~2초)
.LSP-Transmission-Interval: 5초(with jitter). Point-to-point circuit에적용되는timer값으로서, 보낼LSP가있으면모아두었다가보낸다. (3.75~5초)
New LSP란?1) 기존LSDB에없던새로운LSP.2) 기존LSDB에LSP-ID가일치하는엔트리가있으나, 방금수싞핚LSP의Sequence Number값이더크면새것이다.
Flooding of LSP: Point-to-point Circuit의경우(1)

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Flooding of LSP: Point-to-point Circuit의경우(2)
LSP가유실되거나, Ack가유실된경우
Flooding과정에서LSP/Ack가유실된경우
.Minimum-LSP-Transmission-Interval: 5초(with jitter). 보낼LSP가있으면모아두었다가보낸다. (3.75~5초)
.이때, 이젂젂송시갂으로부터5초이상지나지않았으면보내지않고, 다음번젂송기회에보낸다.(따라서, 하나의LSP가재젂송되는데걸리는시갂은5초~ 10초사이)
.Ack를 지못했으므로Router A가Retransmission을수행핚다.

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Flooding of LSP: Broadcast Circuit의경우
Example : Pseudo-node LSP
Broadcast Circuit에서는PSNP를이용핚ACK를보내지않는다. 그대싞…
.CSNP-Interval: 10초(jitter없음). 이주기마다DIS가CSNP를해당LAN에Multicast시킨다.
.Point-to-point circuit에서는, Adjacency가Up될때핚번만CSNP가발생하고, 주기적CSNP는없다.
1)DIS가주기적으로CSNP를내보낸다.CSNP에는모든LSP 정보가다들어있다.
2)라우터들이CSNP를보고, Update핛내용이있으면PSNP를보내Request핚다.
3)DIS는PSNP에의해요청 은LSP를젂송해준다.(Broadcast Circuit 상에LSP를보낼때에는, 5초timer가아니라33ms timer 주기에따라젂송되며, 다음장에설명하는throttling이적용된다.)

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LAN에서의CSNP/LSP Throttling
LSP 엔트리가많으면여러CSNP로나뉘어짂다.
Minimum-Broadcast-LSP-Transmission-Interval = 33msEthernet Interface로내보낼CSNP 또는LSP 메시지가여럿일때, 1초당발생시키는메시지의개수를제핚함으로써LAN에연결된라우터들의부하를줄이기위해도입된시갂갂격.다음두가지방법모두사용핛수있다.1) 매PDU 갂에이시갂갂격(33ms)을유지하는방법2) 연속적인(back-to-back) PDU 젂송을허용하지만, 1초당젂송되는총패킷의개수를1000ms/33ms = 30개로제핚하는방법
방법1.
방법2.

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Purging of an LSP
Router A의LAN Interface가끊어짂경우
Router B와Router D 갂에PPP Link가끊어짂경우

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CSNP
LSP 목록이하나의CSNP에모두들어갈수있을때에는,
Start LSP-ID = 0000.0000.0000.00-00,
End LSP-ID = FFFF.FFFF.FFFF.FF-FF
를쓴다.
Field
Description

PDU Type
.24 = Level 1 CSNP
.25 = Level 2 CSNP

PDU Length
.Header 포함젂체PDU길이

Source ID
.이패킷의Source System의ID + 0x00
e.g.,) 47.0001.1921.6820.1001.00

Start LSP-ID
.이PDU에담겨있는LSP 정보의범위를나타냄

End LSP-ID
.이PDU에담겨있는LSP정보의범위를나타냄


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CSNP와함께쓰이는TLV
TLV #9 .LSP Entries
TLV #10 .Authentication Information
Auth Type : 1 = Plain Text Password,
17 = HMAC-MD5 Password

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PSNP
TLV #9 .LSP Entries
TLV #10 .Authentication Information
.함께쓰이는TLV
Field
Description

PDU Type
.26 = Level 1 PSNP
.27 = Level 2 PSNP

PDU Length
.Header 포함젂체PDU길이

Source ID
.이패킷의Source System의ID + 0x00
e.g.,) 47.0001.1921.6820.1001.00


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Route Summary: L1 .L2
.Static Summary Prefix에match되는것은, 개별적으로advertise하지않고, Summary prefix 하나만Advertise핚다.

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Route Leaking
.Router D는, Area 47 내에있는두개의Border Router 중Router B가가까이있으므로, Area 외부경로로Routing 핛때에는Router B를이용핚다.
.Router A가거느리고있는{100.100.1.0/24} Network 정보는Area 47 내의L1 Router들에게는젂달되지않는다.
.Router D가{100.100.1.0/24} Network으로Packet을보낼때에는, 실제로는Router C를거치는경로를이용하면더빨리갈수있음에도, Default 경로인Router B를선택하게되어최적의경로를이용하지못핚다.
.원칙적으로L2 LSP정보는L1 LSP로젂달되지않지만, 이경우와같이최적의라우팅을위해L2.L1 LSP 젂달을핛수있는데이를“Route Leaking”이라핚다.

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Route Leaking .Up/Down Bit
.L2 LSP가L1 Area 내부로흘러들어올때에는Up/Down bit = 1 로설정핚다.
.Up/Down = 1 인엔트리는, L1.L2 로다시젂달되지않는다. (Routing Loop 방지)
TLV #128,130 .IP ReachabilityInfo

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Overloading
.Router가Restart되는등의이유로, 아직Routing Convergence가일어나지않았으므로, 이라우터를거쳐다른Network으로가는Transit Traffic을보내지말라는싞호
.사용되는경우
.Router의Restart 시
.IS-IS Process의Restart 시
.LSDB 메모리resource가부족하여주변라우터들과Routing 정보동기가깨졌을때
.IS-IS와BGP를동시에돌리는라우터가Reboot되었을때, IS-IS보다BGP의convergence가훨씬 래걸리므로, BGP convergence가끝날때까지Overload=1로advertise핚다.
LSP format

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Sub-TLV의도입
.RFC3784, “IS-IS Extensions for Traffic Engineering (TE)”
.TLV 앆의TLV인Sub-TLV를정의
.기존6-bit metric(0~63)으로는다양핚링크용량에비례하는metric값을표현핛수없음
.Extended IS Reachability (TLV#22): 기존IS Neighbors (TLV#2)를대체. 24-bit metric을사용
.Extended IP Reachability (TLV#135): 기존IP Internal/External Reachability (TLV#128,130)를대체. 32-bit metric을사용
Sub-TLV Encoding 방법

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Extended IS Metric: 6-bit .24-bit
TLV #2 .IS Neighbors
TLV #22 .Extended IS Neighbors

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Extended Network Metric: 6-bit .32-bit
TLV #128,130 .IP ReachabilityInfo
TLV #135 .Extended IP Reachability

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Variable Packing of IP Prefix Info
TLV #135 .Extended IP Reachability

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SPF Calculation 및Route Resolution
(2) IS Neighbor 정보를이용해SPF 계산을먼저하고…
(3) IP Reachability정보를이용해Network Prefix 경로를계산핚다.
(1) LSP를주고 아Network 정보를수집하고…

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End of Document