The Complete IS-IS Routing Protocol- P15

The Complete IS-IS Routing Protocol- P15:IS-IS has always been my favourite Interior Gateway Protocol. Its elegant simplicity, itswell-structured data formats, its flexibility and easy extensibility are all appealing – IS-ISepitomizes link-state routing. Whether for this reason or others, IS-IS is the IGP of choicein some of the world’s largest networks. Thus, if one is at all interested in routing, it is wellworth the time and effort to learn IS-IS.
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The Complete IS-IS Routing Protocol- P15 MPLS Signalling Protocols 411 Adspec Object (13) Flags: [reject if unknown], Class-Type: IntServ (2), length: 48 Msg-Version: 0, length: 40 Service Type: Default/Global Information (1), break bit not set, Service length: 32 Parameter ID: IS hop cnt (4), length: 4, Flags: [0x00] IS hop cnt: 1 Parameter ID: Path b/w estimate (6), length: 4, Flags: [0x00] Path b/w estimate: 0 Mbps Parameter ID: Minimum path latency (8), length: 4, Flags: [0x00] Minimum path latency: don’t care Parameter ID: Composed MTU (10), length: 4, Flags: [0x00] Composed MTU: 1500 bytes Service Type: Controlled Load (5), break bit not set, Service length: 0 ERO Object (20) Flags: [reject if unknown], Class-Type: IPv4 (1), length: 28 Subobject Type: IPv4 prefix, Strict, 10.154.1.5/32, Flags: [none] Subobject Type: IPv4 prefix, Strict, 10.154.6.1/32, Flags: [none] Subobject Type: IPv4 prefix, Strict, 10.254.1.45/32, Flags: [none] Label Request Object (19) Flags: [reject if unknown], Class- Type: without label range (1), length: 8 L3 Protocol ID IPv4 RRO Object (21) Flags: [reject if unknown], Class-Type: IPv4 (1), length: 12 Subobject Type: IPv4 prefix, Strict, 10.154.1.6/32, Flags: [none] This is the response to the previous Label Setup Message. Note that the Session objectcontents need to match in order for the router to match the RSVP message to a certainsession.12:35:51.199611 IP (tos 0xc0, ttl 255, id 6344, offset 0, flags [none], length: 164) 10.154.1.5 > 10.154.1.6: RSVP v: 1, msg-type: Resv, length: 144, ttl: 255, checksum: 0x2efc Session Object (1) Flags: [reject if unknown], Class-Type: Tunnel IPv4 (7), length: 16 IPv4 Tunnel EndPoint: 209.211.134.10, Tunnel ID: 0x0013, Extended Tunnel ID: 209.211.134.9 RSVP Hop Object (3) Flags: [reject if unknown], Class-Type: IPv4 (1), length: 12 Previous/Next Interface: 10.154.1.5, Logical Interface Handle: 0x0853f4c8 Time Values Object (5) Flags: [reject if unknown], Class-Type: 1 (1), length: 8 Refresh Period: 30000ms Style Object (8) Flags: [reject if unknown], Class-Type: 1 (1), length: 8 Reservation Style: Fixed Filter, Flags: [0x00] Flowspec Object (9) Flags: [reject if unknown], Class-Type: IntServ (2), length: 36 Msg-Version: 0, length: 28 Service Type: Controlled Load (5), break bit not set, Service length: 24 Parameter ID: Token Bucket TSpec (127), length: 20, Flags: [0x00] Token Bucket Rate: 0 Mbps Token Bucket Size: 0 bytes Peak Data Rate: inf Mbps Minimum Policed Unit: 20 bytes Maximum Packet Size: 1500 bytes412 14. Traffic Engineering and MPLS FilterSpec Object (10) Flags: [reject if unknown], Class-Type: Tunnel IPv4 (7), length: 12 Source Address: 209.211.134.9, LSP-ID: 0x0005 Label Object (16) Flags: [reject if unknown], Class-Type: Label (1), length: 8 Label 12324 RRO Object (21) Flags: [reject if unknown], Class-Type: IPv4 (1), length: 36 Subobject Type: IPv4 prefix, Strict, 10.154.1.5/32, Flags: [none] Subobject Type: IPv4 prefix, Strict, 10.154.6.1/32, Flags: [none] Subobject Type: IPv4 prefix, Strict, 10.254.1.45/32, Flags: [none] Subobject Type: IPv4 prefix, Strict, 10.254.1.2/32, Flags: [none]The Label Request Object is embedded in a RSVP-TE PATH message and gives RSVP-TE the ability to request a label and subsequently return a label using the Label Object ina RSVP-TE RESV message. The Explicit Route Object (ERO) allows RSVP-TE to spec-ify a set of nodes that an RSVP-TE message has to traverse. Figure 14.12 shows sampleEROs modelled using the Loose and Strict (L/S) path constraint. A Strict hop indicatesthat the next hop must be directly connected to the previous hop. The first example ofFigure 14.12 shows a set of strict hops that specify a path. A sequence of strict hops isoften used to nail down a path – that is, when the network administrator wants to enforcea certain path. A Loose hop means that the node has to be present in the path before thenext hop, but does not have to be the next-hop. The second example of Figure 14.12shows that only a subset of the nodes is listed in the ERO. With the Loose attribute, thismeans that there is some room for re-routing this path. The path could potentially rundirectly from Washington via Frankfurt to Pennsauken. In practice, the Loose optioncauses more problems than it solves. The network is not in full control of the traffic pathanymore and in more complex topologies this may lead to strange results with long delaypaths. The third example in Figure 14.12 shows a mix between loose and strict hops. Thesemantics of the ERO Objects allows for the combination of loose and strict hops in anarbitrary fashion. There are two general ways to create an ERO. The first is a manual specification andthe second, more sophisticated way, is automated computation. The manual configur-ation will be discussed first. You can configure a label switched path using an ERO in similar ways on IOS andJUNOS. First you need to specify the ERO and next you need to link the ERO to a labelswitched path.IOS configurationIn IOS you can specify an ERO manually using the ip explicit-path statement. Thenext-address specifies the next-element in the ERO. By default all hops in the ERO arestrict except when you supply the loose keyword.ip explicit-path identifier name via-Penssauken enable next-address 192.168.1.1 next-address loose 192.168.2.1 […]! ...