Chained Composite Next Hops for Transit Devices for VPNs
The Juniper Networks PTX Series Packet Transport Routers, MX Series 5G Universal Routing Platforms with MIC and MPC interfaces, T4000 Core Routers, and QFX10000 switches are principally designed to handle large volumes of transit traffic in the core of large networks. Chained composite next hops help to facilitate this capability by allowing the router to process much larger volumes of routes. A chained composite next hop allows the router to direct sets of routes sharing the same destination to a common forwarding next hop, rather than having each route also include the destination. In the event that a network destination is changed, rather than having to update all of the routes sharing that destination with the new information, just the shared forwarding next hop is updated with the new information. The chained composite next hops continue to point to this forwarding next hop which now contains the new destination.
When the next hops for MPLS LSPs are created on the routers, the tag information corresponding to the inner-most MPLS label is extracted into a chained composite next hop. The chained composite next hop is stored in the ingress PFE. The chained composite next hop points to a next hop called the forwarding next hop that resides on the egress PFE. The forwarding next hop contains all of the other information (all of the labels except for the inner-most labels; and the IFA/IP information corresponding to the actual next hop node). Many chained composite next hops can share the same forwarding next hop. Additionally, separating the label from the forwarding next hop and storing it on the ingress PFE (within the chained composite next hop) helps to conserve egress PFE memory by reducing the number of rewrite strings stored on the egress PFE.
The support of chained composite next hops for directly connected Provider Edge (PE) routers varies from one platform to another.
On platforms containing only MPCs, such as PTX Series Packet Transport Routers, the MX80 router, the MX2020 router, and the QFX10000 switches, chained composite next hops are enabled by default for the following MPLS and VPN protocols and applications:
Point-to-Multipoint LSPs and Layer 2 VPNs are not supported on the QFX10000 switches.
Labeled BGP
Layer 2 VPNs
Layer 3 VPNs
LDP
MPLS
Point-to-Multipoint LSPs
RSVP
Static LSPs
On MX Series 5G Universal Routing Platforms containing both DPC and MPC FPCs, chained composite next hops are disabled by default.
To enable chained composite next hops on the MX Series routers such as: MX80, MX240, MX480, MX960 and MX2020, the chassis must be configured to use the enhanced-ip option in network services mode.
On T4000 Core Routers containing MPC and FPCs, chained composite next hops are disabled by default.
To enable chained composite next hops on a T4000 router, the chassis must be configured to use the enhanced-mode option in network services mode.
For more information about configuring chassis network services, see the Junos OS Administration Library.