Home > Articles > Networking > Routing & Switching

IP Routing Use Cases

  • Print
  • + Share This
This chapter is from the book

NSF/SSO, NSR, Graceful Restart to Ensure Robust Routing

Nonstop forwarding (NSF) refers to the capability of the data plane to continue to function hitless when the routing plane disappears (momentarily, that is) and most likely fails over to a standby RP. Of course, the routing information and topology might change during this time and result in an invalid FIB, and therefore the switchover times should be as small as possible. The Cisco ASR 1000 provides switchover times of less than 50 ms RP to RP (or IOS daemon [IOSD] to IOSD for the ASR 1002-F/ASR 1002/ASR 1004).

Stateful switchover (SSO) refers to the capability of the control plane to hold configuration and various states during this switchover, and to thus effectively reduce the time to utilize the newly failed-over control plane. This is also handy when doing scheduled hitless upgrades within the ISSU execution path. The time to reach SSO for the newly active RP may vary depending on the type and scale of the configuration.

Graceful restart (GR) refers to the capability of the control plane to delay advertising the absence of a peer (going through control-plane switchover) for a "grace period," and thus help minimize disruption during that time (assuming the standby control plane comes up). GR is based on extensions per routing protocol, which are interoperable across vendors. The downside of the grace period is huge when the peer completely fails and never comes up, because that slows down the overall network convergence, which brings us to the final concept: nonstop routing (NSR).

NSR is an internal (vendor-specific) mechanism to extend the awareness of routing to the standby routing plane so that in case of failover, the newly active routing plane can take charge of the already established sessions.

Table 12-1 shows the compatibility and support matrix for ASR 1000 IOS XE software 2.2, and outlines the various states that are preserved during FP/ESP failover.

Table 12-1. Protocols and Their State Preservation via NSF/SSO

Technology Focus

NSF

SSO

Routing protocols

Enhanced Interior Gateway Routing Protocol (EIGRP), Open Shortest Path First Version 2 (OSPFv2), OSPFv3, Intermediate System-to-Intermediate System (IS-IS), and Border Gateway Protocol Version 4 (BGPv4)

IPv4 services

Address Resolution Protocol (ARP), Hot Standby Routing Protocol (HSRP), IPsec, Network Address Translation (NAT), IPv6 Neighbor Discovery Protocol (NDP), Unicast Reverse Path Forwarding (uRPF), Simple Network Management Protocol (SNMP), Gateway Load Balancing Protocol (GLBP), Virtual Router Redundancy Protocol (VRRP), Multicast (Internet Group Management Protocol [IGMP])

IPv6 services

IPv6 Multicast (Multicast Listener Discovery [MLD], Protocol Independent Multicast-Source Specific Multicast [PIM-SSM], MLD Access group)

L2/L3 protocols

Frame Relay, PPP, Multilink PPP (MLPPP), High-Level Data Link Control (HDLC), 802.1Q, bidirectional forwarding detection (BFD)

Multiprotocol Label Switching (MPLS)

MPLS Layer 3 VPN (L3 VPN), MPLS Label Distribution Protocol (LDP)

SBC

SBC Data Border Element (DBE)

See the "Further Reading" section at the end of this chapter to find out where to look for complete route scale testing details.

Use Case: Achieving High Availability Using NSF/SSO

To command higher revenues and consistent profitability, service providers and enterprises are increasingly putting more mission-critical, time-sensitive services on their IP infrastructure. One of the key challenges to this is achieving and delivering high network availability with strict service level agreement (SLA) requirements. It is universally understood that availability of the network is directly linked with the overall total cost of ownership (TCO).

An enterprise has an ASR 1006 / ASR1000-ESP10 router used in the core of the network running OSPF as the routing protocol used to connect to multiple distribution hub routers, where distribution hub routers might not all be Cisco.

The goal is to reduce the route/prefix recomputation churn caused by RP switchover and reestablishment of OSPF peers.

To address the requirements, you need to implement Internet Engineering Task Force (IETF) NSF for OSPF because that is interoperable with all vendors that are NSF-aware (a term used for a neighboring router that understands the GR protocol extensions). In this case, when NSF-capable ASR 1000 switches over from active RP to standby RP, there will be no packet loss at all, and downstream neighbors will not restart adjacencies.

Figure 12-1 shows the ASR 1000 core router and its neighbors, which are all NSF-aware and can act as helpers during RP SSO.

Figure 12-1

Figure 12-1 Logical view of many regional WAN aggregation routers coming into a consolidated WAN campus edge router.

To turn on IETF helper mode on all the distribution hub routers, including the Cisco ASR 1000, you need to execute the following configuration steps:

  • Step 1. Configure NSF within the given OSPF process ID:
    ASR1006# configure terminal
    ASR1006(config)# router ospf 100
    ASR1006(config-router)# nsf ietf restart-interval 300
    
          
  • Step 2. Check that the NSF is turned on, for sure, on the helper router:
    Router-helper# show ip ospf 100
    
    
     Routing Process "ospf 100" with ID 172.16.1.2
     ----output truncated----
     IETF Non-Stop Forwarding enabled      
        restart-interval limit: 300 sec    
     IETF NSF helper support enabled       
     Cisco NSF helper support enabled      
     Reference bandwidth unit is 100 mbps
        Area BACKBONE(0)
    ASR1006# sh ip ospf 100
     Routing Process "ospf 1" with ID 10.1.1.1
     ----output truncated----
     IETF Non-Stop Forwarding enabled     
         restart-interval limit: 300 sec  
         IETF NSF helper support enabled  
         Cisco NSF helper support enabled       
    
          
  • Step 3. Now you need to verify that both RPs are active (using the show platform command) and OSPF neighbor relationships are established (using the show ip ospf neighbors command):
    
    ! active ESP:
    
    ASR1006# show platform software ip fp active cef summary
    Forwarding Table Summary
    Name       VRF id   Table id    Protocol      Prefixes    State
    ----------------------------------------------------------------
    Default    0        0           IPv4           10000       cpp:
                                                               0x10e265d8
                                                               (created)
    ! standby ESP:
    
    ASR1006# show platform software ip fp standby cef summary
    Forwarding Table Summary
    Name       VRF id   Table id   Protocol    Prefixes  State
    ---------------------------------------------------------------------
    Default    0        0          IPv4        10000     cpp: 0x10e265d8
                                                         (created)
    

    You can also view the prefixes downloaded into both the active and standby Embedded Service Processor (ESP) before failing over the router.

    The preceding output shows that about 10K routes are created and exist in both ESPs before the failover.

  • Step 4. Now you'll induce the RP SSO failover (using redundancy force-switchover) from the active RP enable mode CLI. The following output shows the effects from the newly active RP:
    ASR1006# show ip ospf 100
     ----output truncated----
     IETF Non-Stop Forwarding enabled
        restart-interval limit: 300 sec, last IETF NSF restart 00:00:10 ago
    IETF NSF helper support enabled
     Cisco NSF helper support enabled
    
  • Step 5. RP SSO will not result in any packet loss, because forwarding continues during this entire process. During this switchover process, you can execute the show platform command to verify that the former active RP is booting ("booting" state).

In case of ASR1000-ESP10 failover, some small packet loss will occur (packets that are being processed inside the QuantumFlow Processor [QFP]), although that would account for much less than 1-ms worth of transit traffic loss.

NSF/SSO allows RPs to fail over without any packet loss, and ESPs can fail over with extremely small packet loss. The Cisco ASR 1000 shows core benefits of a carrier-class router where failover times beat even the Automatic Protection Switching (APS) gold standard of 50 ms.

In today's networks, where SLAs are enforced and networks are participating in life- and mission-critical scenarios, a robust infrastructure with faster failover based on modern architectures is a must.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020