MPLS Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.3.x

MPLS Static Labeling

The MPLS static feature enables you to statically assign local labels to an IPv4 prefix. Also, Label Switched Paths (LSPs) can be provisioned for these static labels by specifying the next-hop information that is required to forward the packets containing static label.

If there is any discrepancy between labels assigned statically and dynamically, the router issues a warning message in the console log. By means of this warning message, the discrepancy can be identified and resolved.

The advantages of static labels over dynamic labels are:

Improve security because the risk of receiving unwanted labels from peers (running a compromised MPLS dynamic labeling protocol) is reduced.
Gives users full control over defined LSPs.
Utilize system resources optimally because dynamic labeling is not processed.
Static labeling on IPv6 packets is supported.

Restrictions

The router does not prevent label discrepancy at the time of configuring static labels. Any generated discrepancy needs to be subsequently cleared.
Equal-cost multi-path routing (ECMP) is not supported.
Interfaces must be explicitly configured to handle traffic with static MPLS labels.
The MPLS per-VRF labels cannot be shared between MPLS static and other applications.

Define Label Range and Enable MPLS Encapsulation

By default, MPLS encapsulation is disabled on all interfaces. MPLS encapsulation has to be explicitly enabled on all ingress and egress MPLS interfaces through which the static MPLS labeled traffic travels.

Also, the dynamic label range needs to be defined. Any label that falls outside this dynamic range is available for manually allocating as static labels. The router does not verify statically-configured labels against the specified label range. Therefore, to prevent label discrepancy, ensure that you do not configure static MPLS labels that fall within the dynamic label range.

Configuration Example

You have to accomplish the following to complete the MPLS static labeling configuration. Values are provided as an example.

Define a dynamic label range, which in this task is set between 17000 and 18000.
Enable MPLS encapsulation on the required interface.
Setup a static MPLS LSP for a specific ingress label 24035.
Specify the forwarding information so that for packets that are received with the label, 24035, the MPLS protocol swaps labels and applies the label, 24036. After applying the new label, it forwards the packets to the next hop, 10.2.2.2, through the specified interface.


RP/0/RP0/CPU0:router(config)#mpls label range table 0 17000 18000
RP/0/RP0/CPU0:router(config)#commit

RP/0/RP0/CPU0:router(config)#mpls static

RP/0/RP0/CPU0:router(config-mpls-static)# interface HundredGigE 0/0/0/3
RP/0/RP0/CPU0:router(config-mpls-static)#address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-mpls-static-af)#local-label 24035 allocate

RP/0/RP0/CPU0:router(config-mpls-static-af-lbl)#forward
RP/0/RP0/CPU0:router(config-mpls-static-af-lbl-fwd)#
path 1 nexthop HundredGigE 0/0/0/1 10.2.2.2 out-label 24036
RP/0/RP0/CPU0:router(config-mpls-static-af-lbl-fwd)# commit

Verification

Verify the interfaces on which MPLS is enabled

RP/0/RP0/CPU0:router# show  mpls interfaces
Mon May 12 06:21:30.937 DST
Interface                  LDP      Tunnel   Static   Enabled
-------------------------- -------- -------- -------- --------
TenGigE0/0/0/5								     No       No       Yes      Yes

Verify that the status is "Created" for the specified label value.

RP/0/RP0/CPU0:router#show mpls static local-label all
Tue Apr 22 18:21:55.764 UTC
Label   VRF             Type         Prefix           RW Configured   Status   
------- --------------- ------------ ---------------- --------------- -------- 
24035   default         X-Connect    NA               Yes             Created

Check the dynamic range and ensure that the specified local-label value is outside this range.

RP/0/RP0/CPU0:router#show mpls label range
Mon Apr 28 19:56:00.596 IST
Range for dynamic labels: Min/Max: 17000/18000

Verify that the MPLS static configuration has taken effect, and the label forwarding is taking place.

RP/0/RP0/CPU0:router#show mpls lsd forwarding         
Wed Nov 25 21:40:57.918 UTC
In_Label, (ID), Path_Info: <Type>
24035, (Static), 1 Paths
   1/1: IPv4, 'default':4U, BE1.2, nh=10.20.3.1, lbl=35001, flags=0x0, ext_flags=0x0

Associated Commands

mpls static
mpls label range
show mpls interfaces

Identify and Clear Label Discrepancy

During configuring or de-configuring static labels or a label range, a label discrepancy can get generated when:

A static label is configured for an IP prefix that already has a binding with a dynamic label.
A static label is configured for an IP prefix, when the same label value is dynamically allocated to another IP prefix.

Verification

Identify label discrepancy by using these show commands.

Router#show mpls static local-label discrepancy 
Tue Apr 22 18:36:31.614 UTC
Label   VRF             Type         Prefix           RW Configured   Status   
------- --------------- ------------ ---------------- --------------- -------- 
24000   default         X-Connect     NA              Yes             Discrepancy

Router#show mpls static local-label all 
Tue Apr 22 18:36:31.614 UTC
Label   VRF             Type         Prefix           RW Configured   Status
------- --------------- ------------ ---------------- --------------- --------
24000   default         X-Connect    N/A              Yes             Discrepancy
24035   default         X-Connect    N/A              Yes             Created

RP/0/RP0/CPU0:router#show log
Thu Apr 24 14:18:57.655 UTC
Syslog logging: enabled (0 messages dropped, 0 flushes, 0 overruns)
    Console logging: level warnings, 199 messages logged
    Monitor logging: level debugging, 0 messages logged
    Trap logging: level informational, 0 messages logged
    Buffer logging: level debugging, 2 messages logged

Log Buffer (307200 bytes):

RP/0/RSP0/CPU0:Apr 24 14:18:53.743 : mpls_static[1043]: %ROUTING-MPLS_STATIC-7-ERR_STATIC_LABEL_DISCREPANCY : 
The system detected 1 label discrepancies (static label could not be allocated due to conflict with other applications).  
Please use 'clear mpls static local-label discrepancy' to fix this issue. 
RP/0/RSP0/CPU0:Apr 24 14:18:53.937 : config[65762]: %MGBL-CONFIG-6-DB_COMMIT : Configuration committed by user 'cisco'. 
Use 'show configuration commit changes 1000000020' to view the changes.

Rectification

Label discrepancy is cleared by allocating a new label to those IP prefixes that are allocated dynamic label. The static label configuration takes precedence while clearing discrepancy. Clearing label discrepancy may result in traffic loss for the dynamic label which got cleared.

Router# clear mpls static local-label discrepancy all

Verify that the discrepancy is cleared.

Router# show mpls static local-label all
Wed Nov 25 21:45:50.368 UTC
Label   VRF             Type         Prefix           RW Configured   Status
------- --------------- ------------ ---------------- --------------- --------
24000   default         X-Connect    N/A              Yes             Created
24035   default         X-Connect    N/A              Yes             Created

Associated Commands

show mpls static local-label discrepancy
clear mpls static local-label discrepancy all

Configuring MPLS Static Labels for IPv6 Prefixes

MPLS static LSPs are created by assigning static labels to incoming IPv4/IPv6 prefixes and then specifying the next hop address for the packets with statically assigned labels. Packets are forwarded in the LSP based on this information. Effective with Cisco IOS-XR 6.2.2, you can assign static labels to IPv6 prefixes and set the next hop address in the static LSP as an IPv6 address. To configure static labels for IPv6 prefixes, you first need to configure named static LSPs and perform the remaining steps under LSP configuration mode.

Configuration Example

This example shows how to assign a static label to an IPv6 prefix and also configures an IPv6 address as the next hop.

RP/0/0/CPU0:Router# configure terminal
RP/0/0/CPU0:Router(config)# mpls static 
RP/0/0/CPU0:Router(config-mpls-static)# lsp ipv6-1
RP/0/0/CPU0:Router(config-mpls-static-lsp)# in-label 25000 allocate per-prefix 2001:DB8:0:1:: /64 
RP/0/0/CPU0:Router(config-mpls-static-lsp)# forward 
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# path 1 nexthop TenGigabitEthernet0/0/0/0 2001:DB8:0:5::64  out-label pop

Verification

The following examples show how to verify MPLS static labels for IPv6 prefixes.


RP/0/0/CPU0:Router# show mpls forwarding

Wed March 29 12:42:41.290 IST
Local  Outgoing    Prefix              Outgoing          Next Hop            Bytes       
Label  Label       or ID               Interface                             Switched    
------ ----------- ------------------  ------------     ---------------      ------------
25000  Pop         2001:DB8:0:1:: /64  TenGigE0/0/0/0     2001:DB8:0:5::64    0

RP/0/0/CPU0:Router# show mpls static lsp ipv6-1 detail 

Wed March 29 12:45:55.574 IST

LSP Name  Label   VRF      AFI  Type       Prefix            RW Configured   Status   
--------  ------- -------  ---- ---------- ----------------  --------------- -------- 
ipv6-1    25000   default  IPv6 Per-Prefix 2001:DB8:0:1:: /64      Yes       Created
    PRIMARY-PATHS:
        PATH 1 :  next-hop TenGigE0/0/0/0  2001:DB8:0:5::64  out-label POP
            STATUS: VALID

Configuring Backup within a Forwarding Set

Various types of FRR backups can be configured between links with in a forwarding path set. You can configure the following types of FRR backups:

Pure FRR Backup
Reciprocal FRR backup
One-way FRR backup

In pure FRR backup, there will be separate primary paths and backup paths. In reciprocal FRR backup, each path can act as both primary and backup. In one-way FRR backup, some paths act as both primary and backup while other paths may be just primary paths or backup paths.

Configuration Example: Pure FRR Backup

This example shows how to configure pure FRR backup with in a forwarding path set.


RP/0/0/CPU0:Router# configure terminal
RP/0/0/CPU0:Router(config)# mpls static
RP/0/0/CPU0:Router(config-mpls-static)# lsp lsp1
RP/0/0/CPU0:Router(config-mpls-static-lsp)# in-label 25000 allocate   
RP/0/0/CPU0:Router(config-mpls-static-lsp)# forward 
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# path 1 nexthop GigabitEthernet0/0/0/0 10.1.0.1 out-label 25000 backup-id 2
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# path 2 nexthop GigabitEthernet0/0/0/1 10.1.0.3 out-label 25001 backup
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# exit
RP/0/0/CPU0:Router(config-mpls-static-lsp)# backup
RP/0/0/CPU0:Router(config-mpls-static-lsp-backup)# path 1 nexthop GigabitEthernet0/0/0/5 10.5.0.1 out-label pop backup-id 2
RP/0/0/CPU0:Router(config-mpls-static-lsp-backup)# path 2 nexthop GigabitEthernet0/0/0/6 10.6.0.2 out-label pop backup
RP/0/0/CPU0:Router(config-mpls-static-lsp-backup)# exit

The following table describes the forwarding behavior for pure FRR backup. Here P1-F and P2-F are the forwarding paths and P1-B and P2-B are the backup paths.


Action	Transient State	Interface Steady State	Forward Steady State
N/A	N/A	P1-F: Up P2-F: Up P1-B: Up P2-B: Up	P1-F: Flow P2-F: Backup P1-B: N/A P2-B: N/A
P1-F Down	P1-F FRR to P2-F	P1-F: Up P2-F: Down P1-B: Up P2-B: Up	P1-F: Down P2-F: Flow P1-B: Backup P2-B: N/A
P2-F Down	P2-F FRR to P1-B	P1-F: Down P2-F: Down P1-B: Up P2-B: Up	P1-F: Down P2-F: Down P1-B: Flow P2-B: Backup
P1-B Down	P1-B FRR to P2-B	P1-F: Down P2-F: Down P1-B: Down P2-B: Up	P1-F: Down P2-F: Down P1-B: Down P2-B: Flow

Configuration Example: Reciprocal FRR Backup

This example shows how to configure reciprocal FRR backup with in a forwarding path set.


RP/0/0/CPU0:Router# configure terminal
RP/0/0/CPU0:Router(config)# mpls static
RP/0/0/CPU0:Router(config-mpls-static)# lsp lsp1
RP/0/0/CPU0:Router(config-mpls-static-lsp)# in-label 25000 allocate   
RP/0/0/CPU0:Router(config-mpls-static-lsp)# forward 
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# path 1 nexthop GigabitEthernet0/0/0/0 10.1.0.1 out-label 25000 primary-and-backup backup-id 2
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# path 2 nexthop GigabitEthernet0/0/0/1 10.1.0.3 out-label 25001 primary-and-backup backup-id 1
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# exit
RP/0/0/CPU0:Router(config-mpls-static-lsp)# backup
RP/0/0/CPU0:Router(config-mpls-static-lsp-backup)# path 1 nexthop GigabitEthernet0/0/0/5 10.5.0.1 out-label pop primary-and-backup backup-id 2
RP/0/0/CPU0:Router(config-mpls-static-lsp-backup)# path 2 nexthop GigabitEthernet0/0/0/6 10.6.0.2 out-label pop primary-and-backup backup-id 1
RP/0/0/CPU0:Router(config-mpls-static-lsp-backup)# exit

The following table describes the forwarding behavior for reciprocal FRR backup.


Action	Transient State	Interface Steady State	Forward Steady State
N/A	N/A	P1-F: Up P2-F: Up P1-B: Up P2-B: Up	P1-F: Flow P2-F: Flow P1-B: N/A P2-B: N/A
P2-F Down	P2-F FRR to P1-F	P1-F: Down P2-F: Up P1-B: Up P2-B: Up	P1-F: Flow P2-F: Down P1-B: Backup P2-B: N/A
P1-F Down	P1-F FRR to P1-B	P1-F: Down P2-F: Down P1-B: Up P2-B: Up	P1-F: Down P2-F: Down P1-B: Flow P2-B: Flow
P2-B Down	P2-B FRR to P1-B	P1-F: Down P2-F: Down P1-B: Up P2-B: Down	P1-F: Down P2-F: Down P1-B: Flow P2-B: Down

Configuration Example: One-way FRR Backup

This example shows how to configure one-way FRR backup with in a forwarding path set.


RP/0/0/CPU0:Router# configure terminal
RP/0/0/CPU0:Router(config)# mpls static
RP/0/0/CPU0:Router(config-mpls-static)# lsp lsp1
RP/0/0/CPU0:Router(config-mpls-static-lsp)# in-label 25000 allocate   
RP/0/0/CPU0:Router(config-mpls-static-lsp)# forward 
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# path 1 nexthop GigabitEthernet0/0/0/0 10.1.0.1 out-label 25000 backup-id 2
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# path 2 nexthop GigabitEthernet0/0/0/1 10.1.0.3 out-label 25001 primary-and-backup 
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# exit
RP/0/0/CPU0:Router(config-mpls-static-lsp)# backup
RP/0/0/CPU0:Router(config-mpls-static-lsp-backup)# path 1 nexthop GigabitEthernet0/0/0/5 10.5.0.1 out-label pop backup-id 2
RP/0/0/CPU0:Router(config-mpls-static-lsp-backup)# path 2 nexthop GigabitEthernet0/0/0/6 10.6.0.2 out-label pop primary-and-backup 
RP/0/0/CPU0:Router(config-mpls-static-lsp-backup)# exit

The following table describes the forwarding behavior for one-way FRR backup.


Action	Transient State	Interface Steady State	Forward Steady State
N/A	N/A	P1-F: Up P2-F: Up P1-B: Up P2-B: Up	P1-F: Flow P2-F: Flow P1-B: N/A P2-B: N/A
P2-F Down	P2-F NO-FRR to P1-F	P1-F: Down P2-F: Up P1-B: Up P2-B: Up	P1-F: Flow P2-F: Down P1-B: Backup P2-B: N/A
P1-F Down	P1-F FRR to P1-B	P1-F: Down P2-F: Down P1-B: Up P2-B: Up	P1-F: Down P2-F: Down P1-B: Flow P2-B: Flow
P1-B Down	P1-B FRR to P2-B	P1-F: Down P2-F: Down P1-B: Down P2-B: Up	P1-F: Down P2-F: Down P1-B: Down P2-B: Flow

Configuring Static LSP Next Hop Resolve

You can specify the outgoing next hop instead of explicitly specifying the outgoing path while configuring static LSPs. This next hop is resolved using the routing information base (RIB) which provides a list of paths to auto-configure. While specifying the next hop for the incoming label in a static LSP, you can specify the next hop address with out the interface using the resolve-nexthop command.

The following restrictions apply for this feature:

Only supports a single next hop address which may resolve to multiple paths.
Non-default VRFs are not supported.
In Cisco IOS-XR 6.2.2, only host routes can be resolved. Host routes are routes with /32 mask for IPv4 addresses and /128 mask for IPv6 addresses.

Configuration Example

This example shows how to configure the static LSP next hop without specifying the interface using the resolve-nexthop command.


RP/0/0/CPU0:Router# configure terminal
RP/0/0/CPU0:Router(config)# mpls static
RP/0/0/CPU0:Router(config-mpls-static)# lsp ipv6-2
RP/0/0/CPU0:Router(config-mpls-static-lsp)# in-label 25000 allocate per-prefix 2001:DB8:0:1:: /64  or  24:24:1::/64
RP/0/0/CPU0:Router(config-mpls-static-lsp)# forward 
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# path 1 resolve-nexthop 2001:DB8:0:2::64 out-label pop
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# exit

Configuring Static LSP Next Hop Resolve with Recursive Prefix

When a routing table entry references to another IP address and not to a directly connected exit interface, the next-hop IP address is resolved using another route with an exit interface. This is known as a recursive look up because multiple lookups are required to resolve the next-hop IP address. Static LSP next hop resolve with recursive prefix feature supports resolution of recursive routes for static LSPs. In this feature, you can specify a next hop which is not directly connected using the resolve-nexthop command for a static LSP.

Restrictions

The following restrictions apply for this feature:

Only eBGP routes are supported.

Configuration Example

This example shows how to configure the static LSP next hop resolve with recursive prefix. Here 192.168.2.1 is a recursive route learnt through eBGP.

RP/0/0/CPU0:Router# configure terminal
RP/0/0/CPU0:Router(config)# mpls static
RP/0/0/CPU0:Router(config-mpls-static)# lsp anycast_5001
RP/0/0/CPU0:Router(config-mpls-static-lsp)# in-label 5001 allocate
RP/0/0/CPU0:Router(config-mpls-static-lsp)# forward 
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# path 1 resolve-nexthop 192.168.2.1 out-label pop
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# exit

Verification

This example shows how to verify the static LSP next hop resolve with recursive prefix configuration.

RP/0/0/CPU0:Router# show  mpls static lsp anycast_5001 detail
Tue Sep 12 20:00:09.248 UTC
LSP Name             Label   VRF             AFI  Type         Prefix           RW Configured   Status   
-------------------- ------- --------------- ---- ------------ ---------------- --------------- -------- 
anycast_5001         5001    default         N/A  X-Connect    N/A              Yes             Created
  PRIMARY SET:
    [resolve-mode: nexthop 192.168.2.1]
    Path 0 : nexthop BVI1 1.1.1.3, out-label Pop, Role: primary, Path-id: 0, Status: valid
    Path 1 : nexthop BVI1 1.1.1.4, out-label Pop, Role: primary, Path-id: 0, Status: valid
    Path 2 : nexthop BVI1 1.1.1.5, out-label Pop, Role: primary, Path-id: 0, Status: valid
    Path 3 : nexthop BVI1 1.1.1.6, out-label Pop, Role: primary, Path-id: 0, Status: valid

Configuring MPLS Static over BVI

A Bridge-group virtual interface (BVI) is a routed interface that represents a set of interfaces that gets bridged. By using BVI, you can convert multiple interfaces as members of a common broadcast domain. MPLS static over BVI feature allows you to specify a BVI interface as next hop while setting up a static LSP.

Only static MPLS tunnels can use BVI as a next hop. Also, a BVI next hop can be a static route, a directly connected route (IP address, not a subnet prefix), or a route resolved through BGP or IGP. The router will do an MPLS label lookup on incoming MPLS traffic, perform a label operation such as SWAP/PHP/POP, and forward the MPLS/IP traffic through the BVI next hop. The router can perform switching for Layer 2 traffic and routing for incoming Layer 3 MPLS traffic.

Restrictions

If a BVI has multiple peers within a subnet, then the subnet prefix cannot be specified as the next hop IP address (though IP addresses within the subnet are BVI peers). You have to specify one of the peers (with a specific IP address) as the next hop.
Back up paths over BVI (IPv4 or IPv6) are not supported.
Fast Reroute (FRR) is not supported.
Dynamic MPLS configuration is not supported. For example, label distribution using LDP is not supported.

Configuration Example

This example shows how to configure a BVI interface as next hop for a static LSP.

RP/0/0/CPU0:Router# configure terminal
RP/0/0/CPU0:Router(config)# mpls static
RP/0/0/CPU0:Router(config-mpls-static)# interface TenGig 0/0/0/0 
RP/0/0/CPU0:Router(config-mpls-static)# lsp bvi 
RP/0/0/CPU0:Router(config-mpls-static-lsp)# in-label 5001 allocate
RP/0/0/CPU0:Router(config-mpls-static-lsp)# forward 
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# path 1 nexthop BVI1 192.168.2.1 out-label pop
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# path 1 nexthop BVI1 192.168.2.1 out-label 4444
RP/0/0/CPU0:Router(config-mpls-static-lsp-fwd)# exit

Bias-Free Language

Book Title

MPLS Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.3.x

Chapter Title

Implementing MPLS Static Labeling

Results

Chapter: Implementing MPLS Static Labeling

Implementing MPLS Static Labeling

MPLS Static Labeling

Restrictions

Define Label Range and Enable MPLS Encapsulation

Configuration Example

Verification

Associated Commands

Identify and Clear Label Discrepancy

Verification

Rectification

Associated Commands

Configuring MPLS Static Labels for IPv6 Prefixes

Configuration Example

Verification

Configuring Backup within a Forwarding Set

Configuration Example: Pure FRR Backup

Configuration Example: Reciprocal FRR Backup

Configuration Example: One-way FRR Backup

Configuring Static LSP Next Hop Resolve

Configuration Example

Configuring Static LSP Next Hop Resolve with Recursive Prefix

Restrictions

Configuration Example

Verification

Configuring MPLS Static over BVI

Restrictions

Configuration Example

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