Conditional ACL to announce Label for loopback of PE

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Jul 24th, 2008
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Hi,


Can some one tell me what is advantage/disadvantage I get by using Conditional ACL to announce lable for only loopback to other LDP neighbour if i want to really propose?


Regards,

Chintan.

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lee.reade Thu, 07/24/2008 - 03:21
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Hi,


Well in the MPLS core you will have a routing protocol, ospf/isis, and when you run LDP/TDP for MPLS labels then every route with be assigned its own label value by each router.


This consumes a lot of resources, cpu & memory etc.


In a normal MPLS Setup, the P routers (the routers of the SP that do not connect to customer routers) are only involved in label forwarding from PE to PE, (PE connects to customer) and this forwarding will be between a pair of PE router loopback address, as BGP is used for MPLS VPN and the loopback address is the next-hop address for the remote CE VPN routes.


So basically, we only really need to label switch the PE loopback address, so by doing this we save resources.


HTH


LR

shivlu jain Mon, 07/28/2008 - 22:43
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main reason for conditional advertisement is that during the loopback only next hop address is loopback of the next router and labels will be swapped for loopback only not for the interfaces.By default labels are generated for all the routes present in routing table but advertise only for those which are bind in acl.


ip access-list standard MPLS_Loopbacks

permit 10.255.240.0 0.0.7.255

permit 10.255.248.0 0.0.7.255


no mpls ldp advertise-labels

mpls ldp advertise-labels for MPLS_Loopbacks


regards

shivlu

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