MPLS Label Distribution Protocol, LDP – Part 5 (Export and Import Policy, Prefix Aggregation) - www.ipcisco.com : www.ipcisco.com
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Export and Import Policy
and Prefix Aggregation with LDP

LDP and Export Policy

By default ALU only distribute a label only for its system addresses. To distribute additional other local prefixes, “export policy” is used.

You can find an “export-policy” example below:

A:>config router policy-options
	begin
	prefix-list “interface1”
		prefix 10.0.0.6/24
		exit
	policy-statement “LDP_Export_Policy1”
		entry 10
			from
				prefix-list “interface1”
				exit
			action accept
			exit
		exit
	exit
	commit

To apply this “export policy” to an LDP, use the below command:

A:>config router ldp export “LDP_Export_Policy1”

LDP and Import Policy



By default ALU accepts all labels form all peers. But with “import policy” certain label bindings can be rejected.

A:>config router policy-options
	begin
	policy-statement “LDP_Import_Policy1”
		entry 10
			action reject
			exit
		exit
	commit

To apply this “import policy” to an LDP use the below command:

A:>config router ldp export “LDP_Import_Policy1”

LDP Aggregate Prefix Match

As you know we can do route summarization on routing protocols. By doing this, sometimes we cause some missing information on the MPLS tables.

Think about two routes 10.0.0.1/32 and 10.0.0.2/32. If I summarize this like 10.0.0.0/24, then my MPLS tables will be like below:

show router ldp bindings (LIB) => 10.0.0.1/32 and 10.0.0.2/32
show router fib 1 (FIB) => 10.0.0.0/24
show router ldp bindings active (LFIB) => Empty!!!

This is a problem. To avoid this situation, “aggregate-prefix-match” command must be issued under the ldp. After the configuration, all the routes loaded in the LFIB.

A:>config router ldp aggregate-prefix-match

show router ldp bindings (LIB) => 10.0.0.1/32 and 10.0.0.2/32
show router fib 1 (FIB) => 10.0.0.0/24
show router ldp bindings active (LFIB) => 10.0.0.1/32 (push, swap) and 10.0.0.2/32 32 (push, swap)

This is also decrease the route table size in the big sized networks.

MPLS Label Distribution Protocol, LDP – Part 1
MPLS Label Distribution Protocol, LDP – Part 2
MPLS Label Distribution Protocol, LDP – Part 3 (Configuration on ALU)
MPLS Label Distribution Protocol, LDP – Part 4 (ECMP)
MPLS Label Distribution Protocol, LDP – Part 5 (Export and Import Policy, Prefix Aggregation)
MPLS Label Distribution Protocol, LDP – Part 6 (T-LDP)
MPLS Label Distribution Protocol, LDP – Part 7 (CR-LDP)

For more information about LDP, T-LDP and CR-LDP, check the related following RFCs…

RFC 5036: LDP Specification
RFC 3815: Definitions of Managed Objects for the MPLS,LDP
RFC 3478: Graceful Restart Mechanism for Label Distribution Protocol
RFC 5443: LDP IGP Synchronization
RFC 7307: LDP Extensions for Multi-Topology
RFC 7361: LDP Extensions for Optimized MAC Address Withdrawal in a H-VPLS
RFC 3212: Constraint-Based LSP Setup using LDP
RFC 3213: Applicability Statement for CR-LDP 
RFC 3214: LSP Modification Using CR-LDP


…YOU CAN REACH ALL THE “MPLS” ARTICLES AND CONFIGURATIONS BELOW…


MPLS Basics
What is MPLS?
Enabling MPLS on Cisco Router

MPLS Label Distribution Protocol, LDP
MPLS Label Distribution Protocol, LDP – Part 1
MPLS Label Distribution Protocol, LDP – Part 2
MPLS Label Distribution Protocol, LDP – Part 3 (Configuration on ALU)
MPLS Label Distribution Protocol, LDP – Part 4 (ECMP)
MPLS Label Distribution Protocol, LDP – Part 5 (Export and Import Policy, Prefix Aggregation)
MPLS Label Distribution Protocol, LDP – Part 6 (T-LDP)
MPLS Label Distribution Protocol, LDP – Part 7 (CR-LDP)

MPLS, RSVP-TE
MPLS, RSVP-TE – Part 1
MPLS, RSVP-TE – Part 2(Alcatel-Lucent Configuration)

MPLS Protection And Restoration
MPLS Protection and Restoration – Part 1
MPLS Protection and Restoration – Part 2 (End-to-End Protection, Secondary Paths)
MPLS Protection and Restoration – Part 3 (Path Diversity in Secondary Paths)
MPLS Protection and Restoration – Part 4 (Local Protection, Fast Reroute)
MPLS Protection and Restoration – Part 5 (Fast Reroute Protection Types)
MPLS Protection and Restoration – Part 6 (RSVP Objects Used for MPLS Fast Reroute)
MPLS Protection and Restoration – Part 7 (Verification Commands on Alcatel-Lucent Routers)
MPLS Protection and Restoration – Part 8 (Actions After the Failure)
MPLS Protection and Restoration – Part 9 (Convergence Factors)
MPLS Protection and Restoration – Part 10 (Juniper Configuration Samples)
MPLS Protection and Restoration – Part 11 (Juniper Configuration Samples)
MPLS Protection and Restoration – Part 12 (Juniper Configuration Samples)
MPLS Protection and Restoration – Part 13 (Juniper Configuration Samples)


…You Can Join Our “IPCisco” Groups Below!!!…




About the Author
Gokhan Kosem is a telecommunation and network engineer. His ambition to IP networks and end-to-end system installation made him to prepare this web-site. By sharing his experiences about various networking protocols beside different system installation experiences and Cisco, Juniper, Alcatel-Lucent devices configurations, he is aimed to be helpful for his collegues in all over the world. He is currently lives in Istanbul, Turkey.

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