How Can You Prevent Loop on Ip/mpls Network
Loop Detection
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• LDP relies on loop detection mechanisms built into IGPs that are used to determine the path.
• If, notwithstanding, a loop is generated (that is, misconfiguration with static routes), the TTL field in the label header is used to foreclose indefinite looping of packets.
• TTL functionality in the label header is equivalent to TTL in the IP headers.
• TTL is normally copied from the IP headers to the label headers (TTL propagation).
Loop detection in an MPLS-enabled network relies on more one mechanism.
Most routing loops are prevented by the IGP used in the network. MPLS for unicast IP forwarding but uses the shortest paths adamant by the IGP. These paths are typically loop-complimentary.
If, nevertheless, a routing loop does occur (for example, because of misconfigured static routes), MPLS labels also incorporate a time-to-live (TTL) field that prevents packets from looping indefinitely.
The TTL functionality in MPLS is equivalent to that of traditional IP forwarding. Furthermore, when an IP packet is labeled, the TTL value from the IP header is copied into the TTL field in the label. This is chosen TTL propagation.
Copyright © 2004, Cisco Systems, Inc. Label Consignment and Distribution 2-27
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• Cisco routers take TTL propagation enabled past default.
• On ingress: TTL is copied from IP header to label header.
• On egress: TTL is copied from characterization header to IP header.
© 2004 Cisco Systems, Inc. All rights reserved. MPLS v2.1—2-27
• Cisco routers take TTL propagation enabled past default.
• On ingress: TTL is copied from IP header to label header.
• On egress: TTL is copied from label header to IP header.
© 2004 Cisco Systems, Inc. All rights reserved. MPLS v2.1—2-27
Continue reading here: Example Normal TTL Operation
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