![]() ![]() Known via "bgp 1", distance 200, metric 1, type internal The following examples show that a valid route to the destination is present in the VRF table for this VPN. Route metric is 0, traffic share count is 1Īt PE1 (the PE router attached to CE1), you can check MPLS VPN specific information. Known via "static", distance 1, metric 0, candidate default path However, CE1 has a valid routing entry for this destination, as shown in the following example. Sending 5, 100-byte ICMP Echos to 192.168.1.196, timeout is 2 seconds: The connectivity between CE1 and the loopback interface of CE2 has been lost, as shown in the following example. The configuration consists of only IP addressing on the Ethernet interface and a static default route to 10.2.2.2. Note: The CE1 configuration has been omitted. !- Routing Information Protocol (RIP) is used for the advertisement !- of routes between the CE and the provider edge (PE) router. Neighbor 10.2.2.2 send-community extended Neighbor 10.2.2.2 update-source Loopback0 !- The VRF interface toward the CE router. Neighbor 10.5.5.5 send-community extended Neighbor 10.5.5.5 update-source Loopback0 !- The VPN Routing and Forwarding (VRF) interface !- toward the customer edge (CE) router. ![]() Router Configurations PE1 Router Configuration Refer to Cisco Technical Tips Conventions for more information on document conventions. The information in this document is based on this software version:Ĭisco IOS® Software release version 12.0(21)ST2 There are no specific requirements for this document. However, the steps used to diagnose and correct this problem are applicable to any problem involving label bindings and the LFIB on routers configured for MPLS. The document covers one scenario wherein label bindings received by a router are not used to forward MPLS-switched packets. This document gives an example of this kind of LSP failure and several possible solutions. In a similar manner, if a router advertises labels for a subnet/subnet mask pair, which do not correspond to the routing updates also advertised by this router for the same subnet/subnet mask pair, these labels will not be used by upstream neighbors and the Label Switched Path (LSP) between these devices will fail. If label bindings are received from a downstream neighbor for prefixes (including subnet mask) which do not appear in a router's routing and CEF tables, these bindings will not be used. Meaning the labels used for forwarding are those received from a router's next hop to a destination, according to the router's Cisco Express Forwarding (CEF) and routing tables. If the labels are received from a downstream neighbor for their FEC, then the labels stored in the LIB are used for packet forwarding by the LFIB. All labels received from neighbors are retained in the LIB, whether or not they are used. For Cisco implementation, labels are sent for all routes in a given router's routing table (with the exception of BGP routes), to all LDP or TDP neighbors. The Label Information Base (LIB) is a structure which stores labels received from all Label Distribution Protocol (LDP) or Tag Distribution Protocol (TDP) neighbors. Another example could be all packets with a given IP precedence going to an Interior Gateway Protocol (IGP) next hop associated with a group of Border Gateway Protocol (BGP) routes. The most simple example of a FEC is all packets traveling to a certain subnet. A FEC is a grouping of IP packets which travel over the same path and receive the same forwarding treatment. Labels are associated with destinations in the LFIB according to Forwarding Equivalence Classes (FECs). A packet leaving a router over a label-switched interface will receive labels with values specified by the LFIB. ![]() MPLS-switched packets are forwarded based on information contained in the Label Forwarding Information Base (LFIB). This document assumes you have a prior understanding of basic Multiprotocol Label Switching (MPLS) concepts.
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