Download Area Address - YSU Computer Science & Information Systems

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© 2002, Cisco Systems, Inc. All rights reserved.
1
Integrated IS-IS
Wayne Lewis / Torrey Suzuki
Session Number
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© 2002, Cisco Systems, Inc. All rights reserved.
2
Agenda
• ISIS Overview
• CLNS Addressing
• ISIS Areas
• ISIS PDUs
• LSP Header
• Flooding
• Configuration
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3
Teminology
•
AFI
Authority and Format Identifier (the first octet of all OSI NSAP
addresses - identifies format of the rest of the address)
•
CLNP
Connection-Less Network Protocol (ISO 8473 - the OSI
connectionless network layer protocol - very similar to IP)
•
ES
End System (The OSI term for a host )
•
IS
Intermediate System (The OSI term for a Router)
•
ES-IS
End System to Intermediate System Routing exchange protocol
(ISO 9542 - OSI protocol between routers and end systems).
•
IS-IS
Intermediate System to Intermediate System Routing Exchange
Protocol (the ISO protocol for routing within a single routing domain.
•
IS-IS Hello
A Hello packet defined by the IS-IS Protocol
•
LSP
Link State Packet (a type of packet used by the IS-IS protocol).
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4
IS-IS Overview
• IS-IS was originally designed for use as a dynamic routing
protocol for the ISO Connectionless Network Protocol
(CLNP). (ISO10589 or RFC 1142)
• Adapted for routing IP in addition to CLNP (RFC1195) as
Integrated or Dual IS-IS
• IS-IS is a Link State Protocol similar to the Open Shortest
Path First (OSPF)
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IS-IS Overview
• IS-IS is an Interior Gateway Protocol (IGP) used for
routing within an Autonomous System (AS), also
referred to as a routing domain.
• BGP is normally used for dynamic routing between IP
domains
• ISO-IGRP is a Cisco proprietary routing protocol that
can be used between CLNP domains
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6
IS-IS Overview
• 3 network protocols work together to deliver the
ISO-defined Connectionless Network Service
 CLNP
 IS-IS
 ES- IS - End System to Intermediate System
Protocol
• All 3 protocols independently ride over layer 2.
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7
IS-IS Overview
• CLNP is the ISO equivalent of IP for datagram
delivery services (ISO 8473, RFC 994)
• IS-IS carries routing information. Integrated IS-IS
works within the ISO CLNS framework even if
used for routing IP (ISO 8473, RFC 1142)
• ES-IS is a dynamic protocol hosts used to
discover routers.
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8
IS-IS Overview
• End System Hellos (ESH) from Hosts and
Intermediate System Hellos (ISH) for Routers are
used for ES-IS neighbor discovery
• Intermediate System to Intermediate Systems
Hellos (IIH) are used for establishing IS-IS layer3
adjacencies
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9
CLNS Addressing
Area
System ID
N-SEL
CLNS Addressing consists of 3 parts
Area – Variable
System ID
N-SEL(ector)
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10
NSAPs and Addressing
• ISO/IEC 10589 distinguishes only 3 fields in the NSAP address format
DSP
IDP
AFI
IDI
High Order DSP
Variable Length Area Address
System ID
6 Bytes
NSEL
1 Byte
• Area Address: variable length field composed of high order octets of the NSAP
excluding the SystemID and SEL fields
• SystemID: defines an ES or IS in an area. Cisco implements a fixed length of 6
octets for the SystemID
• NSEL: selector, also designated as N-selector. It is the last byte of the NSAP and
identifies a network service user (transport entity or the IS network entity itself)
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11
NSAPs and Addressing
• NSAP: Network Service Access Point
•
An NSAP has an address that consists of 3 parts.
 Variable length area-address
 6 Byte system ID
 Byte n-selector (indicating transport layer)
Total length between 8 and 20 bytes
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12
NETs Versus NSAPs
• NET: Network Entity Title
• Is the address of the network entity itself
• A NET is an NSAP where n-selector is 0
• A NET implies the routing layer of the IS itself (no
transport layer)
• ISs (routers) do not have any transport layer (selector=0)
• Multiple NETs are like secondary IP addresses - only use
them when merging or splitting areas
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13
CLNS Addressing: AFI Values
Address Domain
X.121
ISO DCC
ISO 6523
Local
AFI Value
37
39
47
49
• X.121 - Int’l plan for public data networks
• ISO DCC - Data country code
• IS0 6523 ICD - Telex
• Local - For local use within network domain only
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14
CLNS Addressing:
Requirements and Caveats
• All routers in an area must use the same area address.
• An end system may be adjacent to a level 1 router only if they
both share a common area address.
• Each node in an area must have a unique System ID.
• All level 2 routers in a domain must have unique System IDs in
relation to each other.
• All systems belonging to a given domain must have System IDs
of the same length in their NSAP addresses.
• The maximum size of an NSAP is 20 bytes.
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15
CLNS Addressing:
Requirements and Caveats
• Minimum of 8 bytes allowed on Cisco routers.
1 byte for area, 6 bytes for system ID and 1 byte for N-selector. AFI
prefix recommended to make minimum of 9 bytes
• At least one NSAP is required per node.
• All NSAPs on the same router must have the same
system ID.
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16
CLNS Addressing: NSAP Examples
Example 1
47.0001.aaaa.bbbb.cccc.00
Area = 47.0001, SysID = aaaa.bbbb.cccc, NSel = 00
Example 2
39.0f01.0002.0000.0c00.1111.00
Area = 39.0f01.0002, SysID = 0000.0c00.1111, NSel = 00
Example 3
49.0002.0000.0000.0007.00
Area = 49.0002, SysID = 0000.0000.0007, Nsel = 00
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17
CLNS Addressing: NSAP Examples
39.0f01.0003.6666.6666.6666.00
39.0f01.0002.4444.4444.4444.00
39.0f01.0002.3333.3333.3333.00
39.0f01.0004.7777.7777.7777.00
39.0f01.0001.2222.2222.2222.00
39.0f01.0004.8888.8888.8888.00
39.0f01.0001.1111.1111.1111.00
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18
CLNS Addressing: How do most ISPs define
System IDs?
The LOOPBACK IP address: 192.168.3.25
The AREA the router under is: 49.0001
IP Address conversion process to system ID:
192.168.3.25
192.168.003.025
1921.6800.3025
49.0001.1921.6800.3025
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19
Areas and backbone routers
• ISIS has a 2 layer hierarchy

The backbone (level-2)
 The areas (level-1)
• An IS can be

Level-1 router (intra-area routing)
 Level-2 router (inter-area routing)
 Level-1-2 router (intra and inter-area routing)
• For each level (1 and 2) a DIS will be elected on LANs
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Areas and backbone routers
• Level-1 router

Has neighbors only on the same area
 Has the level-1 LSDB with all routing information for the area
 Use the closest Level-2 router to exit the area
 This may result in sub-optimal routing
• Level-2 router

May have neighbors in other areas
 Has a Level-2 LSDB with all information about inter-area routing
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Areas and backbone routers
• Level-1-2 router
May have neighbors on any area.
Has two LSDBs:
 Level-1 for the intra-area routing
 Level-2 for the inter-area routing
If the router has adjacencies to other
areas, it will inform the level-1 routers
(intra-area) it is a potential exit
point for the area
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22
Areas and backbone routers
Area 49.001
L1
L1L2
Area 49.003
Area 49.0002
L1
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L1L2
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L1L2
L1
23
Areas and backbone routers
• Backbone MUST BE L2 contiguous
Area-3
L1-only
L1L2
Area-2
L2-only
L1L2
L1-only
L1L2
Area-4
L1L2
L1-only
Area-1
L1L2
L1-only
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24
Areas and backbone routers
area 1 router
A
“I’m in area 2 and ALL
my neighbors are in the
same area. I must be a
L1-only router ?”
area 2 rtr
D
area 3 rtr
F
C
area 2 rtr
B!! NO !!
area 2 rtr
Rtr C must have a full L2 LSDB
to route between areas 1, 3 and
4. Remember, the backbone
must be contiguous.
area 2 rtr
E
area 4 rtr
G
Remember, the backbone must be contiguous.
ISIS router cannot determine if they need to be L1 or L1L2
So all routers try to be a L1L2 IS by default.
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25
Areas and SPF calculation
• ISs are identified with NETs, 8 to 20 bytes

Variable length area-address

6 Byte system ID (unique in the whole domain
for level-2 routers)

1 Byte n-selector (set to 0)
• Each IS is in exactly ONE area
• Area borders are on links, not on routers.
• 2 Separate LSDBs, 2 separate SPF runs
Level-1 and Level-2 LSDBs
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SPF (Dijkstra) and Partial Route Calculation
• SPF (Dijkstra) is run when topology has to be
calculated (SPF tree)
• PRC (Partial Route Calculation) is executed
when IP routing information has to be calculated
• If an IS receives an LSP where only IP information has
changed, it will run PRC only (less CPU)
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27
ISIS PDUs
• ISIS packets are encapsulated directly in a
data-link frame
• There is no CLNS or IP header
•
Hello PDUs (IIH, ISH, ESH)
•
LSP
– Non-Pseudonode LSP
– Pseudonode LSPs
•
CSNP
•
PSNP
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ISIS Packet Header
# of Octets
Protocol Identifier
1
Header Length
1
Version
1
ID Length
1
Packet Type
1
Version
1
Reserved
1
Max. Area Addresses
1
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29
Summary of Packet Types
Presentation_ID
L1 - LAN
15
L2 - LAN Hello
Hello
Point-to-point Hello
16
L1 LSP
18
L1 CSNP
24
L2 CSNP
25
L1 PSNP
26
L2 PSNP
27
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30
Encapsulation
ISIS
Datalink header
(OSI family 0xFEFE)
ESIS
Datalink header
(OSI family 0xFEFE)
CLNS
Datalink header
(OSI family
0xFEFE)
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ISIS fixed header
(first byte is 0x83)
ISIS TLVs
ESIS fixed header
(first byte is 0x81)
ESIS TLVs
CLNS header (with NSAPs)
(first byte is 0x80)
User data
31
Mac layer addresses
• On LANs IS-IS PDUs are forwarded to the following well
known MAC layer broadcast addresses
AllL1ISs
01-80-C2-00-00-14
AllL2ISs
01-80-C2-00-00-15
AllIntermediateSystems
09-00-2B-00-00-05
AllEndSystems
09-00-2B-00-00-04
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Hello PDUs
# of Octets
Common Fixed Header 8
Circuit
type
Reserved
Source ID
# of Octets
Common Fixed Header 8
1
Circuit
type
Reserved
Source ID
ID Length
1
ID Length
Holding Time
2
Holding Time
2
Packet Length
2
Packet Length
2
Local Circuit ID
1
Point-to-Point ISIS Hello
r
Priority
LAN ID
1
ID Length + 1
LAN ISIS Hello
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33
Hello PDUs
• IIHs are between routers (IS-IS)
• Exchanged by ISs to form adjacencies

Point-to-Point IIH
 Level-1 LAN IIH
 Level-2 LAN IIH
• Mutipoint & P2P IIHs are padded to full MTU Size
Useful to detect MTU inconsistencies
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34
Hello PDUs
• Point-to-Point ISIS Hello
• Circuit-type: 1 - Level 1-Only
2 - Level 2-Only ( no IS-ES hello)
3 - Level 1-2
• Source ID: Transmitting Router’s Network Layer Address
• Holding time: time at which neighbors can legally declare this route dead
if they haven’t gotten a hello from it.
• Packet Length: the Length of the entire ISIS hello message
• Local Circuit ID: identifier to the interface and unique relative to the
transmitting router’s other interfaces
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35
Hello PDUs
• LAN ISIS Hello
• Priority: the transmitting routers’ priority for becoming designated router
on the LAN, with higher #s having a higher priority
• LAN ID: the name of the LAN as assigned by the DIS. It consists of
DIS-ID + extra octet to differentiate this LAN from others
with the same DIS
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Hello PDUs
• ISs form adjacencies by sending/receiving IIH
• ISs discover ES by listening to ESHs
• ESs discover IS by listening to ISHs
• DIS (Designated Intermediate System) will
 drive the flooding on LANs
 create a special LSP describing the LAN topology
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37
Hello PDUs
ES sends ESH
IS send ISH for ES
ISIS adjacency through IIH
• ISs send IIH to establish ISIS adjacencies
• ISs listen to ESH to discover ESs
• ISs send ISH for ESs
• ESs sends ESH and listen to ISH
• ESs select IS as default router by listening to ISH
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Node and Pseudonode LSP
• 2 Kinds of Link State PDUs
•
Non-Pseudonodes represent routers
•
Pseudonodes represents LANs (created by the DIS)
• A level-1 router will create a level-1 LSP
• A level-2 router will create a level-2 LSP
• A level-1-2 router will create
a level-1 LSP and
a level-2 LSP
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Non-Pseudonode LSP generation
•
Each IS will create and flood a new NonPseudonode LSP
 When a new neighbor comes up or goes away
 When new IP prefixes are inserted or removed
 When the metric of a link did change
 When refresh interval timer expires
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Pseudonode LSP generation
• The DIS will create and flood a new Pseudonode LSP
 When a new neighbor comes up or goes away
 When refresh interval timer expires
• Pseudonode LSP is created by the DIS
 One for each level (level-1 and/or level-2)
 One for each LAN
• Reduces adjacencies and flooding over LAN subnets
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Pseudonode LSP generation
DIS
DIS
PSN
• Broadcast link represented as virtual node, referred to as Pseudonode (PSN)
• PSN role played by the Designated Router (DIS)
• DIS election is preemptive, based on interface priority with highest MAC address being
tie breaker
• IS-IS has only one DIS. DIS helps routers on Broadcast link to synchronize their IS-IS
databases
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42
LSPDB without Pseudonode
LSP for routerB
IS: 10 A
10 C
10 D
ES: 10 E
LSP for routerA
IS: 10 B
10 C
10 D
ES: 10 E
LSP for routerD
IS: 10 A
10 B
10 C
ES: 10 E
LSP for routerC
IS: 10 A
10 B
10 D
ES: 10 E
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endsystem
E
43
Pseudonode in the LSPDB
LSP for routerA
IS: 10 P
LSP for routerA
IS: 10 P
LSP for the
Pseudonode P
IS: 0 A
0B
0C
0D
ES: 0 E
LSP for routerA
IS: 10 P
LSP for routerA
IS: 10 P
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endsystem
E
44
CSNP/PSNP
• For both Level 1 & Level 2 Databases, we
have CSNPs & PSNPs
Level 1 CSNP
Level 2 CSNP
Level 1 PSNP
Level 2 PSNP
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CSNP
# of Octets
Common Fixed Header 8
Packet Length
2
Source ID
ID Length + 1
Start LSP ID
ID Length + 2
End LSP ID
ID Length + 2
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Complete Sequence Number PDU
• Describes all LSPs in your LSDB (in range)
 Contains an address range
 LSPid, seqnr, checksum, remaining lifetime
• Used at 2 occasions
 Periodic multicast by DIS (every 10 seconds)
 On p2p links when link comes up
• Created and flooded by the DIS
 Every 10 seconds
 On each LAN the IS is the DIS
• If LSDB is large, multiple CSNPs are sent
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Partial Sequence Number PDU
• PSNPs have 2 functions
 Exchanged by ISs on p2p links (ACKs)
 Acknowledge receipt of an LSP
 Request transmission of latest LSP
• PSNPs describe LSPs by its header
 LSP identifier
 Sequence number
 Remaining lifetime
 LSP checksum
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LSP header
• The LSP header contains

LSP-id
 Sequence number
 Remaining Lifetime
 Checksum
 Type of LSP (level-1, level-2)
 Attached bit
 Overload bit
 Partition bit
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LSP Header
• 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
00c0.0040.1234.01-00
System ID
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Frag-Nr
PN-ID
50
LSP Header
• LSP sequence number
Used to determine the newest LSP version
• LSP remaining lifetime
Used to purge old LSPs
• LSP checksum
• LSP type
Level-1 or Level2
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LSP Header
• LSP Attached bit
 Set in the level-1 LSP by a L1-L2 router if it has connectivity to another
area
 Indicate to the area routers (level-1) that it is a potential exit point of the
area
 Level-1 routers select the closest (best metric) level-2 router with the
ATT-bit set
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LSP Header
• LSP Overload bit
Set by the IS when it has an overload problem on its LSDB
Indicates that the router has an incomplete LS database,
and hence cannot be trusted to compute any correct
routes
Is used in the LSDB but topology behind it is not calculated
Therefore other routers do not compute routes which would
require the PDU to pass through the overloaded router.
Exception - ES neighbors - since these paths are guaranteed to be non looping
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LSP Header
• LSP Partition bit
To recover from partitioned areas ISIS uses virtual links
Router with partition bit set does support partition repair
and may be used as end point of virtual link
Area partitioning is not supported
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54
Reasons for Flooding
• All routers generate an LSP
• All LSPs need to be duplicated and sent to
all routers in the network
if LSPDB is not synchronized, routing loops
might occur
• IS-IS’ two components are the SPF
computation and reliable flooding
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Reasons for Flooding
• Sending needs to be robust
we can not use the routing table or LSPDB to
find a path over which to send LSPs. No smart
tricks.
• Send LSPs over all paths to be sure
except the intf on which we received it
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What triggers a new LSP ?
• When something changes …
 adjacency came up or went down
 interface up/down (connected IP prefix !)
 redistributed IP routes change
 inter-area IP routes change
 an interface is assigned a new metric
 most other config changes
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What to do with a new LSP ?
• Create new LSP, install in your own LSPDB
and mark it for flooding
• Send the new LSP to all neighbors
• Neigbors flood the LSP further
• Only flood new LSPs, ack old ones
because we have state in our LSPDB , we can
prevent infinite looping of LSPs
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58
Basic flooding rules
• When receiving a new LSP, compare with
old version of LSP in LSPDB.
if newer, install it in the LSPDB, flood to all
other neighbors, (except the one you got it
from, send that one an ACK). check if you need
run SPF.
if same age, only send ACK, don’t flood
if older, send latest LSP from our LSPDB
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59
Flooding of LSPs
• New LSPs are flooded to all neighbors
• It is necessary that all ISs get all LSPs
• Each LSP has a sequence number
• Reliable on p2p links with ACKs (PSNPs)
Partial Sequence Number PDU
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60
Flooding on a p2p link
• Once the adjacency is established both IS send
CSNP packet
• Missing LSPs are sent by both ISs if not
present in the received CSNP
• Missing LSPs may be requested through PSNP
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61
Flooding on a p2p link
RTA
RTB
RTC
Interface 1
Interface 4
Interface 2
LSP
RTA.00-00
SEQ#100
PSNP
RTA.00-00
SEQ#100
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Interface 3
LSP
RTA.00-00
SEQ#100
PSNP
RTA.00-00
SEQ#100
62
Flooding on a LAN(Broadcast Links)
• On LANs only, there’s a Designated Router (DIS)
• DIS has two tasks
Creating and updating the Pseudonode LSP
Conducting the flooding over the LAN
• A DIS is elected for each LAN
• DIS election is based on priority
• Breaking-tie is the highest SNPA (MAC address)
• DIS election is deterministic
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63
Flooding on a LAN(Broadcast Links)
Interface 2
RTA (DIS)
RTB
Interface 1
Interface 3
RTC
RTB
RTA
CSNP
LSP
RTA.00-00
SEQ#100
Presentation_ID
RTA
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LSP
RTC.00-00
SEQ#1
PSNP
RTB.00-00
SEQ#200
RTB
64
How to Configure ?
e0
e0
s0
s0
R1
R1
!
interface Loopback0
ip address 172.16.1.1 255.255.255.255
!
interface Ethernet0
ip address 172.16.12.1 255.255.255.0
ip router isis
!
router isis
passive-interface Loopback0
net 49.0001.1720.1600.1001.00
!
Presentation_ID
R3
R2
© 2002, Cisco Systems, Inc. All rights reserved.
R2
!
interface Loopback0
ip address 172.16.2.2 255.255.255.255
!
interface Ethernet0
ip address 172.16.12.2 255.255.255.0
ip router isis
!
interface Serial0
ip address 172.16.23.1 255.255.255.252
!
router isis
passive-interface Loopback0
net 49.0001.1720.1600.2002.00
!
65
Looking at the show commands
R1#show clns neighbor
System Id
Interface
R2
Et0
SNPA
0000.0c47.b947
State
Up
Holdtime
24
Type Protocol
L1L2 IS-IS
R1#show clns interface ethernet 0
Ethernet0 is up, line protocol is up
Checksums enabled, MTU 1497, Encapsulation SAP
Routing Protocol: IS-IS
Circuit Type: level-1-2
Interface number 0x0, local circuit ID 0x1
Level-1 Metric: 10, Priority: 64, Circuit ID: R2.01
Number of active level-1 adjacencies: 1
Level-2 Metric: 10, Priority: 64, Circuit ID: R2.01
Number of active level-2 adjacencies: 1
Next IS-IS LAN Level-1 Hello in 5 seconds
Next IS-IS LAN Level-2 Hello in 1 seconds
Presentation_ID
© 2002, Cisco Systems, Inc. All rights reserved.
66
Looking into the database
R2#show clns neighbor
System Id Interface SNPA
R1
Et0
0000.0c09.9fea
R3
Se0
*HDLC*
State
Up
Up
R2#show isis database
IS-IS Level-1 Link State Database:
LSPID
LSP Seq Num LSP Checksum
R1.00-00
0x0000008B
0x6843
R2.00-00
* 0x00000083
0x276E
R2.01-00
* 0x00000004
0x34E1
R3.00-00
0x00000086
0xF30E
IS-IS Level-2 Link State Database:
LSPID
LSP Seq Num LSP Checksum
R1.00-00
0x00000092
0x34B2
R2.00-00
* 0x0000008A
0x7A59
R2.01-00
* 0x00000004
0xC3DA
R3.00-00
0x0000008F
0x0766
Presentation_ID
© 2002, Cisco Systems, Inc. All rights reserved.
Holdtime
24
28
Type Protocol
L1L2 IS-IS
L1L2 IS-IS
LSP Holdtime
55
77
57
84
ATT/P/OL
0/0/0
0/0/0
0/0/0
0/0/0
LSP Holdtime
41
115
50
112
ATT/P/OL
0/0/0
0/0/0
0/0/0
0/0/0
67
Looking into the Database Detail
R2#show isis database R2.00-00 detail
IS-IS Level-1 LSP R2.00-00
LSPID
LSP Seq Num LSP Checksum LSP Holdtime
R2.00-00
* 0x00000093
0x077E
71
Area Address: 49.0001
NLPID:
0xCC
Hostname: R2
IP Address:
172.16.2.2
Metric: 10
IP 172.16.12.0 255.255.255.0
Metric: 0
IP 172.16.2.2 255.255.255.255
Metric: 10
IP 172.16.23.0 255.255.255.252
Metric: 10
IS R2.01
Metric: 10
IS R3.00
IS-IS Level-2 LSP R2.00-00
LSPID
LSP Seq Num LSP Checksum LSP Holdtime
R2.00-00
* 0x0000009A
0x5A69
103
Area Address: 49.0001
NLPID:
0xCC
Hostname: R2
IP Address:
172.16.2.2
Metric: 10
IS R2.01
Metric: 10
IS R3.00
Metric: 10
IP 172.16.23.0 255.255.255.252
Metric: 10
IP 172.16.1.1 255.255.255.255
Metric: 10
IP 172.16.3.3 255.255.255.255
Metric: 0
IP 172.16.2.2 255.255.255.255
Metric: 10
IP 172.16.12.0 255.255.255.0
Presentation_ID
© 2002, Cisco Systems, Inc. All rights reserved.
ATT/P/OL
0/0/0
ATT/P/OL
0/0/0
68
Looking into the routing-table
R1#show ip route isis
i L1
172.16.2.2/32 [115/10] via 172.16.12.2, Ethernet0
i L1
172.16.3.3/32 [115/20] via 172.16.12.2, Ethernet0
R2#show ip route isis
Presentation_ID
I L1
172.16.1.1/32 [115/10] via 172.16.12.1, Ethernet0
i L1
172.16.3.3/32 [115/10] via 172.16.23.2, Serial0
© 2002, Cisco Systems, Inc. All rights reserved.
69
Presentation_ID
© 2002, Cisco Systems, Inc. All rights reserved.
70