The Complete IS-IS Routing Protocol- P8

The Complete IS-IS Routing Protocol- P8: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- P8 Pseudonodes 197 Point-to-point Adjacency State TLV #240, length: 15 Adjacency State: Up (0) Extended Local circuit-ID: 0x00000041 Neighbor System-ID: 0000.0000.0003 Neighbor Extended Local circuit-ID: 0x0000005e Protocols supported TLV #129, length: 2 NLPID(s): IPv4 (0xcc), IPv6 (0x8e) IPv4 Interface address(es) TLV #132, length: 4 IPv4 interface address: 172.16.0.5 Area address(es) TLV #1, length: 4 Area address (length: 3): 49.0001 Restart Signaling TLV #211, length: 3 Flags [none], Remaining holding time 0s Both IOS and JUNOS support pseudonode suppression. In JUNOS you need toconfigure the point-to-point keyword inside the protocol isis interface{} stanza.JUNOS configurationIn JUNOS pseudonode suppression is activated by adding the point-to-point keywordinside the protocols isis interface {} stanza.hannes@Stockholm> show configuration[ … ]protocols { isis { [ … ] interface ge-2/2/0.0 { point-to-point; } interface lo0.0; }} You can verify if the circuit was assigned to be a p2p media using the show isisinterface command.JUNOS command outputOnce a broadcast circuit is configured for pseudonode suppression the Point to Pointflag is listed instead of the DIS.hannes@Stockholm> show isis interfaceIS-IS interface database:Interface L CirID Level 1 DR Level 2 DR L1/L2 Metric[ … ]ge-2/2/0.0 3 0x1 Point to Point Point to Point 10000/10000lo0.0 0 0x1 Passive Passive 0/0198 7. Pseudonodes and Designated Routers The IOS configuration is similar to JUNOS. Pseudonode suppression is once again aninterface property and can be configured using the isis network point-to-point configuration statement.IOS configurationThe IOS configuration requires the isis network point-to-point statement to sup-press pseudonodes.Amsterdam# show running-config[ … ]!interface GigabitEthernet0/0 ip address 172.16.26.170 255.255.255.0 ip router isis [ … ] isis network point-to-point! Unfortunately there is no explicit hint in IOS to display if the interface is actually run-ning in p2p mode. The only difference to a regular broadcast interface is that the DR IDline is missing in the output.IOS command outputOn a point-to-point network configuration the output of the show clns interface com-mand does omit the DR IDs.Amsterdam#show clns interface GigabitEthernet0/0GigabitEthernet0/0 is up, line protocol is up Checksums enabled, MTU 1497, Encapsulation SAP ERPDUs enabled, min. interval 10 msec. CLNS fast switching disabled CLNS SSE switching disabled DEC compatibility mode OFF for this interface Next ESH/ISH in 30 seconds Routing Protocol: IS-IS Circuit Type: level-1-2 Interface number 0x6, local circuit ID 0x2 Neighbor System-ID: Stockholm Level-1 Metric: 10, Priority: 64, Circuit ID: Amsterdam.02 Number of active level-1 adjacencies: 1 Neighbor System-ID: Stockholm Level-2 Metric: 10, Priority: 64, Circuit ID: Amsterdam.02 Number of active level-2 adjacencies: 1 Next IS-IS LAN Level-1 Hello in 2 seconds Next IS-IS LAN Level-2 Hello in 1 seconds Another possibility is actually looking at the link-state database if one of the tworouters on the LAN generates a pseudonode. DIS and DIS Election Procedure 199IOS command outputThe database output shows that there is no pseudonode generated by either theStockholm or Amsterdam router in the database. Additional evidence is that the tworouters did link their adjacencies directly (targeting the .00 incarnation) to each other.Amsterdam#show isis database detailIS-IS Level-1 Link State DatabaseLSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OLAmsterdam.00-00 * 0x0000019A 0xF613 818 0/0/0 Area Address: 49.0001 NLPID: 0xCC Router ID: 192.168.1.17 IP Address: 192.168.1.17 Hostname: Amsterdam Metric: 10 IS-Extended Stockholm.00 Metric: 10 IP 172.16.1.0/24 Metric: 0 IP 192.168.1.17/32Stockholm.00-00 0x0000c1E9 0xE448 414 0/0/0 Area Address: 49.0001 NLPID: 0xCC Hostname: Stockholm Router ID: 192.168.1.8 IP Address: 192.168.1.8 Metric: 10 IS-Extended Amsterdam.00 Metric: 10 IP 172.16.1.0/24 Metric: 0 IP 192.168.1.8/32 The output reveals that no pseudonode is in the database and two routers are linkeddirectly to each other as shown in the top right corner of Figure 7.10. If we allow pseudonode generation then we have silently assumed so far that there isa DIS on the LAN that generates the pseudonode on behalf of the LAN. Before that hap-pens a DIS needs to get elected. The following paragraph describes DIS election proced-ures and timing.7.3 DIS and DIS Election ProcedureThe good news is that the DIS election procedure is a very simple process. Due to its state-less nature a receiving router can immediately determine the DIS on the LAN. For DISelections there are two fields in the LAN IIH header (see Figure 5.2) that are relevant:• Priority field in the LAN-IIH• The Source SNPA ( MAC address) of the sender The Priority field is 7-bits wide and therefore Priority values between 0 and 127 canbe configured. A Priority value of zero means that this system does not wish to becomea DIS at all. In case there are many routers with the same Priority competing for the DIS200 7. Pseudonodes and Designated Routersthen the Source SNPA ( the MAC address) tie breaks. The system with the numericallyhighest source MAC address then wins the beauty contest. Each ...