TAILIEUCHUNG - The Complete IS-IS Routing Protocol- P40

The Complete IS-IS Routing Protocol- P40: IS-IS has always been my favourite Interior Gateway Protocol. Its elegant simplicity, its well-structured data formats, its flexibility and easy extensibility are all appealing – IS-IS epitomizes link-state routing. Whether for this reason or others, IS-IS is the IGP of choice in some of the world’s largest networks. | 390 13. IS-IS Extensions Figure . The Restart Signaling TLV is used for requesting an granting a new Hold timer RFC 3847 describes the optional Restart Signaling TLV 211 that can be used to signal a grace period until adjacency formation is completed. Figure illustrates the 3-byte fixed length TLV. The first byte contains the Restart Request and the Restart Acknowledge Flag. The remaining 16-bits contain the hold time that a node sets itself for performing the reboot. Both IOS and JUNOS generate the Restart Signaling TLVs per default to indicate to remote neighbours that they support graceful restart in general. Tcpdump output TLV 211 under normal working conditions has the RR and RA Bits cleared and the remaining Hold timer set to 0s. 02 00 Out OSI IS-IS length 82 point-to-point IIH hlen 20 v 1 pdu-v 1 sys-id-len 6 0 max-area 3 0 source-id holding time 27s circuit-id 0x01 Flags L1L2 . Restart Signaling TLV 211 length 3 Restart Request bit clear Restart Acknowledgement bit clear Remaining holding time 0s In both IOS and JUNOS the restart capability is indicated in the detailed adjacency output. IOS command output The show clns neighbors detail command shows if the neighbour supports graceful restart. London show clns neighbors detail System Id Interface SNPA State Holdtime Type Protocol Frankfurt POS2 0 PPP Up 25 L2 M-ISIS Area Address es IP Address es IPv6 Address es FE80 2A0 A5FF FE12 3398 Uptime 00 15 41 NSF capable Topology IPv4 IPv6 Graceful Restart 391 In the IOS terminology Non Stop Forwarding NSF is an alternative term for graceful restart. JUNOS command output hannes@Frankfurt show isis adjacency detail . London Interface so-1 2 Level 2 State Up Expires in 23 secs Priority 0 Up Down transitions 11 Last transition 00 24 12 ago Circuit type 3 Speaks IP IPv6 Topologies Unicast IPV6-Unicast Restart capable Yes IP addresses IPv6 addresses fe80 203 fdff fec8 3c00 . Graceful restart will .

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