Juniper MPLS Tutorial by Soricelli
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MPLS provides mechanisms for traffic engineering by allowing routers to forward packets based on fixed-length labels rather than long variable length IP addresses. MPLS labels are assigned to packets at ingress routers and swapped or removed by transit and egress routers along the Label Switched Path (LSP). Routers can be configured with constraints and administrative groups to calculate optimal LSP paths using protocols like RSVP and LDP.
![RSVP Configuration
Routers must be enabled to support MPLS and
RSVP
[edit] mpls traffic-eng tunnels
user@host# show interfaces !
ge-0/2/0 { interface POS0/0/0
unit 0 { ip address 10.222.28.1 255.255.255.0
family inet { no ip directed-broadcast
address 10.222.29.1/24; mpls traffic-eng tunnels
}
family mpls;
}
}
[edit]
user@host# show protocols
rsvp {
interface all;
}
mpls {
interface all;
}
1 June 2003](https://image.slidesharecdn.com/soricelli-100526234613-phpapp02/85/Juniper-MPLS-Tutorial-by-Soricelli-48-320.jpg)
![RSVP Configuration
Explicit networks paths can be established
[edit]
user@host# show protocols mpls
path user-defined-ERO { ip explicit-path name user-defined-ERO enable
192.168.20.1 loose; next-address loose 192.168.20.1
192.168.24.1 loose; next-address loose 192.168.24.1
192.168.36.1 loose; next-address loose 192.168.36.1
192.168.40.1 loose; next-address loose 192.168.40.1
}
1 June 2003](https://image.slidesharecdn.com/soricelli-100526234613-phpapp02/85/Juniper-MPLS-Tutorial-by-Soricelli-49-320.jpg)
![RSVP Configuration
Configure the ingress router to support the LSP
[edit]
user@host# show protocols mpls
label-switched-path ingress-to-egress {
to 192.168.32.1;
primary user-defined-ERO;
}
path user-defined-ERO {
192.168.20.1 loose;
192.168.24.1 loose;
192.168.36.1 loose;
192.168.40.1 loose;
}
interface Tunnel10
ip unnumbered Loopback 0
no ip directed-broadcast
tunnel destination 192.168.32.1
tunnel mode mpls traffic-eng
tunnel mpls traffic-eng priority 1 1
tunnel mpls traffic-eng path-option 1 explicit name user-defined-ERO
1 June 2003](https://image.slidesharecdn.com/soricelli-100526234613-phpapp02/85/Juniper-MPLS-Tutorial-by-Soricelli-50-320.jpg)
Juniper MPLS Tutorial by Soricelli
- 1. Tutorial: Introduction to MPLS Joseph M. Soricelli ([email protected]) NANOG 28, Salt Lake City, Utah
- 2. Caveats and Assumptions The views presented here are those of the author and they do not necessarily represent the views of Juniper Networks You will ask a question when you don’t understand! 1 June 2003
- 3. What is MPLS? Forwarding of user data traffic using fixed sized headers which contain a label value Virtual Circuit for IP Unidirectional path through the network Tunnel through the network Traffic Engineering Using paths other than the IGP shortest-path Mapping IP prefixes to LSPs Forwarding Equivalence Class (FEC) 1 June 2003
- 4. MPLS Labels Fixed Length Local Significance Labels usually change on each network segment Assigned upstream by signaling protocols Four defined fields Label Experimental Stack Bit (0=additional labels 1=end of stack) Time-to-Live Label (20 bits) CoS S TTL 1 June 2003
- 5. MPLS Shim Header Labels are placed between L2 header and L3 data Multiple labels may be stacked together L2 Header MPLS Header L3 Data L2 Header MPLS Header MPLS Header L3 Data L2 Header MPLS Header MPLS Header MPLS Header L3 Data 1 June 2003
- 6. Label Space 20 bits of label allows for values between 0 and 1,048,575 Labels 0 through 15 are reserved by IETF Label 0 – IPv4 Explicit NULL Label 1 – Router Alert Label 2 – IPv6 Explicit NULL Label 3 – IPv4 Implicit NULL All other labels may be allocated at random Some vendors allocate dynamic labels from certain ranges The JUNOS software begins at 100,000 1 June 2003
- 7. MPLS Labels Label Distribution Downstream-on-Demand “Ask and you shall receive” Unsolicited Downstream Sent without a request “Here’s a label to use for this prefix” Label Retention Liberal (Keep all received labels) Conservative (Keep only labels you use) Label Control Ordered Allocate a label after receiving a label or if you are egress Independent Allocate a label at any time 1 June 2003
- 8. Link-Layer Support for MPLS PPP protocol ID value of 0x0281 PPP NCP ID value of 0x8281 All other Layer 2 encapsulations use 0x8847 Ethernet HDLC GRE Tunnel Frame Relay ATM AAL5 SNAP 1 June 2003
- 9. Label Switched Path (LSP) Unidirectional path through the network 1 June 2003
- 10. Router Types - Ingress Ingress Router Packets enter the LSP Head-end router Upstream from other routers in the LSP “Gozinta” router Performs a label push operation Ingress 1 June 2003
- 11. Router Types - Transit Transit Router Zero or more transit routers in an LSP Maximum of 253 Sends traffic to the downstream physical next-hop of the LSP Performs a label swap operation Transit Transit Transit 1 June 2003
- 12. Router Types - Penultimate Penultimate Router Immediate upstream router from the egress router Often performs a label pop operation Penultimate Hop Popping (PHP) Remaining packet contents sent to the egress router Can perform a label swap operation Penultimate 1 June 2003
- 13. Router Types - Egress Egress Router Packets exit the LSP Tail-end router Downstream from other routers in the LSP “Gozoutta” router Can perform a label pop operation Egress 1 June 2003
- 14. Ultimate Hop Popping (UHP) The egress router signals a label value of 0 to the penultimate router The packet sent to the egress contains an MPLS header with a label value of 0 Egress router pops the label and performs an IPv4 route lookup before forwarding the packet Egress 0 1 June 2003
- 15. Penultimate Hop Popping (PHP) The egress router signals a label value of 3 to the penultimate router The penultimate router pops the top label from the packet the forwards the remaining data to the egress router Native IPv4 packet MPLS header when label stacking is used Egress router performs an appropriate lookup Route lookup for IPv4 packets MPLS switching table lookup for labeled packets 1 June 2003
- 16. Penultimate Hop Popping (PHP) Helps the egress router offload processing Very beneficial for non-ASIC devices Penultimate 3 3 Egress 3 Penultimate 1 June 2003
- 17. LSP Forwarding - Ingress An IPv4 packet arrives at the ingress router with a destination address of 192.168.1.1 Ingress router has a route for 192.168.1.0/24 with a next-hop of the LSP MPLS header with a label of 101,456 is appended to the packet and forwarded downstream 192.168.1.0/24 101,456 108,101 100,001 3 101,456 IP 1 June 2003
- 18. LSP Forwarding - Transit Each transit router receives a labeled packet and performs a switching table lookup Each transit router performs a label swap operation 101,456 swapped for 108,101 108,101 swapped for 100,001 192.168.1.0/24 101,456 108,101 100,001 3 108,101 IP 100,001 IP 1 June 2003
- 19. LSP Forwarding - Penultimate The penultimate router receives a labeled packet and performs a switching table lookup Since the egress router signaled a label value of 3, the penultimate router pops the top label and forwards the remaining data 192.168.1.0/24 101,456 108,101 100,001 3 IP 1 June 2003
- 20. LSP Forwarding - Egress The egress router receives a native IPv4 packet Route lookup performed Packet forwarded to the appropriate next-hop router 192.168.1.0/24 101,456 108,101 100,001 3 IP 1 June 2003
- 21. LSP Signaling Protocols Resource Reservation Protocol (RSVP) Well-known signaling protocol Extended to support traffic engineering Supports explicit paths and bandwidth reservations Labels allocated only along the defined LSP path Label Distribution Protocol (LDP) Uses the same shortest-path as IGP for forwarding Labels allocated and exchanged between neighbors Constrained Routing LDP (CR-LDP) Adds traffic engineering capabilities to LDP Limited support from vendors 1 June 2003
- 22. RSVP Session Uniquely defines and identifies the LSP throughout the network Destination address of LSP Tunnel ID value Protocol number (often set to 0) An individual session may have multiple defined senders LSP ID defines a sender Ingress router creating an additional path for the LSP Secondary path Fast Reroute Detour Routers become RSVP neighbors after session establishment 1 June 2003
- 23. RSVP Path and Resv Messages Path messages sent downstream Addressed to the egress router Contains the router alert option Establishes protocol state along the way Resv messages sent upstream Addressed to the next upstream node Finalizes protocol state Assigns and allocates resources Path Path Path Path Resv Resv Resv Resv 1 June 2003
- 24. RSVP PathTear and ResvTear Messages LSP already established and operational Link failure causes protocol state to be removed PathTear messages sent downstream Addressed to the egress router Contains the router alert option Removes protocol state along the way ResvTear messages sent upstream Addressed to the next upstream node Removes protocol state PathTear PathTear X ResvTear 1 June 2003
- 25. RSVP PathErr and ResvErr Messages Error messages signal problems to the ingress or egress routers No protocol state removed by error messages Ingress or egress routers may initiate a teardown of the LSP due to receipt of an error message PathErr messages sent upstream ResvErr messages sent downstream PathErr PathErr ResvErr ResvErr 1 June 2003
- 26. RSVP Path Message Objects Objects used to define the LSP and request resources Session Defines the address of the egress router Contains the Tunnel ID value associated with the LSP RSVP-Hop Interface address of the previous hop of the LSP Sender-Template Defines the address of the ingress router Contains a unique LSP ID Sender-Tspec Displays any request bandwidth reservations Session Attribute Contains LSP priority values as well as the ASCII name of the LSP 1 June 2003
- 27. RSVP Path Message Objects Objects used to define the LSP and request resources Label Request Explicit Route Defines the requested path of the LSP through the network Can be manually created Can be the output of Constrained SPF calculation Record Route Contains the actual path of the LSP through the network Used for loop detection and prevention 1 June 2003
- 28. RSVP Resv Message Objects Objects used to allocate resources and establish the LSP Session Contains the egress address and Tunnel ID RSVP-Hop Interface address of the downstream hop of the LSP Style Type of resource allocation performed Fixed Filter (FF) Shared Explicit (SE) FlowSpec Displays the bandwidth reserved by the LSP Matches the information in the Sender-Tspec object 1 June 2003
- 29. RSVP Resv Message Objects Objects used to define the LSP and request resources Filter-Spec Contains the ingress address and LSP ID Matches the information in the Sender-Template object Label Contains the 20-bit label value to be used for traffic forwarding Record Route Contains the actual path of the LSP through the network Used for loop detection and prevention 1 June 2003
- 30. RSVP Bandwidth By default, each interface uses 100% of its capacity as reservable bandwidth You may change this percentage An LSP may request a bandwidth reservation during its establishment in the network Only determines if the LSP is setup of not The BW reservation is NOT used to police traffic 1 June 2003
- 31. Explicit Route Object (ERO) Puts the “engineering” in TE Allows the ingress router to define the path of the LSP through the network May contain loose hop information Loose hop defines a node the LSP must pass through at some point IPv4 shortest-path routing used for forwarding Path messages: From ingress to first loose hop Between loose hops From last loose hop to egress router May contain strict hop information Strict hop must be the next downstream router Must be directly connected to the local router 1 June 2003
- 32. Loose Hop ERO Ingress uses routing table to forward the Path message towards RTR-D RTR-D uses routing table to forward message to egress router A B C ERO: D E D — Loose 1 June 2003
- 33. Strict Hop ERO Ingress consults ERO to locate the first strict hop Forwards Path message out interface associated with that hop Each transit router ensure it is next strict hop in the path If so, message forwarded to next strict hop If not, PathErr message sent back to ingress router A B C ERO: D — Strict B — Strict D E E — Strict C — Strict 1 June 2003
- 34. Mixing Strict and Loose Hops An ERO may contain both strict and loose hops Loose hops are routed using routing table Strict hops receive messages when they are directly connected A B C ERO: D E D — Strict B — Loose 1 June 2003
- 35. Manual ERO Concerns Manual use of EROs requires knowledge of the network topology Loop detection might cause LSP setup to fail IGP metrics shown below RTR-E forwards Path message back to RTR-B Loop detection in RRO by RTR-B prompts creation of PathErr message A B C 1 1 1 1 1 5 ERO: D E B — Loose 1 E — Loose 1 June 2003
- 36. Automatic EROs The ingress router can automatically create an ERO for the LSP Contains all strict hops for the complete path Formed from information contained in the Traffic Engineering Database (TED) TED is populated by information advertised by the Interior Gateway Protocols Both OSPF and IS-IS have been extended to support traffic engineering OSPF Opaque LSA 10 (Area-Scope Flooding) IS-IS TLV 22 (Extended IS Reachability) IS-IS TLV 135 (Extended IP Reachability) 1 June 2003
- 37. IGP Extensions Both link-state IGPs may advertise information which is stored in the TED Interface and neighbor interface addresses Maximum reservable bandwidth per network link Current reservable bandwidth Traffic Engineering metric Administrative group information Affinity classes Colors The ingress router uses a modified form of the SPF algorithm within the TED to generate the ERO Constrained Shortest-Path First (CSPF) Takes user-defined constraints into account 1 June 2003
- 38. CSPF Algorithm When the ingress router invokes the CSPF algorithm, it creates a subset of the TED information based on the constraints provided 1. Prune all links which don’t have enough reservable BW 2. Prune all links which don’t contain an included administrative group color 3. Prune all links which do contain an excluded administrative group color 4. Calculate a shortest path from the ingress to egress using the subset of information Manual ERO definitions taken into account Run CSPF from ingress to first ERO node Run second CSPF from ERO node to egress 1 June 2003
- 39. CSPF Algorithm (Contd.) When the subset of information used by CSPF returns multiple equal-cost paths: 5. Prefer the path where the last-hop address equals the egress address 6. Should equal-cost paths still exist, select the one with the fewest physical hops 7. Should equal-cost paths still exist, pick one based on the load-balancing configuration of the LSP Random Most-fill Least-fill The result of CSPF (strict-hop ERO) is passed to RSVP for LSP signaling 1 June 2003
- 40. Administrative Groups Each interface may be assigned to one or multiple administrative groups Colors are often used to describe these groups (Gold, Silver, Bronze) User-friendly names can be used as well (Voice, Management, Best-Effort) Names are locally significant to the router Group information is propagated by the IGP as a 32-bit vector Bits 0 through 31 Stored in the TED 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 1 June 2003
- 41. Administrative Groups The LSP can be configured to include or exclude certain group values Include requires each link to contain the specified group value Multiple values are combined as a logical OR Exclude requires each link to not contain the value Multiple values are combined as a logical OR LSP performs a logical AND on the include and exclude groups 1 June 2003
- 42. Administrative Groups Example-Include The LSP can be configured to include certain group values LSP from C to E should include Gold or Silver All IGP link metrics are set to 1 Bronze A B Gold Silver Silver Bronze Management C D E Bronze Silver Gold Silver Best Effort Silver F G 1 June 2003
- 43. Administrative Groups Example-Include After pruning all links which do not contain either Gold or Silver, SPF is run and the ERO is formed A B Gold Silver Silver C D E Silver Gold Silver Best Effort Silver F G 1 June 2003
- 44. Administrative Groups Example-Exclude The LSP can be configured to exclude certain group values LSP from C to E should exclude Best Effort All IGP link metrics are set to 1 Bronze A B Gold Silver Silver Bronze Management C D E Bronze Silver Gold Silver Best Effort Silver F G 1 June 2003
- 45. Administrative Groups Example-Exclude After pruning all links which contain Best Effort, SPF is run and the ERO is formed Bronze A B Gold Silver Silver Bronze Management C D E Bronze Gold Silver Silver F G 1 June 2003
- 46. Administrative Groups Example-Both Both include and exclude can be used together LSP from C to E should (include Gold or Silver) and (exclude Best Effort) All IGP link metrics are set to 1 Bronze A B Gold Silver Silver Bronze Management C D E Bronze Silver Gold Silver Best Effort Silver F G 1 June 2003
- 47. Administrative Groups Example-Both First, all links which do not contain either Gold or Silver are pruned Second, all links containing Best Effort are pruned Third, SPF is run and the ERO is formed A B Gold Silver Silver C D E Silver Gold Silver F G 1 June 2003
- 48. RSVP Configuration Routers must be enabled to support MPLS and RSVP [edit] mpls traffic-eng tunnels user@host# show interfaces ! ge-0/2/0 { interface POS0/0/0 unit 0 { ip address 10.222.28.1 255.255.255.0 family inet { no ip directed-broadcast address 10.222.29.1/24; mpls traffic-eng tunnels } family mpls; } } [edit] user@host# show protocols rsvp { interface all; } mpls { interface all; } 1 June 2003
- 49. RSVP Configuration Explicit networks paths can be established [edit] user@host# show protocols mpls path user-defined-ERO { ip explicit-path name user-defined-ERO enable 192.168.20.1 loose; next-address loose 192.168.20.1 192.168.24.1 loose; next-address loose 192.168.24.1 192.168.36.1 loose; next-address loose 192.168.36.1 192.168.40.1 loose; next-address loose 192.168.40.1 } 1 June 2003
- 50. RSVP Configuration Configure the ingress router to support the LSP [edit] user@host# show protocols mpls label-switched-path ingress-to-egress { to 192.168.32.1; primary user-defined-ERO; } path user-defined-ERO { 192.168.20.1 loose; 192.168.24.1 loose; 192.168.36.1 loose; 192.168.40.1 loose; } interface Tunnel10 ip unnumbered Loopback 0 no ip directed-broadcast tunnel destination 192.168.32.1 tunnel mode mpls traffic-eng tunnel mpls traffic-eng priority 1 1 tunnel mpls traffic-eng path-option 1 explicit name user-defined-ERO 1 June 2003
- 51. LDP Neighbors Two connected LDP routers form a neighbor relationship Hello messages multicast to 224.0.0.2 UDP port 646 Included transport address or source IP address of message is used as session identifier Two remote LDP routers can also become neighbors Targeted hello messages Unicast to the remote neighbor UDP port 646 Transport address included in message Label space advertised as part of LDP ID 1 June 2003
- 52. LDP ID Each router creates an LDP ID 6-byte value separated by a colon 192.168.1.1:0 First 4 bytes are the router ID of the node Last two bytes are used to define the type of labels allocated A value of 0, the default, means labels are handed out on a per-node basis 1 June 2003
- 53. LDP Sessions After becoming neighbors, each LDP router decides which router should be the active node Highest router ID is the active node Active node creates a TCP connection between the routers TCP port 646 Once connection between peers even when multiple physical links (multiple neighbors) exist Active node then creates an LDP session by sending initialization messages to the passive peer 1 June 2003
- 54. LDP Session Initialization Initialization message includes: Local LDP ID Remote LDP ID Protocol version Negotiable hold time value The passive node examines the LDP ID values to verify that an active neighbor relationship is in place for this new session If acceptable, a keepalive message is returned Passive node generates its own initialization message and sends it to the active node If accepted, a keepalive message is returned The peers now have an operational session between themselves 1 June 2003
- 55. Advertising Information in LDP Two new LDP peers exchange interface addresses in Address messages All directly connected addresses are advertised Allows each peer to associate a label advertisement from the session to a physical next-hop interface The peers then advertise FEC and label information Local FEC includes prefixes reachable from the router as an egress router (loopback address) FEC may also include information received from other LDP sessions Labels are allocated for all reachable FEC information 1 June 2003
- 56. LDP Database All LDP routers maintain an LDP database FEC/Labels received across a particular session FEC/Labels advertised across a particular session By default, FEC/Label information is flooded to all LDP peers for all possible prefixes Full-mesh of information for the entire LDP network Possible routing loop issues Full mesh of LSPs results from complete FEC prefix knowledge Each router is an ingress router for every FEC Each router is also an egress router for the FEC it advertised 1 June 2003
- 57. LDP Database Example user@host> show ldp database Input label database, 192.168.16.1:0--192.168.20.1:0 Label Prefix 100352 192.168.16.1/32 3 192.168.20.1/32 100368 192.168.24.1/32 100304 192.168.32.1/32 100320 192.168.36.1/32 100336 192.168.40.1/32 Output label database, 192.168.16.1:0--192.168.20.1:0 Label Prefix 3 192.168.16.1/32 100112 192.168.20.1/32 100096 192.168.24.1/32 100128 192.168.32.1/32 100144 192.168.40.1/32 1 June 2003
- 58. LDP Loop Avoidance LDP consults the IGP shortest-path information to avoid loops Results in the forwarding path for LDP and the IGP being identical For example: Suppose that 192.168.1.1 is reachable via IS-IS over the fe-0/0/0.0 interface The LDP database reports that a label has been received from two LDP peers for 192.168.1.1 One is reachable over the fe-0/0/0.0 interface The other is reachable over the fe-0/1/1.0 interface The LDP process installs the label information associated with the fe-0/0/0.0 interface 1 June 2003
- 59. Using RSVP for LDP Traffic Engineering Established RSVP tunnels can be used to engineer LDP forwarding paths through the network The RSVP ingress and egress routers form an LDP session using targeted hello messages Once the session is formed, address and FEC information is advertised Advertised and received FEC/Label information is stored in the LDP database FEC/Label information is re-advertised to other LDP peers Label stacking is performed across the RSVP LSP 1 June 2003
- 60. LDP Tunneling and Label Stacking LDP neighbor relationships between: A and B via the physical interface B and E via bi-directional RSVP LSPs E and F via the physical interface RTR-B performs a swap and push operation Swap label 101,583 for label 100,001 (advertised by E) Push label 106,039 (advertised by C) to reach RTR-E LDP: 100,001 A B C D E F LDP: 101,583 RSVP: 106,039 RSVP: 105,821 RSVP: 3 LDP: 3 106,039 105,821 101,583 100,001 100,001 100,001 IP IP IP IP IP 1 June 2003
- 61. Questions and Comments We’ve just barely scratched the surface here LSP protection Primary and secondary paths Fast Reroute Policy control and LSP selection LSP Preemption Class of Service Using MPLS to support services (L3VPN, L2VPN, VPLS) Feedback on this presentation is highly encouraged [email protected] Questions? 1 June 2003