• Author : Arpit Bansal

 
 

IGP shortcut in IS-IS

Description IGP shortcuts enable traffic to get forwarded along paths computed to take advantage of traffic-engineered paths setup using RSVP using a modified SPF algorithm.  This enables operators to take advantage of TE capabilities of RSVP  tunnels which traverse over links satisfying bandwidth, latency or fast reroute considerations.  IGP shortcuts can be enabled on a RSVP Label Edge Router (LER) selectively on specific RSVP tunnels. When enabled, traffic to destination prefixes reachable via or beyond these tunnels, is forwarded through these tunnels. RFC 3906 describes the mechanism by which IGP shortcut paths are computed. When IGP shortcut is enabled, IP...
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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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