Home > Articles > Networking > Voice/IP Communications

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

This chapter is from the book

Fast Reroute

MPLS TE supports local repair of TE LSPs using FRR. Traffic protection in case of a network failure is critical for real-time traffic or any other traffic with strict packet-loss requirements. In particular, FRR uses a local protection approach that relies on a presignaled backup TE LSP to reroute traffic in case of a failure. The node immediately next to the failure is responsible for rerouting the traffic and is the headend of the backup TE LSP. Therefore, no delay occurs in the propagation of the failure condition, and no delay occurs in computing a path and signaling a new TE LSP to reroute the traffic. FRR can reroute traffic in tens of milliseconds. RFC 4090 describes the operation and the signaling extensions that MPLS TE FRR requires.

Figure 2-8 shows an example of an MPLS network using FRR. In this case, node E signals a TE LSP toward node H. The network protects this TE LSP against a failure of the link between nodes F and G. Given the local protection nature of FRR, node F is responsible for rerouting the traffic into the backup TE LSP in case the link between nodes F and G fails. This role makes node F the point of local repair (PLR). It has presignaled a backup TE LSP through node I toward node G to bypass the potential link failure. The PLR is always the headend of the backup TE LSP. Node G receives the name of merge point (MP) and is the node where the protected traffic will exit the backup TE LSP during the failure and retake the original path of the protected TE LSP.

qm880208.gif

Figure 2-8 MPLS Network Using FRR

MPLS TE FRR introduces a few RSVP extensions for the signaling of the protected TE LSP, as follows:

  • A new FAST_REROUTE object defines the characteristics for the backup TE LSP. These characteristics include priorities (setup and holding), hop limit, bandwidth, and attributes. The FAST_REROUTE object also specifies whether nodes should use facility backup or one-to-one backup to protect the TE LSP.
  • The extended RECORD_ROUTE object indicates protection availability at each hop and its type (link, node, or bandwidth protection).
  • The extended SESSION_ATTRIBUTE object signals whether the TE LSP desires protection and its type (link, node, or bandwidth protection).

Table 2-12 summarizes these extensions.

Table 2-12. RSVP Objects Used for MPLS TE FRR

RSVP Object

RSVP Message

FRR Function

FAST_REROUTE

Path

Specifies the desired FRR technique (facility backup or one-to-one backup) and the desired characteristics (priority, bandwidth, attributes, and so on) of the backup TE LSP

RECORD_ROUTE

Path, Resv

Records a list of hops/labels for the protected TE LSP, including protection status and type at each hop

SESSION_ATTRIBUTE

Path

Indicates whether the TE LSP requires protection and the type of protection

MPLS TE FRR can use global or local restoration of the protected TE LSP as a result of a network failure. The global restoration approach relies on the headend rerouting the protected TE LSP. When the failure of a protected facility occurs, the PLR sends a PathErr message toward the headend of the protected TE LSP. In addition to the RSVP notification, the headend may also learn about the failure condition from IGP updates if the failure happens in the same IGP area. When the headend receives the failure notification, it can reroute the protected TE LSP permanently around the failure. When a PLR uses local restoration instead, it reroutes the protected TE LSPs through the backup while the failure persists. When the facility is back in service, the PLR resignals the protected TE LSP through its original path. Global restoration is more desirable as it relies on the headend to re-optimize the protected TE LSP. That node typically has a more complete view of the network resources and TE LSP constraints.

Link Protection

Link protection uses a backup TE LSP destined to the PLR next hop (NHOP). When a node signals a TE LSP with link protection desired, nodes along the path attempt to associate the TE LSP with a backup TE LSP to the NHOP downstream. The backup TE LSP could exist already, or the node may attempt to compute a suitable path and signal it. Any node that finds a TE backup LSP becomes a potential PLR and signals back to the protected TE LSP headend the protection availability at that location using the RECORD_ROUTE object. When a link fails, the PLR reroutes all the identified TE LSPs using the backup TE LSP. The rerouting process involves pushing the protected TE LSP label (as done before the failure) and then stacking the backup TE LSP label on top.

Figure 2-9 illustrates the operation of link protection. Node E signals a TE LSP toward node H, indicating in the SESSION_ATTRIBUTE that the TE LSP desires protection for link failures. When node F processes the object, it finds a suitable backup to the NHOP (node G) through node I. When the link between nodes F and G fails, node F detects the failure locally and modifies the output encapsulation of the protected TE LSP. It continues to push label 35 as expected by the NHOP and, in addition, it pushes label 16 to reroute the traffic through the backup TE LSP. Node I switches the backup TE LSP packets without any knowledge of the protected TE LSP. In this case, node I performs a PHP operation and the packets finally arrive at the MP (node G) with label 35 to continue toward node H.

qm880209.gif

Figure 2-9 MPLS TE FRR Link Protection Operation

Link protection can also protect against the failure of shared-risk link groups (SLRG). In some cases, multiple links in a network have a high probability of failing at the same time. Generally, these SRLGs are the result of multiple links sharing the same underlying infrastructure (Layer 2, Layer 1, or actual physical facilities). The path computation for the backup TE LSP should take into account these SLRGs to avoid using links that could fail at the same time as the protected link. PLRs can learn about SRLGs dynamically from IGP extensions or through local configuration. SRLGs affect the path computation that the PLR may perform the backup TE LSP. However, they do not impact the operation of link protection.

Node Protection

Node protection uses a backup TE LSP destined to the PLR next-next hop (NNHOP). When a node signals a TE LSP with node protection desired, nodes along the path attempt to associate it with a backup TE LSP to the NNHOP downstream. The backup TE LSP could exist already, or the node may attempt to compute a suitable path and signal it. Nodes that find a TE backup LSP become a potential PLR and signal back to the protected TE LSP headend the protection availability at their location using the RECORD_ROUTE object. When the NHOP fails, the PLR reroutes all the identified TE LSPs using the backup TE LSP. The rerouting process involves pushing the protected TE LSP label expected by the NNHOP and then stacking the TE backup LSP label on top. The PLR learns the NNHOP label from the RECORD_ROUTE object in Resv messages. Node protection can also protect against SRLG failures. As described in the previous section, SRLGs affect backup path computation but have no impact on the operation FRR, and in this case, node protection.

Figure 2-10 shows the operation of node protection. Node E signals a TE LSP toward node H, this time indicating in the SESSION_ATTRIBUTE that the TE LSP desires node protection. In this case, node E itself finds a suitable backup to the NNHOP (node G) through nodes B and I. When node F fails, node E detects the failure locally and modifies the output encapsulation of the protected TE LSP. Instead of pushing label 20 as performed before the failure, node E now pushes label 35 as expected by the node G and, in addition, it pushes label 16 to reroute the traffic through the backup TE LSP. Node B and I switch the backup TE LSP packets without any awareness of the protected TE LSP. Packets finally arrive at the MP (node G) with label 35 to continue toward node H.

qm880210.gif

Figure 2-10 MPLS TE FRR Node Protection Operation

  • + 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