Release 5.1, Revision 0 Copyright © 2001, Juniper Networks, Inc. Advanced Juniper Networks Routing Module 4: Intermediate System To Intermediate System (IS-IS)

Copyright © 2001, Juniper Networks, Inc. Module Objectives Review the basic components and functionality of the IS-IS Protocol Take a look at the IS-IS addressing schemes and the different topology levels Discuss neighbor adjacency formations Configure IS-IS on a Juniper Networks router

Copyright © 2001, Juniper Networks, Inc. IS-IS PDUs IS-IS exchanges protocol information using protocol data units (PDUs) – IS-IS hello (IIH) PDUs – Link-state PDUs (LSPs) – Sequence Number Packets (SNP)  Complete sequence number PDUs (CSNPs)  Partial sequence number PDUs (PSNPs) IS-IS hello (IIH) PDUs – Broadcast to discover identity of neighboring IS-IS systems – Determine whether neighbors are Level 1 or Level 2 intermediate systems Link-state PDUs (LSPs) – Describes the state of adjacencies in neighboring IS-IS systems – Flooded periodically throughout an area

Copyright © 2001, Juniper Networks, Inc. IS-IS PDU Format Describes the state of adjacencies in neighboring IS-IS systems Flooded periodically throughout an area Contains multiple type, length, value (TLV) segments Protocol identifier Header length Version ID length PDU type VersionReserved Maximum area address Field length, in bytes PDU length Remaining lifetime LSP ID Sequence number Checksum P, ATT, & IS Type Bits TLVs Variable

Copyright © 2001, Juniper Networks, Inc. IS-IS PDU Notes PDU type field denotes a L1 or L2 PDU – Level 1 PDU = 18 – Level 2 PDU = 20 ATT bit is set if IS is connected to another area OL bit is set is the link-state database is overloaded IS Type bits determine a L1 or L2 router – Level 1 router = 1 – Level 2 router = 3 TLVs populate the LSDB – Level 1 PDU = 1, 2, 10, 22, 128, 129, 132, 134, 135, 137, 222, 229, 232, 235, 236 – Level 2 PDU = 1, 2, 10, 22, 128, 129, 130, 132, 134, 135, 137, 222, 229, 232, 235, 236

Copyright © 2001, Juniper Networks, Inc. PDU TLVs TLVs are added to LSPs as needed – TLV 1 = Area Address – TLV 2 = IS reachability – TLV 10 = Authentication – TLV 22 = Extended IS reachability – TLV 128 = IP internal reachability – TLV 129 = Protocols supported – TLV 130 = IP external reachability – TLV 132 = IP interface address – TLV 134 = TE IP router ID – TLV 135 = Extended IP reachability – TLV 137 = Dynamic hostname resolution Multiple topologies (routing instances) are supported – TLVs 222, 229, and 235 IPv6 is supported via TLVs 232 and 236

Copyright © 2001, Juniper Networks, Inc. Level 2 PDU Headers show isis database extensive Tokyo Sequence: 0x6, Checksum: 0xcf2c, Lifetime: 1190 secs Header: LSP id: Tokyo.00-00, Length: 218 bytes Allocated length: 218 bytes, Router ID: Remaining lifetime: 1190 secs, Level: 2,Interface: 4 Estimated free bytes: 0, Actual free bytes: 0 Aging timer expires in: 1190 secs Protocols: IP Packet: LSP id: Tokyo.00-00, Length: 218 bytes, Lifetime : 1198 secs Checksum: 0xcf2c, Sequence: 0x6, Attributes: 0x3 NLPID: 0x83, Fixed length: 27 bytes, Version: 1, Sysid length: 0 bytes Packet type: 20, Packet version: 1, Max area: 0

Copyright © 2001, Juniper Networks, Inc. Level 2 PDU TLVs show isis database extensive TLVs: Area address: (3) Speaks: IP Speaks: IPv6 IP router id: IP address: Hostname: Tokyo IS neighbor: HongKong.00, Internal, Metric: default 10 IS neighbor: London.00, Internal, Metric: default 10 IS neighbor: HongKong.00, Metric: default 10 IP address: Neighbor's IP address: IS neighbor: London.00, Metric: default 10 IP address: Neighbor's IP address: IP prefix: /24, Internal, Metric: default 10 IP prefix: /24, Internal, Metric: default 10 IP prefix: /32, Internal, Metric: default 0 IP prefix: /24 metric 10 up IP prefix: /24 metric 10 up IP prefix: /32 metric 0 up IP external prefix: /24, Internal, Metric: default 20 IP prefix: /24 metric 20 up No queued transmissions TLV 1 TLV 129 TLV 134 TLV 137 TLV 2 TLV 128 TLV 130 TLV 132

Copyright © 2001, Juniper Networks, Inc. Sample IS-IS Database show isis database IS-IS level 1 link-state database: LSP ID Sequence Checksum Lifetime Attributes HongKong x8 0xcc L1 L2 Attached SanJose x9 0xbdfa 1055 L1 Montreal x7 0x54d2 500 L1 Montreal x4 0xdddb 677 L1 4 LSPs IS-IS level 2 link-state database: LSP ID Sequence Checksum Lifetime Attributes HongKong x6 0xa5a L1 L2 Tokyo x9 0xc92f 909 L1 L2 London x6 0xd7d L1 L2 3 LSPs

Copyright © 2001, Juniper Networks, Inc. LSP Flooding Scopes Area Area Area External Routes Area L2 PDU Area L1 PDU L1L2 Area L1 PDU Area L1 PDU Area L2 PDU Area L2 PDU Area L2 PDU Area L2 PDU Area L2 PDU Area L2 PDU Area L2 PDU Area L2 PDU

Copyright © 2001, Juniper Networks, Inc. IS-IS Cost Cost of an interface indicates the overhead required to send packets out a particular interface Default IS-IS cost for all links is 10 Cost can be set on a per interface basis – Each level on an interface can also have a different cost [edit protocols] show isis { interface so-0/0/0.0 { level 2 metric 10; level 1 metric 20; } interface ge-0/1/0.0 { level 2 metric 5; }

Copyright © 2001, Juniper Networks, Inc. Reference Bandwidth The interface cost can be changed to use the formula reference-bandwidth/bandwidth – Automatically alters the cost of interfaces – Allows for a consistent change across all interfaces Use the reference-bandwidth command within [edit protocols isis] [edit protocols isis] set reference-bandwidth 1g [edit protocols isis] show isis { reference-bandwidth 1g; interface so-0/0/0.0; interface ge-0/1/0.0; }

Copyright © 2001, Juniper Networks, Inc. IS-IS Wide Metrics The maximum metric supported on an individual interface is 63 All values advertised in an LSP that have a higher value are interpreted as a metric of 63 The use of wide metrics allows for a maximum value of 16,777,215 – Configured for an entire level [edit protocols isis] set level 2 wide-metrics-only [edit protocols isis] show isis { level 2 { wide-metrics-only; } interface so-0/0/0.0; interface ge-0/1/0.0; }

Copyright © 2001, Juniper Networks, Inc. Effects of Altering Metrics Metric values are advertised via the TLV values within a LSP and populate link-state database As each router runs SPF algorithm, each LSP is examined individually for cost of outgoing interface – That cost is used in the final metric calculation Routers can disagree about the cost on a network link – HongKong sees a cost of 45 to reach Amsterdam – Amsterdam sees a cost of 60 to reach HongKong HongKong SanJoseMontreal Amsterdam

Copyright © 2001, Juniper Networks, Inc. IS-IS Authentication Authentication can occur within multiple places – Link-state PDUs and sequence number packets within:  The entire domain  A single IS-IS level 1 area  A single IS-IS level 2 area – IS-IS Hello packets:  On a specific interface Three authentication types are supported – None (default) – Simple – MD5 MD5 includes an encrypted checksum with all packets – Provides better security than type simple

Copyright © 2001, Juniper Networks, Inc. Authentication Configuration [edit protocols isis] show /* This is for the entire IS-IS Domain */ authentication-key "$9$bssYomPQ69pkq39puhc8X7V2a"; # SECRET-DATA authentication-type md5; level 2 { /* This is for the entire IS-IS Level */ authentication-key "$9$dXVYoDjqQ39gomTz6CAvW8X-ViHmFnCDi1h"; # SECRET-DATA authentication-type simple; } interface so-0/0/0.0 { /* This is for all hellp packets on this interface */ hello-authentication-key "$9$1sEEclws4JUH-db2oGq.Ctp01h7NbgaU"; # SECRET-DATA hello-authentication-type md5; } More specific level authentication references take precedence over global settings Comments are made with the annotate command

Copyright © 2001, Juniper Networks, Inc. Authentication Issues Hello authentication only secures IS-IS Hello packets – Determines whether an adjacency forms between 2 routers Global or level authentication secures: – LSP packets – CSNP packets – PSP packets – IS-IS Hello packets Authentication for LSPs allows other routers to read the TLV values and use that information in the SPF calculation The authentication check can be disabled with the no- authentication-check command – Useful for migration purposes

Copyright © 2001, Juniper Networks, Inc. Mesh Groups IS-IS LSPs are flooded to all neighbors by default Certain physical topologies make this unnecessary – Amsterdam will receive 3 copies of the same LSP Once configured, the group members will not re-flood LSPs within the group HongKong SanJose Montreal Amsterdam

Copyright © 2001, Juniper Networks, Inc. Mesh Group Configuration Each interface is configured with a group number – 32-bit numbers can be different on separate interfaces To prevent an interface from flooding any LSPs, the keyword blocked can be used [edit protocols] show isis { interface so-0/0/0.0 { mesh-group 2; } interface ge-0/1/0.0 { mesh-group 1; } interface at-0/2/0.100 { mesh-group blocked; }

Copyright © 2001, Juniper Networks, Inc. Overload Bit Used to advertise information to neighbors, but not be used for transit traffic – Other routers ignore the LSP during SPF calculation Can be set permanently or with a timeout value – Timer is between 60 and 1800 seconds – Timer only runs after RPD starts [edit protocols] show isis { overload; interface so-0/0/0.0; interface ge-0/1/0.0; } show isis database IS-IS level 2 link-state database: LSP ID Sequence Checksum Lifetime Attributes Router x36f 0x8cf L1 L2 host x37f 0x4c3a 1067 L1 L2 Overload

Copyright © 2001, Juniper Networks, Inc. CSNP Interval CSNP packets are sent on a LAN interface every 10 seconds if you are the DIS Can be altered on a per interface basis – Value can be between 1 and 65,535 seconds [edit] run show isis interface detail IS-IS interface database: ge-0/2/0.0 Index: 3, State: 0x6, Circuit id: 0x2, Circuit type: 2 LSP interval: 100 ms, CSNP interval: 10 s Level Adjacencies Priority Metric Hello (s) Hold (s) Designated Router SanJose.02 (us) [edit] set protocols isis interface ge-0/2/0 csnp-interval 40 [edit] run show isis interface detail IS-IS interface database: ge-0/2/0.0 Index: 3, State: 0x6, Circuit id: 0x2, Circuit type: 2 LSP interval: 100 ms, CSNP interval: 40 s Level Adjacencies Priority Metric Hello (s) Hold (s) Designated Router SanJose.02 (us)

Copyright © 2001, Juniper Networks, Inc. IS-IS Configuration Configured at the [edit protocols] hierarchy level List each interface separately – Loopback 0 must be explicitly configured protocols { isis { interface ; }

Copyright © 2001, Juniper Networks, Inc. Review Questions