• Author : Arpit Bansal

 
 

Support for TI-LFA FRR using IS-IS Segment Routing

Description Topology Independent Fast Reroute, or TI-LFA, uses IS-IS SR to build loop-free alternate paths along the post-convergence path. These loop-free alternates provide fast convergence in the range of sub-50 ms. The PLR ( point of local repair – the router where TI-LFA is configured ) switches to these loop-free alternate backup paths in the event of a link down ( link-protection ) or BFD neighbor down (node-protection) event, protecting traffic destined to IS-IS SR node segments, adjacency segments, and anycast segments while the IGP converges and the post-convergence paths are computed. Anycast segment protection is restricted to those segments...
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IS-IS set-attached-bit

Level-1-2 routers set attached-bit in their Level-1 LSPs to indicate their reachability to the rest of the network. A Level-1-2 router is considered attached only if it is able to reach a Level-2 router in a different area. Level-1 routers use this attached-bit information to install a default route to the closest attached Level-1-2 router and use it to route inter-area traffic. A route-map can be configured on a Level-1-2 router to control the setting of attached-bit in Level-1 LSPs with set-attached-bit route-map <name>. Attached-bit will be set only if the route-map is satisfied in addition to the Level-2 reachability...
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IS-IS set-attached-bit

Level-1-2 routers set attached-bit in their Level-1 LSPs to indicate their reachability to the rest of the network. A Level-1-2 router is considered attached only if it is able to reach a Level-2 router in a different area. Level-1 routers use this attached-bit information to install a default route to the closest attached Level-1-2 router and use it to route inter-area traffic. A route-map can be configured on a Level-1-2 router to control the setting of attached-bit in Level-1 LSPs with set-attached-bit route-map <name>. Attached-bit will be set only if the route-map is satisfied in addition to the Level-2 reachability...
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IS-IS Level-1-2 router

An IS-IS router can be configured as Level-1-2 which can form adjacencies and exchange routing information with both Level-1 and Level-2 routers. A Level-1-2 router can be configured to transfer routing information from Level-1 to Level-2 areas and vice versa(via route leaking). By default, all routes from Level-1 area are always leaked into Level-2 network. Level-1 routers usually rely on a default route to closest attached Level-1-2 router for connectivity which may lead to sub optimal routing. More specific prefixes can thus be leaked by Level-1-2 router into Level-1 network, for optimal routing. Configuration IS-IS router is a Level-1-2 router...
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Redistribution of IS-IS routes into BGP and BGP routes into IS-IS

This feature allows to advertise routes learnt via BGP into IS-IS network or IS-IS routes into BGP network. It also allows to selectively advertise some routes and modify route attributes before advertising using route-maps. Configuration Switch(config)#router isis 1 Switch(config-router-isis)#address-family ipv4 Switch(config-router-isis-af)#redistribute bgp route-map bgp-to-isis-v4 Switch(config)#router bgp 1 Switch(config-router-bgp)#address-family ipv4 Switch(config-router-bgp-af)#redistribute isis level-1 route-map isis-to-bgp-v4 Alternatively same commands are available in router isis mode and router bgp where if configured it will apply to both IPv4 and IPv6 routes. Switch(config)#router isis 1 Switch(config-router-isis)#redistribute bgp route-map bgp-to-isis Switch(config)#router bgp 1 Switch(config-router-bgp)#redistribute isis level-1 route-map isis-to-bgp Note these commands cannot be configured in...
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