introduction to isisftp.ipsyn.net/.../isp-routing/3-introduction_to_isis-1up.pdf · 2001. 5. 1. ·...
TRANSCRIPT
1© 1999, Cisco Systems, Inc.
Introduction to ISISIntroduction to ISISIntroduction to ISIS
ISP/IXP WorkshopsISP/IXP WorkshopsISP/IXP Workshops
2ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
AcknowledgementsAcknowledgementsAcknowledgements
• Thanks to Stefano Previdi
• Any questions
3© 1999, Cisco Systems, Inc.
Basic ISISBasic ISISBasic ISIS
3ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
4ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
ISIS - Intermediate System toISIS - Intermediate System toIntermediate SystemIntermediate System
• Link state protocol for IP and CLNS,RFC1195, ISO 10589
• Each router sends Hello PDU IIHs andbuild adjacencies with neighbours
• Each router creates an LSP and floodit to neighbours
• Each router receives all LSPs fromneighbours
5ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Introduction to ISISIntroduction to ISIS
• Each router maintains database (L1, L2, orboth)
• Each router runs the Dijkstra (SPF)algorithm on the database to calculatetopology
• Each router runs Partial Route Calculation(PRC) to calculate IP routing information
• Each router has the full visibility of thenetwork (or the area)
6ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
ISIS LevelsISIS Levels
• ISIS has a 2 layer hierarchy
Level-2 (the backbone)
Level-1 (the areas)
• A router can be
Level-1 (L1) router
Level-2 (L2) router
Level-1-2 (L1L2) router
7ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
ISIS LevelsISIS Levels
• Level-1 router
Has neighbours only on the same area
Has a level-1 LSDB with all routing information for thearea
• Level-2 routerMay have neighbours in the same or other areas
Has a Level-2 LSDB with all routing information aboutinter-area
• Level-1-2 router
May have neighbours on any area.
Has two separate LSDBs: level-1 LSDB & level-2 LSDB
8ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
BackboneBackbone
• ISIS does not have a backbone
area
• The backbone is the contiguous
collection of Level-2 capable
routers
9ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
L1L2
L1L2
L1L2
L1L2
L1L2
L1-only
L2-only
L1-only
L1, L2, and L1L2 Routers
Area-2
Area-1
Area-3
Area-4
L1-only
L1-only
10ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
ISIS AreasISIS Areas
• ISIS area borders are on links, notrouters
• Each router is identified withNetwork Entity Title (NET)
• NET: An NSAP where n-selector is 0
11ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
NSAP and AddressingNSAP and Addressing
• NSAP: Network Service Access Point
Total length between 8 and 20 bytes
Area Address: variable length field (up to 13 bytes)
System ID: defines an ES or IS in an area.
NSEL: N-selector. identifies a network service user(transport entity or the IS network entity itself)
• NET: the address of the network entity itself
12ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
An Addressing ExampleAn Addressing Example
39.0f01.0002.3333.3333.3333.00
39.0f01.0001.2222.2222.2222.00
39.0f01.0001.1111.1111.1111.00
39.0f01.0004.7777.7777.7777.00
39.0f01.0003.6666.6666.6666.00
39.0f01.0004.8888.8888.8888.00
39.0f01.0002.4444.4444.4444.00
Area 1
Area 3
Area 4
Area 2
13ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
• Hello PDU IIHs are exchangedbetween routers to formadjacencies
• Area addresses are exchanged inIIH PDUs
AdjacenciesAdjacencies
ISIS adjacency through IIH
14ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Link State PDU (LSP)Link State PDU (LSP)
• Each router creates an LSP and flood it
to neighbors
• A level-1 router will create level-1 LSP(s)
• A level-2 router will create level-2 LSP(s)
• A level-1-2 router will create
level-1 LSP(s) and
level-2 LSP(s)
15ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
LSP headerLSP header
• LSPs have
Fixed header
TLV coded contents
• The LSP header contains
LSP-id
Sequence number
Remaining Lifetime
Checksum
Type of LSP (level-1, level-2)
Attached bit
Overload bit
16ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
LSP ContentsLSP Contents
• The LSP contents are coded asTLV (Type, Length, Value)
Area addresses
IS neighbors
Authentication Info
17ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
LSDB contentLSDB content
• Each router maintains a separate LSDB forlevel-1 and level-2 LSPs
• LSP headers and contents
• SRM bits: set per interface when router has to flood this LSP
• SSN bits: set per interface when router has to send a PSNP for this LSP
18ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Flooding of LSPsFlooding of LSPs
• New LSPs are flooded to all neighbors
• It is necessary that all routers get allLSPs
• Each LSP has a sequence number
• 2 kinds of flooding
Flooding on a p2p link
Flooding on LAN
19ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Flooding on a p2p linkFlooding on a p2p link
• Once the adjacency isestablished both routers sendCSNP packet
• Missing LSPs are sent by bothrouters if not present in thereceived CSNP
• Missing LSPs may be requestedthrough PSNP
20ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Flooding on a P2P LinkFlooding on a P2P Link
Receives LSPid=x seqnr=22
It’s new.Put it in the LSDBNow let’s flood itSet SRM bitSend over p2p
Received ackClear SRM bit
Received it.My own copyhas seqnr=21.So it is new,Install it in LSDB.Acknowledge it.Maybe flood further.
LSP ->id=x seqnr=22
<- PSNPid=x seqnr=22
21ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Flooding on a LANFlooding on a LAN
• There’s a Designated Router (DIS)
• DIS election is based on priority
• Breaking-tie is the highest MAC address
• DIS has two tasksConducting the flooding over the LANCreating and updating a special LSP describing the
LAN topology (Pseudonode LSP)
• Pseudonode represents LAN (created by theDIS)
22ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Flooding on a LAN Flooding on a LAN
LAN
Physical view Logical view
the DIS
the DIS
a Pseudonode
ES ES
23ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Flooding on a LANFlooding on a LAN
• DIS conducts the flooding over theLAN
• DIS multicasts CSNP every 10seconds
• All routers in the LAN check theCSNP against their own LSDB (andmay ask specific re-transmissionswith PSNPs)
24ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
<- CSNPid=y seqnr=...id=x seqnr=22id=z ...
<- LSP
Flooding on a LANFlooding on a LANReceived new LSPid=x seqnr=22Install in LSDBSet SRM bitFlood the LSPClear SRM bit !
Periodic CSNPevery 10 sec's
Oh, he has an oldLSP, better resendhim latestPSNP ->
id=xseqnr=21
a LANthe DISAn ordinary
router
Dropped LSP !(bad bad) :-
Gosh, I’ve gotup-to-date y and zBut my x is old !Request latest x
Got it. Install andrun SPF, but don’tsend PSNP <- LSP
id=x seqnr=22
25ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Complete Sequence NumberComplete Sequence NumberPDUPDU
• Describes all LSPs in your LSDB (inrange)
• If LSDB is large, multiple CSNPs aresent
• Used at 2 occasionsPeriodic multicast by DIS (every 10
seconds) to synchronise LSDB overLAN subnets
On p2p links when link comes up
26ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Partial Sequence Number Partial Sequence Number PDUsPDUs
• PSNPs Exchanged on p2p links (ACKs)
• Two functionsAcknowledge receipt of an LSPRequest transmission of latest LSP
• PSNPs describe LSPs by its headerLSP identifierSequence numberRemaining lifetimeLSP checksum
27ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
ConfigurationConfiguration
• L1, L2, L1-L2By default cisco routers will be L1L2 routersRouters can be manually configured to
behave asLevel-1 only, Level-2 only, Level-1-2
Configuration can be done perinterface or at the router level
Area-2 Area-3 Area-1
Rtr-A Rtr-B Rtr-C
28ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
ConfigurationConfiguration
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Router-B
Interface Loopback0ip address 192.168.1.1 255.255.255.255!Interface Pos2/0/0ip address 192.168.222.1 255.255.255.0ip router isisisis circuit-type level-2!FastEthernet4/0/0ip address 192.168.120.10 255.255.255.0ip router isisisis circuit-type level-1!router isispassive-interface Loopback0net 49.0001.1921.6800.1001.00
Router-A
Interface Loopback0ip address 192.168.1.5 255.255.255.255!interface FastEthernet0/0ip address 192.168.120.5 255.255.255.0ip router isis!router isisis-type level-1passive-interface Loopback0net 49.0001.1921.6800.1005.00
29ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
ConfigurationConfiguration
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Router-C
Interface Loopback0ip address 192.168.2.2 255.255.255.255!Interface Pos1/0/0ip address 192.168.222.2 255.255.255.0ip router isisisis circuit-type level-2!interface Fddi3/0ip address 192.168.111.2 255.255.255.0ip router isisisis circuit-type level-1!router isispassive-interface Loopback0net 49.0002.1921.6800.2002.00
Router-D
Interface Loopback0ip address 192.168.2.4 255.255.255.255!interface Fddi6/0ip address 192.168.111.4 255.255.255.0ip router isis!router isisis-type level-1passive-interface Loopback0net 49.0002.1921.6800.2004.00
30ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Show CLNSShow CLNS
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> sh clnsGlobal CLNS Information: 2 Interfaces Enabled for CLNS NET: 49.0001.1921.6800.1001.00 Configuration Timer: 60, Default Holding Timer: 300, PacketLifetime 64 ERPDU's requested on locally generated packets Intermediate system operation enabled (forwarding allowed) IS-IS level-1-2 Router: Routing for Area: 49.0001
31ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Show Show clns clns neighborsneighbors
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> show clns neighborsSystem Id SNPA Interface State Holdtime Type Protocol1921.6800.2002 *PPP* PO2/0/0 Up 29 L2 IS-IS1921.6800.1005 00e0.1492.2c00 Fa4/0/0 Up 9 L1 IS-IS
32ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Show Show clns clns interfaceinterface
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> sh clns int POS2/0/0POS2/0/0 is up, line protocol is up Checksums enabled, MTU 4470, Encapsulation PPP ERPDUs enabled, min. interval 10 msec. RDPDUs enabled, min. interval 100 msec., Addr Mask enabled Congestion Experienced bit set at 4 packets CLNS fast switching disabled CLNS SSE switching disabled DEC compatibility mode OFF for this interface Next ESH/ISH in 47 seconds Routing Protocol: IS-IS Circuit Type: level-1-2 Interface number 0x0, local circuit ID 0x100 Level-1 Metric: 10, Priority: 64, Circuit ID: 1921.6800.2002.00 Number of active level-1 adjacencies: 0 Level-2 Metric: 10, Priority: 64, Circuit ID: 1921.6800.1001.00 Number of active level-2 adjacencies: 1 Next IS-IS Hello in 2 seconds
33ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
ShowShow clns clns interface interface
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> sh clns int FastEthernet4/0/0FastEthernet4/0/0 is up, line protocol is up Checksums enabled, MTU 1497, Encapsulation SAP ERPDUs enabled, min. interval 10 msec. RDPDUs enabled, min. interval 100 msec., Addr Mask enabled Congestion Experienced bit set at 4 packets CLNS fast switching enabled CLNS SSE switching disabled DEC compatibility mode OFF for this interface Next ESH/ISH in 1 seconds Routing Protocol: IS-IS Circuit Type: level-1 Interface number 0x1, local circuit ID 0x1 Level-1 Metric: 10, Priority: 64, Circuit ID: 1921.6800.1005.01 Number of active level-1 adjacencies: 1 Next IS-IS LAN Level-1 Hello in 3 seconds
34ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Show Show clns clns protocolprotocol
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> show clns protocolIS-IS Router: <Null Tag> System Id: 1921.6800.1001.00 IS-Type: level-1-2 Manual area address(es): 49.0001 Routing for area address(es): 49.0001 Interfaces supported by IS-IS: FastEthernet4/0/0 - IP POS2/0/0 - IP Redistributing: static Distance: 110Rtr-B>
35ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Show Show clns clns traffictraffic
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> show clns trafficCLNS & ESIS Output: 14, Input: 436CLNS Local: 0, Forward: 0CLNS Discards: Hdr Syntax: 0, Checksum: 0, Lifetime: 0, Output cngstn: 0 No Route: 0, Dst Unreachable 0, Encaps. Failed: 0 NLP Unknown: 0, Not an IS: 0CLNS Options: Packets 0, total 0, bad 0, GQOS 0, cngstn exprncd 0CLNS Segments: Segmented: 0, Failed: 0CLNS Broadcasts: sent: 0, rcvd: 0Echos: Rcvd 0 requests, 0 replies Sent 0 requests, 0 repliesESIS(sent/rcvd): ESHs: 0/0, ISHs: 14/15, RDs: 0/0, QCF: 0/0ISO-IGRP: Querys (sent/rcvd): 0/0 Updates (sent/rcvd): 0/0ISO-IGRP: Router Hellos: (sent/rcvd): 0/0ISO-IGRP Syntax Errors: 0IS-IS: Level-1 Hellos (sent/rcvd): 84/244IS-IS: Level-2 Hellos (sent/rcvd): 0/0IS-IS: PTP Hellos (sent/rcvd): 84/82
36ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
ShowShow clns clns traffic traffic
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
IS-IS: Level-1 LSPs sourced (new/refresh): 7/1IS-IS: Level-2 LSPs sourced (new/refresh): 5/0IS-IS: Level-1 LSPs flooded (sent/rcvd): 5/5IS-IS: Level-2 LSPs flooded (sent/rcvd): 1/6IS-IS: LSP Retransmissions: 0IS-IS: Level-1 CSNPs (sent/rcvd): 0/82IS-IS: Level-2 CSNPs (sent/rcvd): 1/1IS-IS: Level-1 PSNPs (sent/rcvd): 1/0IS-IS: Level-2 PSNPs (sent/rcvd): 3/1IS-IS: Level-1 DR Elections: 2IS-IS: Level-2 DR Elections: 1IS-IS: Level-1 SPF Calculations: 3IS-IS: Level-2 SPF Calculations: 3IS-IS: Level-1 Partial Route Calculations: 0IS-IS: Level-2 Partial Route Calculations: 0IS-IS: LSP checksum errors received: 0IS-IS: Update process queue depth: 0/200IS-IS: Update process packets dropped: 0
37ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Show Show isis isis databasedatabase
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routersRtr-B> show isis databaseIS-IS Level-1 Link State DatabaseLSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL1921.6800.1001.00-00* 0x00000019 0x2783 1153 1/0/0 (11)1921.6800.1005.00-00 0x0000000C 0x2179 905 0/0/0 (5)1921.6800.1005.01-00 0x00000009 0x40EC 831 0/0/0 (4)
IS-IS Level-2 Link State DatabaseLSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL1921.6800.1001.00-00* 0x00000010 0xFC45 1153 0/0/0 (9)1921.6800.1001.01-00* 0x00000001 0x4CB7 1137 0/0/0 (10)1921.6800.2002.00-00 0x00000018 0x86A6 1141 0/0/0 (3)1921.6800.2002.02-00 0x00000004 0x8558 881 0/0/0 (2)
38ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
ShowShow isis isis database database
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> sh isis database 1921.6800.1001.00-00 detail
IS-IS Level-1 LSP 1921.6800.1001.00-00LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL1921.6800.1001.00-00* 0x00000006 0x4D70 991 1/0/0 (1) Area Address: 49.0001 NLPID: 0xCC IP Address: 192.168.120.10 Metric: 10 IP 192.168.222.0 255.255.255.0 Metric: 10 IP 192.168.120.0 255.255.255.0 Metric: 0 IP 192.168.1.1 255.255.255.255 Metric: 10 IS 1921.6800.1005.01 Metric: 0 ES 1921.6800.1001
39ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
ShowShow isis isis database database
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
IS-IS Level-2 LSP 1921.6800.1001.00-00LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL1921.6800.1001.00-00* 0x00000004 0x1539 980 0/0/0 (2) Area Address: 49.0001 NLPID: 0xCC IP Address: 192.168.222.1 Metric: 10 IS 1921.6800.1001.01 Metric: 10 IS 1921.6800.2002.00 Metric: 10 IP 192.168.120.0 255.255.255.0 Metric: 0 IP 192.168.1.1 255.255.255.255 Metric: 10 IP 192.168.1.5 255.255.255.255 Metric: 10 IP 192.168.222.0 255.255.255.0
40ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Show Show isis spfisis spf-log-log
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routersRtr-B> show isis spf-log Level 1 SPF log When Duration Nodes Count Last trigger LSP Triggers00:06:30 0 1 6 1921.6800.1001.00-00 NEWAREA RTCLEARED NEWADJ NEWLSP
TLVCONTENT00:06:20 0 3 3 1921.6800.1005.01-00 NEWADJ TLVCONTENT00:06:05 0 3 2 1921.6800.1001.00-00 ATTACHFLAG LSPHEADER
Level 2 SPF log When Duration Nodes Count Last trigger LSP Triggers00:06:31 0 1 2 1921.6800.1001.00-00 RTCLEARED NEWLSP00:06:21 0 1 3 1921.6800.1001.00-00 NEWADJ TLVCODE TLVCONTENT00:06:11 0 2 1 1921.6800.2002.00-00 LSPHEADER
41ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Network Design IssuesNetwork Design Issues
• As in all IP network designs, the key issueis the addressing lay-out
• ISIS support large number of routers in asingle area
• When using areas, use summary-addresses
• 400 routers in the backbone has been done
42ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Network Design IssuesNetwork Design Issues
• Possible link costDefault on all interface is 10Manually configured according to routing strategy
• Summary address cost
Equal to the best more specific cost
Plus cost to reach neighbor of best specific
• Backbone has to be contiguous
Ensure continuity by redundancy
• Area partitioningDesign so that backbone can not be partitioned
43ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Scaling IssuesScaling Issues
• Areas vs. single areaUse areas where
sub-optimal routing is not an issue
areas with one single exit point
Start with L2-only everywhere is a goodchoice
Future implementation of level-1 areas will beeasier
Backbone continuity is ensured from start
44© 1999, Cisco Systems, Inc.
Advanced ISISAdvanced ISISAdvanced ISIS
44ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
45ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
ISIS LevelsISIS Levels
•Level-1 router
Use the closest Level-2 router to exitthe area
•Level-1-2 router
If the router has adjacencies to otherareas, it will inform the level-1 routers(intra-area) it is a potential exit pointfor the area
46ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Non-Pseudonode LSPNon-Pseudonode LSP
• Non-Pseudonode LSP represents router
• Each router will create and flood a newNon-Pseudonode LSPWhen a new neighbor comes up or goes away
When new IP prefixes are inserted or removed
When the metric of a link is changed
When refresh interval timer expires
47ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Pseudonode LSPPseudonode LSP
• Pseudonode LSP represents LAN
• The DIS will create and flood anew Pseudonode LSPWhen a new neighbour comes up or
goes away
When refresh interval timer expires
• Reduces adjacencies and floodingover LAN subnets
48ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
LSP IdentifierLSP Identifier
• LSP identifier consists of 3 partsSource ID
System-ID of router (non-PN) or DIS (Pseudonode)
Pseudonode IDZero for router LSP, non-zero for Pseudonode LSP
LSP numberFragmentation number
• Example: 00c0.0040.1234.02-00
SystemID
PN-ID
Frag-Nr
49ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
LSP HeaderLSP Header
• LSP sequence numberUsed to determine the newest LSP
version
• LSP remaining lifetimeUsed to purge old LSPs
• LSP checksum
• LSP typelevel-1 or level2
50ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
LSP HeaderLSP Header
• LSP Attached bitSet in the level-1 LSP by a L1-L2 router
if it has connectivity to another areaIndicate to the area routers (level-1)
that it is a potential exit point of thearea
Level-1 routers select the closest (bestmetric) level-2 router with the ATT-bitset
51ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
LSP HeaderLSP Header
• LSP Overload bit
Set by the router when it has an overloadproblem on its LSDB
The O-bit Indicates that the router has anincomplete LSP database, and hence cannot betrusted to compute any correct routes
LSP with O-bit is used in the LSDB but topologybehind it is not calculated
Therefore other routers do not compute routeswhich would require the PDU to pass throughthe overloaded router
52ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Flooding in depthFlooding in depth
• LSPs hold a Remaining LifetimeSet to 20 minutes by the originating routerAfter 20 min. each router must remove the LSPPrevents old LSPs to stay in the LSDB forever
• Periodic refresh of LSPsrouter resends LSP at least every 15 mins
• Can be set up to 18.7 HoursCut back on “background LSP noise”
53ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Flooding in depthFlooding in depth
• Network wide LSP purgesWhen a router detects a corrupted or an
expired LSP, it sets RL to 0, and floods theLSP header
All routers will now remove the LSPsimultaneous
New DIS purges old Pseudonode LSP
• LSPs hold a checksum
To detect LSDB corruption in router’s memory
54ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Flooding in depthFlooding in depth
• Sequence number overflow is unlikelyto happen4 Bytes seqnr is enough for 120 years
• Restarting of a routerUse sequence number = 1Neighbour will flood old LSP with old
sequence numberRouter can now set sequence number higher
then before reboot, so everyone will usethe latest LSP
55ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
LSP refreshLSP refresh
• LSP are refreshed when refresh timerexpiresRefresh-timer trigger new LSP generation and
flooding
LSP lifetime (LSP header) gives remaining time
LSP lifetime is used by routers anddecremented
When lifetime is 0, LSP purged from LSDB
Decrement allows different lifetimes per router
56ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Configurable TimersConfigurable Timers
• Timers are configurablecsnp-interval Set CSNP interval in seconds
hello-interval Set Hello interval in seconds
hello-multiplier Set multiplier for Hello holding time
lsp-interval Set LSP transmission interval
retransmit-interval Set per-LSP retransmission interval
retransmit-throttle-interval Set interface LSP retransmission interval
lsp-gen-interval Minimum interval between regenerating same LSP
lsp-refresh-interval Set LSP refresh interval
max-lsp-lifetime Set maximum LSP lifetime
prc-interval Minimum interval between partial route calculations
spf-interval Minimum interval between SPF calculations
57ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
New FeaturesNew Features
• Metrics are 3 bytes (2^24) wide with 12.0S
• Specific routes leaking from L2 to L1 with12.0S
• Mesh-groups
Mesh-groups allow LSP flooding on selected sub-interface (thus neighbours)
Avoid flooding over all interfaces
Use is recommended on NBMA clouds
58ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Mesh-groupMesh-group
• Router-B will receive 4 instances of Router-A LSP
• Mesh-groups will allow to flood only on selected links
• Mesh-groups are configured on interfaces
Router-B
Router-A
59ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Timer IssuesTimer Issues
• Timers can be adapted to large topologiesLSP, Hello, CSNP, retransmission intervals
Refresh intervalTrade-off between reduced flooding and purge of corrupted
LSPs
SPF and PRC interval
LSP maximum lifetimeMaximum value is recommended
Will significantly reduce LSP re-flooding
Old copies of LSPs may be present in LSDB (but will not beused).
60ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Timer IssuesTimer Issues
• In some topological cases really fastconvergence is needed
HSRP and ISISWith HSRP the routers have to converge
rapidly in order to switch from/to active andpassive states
Hello-interval and lsp-gen-interval can bereduced
routing traffic will increase (possible routeflapping)
61ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
IP SummarisationIP Summarisation
• A L1L2 router will insert L1 IPprefixes into its L2 LSP
• Summarisation reduces L2 LSDBsize
• Configurable on Level-1 andLevel-2 routers
• More specific should be present
62ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
IP SummarisationIP Summarisation
• Summary addresses for level-1summary address is created forredistributed prefixes
• Summary addresses for level-2summary address is created for
redistributed prefixes
L1 routes
63ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
IP specificIP specific
• Default routingBoth level-1 and level-2 ISs can
generate a default routeA level-1 IS will always prefer a level-1
default route BEFORE using the ATT(closest level-2 capable IS)
Creates an IP External prefix in L1 or L2non-PN LSP
64ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Default routeDefault route
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-A> show ip routeGateway of last resort is 192.168.120.10 to network 0.0.0.0
C 192.168.120.0/24 is directly connected, FastEthernet0/0 192.168.1.0/32 is subnetted, 2 subnetsi L1 192.168.1.1 [115/10] via 192.168.120.10, FastEthernet0/0C 192.168.1.5 is directly connected, Loopback0i L1 192.168.222.0/24 [115/20] via 192.168.120.10, FastEthernet0/0i*L1 0.0.0.0/0 [115/10] via 192.168.120.10, FastEthernet0/0
65ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Summary routeSummary route
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routersrouter isis summary-address 55.0.0.0 255.0.0.0 level-1-2 summary-address 192.168.1.0 255.255.255.0 level-1-2 redistribute static ip metric 44 level-1-2 passive-interface Loopback0 net 49.0001.1921.6800.1001.00!ip route 55.1.0.0 255.255.0.0 Null0ip route 55.2.0.0 255.255.0.0 Null0
66ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Summary routeSummary route
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> sh isis da 1921.6800.1001.00-00 det
IS-IS Level-1 LSP 1921.6800.1001.00-00LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL1921.6800.1001.00-00* 0x00000062 0x770C 1028 1/0/0 (1) Area Address: 49.0001 NLPID: 0xCC IP Address: 192.168.120.10 Metric: 10 IP 192.168.222.0 255.255.255.0 Metric: 10 IP 192.168.120.0 255.255.255.0 Metric: 0 IP 192.168.1.1 255.255.255.255 Metric: 10 IS 1921.6800.1005.01 Metric: 0 ES 1921.6800.1001 Metric: 44 IP-External 171.68.0.0 255.255.0.0 Metric: 44 IP-External 172.17.0.0 255.255.0.0 Metric: 44 IP-External 144.254.0.0 255.255.0.0 Metric: 44 IP-External 55.0.0.0 255.0.0.0
67ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Summary routeSummary route
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
IS-IS Level-2 LSP 1921.6800.1001.00-00
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
1921.6800.1001.00-00* 0x0000005F 0xB264 1027 0/0/0 (2)
Area Address: 49.0001
NLPID: 0xCC
IP Address: 192.168.222.1
Metric: 10 IS 1921.6800.1001.01
Metric: 10 IS 1921.6800.2002.00
Metric: 44 IP-External 171.68.0.0 255.255.0.0
Metric: 10 IP 192.168.120.0 255.255.255.0
Metric: 44 IP-External 172.17.0.0 255.255.0.0
Metric: 44 IP-External 144.254.0.0 255.255.0.0
Metric: 10 IP 192.168.222.0 255.255.255.0
Metric: 44 IP-External 55.0.0.0 255.0.0.0
Metric: 0 IP 192.168.1.0 255.255.255.0
68ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Attached bitAttached bit
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-A> show isis database
IS-IS Level-1 Link State DatabaseLSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL1921.6800.1001.00-00 0x00000006 0x4D70 666 1/0/0 (4)1921.6800.1001.01-00 0x00000001 0x1136 0 (648) 0/0/0 (3)1921.6800.1005.00-00* 0x00000002 0x356F 647 0/0/0 (1)1921.6800.1005.01-00* 0x00000001 0x50E4 647 0/0/0 (2)
69ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Debug Debug isis adjisis adj-packets-packets
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B# debug isis adj-packets
ISIS-Adj: Rec L1 IIH from 00e0.1492.2c00 (FastEthernet4/0/0), cir type 1, cir id 1921.6800.1005.01 ISIS-Adj: Sending L1 IIH on FastEthernet4/0/0 ISIS-Adj: Rec L1 IIH from 00e0.1492.2c00 (FastEthernet4/0/0), cir type 1, cir id 1921.6800.1005.01 ISIS-Adj: Sending serial IIH on POS2/0/0 ISIS-Adj: Rec serial IIH from *PPP* on POS2/0/0, cir type 3, cir id 00
70ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Debug Debug isis spfisis spf-events-events
Rtr-B# debug isis spf-eventsISIS-SPF: Compute L1 SPTISIS-SPF: Move 1921.6800.1001.00-00 to PATHS, metric 0ISIS-SPF: thru 2147483647/2147483647/2147483647, delay 0/0/0, mtu 2147483647/2147483647/2147483647, hops 0/0/0, ticks 0/0/0ISIS-SPF: Add 1921.6800.1005.01-00 to TENT, metric 10ISIS-SPF: Next hop localISIS-SPF: Move 1921.6800.1005.01-00 to PATHS, metric 10ISIS-SPF: thru 2147483647/2147483647/2147483647, delay 0/0/0, mtu 2147483647/2147483647/2147483647, hops 0/0/0, ticks 0/0/0ISIS-SPF: considering adj to 1921.6800.1005 (FastEthernet4/0/0) metric 10ISIS-SPF: (accepted)ISIS-SPF: Add 1921.6800.1005.00-00 to TENT, metric 10ISIS-SPF: Next hop 1921.6800.1005 (FastEthernet4/0/0)ISIS-SPF: Move 1921.6800.1005.00-00 to PATHS, metric 10ISIS-SPF: Add 192.168.120.0/255.255.255.0 to IP route table, metric 20ISIS-SPF: Next hop 1921.6800.1005/192.168.120.5 (FastEthernet4/0/0) (rejected)ISIS-SPF: Add 192.168.1.5/255.255.255.255 to IP route table, metric 10ISIS-SPF: Next hop 1921.6800.1005/192.168.120.5 (FastEthernet4/0/0) (accepted)ISIS-SPF: Add 144.254.0.0/255.255.0.0 to IP route table, metric 60ISIS-SPF: Next hop 1921.6800.1005/192.168.120.5 (FastEthernet4/0/0) (rejected)
71ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Debug Debug isis snpisis snp-packets-packets
Rtr-B# debug isis snp-packets
ISIS-SNP: Rec L1 CSNP from 1921.6800.1005 (FastEthernet4/0/0)ISIS-SNP: CSNP range 0000.0000.0000.00-00 to FFFF.FFFF.FFFF.FF-FFISIS-SNP: Same entry 1921.6800.1001.00-00, seq 93ISIS-SNP: Same entry 1921.6800.1005.00-00, seq 78ISIS-SNP: Same entry 1921.6800.1005.01-00, seq 76
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
72ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
Area 49.0001 Area 49.0002
Rtr-C Rtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Debug Debug isis spfisis spf-update-update
Rtr-B(config)#int fa4/0/0Rtr-B(config-if)#isis metric 13Rtr-B(config-if)#^ZRtr-B#ISIS-SPF-TRIG: L1, new metricISIS-Update: Building L1 LSPISIS-Update: TLV contents different, code 80ISIS-Update: TLV contents different, code 2ISIS-SPF-TRIG: L1, 1921.6800.1001.00-00 TLV contents changed, code 2ISIS-Update: Full SPF requiredISIS-Update: Sending L1 LSP 1921.6800.1001.00-00, seq 96, ht 1199 on FastEthernet4/0/0ISIS-SNP: Rec L1 CSNP from 1921.6800.1005 (FastEthernet4/0/0)ISIS-Stats: Compute L1 SPTISIS-Stats: Complete L1 SPT, Compute time 0.000, 3 nodes, 2 links on SPT, 0 suspendsISIS-Update: Building L2 LSPISIS-Update: TLV contents different, code 80ISIS-Update: TLV contents different, code 80ISIS-Update: Leaf routes changedISIS-Update: Sending L2 LSP 1921.6800.1001.00-00, seq 96, ht 1199 on POS2/0/0ISIS-Update: Building L2 LSPISIS-Update: Rate limiting L2 LSP 1921.6800.1001.00-00, seq 97ISIS-Update: TLV contents different, code 80ISIS-Update: TLV contents different, code 80ISIS-Update: Leaf routes changedISIS-Update: Sending L2 LSP 1921.6800.1001.00-00, seq 97, ht 1196 on POS2/0/0
73ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
2 routers with the same System-ID2 routers with the same System-ID
• This is an illegal configuration
• “Possible duplicate System-IDs” warning2 Routers with same System-ID will see each
others LSP as their own, but not correct. Sothey will generate a new LSP with highersequence number.
This is an infinite ping-pong gameWhen an IS has to regenerate its LSP frequently,
it will generate the above warning
74ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
<- LSPid=x.00-00 seqnr=1
Two ISs Have Same SystemID xTwo ISs Have Same SystemID x
this IS has generatedan LSP withLSPid=x.00-00and seqnr=22
we ignore the LSPwith seqnr=1, aswe think it is old
we try to overrideseqnr=23
now this IS bootswith SystemID=x
during the floodingthey will notice themismatch.
when we receiveseqnr=22, we tryto override it bycreating a new LSPwith seqnr=23
<- LSPid=x.00-00 seqnr=23
<- LSPid=x.00-00 seqnr=25
LSP ->id=x.00-00 seqnr=24
LSP ->id=x.00-00 seqnr=22
etc, etc, etc .....
75ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
LSP Corruption StormsLSP Corruption Storms
• Suppose a link that corrupt packets,but regenerates the data-link layerCRC
Example is frame-relay to ATM switches
• ISIS gets LSP with incorrectchecksum
• Receiving router will do network-wide purge
76ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
LSP Corruption StormsLSP Corruption Storms
• Originating router will regenerateLSP
• This can create purge/re-floodstorms
• Configure “ignore-LSP-errors”
• New spec will allow the LSP discardwithout network-wide purge
77ISP/IXP Workshops © 1999, Cisco Systems, Inc. www.cisco.com
LSP ->id=x.00-00seqnr=22RL=1200
LSP Checksum ThrashingLSP Checksum Thrashing
<- LSPid=x.00-00seqnr=22RL=0
LSP -> id=x.00-00 seqnr=23 RL=1200
LSP ->id=x.00-00seqnr=22RL=1193
this IS got the LSP witha checksum error.So it purges it.
<- LSPid=x.00-00seqnr=22RL=0
LSP ->id=x.00-00seqnr=23RL=1194
someone purgedour LSP. let’sregenerate it
And on and on and ...
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