Contents
The NSF/SSO--MPLS VPN feature allows a provider edge (PE) router to preserve data forwarding information in a Multiprotocol Label Switching (MPLS) Virtual Private Network (VPN) when the primary Route Processor (RP) restarts. This module describes how to enable nonstop forwarding (NSF) in a basic MPLS VPN network.
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
You must have a supported MPLS VPN network configuration. See Configuring MPLS VPNs for more information.
The networking device that is to be configured for NSF must first be configured for stateful switchover (SSO). See Stateful Switchover for more information
You must enable NSF on the routing protocols running between the provider (P) routers, provider edge (PE) routers, and customer edge (CE) routers. The supported routing protocols are Border Gateway Protocol (BGP), Open Shortest Path First (OSPF), and Intermediate System-to-Intermediate System (IS-IS). See Configuring Nonstop Forwarding for more information.
You must configure Cisco NSF support on the routers for Cisco Express Forwarding. See Configuring Nonstop Forwarding for more information.
All neighbor networking devices must be NSF-aware. Peer routers must support the graceful restart of the protocol used to communicate with the NSF/SSO--MPLS VPN-capable router.
VPN NSF requires several elements in order to work:
VPN NSF uses the BGP Graceful Restart mechanisms to create MPLS forwarding entries for VPNv4 prefixes in NSF mode. The forwarding entries are preserved during a restart. BGP also saves prefix and corresponding label information and recovers the information after a restart.
The NSF/SSO--MPLS VPN feature also uses NSF for the label distribution protocol in the core network (either MPLS Label Distribution Protocol, traffic engineering, or static labeling).
The NSF/SSO--MPLS VPN feature uses NSF for the Interior Gateway Protocol (IGP) used in the core (OSPF or IS-IS).
The NSF/SSO--MPLS VPN feature uses NSF for the routing protocols between the PE and CE routers.
When BGP allocates local labels for prefixes, it checkpoints the local label binding in the backup RP. The checkpointing function copies state information from the active RP to the backup RP, thereby ensuring that the backup RP has an identical copy of the latest information. If the active RP fails, the backup RP can take over with no interruption in service. Checkpointing begins when the active RP does a bulk synchronization, which copies all of the local label bindings to the backup RP. After that, the active RP dynamically checkpoints individual prefix label bindings when a label is allocated or freed. This allows forwarding of labeled packets to continue before BGP reconverges.
When a BGP Graceful Restart-capable router loses connectivity, it performs the following actions as the restarting router:
The restarting router establishes BGP sessions with other routers and relearns the BGP routes from other routers that are also capable of Graceful Restart. The restarting router waits to receive updates from the neighboring routers. When the neighboring routers send end-of-Routing Information Base (RIB) markers to indicate that they are done sending updates, the restarting router starts sending its own updates.
The restarting router accesses the checkpoint database to find the label that was assigned for each prefix. If it finds the label, it advertises it to the neighboring router. If it does not find the label, it allocates a new label and advertises it.
The restarting router removes any stale prefixes after a timer for stale entries expires.
A BGP Graceful Restart-capable peer router performs the following actions when it encounters a restarting router:
The peer router sends all the routing updates to the restarting router. When it has finished sending updates, the peer router sends an end-of-RIB marker to the restarting router.
The peer router does not immediately remove the BGP routes learned from the restarting router from its BGP routing table. As it learns the prefixes from the restarting router, the peer refreshes the stale routes if the new prefix and label information matches the old information.
If a router is not configured for the NSF/SSO--MPLS VPN feature and it attempts to establish a BGP session with a router that is configured with the NSF/SSO--MPLS VPN feature, the two routers create a normal BGP session but do not have the ability to perform the NSF/SSO--MPLS VPN feature.
1.
enable
2.
configure
terminal
3.
ip
cef
[distributed]
4.
router
bgp
autonomous-system-number
5.
bgp
graceful-restart
6.
bgp
graceful-restart
restart-time
seconds
7.
bgp
graceful-restart
stalepath-time
seconds
8.
end
1.
show
ip
bgp
vpnv4
all
labels
2.
show
ip
bgp
vpnv4
all
neighbors
3.
show
ip
bgp
labels
4.
show
ip
bgp
neighbors
| Step 1 |
show
ip
bgp
vpnv4
all
labels
This command displays incoming and outgoing BGP labels for each route distinguisher. The following is sample output from the command: Example:
Router# show ip bgp vpnv4 all labels
Network Next Hop In label/Out label
Route Distinguisher: 100:1 (vpn1)
10.3.0.0/16 10.0.0.5 25/20
10.0.0.1 25/23
10.0.0.2 25/imp-null
10.0.0.9/32 10.0.0.1 24/22
10.0.0.2 24/imp-null
|
| Step 2 |
show
ip
bgp
vpnv4
all
neighbors
This command displays whether the BGP peers are capable of Graceful Restart. The following is sample output from the command: Example:
Router# show ip bgp vpnv4 all neighbors
BGP neighbor is 10.0.0.1, remote AS 100, internal link
BGP version 4, remote router ID 10.0.0.1
BGP state = Established, up for 02:49:47
Last read 00:00:47, hold time is 180, keepalive interval is 60 seconds
Neighbor capabilities:
Route refresh: advertised and received(new)
Address family VPNv4 Unicast: advertised and received
Graceful Restart Capabilty: advertised and received
Remote Restart timer is 120 seconds
Address families preserved by peer:
VPNv4 Unicast
.
.
.
|
| Step 3 |
show
ip
bgp
labels
This command displays information about MPLS labels in the Exterior Border Gateway Protocol (EBGP) route table. The following is sample output from the command: Example:
Router# show ip bgp labels
Network Next Hop In label/Out label
10.3.0.0/16 10.0.0.1 imp-null/imp-null
0.0.0.0 imp-null/nolabel
10.0.0.9/32 10.0.0.1 21/29
10.0.0.11/32 10.0.0.1 24/38
10.0.0.13/32 0.0.0.0 imp-null/nolabel
10.0.0.15/32 10.0.0.1 29/nolabel
10.0.0.1 29/21
|
| Step 4 |
show
ip
bgp
neighbors
This command displays whether the BGP peers are capable of Graceful Restart. The following is sample output from the command: Example:
Router# show ip bgp neighbors
BGP neighbor is 10.0.0.1, remote AS 100, external link
BGP version 4, remote router ID 10.0.0.5
BGP state = Established, up for 02:54:19
Last read 00:00:18, hold time is 180, keepalive interval is 60 seconds
Neighbor capabilities:
Route refresh: advertised and received(new)
Address family IPv4 Unicast: advertised and received
ipv4 MPLS Label capability: advertised and received
Graceful Restart Capabilty: advertised and received
Remote Restart timer is 120 seconds
Address families preserved by peer:
IPv4 Unicast
.
.
.
|
The following sample output shows the configuration of the NSF/SSO--MPLS VPN feature on the CE and PE routers. SSO is enabled by default, and LDP is the default MPLS label protocol.
ip cef no ip domain-lookup ! interface Loopback0 ip address 10.10.10.10 255.255.255.255 ! interface GigabitEthernet1/0/4 ip address 10.0.0.1 255.0.0.0 media-type 10BaseT ! router ospf 100 redistribute bgp 101 nsf enforce global passive-interface GigabitEthernet1/0/4 network 10.0.0.0 0.255.255.255 area 100 ! router bgp 101 no synchronization bgp graceful-restart restart-time 120 bgp graceful-restart stalepath-time 360 bgp graceful-restart network 10.0.0.0 network 10.0.0.0 neighbor 10.0.0.2 remote-as 100
redundancy mode sso ! ip cef distributed mpls ldp graceful-restart mpls label protocol ldp ip vrf vpn1 rd 100:1 route-target export 100:1 route-target import 100:1 no mpls aggregate-statistics ! interface Loopback0 ip address 10.12.12.12 255.255.255.255 ! interface GigabitEthernet1/0/4 ip vrf forwarding vpn1 ip address 10.0.0.2 255.0.0.0 ! mpls ip interface ATM3/0/0 no ip address ! interface ATM3/0/0.1 point-to-point ip unnumbered Loopback0 mpls ip ! router ospf 100 passive-interface GigabitEthernet1/0/4 nsf enforce global network 10.0.0.0 0.255.255.255 area 100 ! router bgp 100 no synchronization bgp graceful-restart restart-time 120 bgp graceful-restart stalepath-time 360 bgp graceful-restart no bgp default ipv4-unicast neighbor 10.14.14.14 remote-as 100 neighbor 10.14.14.14 update-source Loopback0 ! address-family ipv4 vrf vpn1 neighbor 10.0.0.1 remote-as 101 neighbor 10.0.0.1 activate exit-address-family ! address-family vpnv4 neighbor 10.14.14.14 activate neighbor 10.14.14.14 send-community extended exit-address-family
redundancy mode sso ! ip cef distributed mpls ldp graceful-restart mpls label protocol ldp ! ip vrf vpn1 rd 100:1 route-target export 100:1 route-target import 100:1 no mpls aggregate-statistics ! ! interface Loopback0 ip address 10.14.14.14 255.255.255.255 ! interface ATM1/0 no ip address ! interface ATM1/0.1 point-to-point ip unnumbered Loopback0 mpls ip ! interface FastEthernet3/0/0 ip vrf forwarding vpn1 ip address 10.0.0.1 255.0.0.0 ip route-cache distributed ! router ospf 100 nsf enforce global passive-interface FastEthernet3/0/0 network 10.0.0.0 0.255.255.255 area 100 ! router bgp 100 no synchronization bgp graceful-restart restart-time 120 bgp graceful-restart stalepath-time 360 bgp graceful-restart no bgp default ipv4-unicast neighbor 10.12.12.12 remote-as 100 neighbor 10.12.12.12 update-source Loopback0 ! address-family ipv4 vrf vpn1 neighbor 10.0.0.2 remote-as 102 neighbor 10.0.0.2 activate exit-address-family ! address-family vpnv4 neighbor 10.12.12.12 activate neighbor 10.12.12.12 send-community extended exit-address-family
ip cef ! interface Loopback0 ip address 10.13.13.13 255.255.255.255 ! interface FastEthernet0/1 ip address 10.0.0.2 255.0.0.0 no ip mroute-cache ! router ospf 100 redistribute bgp 102 nsf enforce global passive-interface FastEthernet0/1 network 10.0.0.0 0.255.255.255 area 100 ! router bgp 102 no synchronization bgp graceful-restart restart-time 120 bgp graceful-restart stalepath-time 360 bgp graceful-restart network 10.0.0.0 network 10.0.0.0 neighbor 10.0.0.1 remote-as 100
The following sections provide references related to the MPLS High Availability feature.
|
Standard |
Title |
|---|---|
|
draft-ietf-mpls-bgp-mpls-restart.txt |
Graceful Restart Mechanism for BGP with MPLS |
|
draft-ietf-mpls-idr-restart.txt |
Graceful Restart Mechanism for BGP |
|
MIB |
MIBs Link |
|---|---|
|
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: |
|
RFC |
Title |
|---|---|
|
RFC 3478 |
Graceful Restart Mechanism for Label Distribution |
|
Description |
Link |
|---|---|
|
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The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to . An account on Cisco.com is not required.|
Feature Name |
Releases |
Feature Information |
|---|---|---|
|
NSF/SSO--MPLS VPN |
Cisco IOS XE Release 2.1 |
This feature allows a provider edge router to preserve data forwarding information in a Multiprotocol Label Switching (MPLS) Virtual Private Network (VPN) when the primary Route Processor restarts. |