3 Introduction to ISIS 6up
-
Upload
suaknta-sarkar -
Category
Documents
-
view
237 -
download
0
Transcript of 3 Introduction to ISIS 6up
-
8/12/2019 3 Introduction to ISIS 6up
1/13
1Page 1
11999,CiscoSystems,Inc.
Introduction to ISISIntroduction to ISISIntroduction to ISIS
ISP/IXP WorkshopsISP/IXP WorkshopsISP/IXP Workshops
2ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
AcknowledgementsAcknowledgementsAcknowledgements
Thanks to Stefano Previdi
Any questions
31999,CiscoSystems,Inc.
Basic ISISBasic ISISBasic ISIS
3ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
4ISP/IXP Workshops 1999,CiscoSystems,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,CiscoSystems,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,CiscoSystems,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) routerLevel-2 (L2) router
Level-1-2 (L1L2) router
-
8/12/2019 3 Introduction to ISIS 6up
2/13
2Page 2
7ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
ISIS LevelsISIS Levels
Level-1 routerHas neighbours only on the same area
Has a level-1 LSDB with all routing information for thearea
Level-2 router
Mayhave 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,CiscoSystems,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,CiscoSystems,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,CiscoSystems,Inc. www.cisco.com
ISIS AreasISIS Areas
ISIS area borders are on links, not
routers
Each router is identified with
Network Entity Title (NET)
NET: An NSAP where n-selector is 0
11ISP/IXP Workshops 1999,CiscoSystems,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 itself12ISP/IXP Workshops 1999,CiscoSystems,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
-
8/12/2019 3 Introduction to ISIS 6up
3/13
3Page 3
13ISP/IXP Workshops 1999,CiscoSystems,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,CiscoSystems,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,CiscoSystems,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,CiscoSystems,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,CiscoSystems,Inc. www.cisco.com
LSDB contentLSDB content
Each router maintains a separate LSDB for
level-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,CiscoSystems,Inc. www.cisco.com
Flooding of LSPsFlooding of LSPs
New LSPs are flooded to all neighbors
It is necessary that all routers get all
LSPs
Each LSP has a sequence number
2 kinds of flooding
Flooding on a p2p link
Flooding on LAN
-
8/12/2019 3 Introduction to ISIS 6up
4/13
-
8/12/2019 3 Introduction to ISIS 6up
5/13
5Page 5
25ISP/IXP Workshops 1999,CiscoSystems,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 occasions
Periodic multicast by DIS (every 10seconds) to synchronise LSDB overLAN subnets
On p2p links when link comes up
26ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
Partial Sequence NumberPartial Sequence Number PDUsPDUs
PSNPs Exchanged on p2p links (ACKs)
Two functions
Acknowledge receipt of an LSP
Request transmission of latest LSP
PSNPs describe LSPs by its header
LSP identifier
Sequence number
Remaining lifetime
LSP checksum
27ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
ConfigurationConfiguration
L1, L2, L1-L2
By default cisco routers will be L1L2 routers
Routers can be manually configured tobehave as
Level-1 only, Level-2 only, Level-1-2
Configuration can be done perinterface or at the router level
Area-2 Area-3Area-1
Rtr-A Rtr-BRtr-C
28ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
ConfigurationConfiguration
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Router-B
Interface Loopback0
ip address 192.168.1.1 255.255.255.255
!
Interface Pos2/0/0
ip address 192.168.222.1 255.255.255.0
ip router isis
isis circuit-type level-2
!
FastEthernet4/0/0ip address 192.168.120.10 255.255.255.0
ip router isis
isis circuit-type level-1
!
router isis
passive-interface Loopback0
net 49.0001.1921.6800.1001 .00
Router-A
Interface Loopback0
ip address 192.168.1.5 255.255.255.255
!interface FastEthernet0/0
ip address 192.168.120.5 255.255.255.0
ip router isis
!
router isis
is-type level-1
passive-interface Loopback0
net 49.0001.1921.6800.1005 .00 29ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
ConfigurationConfiguration
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Router-C
Interface Loopback0
ip address 192.168.2.2 255.255.255.255
!
Interface Pos1/0/0
ip address 192.168.222.2 255.255.255.0
ip router isis
isis circuit-type level-2
!
interface Fddi3/0
ip address 192.168.111.2 255.255.255.0
ip router isis
isis circuit-type level-1
!
router isis
passive-interface Loopback0
net 49.0002.1921.6800.2002 .00
Router-D
Interface Loopback0
ip address 192.168.2.4 255.255.255.255
!
interface Fddi6/0
ip address 192.168.111.4 255.255.255.0
ip router isis
!
router isis
is-type level-1
passive-interface Loopback0
net 49.0002.1921.6800.2004 .00 30ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
Show CLNSShow CLNS
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> sh clnsGlobal CLNS Information:
2 Interfac es Enabled for CLNS NET: 49.0001.1921.6800.1001.00
Con figuration Timer: 60, Default Holding Timer: 300, Packet
Lifetime 64 ERPDU's requested on locally generated packets
Int ermediate system operation enabled (forwarding allowed) IS-IS level-1-2 Router:
Routing for Area: 49.0001
-
8/12/2019 3 Introduction to ISIS 6up
6/13
6Page 6
31ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
ShowShow clnsclns neighborsneighbors
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> show clns neighbors
System Id SNPA Interface State Holdtime Type Protocol
1921.6800.2002 *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,CiscoSystems,Inc. www.cisco.com
ShowShow clnsclns interfaceinterface
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> s h clns int POS2/0/0POS2/0/0 is up, line protocol is up
Checksums enabled , MTU 4470, Encapsulation PPP
ERPDUs enabled, min. interval 10msec.
RDPDUs enabled, min. interval 100 msec.,AddrMask enabled
Congestion Experienced bit set at 4 packets
CLNS fast switching disabled
CLNS SSE switching disabled
DEC compatibility mode OFF for this interface
Nex t 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: 1921.6800.2 002.00
Number of active level-1 adjacencies: 0
Level-2 Metric: 10, Priority: 64, Circuit ID: 1921.6800.1 001.00
Number of active level-2 adjacencies: 1
Next IS-IS Hello in 2 seconds
33ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
ShowShowclnsclnsinterfaceinterface
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> sh clns int FastEthernet4/0/0
FastEthernet4/0/0 is up, line protocol is up
Checksums enabled, MTU 1497, Encapsulation SAP
ERPDUs enabled, min. interval 10msec.
RDPDUs enabled, min. interval 100 msec.,AddrMask 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,CiscoSystems,Inc. www.cisco.com
ShowShow clnsclns protocolprotocol
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> show cln sprotocol
IS-IS Router:
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: 110
Rtr-B>
35ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
ShowShow clnsclns traffictraffic
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> show clnstraffic
CLNS & ESIS Output: 14, Input: 436
CLNS Local: 0, Forward: 0
CLNS 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: 0
CLNS Options: Packets 0, total 0, bad 0, GQOS 0, cngstn exprncd 0
CLNS Segments: Segmented: 0, Failed: 0
CLNS Broadcasts: sent: 0, rcvd: 0
Echos: Rcvd 0 requests, 0 replies
Sent 0 requests, 0 replies
ESIS(sent/rcvd): ESHs: 0/0, ISHs: 14/15,RDs: 0/0, QCF: 0/0
ISO-IGRP: Querys (sent/rcvd): 0/0 Updates (sent/rcvd): 0/0
ISO-IGRP: Router Hellos: (sent/rcvd): 0/0
ISO-IGRP Syntax Errors: 0
IS-IS: Level-1 Hellos (sent/rcvd): 84/244
IS-IS: Level-2 Hellos (sent/rcvd): 0/0
IS-IS: PTP Hellos (sent/rcvd): 84/82
36ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
ShowShowclnsclnstraffictraffic
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
IS-IS: Level-1 LSPs sourced (new/refresh): 7/1
IS-IS: Level-2 LSPs sourced (new/refresh): 5/0
IS-IS: Level-1 LSPs flooded (sent/rcvd): 5/5
IS-IS: Level-2 LSPs flooded (sent/rcvd): 1/6
IS-IS: LSP Retransmissions: 0
IS-IS: Level-1 CSNPs (sent/rcvd): 0/82
IS-IS: Level-2 CSNPs (sent/rcvd): 1/1
IS-IS: Level-1 PSNPs (sent/rcvd): 1/0
IS-IS: Level-2 PSNPs (sent/rcvd): 3/1
IS-IS: Level-1 DR Elections: 2
IS-IS: Level-2 DR Elections: 1
IS-IS: Level-1 SPF Calculations: 3
IS-IS: Level-2 SPF Calculations: 3
IS-IS: Level-1 Partial Route Calculations: 0
IS-IS: Level-2 Partial Route Calculations: 0
IS-IS: LSP checksum errors received: 0IS-IS: Update process queue depth: 0/200
IS-IS: Update process packets dropped: 0
-
8/12/2019 3 Introduction to ISIS 6up
7/13
7Page 7
37ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
ShowShow isisisis databasedatabase
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routersRtr-B> show isis database
IS-IS Level-1 Link State Database
LSPID LSP Seq Num LSP Checksum LSPHoldtime ATT/P/OL
1921.6800.1001.00-00* 0x00000019 0x2783 1153 1/0/0 (11)
1921.6800.1005.00-0 0 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 Database
LSPID LSP Seq Num LSP Checksum LSPHoldtime ATT/P/OL
1921.6800.1001.00-00* 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,CiscoSystems,Inc. www.cisco.com
ShowShowisisisisdatabasedatabase
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> sh isisdatab ase 1921.6800.1001.00-00 detail
IS-IS Level-1 LSP 1921.6800.1001.00-00
LSPID LSP Seq Num LSP Checksum LSPHoldtime ATT/P/OL
1921.6800.10 01.00-00* 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,CiscoSystems,Inc. www.cisco.com
ShowShowisisisisdatabasedatabase
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
IS-IS Level-2 LSP 1921.6800.1001.00-00
LSPID LSP Seq Num LSP Checksum LSPHoldtime ATT/P/OL
1921.6800.1001.00-00* 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,CiscoSystems,Inc. www.cisco.com
ShowShow isis spfisis spf-log-log
Area 49.0001 Area 49.0002
Rtr-CRtr-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 1921.6800.1 001.00-00 ATTACHFLAG LSPHEADER
Level 2 SPF log When Duration Nodes Count Last trigger LSP Triggers00:06:31 0 1 2 1921.6800.100 1.00-00 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,CiscoSystems,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 a
single area
When using areas, use summary-addresses
400 routers in the backbone has been done
42ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
Network Design IssuesNetwork Design Issues
Possible link cost
Default on all interface is 10
Manually 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 contiguousEnsure continuity by redundancy
Area partitioning
Design so that backbone can not be partitioned
-
8/12/2019 3 Introduction to ISIS 6up
8/13
8Page 8
43ISP/IXP Workshops 1999,CiscoSystems,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
441999,CiscoSystems,Inc.
Advanced ISISAdvanced ISISAdvanced ISIS
44ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com 45ISP/IXP Workshops 1999,CiscoSystems,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,CiscoSystems,Inc. www.cisco.com
Non-Pseudonode LSPNon-Pseudonode LSP
Non-Pseudonode LSP represents router
Each router will create and flood a newNon-Pseudonode LSP
When 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,CiscoSystems,Inc. www.cisco.com
Pseudonode LSPPseudonode LSP
Pseudonode LSP represents LAN
The DIS will create and flood anew Pseudonode LSP
When a new neighbour comes up orgoes away
When refresh interval timer expires Reduces adjacencies and flooding
over LAN subnets
48ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
LSP IdentifierLSP Identifier
LSP identifier consists of 3 parts
Source ID
System-ID of router (non-PN) or DIS (Pseudonode)
Pseudonode ID
Zero for router LSP, non-zero for Pseudonode LSP
LSP number
Fragmentation number
Example: 00c0.0040.1234.02-00
SystemID
PN-ID
Frag-Nr
-
8/12/2019 3 Introduction to ISIS 6up
9/13
9Page 9
49ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
LSP HeaderLSP Header
LSP sequence numberUsed to determine the newest LSP
version
LSP remaining lifetime
Used to purge old LSPs
LSP checksum
LSP type
level-1 or level250ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
LSP HeaderLSP Header
LSP Attached bit
Set in the level-1 LSP by a L1-L2 routerif it has connectivity to another area
Indicate 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,CiscoSystems,Inc. www.cisco.com
LSP HeaderLSP Header
LSP Overload bitSet by the router when it has an overload
problem 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 through
the overloaded router
52ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
Flooding in depthFlooding in depth
LSPs hold a Remaining LifetimeSet to 20 minutes by the originating router
After 20 min. each router must remove the LSP
Prevents old LSPs to stay in the LSDB forever
Periodic refresh of LSPs
router resends LSP at least every 15 mins
Can be set up to 18.7 Hours
Cut back on background LSP noise
53ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
Flooding in depthFlooding in depth
Network wide LSP purges
When a router detects a corrupted or anexpired 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 routers memory
54ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
Flooding in depthFlooding in depth
Sequence number overflow is unlikelyto happen
4 Bytes seqnr is enough for 120 years
Restarting of a router
Use sequence number = 1
Neighbour will flood old LSP with old
sequence numberRouter can now set sequence number higher
then before reboot, so everyone will usethe latest LSP
-
8/12/2019 3 Introduction to ISIS 6up
10/13
1Page 10
55ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
LSP refreshLSP refresh
LSP are refreshed when refresh timerexpires
Refresh-timer trigger new LSP generation andflooding
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,CiscoSystems,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-lifet ime Set maximum LSP lifetime
prc-interval Minimum interval between partial route calculations
spf-interval Minimum interval between SPF calculations
57ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
New FeaturesNew Features
Metrics are 3 bytes (2^24) wide with 12.0S
Specific routes leaking from L2 to L1 with
12.0S
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,CiscoSystems,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,CiscoSystems,Inc. www.cisco.com
Timer IssuesTimer Issues
Timers can be adapted to large topologies
LSP, Hello, CSNP, retransmission intervals
Refresh interval
Trade-off between reduced flooding and purge of corrupted
LSPs
SPF and PRC interval
LSP maximum lifetime
Maximum value is recommended
Will significantly reduce LSP re-flooding
Old copies of LSPs may be present in LSDB (but will not be
used).60ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
Timer IssuesTimer Issues
In some topological cases really fastconvergence is needed
HSRP and ISIS
With HSRP the routers have to convergerapidly in order to switch from/to active andpassive states
Hello-interval and lsp-gen-interval can bereduced
routing traffic will increase (possible routeflapping)
-
8/12/2019 3 Introduction to ISIS 6up
11/13
1Page 11
61ISP/IXP Workshops 1999,CiscoSystems,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,CiscoSystems,Inc. www.cisco.com
IP SummarisationIP Summarisation
Summary addresses for level-1
summary address is created forredistributed prefixes
Summary addresses for level-2
summary address is created for
redistributed prefixes
L1 routes
63ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
IP specificIP specific
Default routingBoth level-1 and level-2 ISs can
generate a default route
A level-1 IS will always prefer a level-1default 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,CiscoSystems,Inc. www.cisco.com
Default routeDefault route
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-A> show ip route
Gateway of last resort is 192.168.120.10 to network 0.0.0.0C 192.168.120.0/24 is directly connected, FastEthernet0/0
192.168.1.0/32 is subnetted, 2 subnet s
i L1 192.168.1.1 [115/10] via 192.168.120.10, FastEthernet0/0
C 192.168.1.5 is directly connected, Loopback0
i L1 192.168.222.0/24 [115/20] via 192.168.120.10, FastEthernet0/0
i*L1 0.0.0.0/0 [115/10] via 192.168.120.10, FastEthernet0/0
65ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
Summary routeSummary route
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routersrouterisis
summary-address 55.0.0.0 255.0.0.0 level-1-2summary-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 Null0
ip route 55.2.0.0 255.255.0.0 Null0
66ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
Summary routeSummary route
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-B> sh isis da 1921.6800.1001.00-00 det
IS-IS Level-1 LSP 1921.6800.1001.00-00
LSPID LSP Seq Num LSP Checksum LSPHoldtime ATT/P/OL
1921.6800.1001.00-00* 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 1921.6800.1001Metric: 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
-
8/12/2019 3 Introduction to ISIS 6up
12/13
1Page 12
67ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
Summary routeSummary route
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
IS-IS Level-2 LSP 1921.6800.1001.00-00
LSPID LSP Seq Num LSP Checksum LSPHoldtime ATT/P/OL
1921.6800.100 1.00-00* 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,CiscoSystems,Inc. www.cisco.com
Attached bitAttached bit
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
Rtr-A> showisis database
IS-IS Level-1 Link State Database
LSPID LSP Seq Num LSP Checksum LSPHoldtime ATT/P/OL
1921.6800.10 01.00-00 0x00000006 0x4D70 666 1/0/0 (4)
1921.6800.1001.0 1-00 0x00000001 0x1136 0 (648) 0/0/0 (3)
1921.6800.1005.00-00* 0x00000002 0x356F 647 0/0/0 (1)
1921.6800.100 5.01-00* 0x00000001 0x50E4 647 0/0/0 (2)
69ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
DebugDebug isis adjisis adj-packets-packets
Area 49.0001 Area 49.0002
Rtr-CRtr-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),cirtype 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),cirtype 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, cirid 00
70ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
DebugDebug isis spfisis spf-events-events
Rtr-B#debug isis spf-events
ISIS-SPF: Compute L1 SPT
ISIS-SPF: Move 1921.6800.1001.00-00 to PATHS, metric 0
ISIS-SPF:thru2147483647/2147483647/2147483647, delay 0/0/0,mtu2147483647/2147483647/2147483647, hops 0/0/0, ticks 0/0/0
ISIS-SPF:Add 1921.6800.1005.01-00to TENT,metric 10
ISIS-SPF: Nexthop local
ISIS-SPF: Move 1921.6800.1005.01-00 to PATHS, metric 10
ISIS-SPF:thru2147483647/2147483647/2147483647, delay 0/0/0,mtu2147483647/2147483647/2147483647, hops 0/0/0, ticks 0/0/0
ISIS-SPF: considering adj to 1921.6800.1005 (FastEthernet4/0/0) metric 10
ISIS-SPF: (accepted)
ISIS-SPF:Add 1921.6800.1005.00-00to TENT,metric 10ISIS-SPF: Next hop 1921.6800.1005 (FastEthernet4/0/0)
ISIS-SPF: Move 1921.6800.1005.00-00 to PATHS, metric 10
ISIS-SPF: Add 192.168.120.0/255.255.255.0 to IP route table, metric 20
ISIS-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 10
ISIS-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 60
ISIS-SPF: Next hop 1921.6800.1005/192.168.120.5 (FastEthernet4/0/0) (rejected)71ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
DebugDebug isis snpisis snp-packets-packets
Rtr-B# debug isis snp-packets
ISIS-SNP: Rec L1 CSNP from 1921.6800.1005 (FastEthe rnet4/0/0)
ISIS-SNP: CSNP range 0000.0000.0000.00-00 to FFFF.FFFF.FFFF.FF-FF
ISIS-SNP: Same entry 1921.6800.1001.00-00,seq93
ISIS-SNP: Same entry 1921.6800.1005.00-00,seq78
ISIS-SNP: Same entry 1921.6800.1005.01-00,seq76
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
72ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
Area 49.0001 Area 49.0002
Rtr-CRtr-B
Rtr-A Rtr-D
L1L2 routers
L1routers
DebugDebug isis spfisis spf-update-update
Rtr-B(config)#intfa4/0/0
Rtr-B(config -if)#isis metric 13Rtr-B(config-if)#^Z
Rtr-B#
ISIS-SPF-TRIG: L1, new metric
ISIS-Update: Building L1 LSP
ISIS-Update: TLV contents different, code 80ISIS-Update: TLV contents different, code 2
ISIS-SPF-TRIG: L1, 1921.6800.1001.00-00 TLV contents changed, code 2
ISIS-Update: Full SPF required
ISIS-Update: Sending L1 LSP 1921.6800.1001.00-00, seq 96, ht 1199 on FastEthernet4/0/0
ISIS-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 suspends
ISIS-Update: Building L2 LSP
ISIS-Update: TLV contents different, code 80
ISIS-Update: TLV contents different, code 80
ISIS-Update: Leaf routes changedISIS-Update: Sending L2 LSP 1921.6800.1001.00-00, seq 96, ht 1199 on POS2/0/0
ISIS-Update: Building L2 LSP
ISIS-Update: Rate limiting L2 LSP 1921.6800.1001.00-00,seq 97
ISIS-Update: TLV contents different, code 80
ISIS-Update: TLV contents different, code 80
ISIS-Update: Leaf routes changedISIS-Update: Sending L2 LSP 1921.6800.1001.00-00, seq 97, ht 1196 on POS2/0/0
-
8/12/2019 3 Introduction to ISIS 6up
13/13
1Page 13
73ISP/IXP Workshops 1999,CiscoSystems,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 warning
2 Routers with same System-ID will see eachothers LSP as their own, but not correct. Sothey will generate a new LSP with highersequence number.
This is an infinite ping-pong game
When an IS has to regenerate its LSP frequently,it will generate the above warning
74ISP/IXP Workshops 1999,CiscoSystems,Inc. www.cisco.com
id=x.00-00
seqnr=22
RL=1200
LSP Checksum ThrashingLSP Checksum Thrashing
id=x.00-00
seqnr=23
RL=1200
LSP ->id=x.00-00
seqnr=22
RL=1193
this IS got the LSP with
a checksum error.
So it purges it.
id=x.00-00
seqnr=23
RL=1194
someone purged
our LSP. lets
regenerate it
And on and on and ...
78