Table Of Contents
Failure Scenarios
This chapter provides details of all failure scenarios reported by the Cisco MPLS Diagnostics Expert (MDE) 2.1.3 application for the Cisco IP Solution Center (ISC) Release 5.1. It also details IOS XR support caveats.
This chapter provides the following information:
For more information, e-mail: mpls-diagnostics-expert@cisco.com
1.1 Failure Scenarios1
This section lists the failure scenarios reported by MDE, as follows:
Note
Each failure scenario provides a table that lists whether the failure scenario is supported by each of the five MDE test types. This table also details whether the failure scenario is supported on IOS and IOS XR.
1.1.1 Access Circuit
Access Circuit Blocking IP Connectivity
There is a blocking access list preventing IP connectivity from an access circuit interface on the provider (PE) router to the destination.
Yes
Yes
Yes
No
No
Yes
Yes
An Invalid PE Interface has been Specified
Interface does not exist on the PE router.
Yes
Yes
Yes
Yes
No
Yes
Yes
ATM Interface Has No VPI/VCI
An asynchronous transfer mode (ATM) access circuit interface on a PE router has no virtual path identifier (VPI), or virtual channel identifier (VCI) assigned to it, or no VPI/VCI maps to the destination IP address.
Yes
Yes
Yes
No
No
Yes
Yes
ATM Interface Is Protocol Down
An ATM access circuit interface on a PE router is protocol down. See the "IOS XR Support" section.
Yes
Yes
Yes
No
No
Yes
Yes
ATM Sub-interface is Protocol Down
An ATM access circuit subinterface on a PE router is protocol down. This might be caused by incorrect subinterface parameters or by ATM Operation, Administration, and Maintenance (OAM) detecting a fault and bringing the interface down automatically. See the "IOS XR Support" section.
Yes
Yes
Yes
No
No
Yes
Yes
Calculation of the CE Access Circuit Interface IP Address is only possible if the PE interface is not Unnumbered and has a /30 Subnet mask Interface on PE
Unable to calculate the customer edge (CE) access circuit interface IP address for the PE.
Yes
Yes
Yes
No
No
Yes
Yes
eBGP Max Prefix Exceeded for Peer
Exterior border gateway protocol (eBGP) is running between the PE and CE, however the border gateway protocol (BGP) neighbor is not established. The peer has exceeded the configured maximum number of prefixes.
Yes
Yes
Yes
No
No
Yes
No
eBGP Neighbor Not Established, No Route Present
eBGP is running between the PE and CE, but the BGP Neighbor on the PE is not established. The BGP neighbor is on a different subnet from the PE and there is no route to the neighbor in the VPN routing/forwarding (VRF).
Yes
Yes
Yes
No
No
Yes
No
eBGP Neighbor Not Established, Possible Misconfiguration
eBGP is running between the PE and CE, but the BGP neighbor on the PE is not established. There is a route to the BGP neighbor in the VRF and it is reachable via ping. Possible CE or PE BGP configuration problem.
Yes
Yes
Yes
No
No
Yes
No
eBGP Neighbor Not Established, Route Present
eBGP is running between the PE and CE, but the BGP neighbor on the PE is not established. The BGP neighbor is on a different subnet from the PE and there is a route to the neighbor in the VRF. However, the BGP neighbor is unreachable via ping.
Yes
Yes
Yes
No
No
Yes
No
EIGRP Not Exchanging Routes
The enhanced interior gateway routing protocol (EIGRP) is running between the PE and CE and a peer relationship has been established. However, no routes have been received from EIGRP on the CE.
Yes
Yes
Yes
No
No
Yes
No
Ethernet Interface Protocol Down
An Ethernet access circuit interface on the PE router protocol is down.
Yes
Yes
Yes
No
No
Yes
Yes
Ethernet Sub-Interface Protocol Down
An Ethernet access circuit subinterface on the PE router protocol is down.
Yes
Yes
Yes
No
No
Yes
Yes
Frame Relay Interface Has No DLCI
A Frame Relay access circuit interface on the PE router has no data-link connection identifier (DLCI) assigned to it, or no DLCI maps to the destination IP address.
Yes
Yes
Yes
No
No
Yes
Yes
Frame Relay Interface Protocol Down
A Frame Relay access circuit interface on the PE router protocol is down. This might be because of line parameters or cabling faults.
Yes
Yes
Yes
No
No
Yes
Yes
Frame Relay PVC Marked as Deleted
A multipoint Frame Relay permanent virtual circuit (PVC) on an access circuit interface on the PE router has no DLCI that maps to the destination IP address.
Yes
Yes
Yes
No
No
Yes
No
Frame Relay PVC Marked as Deleted
A point-to-point Frame Relay PVC on an access circuit interface on the PE router has no DLCI assigned to it.
Yes
Yes
Yes
No
No
Yes
Yes
Frame Relay PVC Marked as Deleted
A Frame Relay PVC on an access circuit interface on the PE router is marked as deleted.
Yes
Yes
Yes
No
No
Yes
No
Frame Relay PVC Marked as Down
A multipoint Frame Relay PVC on an access circuit interface on the PE router is marked as down.
Yes
Yes
Yes
No
No
Yes
No
Frame Relay PVC Marked as Down
A point-to-point Frame Relay PVC on an access circuit interface on the PE router is marked as down.
Yes
Yes
Yes
No
No
Yes
Yes
Incomplete Carrier on Serial Interface
A serial access circuit interface on the PE router has an incomplete carrier.
Yes
Yes
Yes
No
No
Yes
Yes
Interface Administratively Down
An access circuit interface (or subinterface) on the PE router is administratively down.
Yes
Yes
Yes
No
No
Yes
Yes
Interface Administratively Down
An access circuit subinterface on the PE router is administratively down.
Yes
Yes
Yes
No
No
Yes
Yes
Interface in Protocol Down State
An access circuit interface on the PE router protocol is down.
Yes
Yes
Yes
No
No
Yes
Yes
Interface on the PE is a Bundle Link Virtual-Access Interface
The interface on the PE is not a valid access circuit interface.
Yes
Yes
Yes
Yes
No
Yes
No
Interface Operationally Down
An access circuit interface on the PE router is operationally down.
Yes
Yes
Yes
No
No
Yes
Yes
Intermittent ATM Failure (to the ATM Next Hop)
ATM access circuit has intermittent ATM access to the ATM next hop. See the "IOS XR Support" section.
Yes
Yes
Yes
No
No
Yes
Yes
Intermittent ATM Failure (to the Destination)
ATM access circuit has intermittent ATM access to the destination. See the "IOS XR Support" section.
Yes
Yes
Yes
No
No
Yes
Yes
Invalid Access Circuit IP Address Configuration
The CE router access circuit interface IP address is not in the same subnet as the attached PE access circuit interface IP address.
Yes
Yes
Yes
No
No
Yes
Yes
Invalid Access Circuit IP Address Configuration
The CE access circuit interface IP address is a network address.
Yes
Yes
Yes
No
No
Yes
Yes
Invalid Access Circuit IP Address Configuration
The CE access circuit interface IP address is a network broadcast address.
Yes
Yes
Yes
No
No
Yes
Yes
Invalid Access Circuit IP Address Configuration
The CE access circuit interface IP address is the same as the attached PE access circuit interface IP address.
Yes
Yes
Yes
No
No
Yes
Yes
IP Connectivity Problem
Unknown IP connectivity issue. An access circuit connectivity problem in the VRF instance from the PE interface to the CE.
No
Yes
No
No
No
Yes
Yes
Missing Route
There is no route from the access circuit interface on the PE router to the destination.
Yes
Yes
Yes
No
No
Yes
Yes
Missing Route
There is no route from the access circuit interface on the PE router to the customer destination.
Yes
Yes
Yes
No
No
Yes
Yes
No EIGRP Peer Relationship Established
The EIGRP is running between the PE and CE, however no peer relationship has been established.
Yes
Yes
Yes
No
No
Yes
No
No EIGRP Peer Relationship Established
The routing protocol EIGRP is running between the PE and CE. The PE and CE interfaces are on different subnets and are not using IP unnumbered. No peer relationship has been established as the PE and CE are on different subnets.
Yes
Yes
Yes
No
No
Yes
No
No OSPF Peers
Open shortest path first (OSPF) is running between the PE and CE, but no peer exists on the PE.
Yes
Yes
Yes
No
No
Yes
No
No Routing Protocol has been Determined Running between the PE and CE and no Static Route is Present
An access circuit connectivity problem in VRF.
Yes
Yes
Yes
No
No
Yes
No
OSPF Not Exchanging Routes
OSPF is running between the PE and CE, but a peer relationship has been established. However, no routes have been received from OSPF on the CE.
Yes
Yes
Yes
No
No
Yes
No
OSPF Peers Not Established
OSPF is running between the PE and CE, but a peer relationship has not been established.
Yes
Yes
Yes
No
No
Yes
No
OSPF Peers Not Established
OSPF is running between the PE and CE. However, a peer relationship has not been established as PE and CE interfaces are on different subnets and are not using IP unnumbered.
Yes
Yes
Yes
No
No
Yes
No
PE has No Route to CE
Connected PE and CE interfaces are on different subnets. No routing protocol has been determined running between the PE and CE and no static route to the CE is present.
Yes
Yes
Yes
No
No
Yes
No
RIB Failure
A route from the PE to a destination in a VRF has not been installed in the VRF routing table. This has been identified as a Routing Information Base (RIB) failure.
Yes
Yes
Yes
Yes
No
Yes
No
RIP Misconfiguration
Routing information protocol (RIP) is running between the PE and CE, but no routes have been received from RIP on the CE.
Yes
Yes
Yes
No
No
Yes
No
RIP Not Exchanging Routes
RIP is running between the PE and CE, but no routes have been received from RIP on the CE as the PE and CE interfaces are on different subnets and are not using IP unnumbered.
Yes
Yes
Yes
No
No
Yes
No
Serial Interface in Loopback Mode
A serial access circuit interface on the PE router is configured in loopback mode.
Yes
Yes
Yes
No
No
Yes
Yes
Serial Interface Operationally Down
A serial access circuit interface on the PE router is operationally down.
Yes
Yes
Yes
No
No
Yes
Yes
Static IP address on ATM Point-to-Point Interface
ATM access circuit has a static IP address mapping on an ATM point-to-point subinterface. Neither a static mapping nor an address resolution protocol (ARP) are required on a point-to-point subinterface because there is a single VC and a single path for the traffic. See the "IOS XR Support" section.
Yes
Yes
Yes
No
No
Yes
Yes
Sub-interface in Protocol Down State
An access circuit subinterface on the PE router protocol is down.
Yes
Yes
Yes
No
No
Yes
Yes
Undiagnosed ATM Failure (ATM Pings Failed but the ATM Segment Ping Succeeded)
ATM access circuit connection is broken. The end-to-end ATM ping failed, but the ATM segment ping succeeded. This might be caused by various issues such as incorrect ATM line parameters, misconfigured ATM routing, CE or ATM cloud interfaces being down, or devices being down. See the "IOS XR Support" section.
Yes
Yes
Yes
No
No
Yes
Yes
Undiagnosed ATM Failure (End to End and Segment ATM Pings Failed)
ATM access circuit connection is broken. Both the end-to-end and segment ATM pings failed. This might be caused by various issues such as incorrect ATM line parameters, misconfigured ATM routing on the ATM next hop, next hop interfaces being down, or devices being down. See the IOS XR Support.
Yes
Yes
Yes
No
No
Yes
Yes
Virtual Template Interface has been Specified for the PE Access Circuit Interface
The PE interface on the PE is not a valid access circuit interface.
Yes
Yes
Yes
Yes
No
Yes
No
1.1.2 MPLS Edge
BGP Next Hop Interface Admin Down
BGP next hop on PE is assigned to a loopback interface. However, that interface is administratively down.
Yes
No
Yes
Yes
Yes
Yes
Yes
BGP Next Hop is Not Assigned to an Interface
The BGP next hop for routes to the remote site PE is not assigned to an interface on the remote PE.
Yes
No
Yes
Yes
Yes
Yes
Yes
BGP Not Active
BGP is not active on the PE router.
Yes
Yes
Yes
Yes
No
Yes
Yes
BGP Peers Using Same BGP Next Hop
BGP VPNv4 peers use the same BGP next hop. This prevents correct route distribution of PE routes. Other routing problems might also be encountered.
Yes
No
Yes
Yes
No
Yes
Yes
BGP Peers Using Same Router Identifier (RID)
BGP VPNv4 peers use the same router identifier. This prevents correct route distribution of PE routes. Other routing problems might also be encountered.
Yes
No
Yes
Yes
Yes
Yes
Yes
BGP to LFIB Mismatch
Untagged entry has mismatch between BGP and label forwarding information base (LFIB) tables.
Yes
Yes
Yes
Yes
No
Yes
Yes
BGP to LFIB Mismatch
The forwarding information base (FIB) and BGP entries are inconsistent.
Yes
Yes
Yes
Yes
No
Yes
Yes
Duplicate BGP Next Hop
Duplicate IP address found in the network for the BGP next hop on PE.
Yes
No
Yes
Yes
Yes
Yes
Yes
Duplicate IP Address
There is a duplicate IP address configured on the PE router that conflicts with an access circuit interface.
Yes
Yes
Yes
No
No
Yes
Yes
Duplicate IP Address
Duplicate IP address found in the network for the BGP router identifier on PE.
Yes
No
Yes
Yes
Yes
Yes
Yes
eBGP not Redistributing Connected Routes into MP-BGP
The routing protocol eBGP is running between the PE and CE, but eBGP on the PE is not redistributing connected routes into Multi Protocol (MP)-BGP.
Yes
Yes
Yes
No
No
Yes
No
FIB to LFIB Mismatch
Aggregate entry has mismatch between FIB and LFIB tables.
Yes
Yes
Yes
No
No
Yes
Yes
Ingress FIB to Egress LFIB Mismatch
Egress LFIB and Ingress FIB inconsistency.
Yes
Yes
Yes
Yes
No
Yes
Yes
Inconsistent BGP Entries
BGP entries are inconsistent for the VRF.
Yes
Yes
Yes
Yes
No
Yes
Yes
IP Unnumbered Borrowed Interface Administratively Down
The interface from which an IP address is borrowed for an IP unnumbered interface on the PE router is administratively down.
Yes
Yes
Yes
No
No
Yes
Yes
Missing Router Identifier (RID)
Unable to determine the local router identifier on the PE.
No
No
No
No
Yes
Yes
Yes
Missing VPNv4 Address Family Configuration
VPNv4 configuration missing; Virtual private network (VPN) label exchange problem. VPNv4 address family configuration missing from BGP router configuration on the PE router. This results in routes being dropped.
Yes
No
Yes
Yes
No
Yes
Yes
MPLS LDP Package not enabled on IOS XR Router
The MPLS LDP package is not enabled on the IOS XR router.
Yes
No
Yes
Yes
Yes
No
Yes
MPLS Package installed but not active on IOS XR Router
The MPLS package is installed, but it is not active on the IOS XR router.
Yes
No
Yes
Yes
Yes
No
Yes
MPLS Package not installed on IOS XR Router
The MPLS package is not installed on the IOS XR router.
Yes
No
Yes
Yes
Yes
No
Yes
MPLS Troubleshooting is Only Possible on Cisco Devices in the ISC Inventory
Label-switched path (LSP) connectivity failure lies between the upstream neighbor and the remote PE. Unable to log in to the device to localize further, as it is not present in ISC inventory (it is potentially a non-Cisco device).
Yes
No
Yes
Yes
Yes
Yes
Yes
No MP-BGP Neighbors
There are no MP-BGP neighbors defined on the PE router.
Yes
No
Yes
Yes
No
Yes
Yes
No MP-BGP Neighbor Session Established
No MP-BGP neighbor session established on the PE router.
Yes
No
Yes
Yes
No
Yes
Yes
No VPN Label For Prefix
No VPN label has been allocated for the prefix.
Yes
No
Yes
Yes
No
Yes
Yes
No VRF Associated with IP Unnumbered Borrowed Interface
The interface from which an IP address is borrowed for an IP unnumbered interface on the PE router has no VRF associated.
Yes
No
Yes
Yes
No
Yes
Yes
No VRF Associated with PE Interface
An interface on the PE router has no VRF associated.
Yes
No
Yes
Yes
No
Yes
Yes
OSPF Loopback Interface Uses A Non /32 Netmask
VPNv4 routes are being advertised to IBGP neighbors by the PE. The address of the next hop is a loopback interface that does not have a /32 mask defined. OSPF is being used on this loopback interface, and the OSPF network type of this interface is loopback. OSPF advertises this IP address as a host route (with mask /32), regardless of what mask is configured. This advertising conflicts with TDP/LDP, that uses configured masks, so the TDP/LDP neighbors might not receive a label for the routes advertised by this router. This condition could break connectivity between sites that belong to the same VPN.
Yes
No
Yes
Yes
Yes
Yes
No
PE Interface Has No IP Address
An interface on the PE router has no IP address.
Yes
No
Yes
Yes
No
Yes
Yes
Router ID Loopback Interface Down
The loopback interface used to assign the local router ID on the PE is administratively down.
Yes
Yes
Yes
No
No
Yes
Yes
Routes not Redistributed to or from MP-BGP
Routes are not being redistributed to or from MP-BGP on the PE.
Yes
Yes
Yes
No
No
Yes
No
Routing Protocol eBGP is running between PE and CE and is not Redistributing Connected Routes into MP-BGP
VPN connectivity problem in VRF to destination.
Yes
No
Yes
Yes
No
Yes
Yes
Static Route to Remote Prefix
A static route to a remote prefix has been configured within a VRF on the PE.
Yes
No
Yes
Yes
No
Yes
Yes
Traffic Administratively Blocked
VPN connectivity problem from the PE to the destination due to traffic being administratively blocked.
Yes
No
Yes
No
No
Yes
Yes
Troubleshooting of the Layer 3 VPN has been Unable to Find the Cause of the Failure
LSP connectivity problem.
Yes
No
Yes
Yes
Yes
Yes
Yes
Troubleshooting of the Layer 3 VPN has been Unable to Find the Cause of the Failure
VPN connectivity problem in VRF from PE to destination.
Yes
No
Yes
Yes
No
Yes
Yes
VRF Route Target Import/Export Mismatch
VRF route target import/export mismatch between the PE devices.
Yes
No
Yes
Yes
No
Yes
Yes
1.1.3 MPLS Core
An Invalid PE Interface has been Specified
Interface supplied as the LSP Endpoint does not exist on the PE router.
No
No
No
No
Yes
Yes
Yes
Broken LDP Neighbor Session
LDP session with downstream neighbor broken. Route processor/line card forwarding discrepancy on the router. See the "IOS XR Support" section.
Yes
No
Yes
Yes
Yes
Yes
No
CEF Not Enabled On Router
CEF has not been enabled on a router. See the "IOS XR Support" section.
Yes
No
Yes
Yes
Yes
Yes
No
Distributed LFIB Table Discrepancy
There is a discrepancy in the LFIB table between the route processor and line cards.
Yes
No
Yes
Yes
No
Yes
Yes
Distributed LFIB Table Discrepancy
There is a discrepancy in the FIB table between the route processor and line cards.
Yes
No
Yes
Yes
No
Yes
Yes
Label Inconsistency
LFIB local tag, received packet, and LDP local binding label inconsistent on the router. See the "IOS XR Support" section.
Yes
No
Yes
Yes
Yes
Yes
No
LDP Host Not Reachable
The host is not reachable from the label switch router (LSR). This could be caused by no LDP session on router for the downstream router, LDP ID not reachable because of IGP problem, ACL configured that is blocking LDP packets, or an authentication problem.
Yes
No
Yes
Yes
Yes
Yes
Yes
LDP Label Mismatch
Label received for a prefix did not match the label sent. See the "IOS XR Support" section.
Yes
No
Yes
Yes
Yes
Yes
No
LDP Neighbors Not Discovered
LDP neighbors have not been discovered. Generic LDP discovery problem found on an interface of the device with its downstream neighbor. See the "IOS XR Support" section.
Yes
No
Yes
Yes
Yes
Yes
No
LDP Neighbors Not Discovered
LDP neighbors have not been discovered. An interface on a router has an ACL configured that could be preventing LDP neighbor discovery.
Yes
No
Yes
Yes
Yes
Yes
Yes
LDP Neighbors Not Established
LSP connectivity problem, control plane issue. The LDP session is not established. The interface has an ACL configured that could be blocking LDP session establishment on port 646.
Yes
No
Yes
Yes
Yes
Yes
Yes
LDP/TDP Mismatch
LDP and TDP have been enabled on opposite ends of a link. See the "IOS XR Support" section.
Yes
No
Yes
Yes
Yes
Yes
Yes
LSP Reply Path Problem
LSP connectivity problem with the reply path. See the "IOS XR Support" section.
Yes
No
Yes
Yes
Yes
Yes
No
LSP Visualization
LSP is displayed, but is incomplete. Failures could have occurred since the previous MPLS VPN Connectivity Verification test was run.
Yes
Yes
Yes
No
No
Yes
Yes
Missing LFIB Entry
LFIB entry missing. Could be because of misrouting in an earlier router, or due to duplicate loopbacks. See the "IOS XR Support" section.
Yes
No
Yes
Yes
Yes
Yes
No
Missing or Untagged Return Path
Return path from the core router absent or untagged for the prefix. See the "IOS XR Support" section.
Yes
No
Yes
Yes
Yes
Yes
No
MPLS Label Space Exhausted
MPLS label space exhausted on a router.
Yes
No
Yes
Yes
Yes
Yes
Yes
MPLS Not Enabled Globally
MPLS has not been enabled globally on router.
Yes
No
Yes
Yes
Yes
Yes
No
MPLS Not Enabled On Interface
MPLS has not been enabled on an interface. See the "IOS XR Support" section.
Yes
No
Yes
Yes
Yes
Yes
Yes
No Entry for Label
No entry in LFIB for incoming label going to the destination prefix. See the "IOS XR Support" section.
Yes
No
Yes
Yes
Yes
Yes
No
No LDP Session with Neighbor
No LDP session on router exists with neighbor.
Yes
No
Yes
Yes
Yes
Yes
Yes
No Valid Next-Hop Entry
No valid entry can be found for the next-hop from the current device. See the "IOS XR Support" section.
Yes
No
Yes
Yes
Yes
Yes
No
Routing Loop In Forwarding Path
A routing loop is present in the forwarding path.
Yes
No
Yes
Yes
Yes
Yes
Yes
Tag Advertising Not Enabled
tag-switching advertise-tags is not enabled on router.
Yes
No
Yes
Yes
Yes
Yes
Yes
Tag Advertising Possibly Denied by ACL
tag-switching advertise-tags has been globally disabled, but selectively enabled for one or more access lists. The ACLs might be denying the advertising of tags to the destination prefix.
Yes
No
Yes
Yes
Yes
Yes
Yes
TTL Propagation Disabled
Could not troubleshoot or detect failure point because the device is not propagating the Time To Live (TTL).
Yes
No
Yes
Yes
Yes
Yes
Yes
Tunnel Connectivity Failure
Unknown MPLS TE connectivity problem.
Yes
No
Yes
Yes
Yes
Yes
Yes
Tunnel Connectivity Failure No Targeted LDP Configuration
LDP discovery failure for the neighbor devices. The tunnel tail end device is not accepting LDP targeted hellos.
Yes
No
Yes
Yes
Yes
Yes
Yes
Unable to Troubleshoot MPLS TE Connectivity Problem
Router is running a non-OAM Cisco IOS version. The connectivity of the tunnel cannot be tested.
Yes
No
Yes
Yes
Yes
Yes
Yes
Unknown LSP Connectivity Problem
LSP connectivity problem, data plane issue, or unknown cause.
Yes
No
Yes
Yes
Yes
Yes
Yes
Unsupported IOS Version
Core router running an unsupported IOS version. This version of IOS does not support the required OAM functionality.
Yes
No
Yes
Yes
Yes
Yes
No
VPN Connectivity Tests have been Exercised and No Failures Found (However as Pings are Blocked to the CE, it is Not Possible to Verify VPN Connectivity)
Unable to verify VPN connectivity in VRF from PE to destination.
Yes
Yes
Yes
Yes
Yes
Yes
Yes
1.1.4 Customer Site
Possible Customer Routing Issue
The PE has some routes from the CE, but the CE is unable to respond to pings.
Yes
Yes
Yes
No
No
Yes
Yes
1.2 IOS XR Support
This section details the IOS XR support caveats:
1.
IOS XR has the concept of packages. One of the packages relevant to MDE is the MPLS package. When MDE troubleshooting focuses on an IOS XR router in the core, various preparation checks are carried out to ensure that the router is configured sufficiently; that is, that the MPLS package is installed and active, and then to check for the required features being enabled (MPLS OAM and MPLS LDP). If any of these checks fail, a failure scenario is reported. MPLS Not Enabled On Interface remains valid for IOS devices, or when MPLS is disabled on an interface on an IOS XR device.
It is still possible for MDE to determine cases where CEF is disabled on IOS routers in the core, for example, CEF could be disabled via CLI configuration, or when the router is overloaded and shuts itself down. In such cases, the IOS CLI command show cef state reports that CEF is either enabled/running or disabled/not running, and MDE can determine that CEF is disabled.
CEF cannot be disabled on an IOS XR router. When the CEF switching feature on an IOS XR router becomes overloaded, it does not shut down. Instead, it applies back pressure to the queue of outstanding requests in an effort to reduce the load on the CEF switching process. Therefore, in an IOS XR router, the relevant CLI show command does not report that CEF is nonoperational, and thus this failure scenario is not valid on an IOS XR router.
This is not a valid scenario where directly connected IOS XR routers are present, because IOS XR only supports a single label distribution protocol - that is LDP. It is possible for the application to find LDP-TDP mismatch if it is configured in IOS-IOS XR, IOS XR-IOS, or IOS-IOS configurations.
4.
Missing or Untagged Return Path
These failure scenarios are due to specific bugs in IOS versions, and are not applicable to IOS XR.
5.
ATM Sub-interface is Protocol Down
Intermittent ATM Failure (to the ATM Next Hop)
Intermittent ATM Failure (to the Destination)
Static IP address on ATM Point-to-Point Interface
Undiagnosed ATM Failure (ATM Pings Failed but the ATM Segment Ping Succeeded)
Undiagnosed ATM Failure (End to End and Segment ATM Pings Failed)
These are ATM failure scenarios, and because IOS XR currently does not support ATM interfaces on the CRS-1, they are not applicable for the CRS-1 platform. However, they continue to be applicable on IOS devices and for IOS XR on the Cisco 12000 XR Series.
1 Cisco MPLS Diagnostics Expert patent pending.
