01 introduction to mpls
0 likes1,204 views
The document provides an introduction to MPLS (Multi-Protocol Label Switching) covering its definition, advantages, architecture, labels, label switching path setup, and forwarding operations. Key points include: - MPLS encapsulates packets with short fixed-length labels to enable faster forwarding based on the label rather than the IP address. - MPLS decouples routing from forwarding and supports traffic engineering and virtual private networks. - The MPLS architecture consists of label edge routers, label switch routers, label distribution protocols, and label forwarding tables. - Labels are assigned and distributed to establish label switched paths for forwarding packets across the MPLS network.
![MPLS LSP Trace
25
MPLS Domain
R2 R3 R4R1
4.4.4.4/32
R1#traceroute mpls ipv4 4.4.4.4/32
Tracing MPLS Label Switched Path to 4.4.4.4/32, timeout is 2 seconds
Codes: '!' - success, 'Q' - request not sent, '.' - timeout,
'L' - labeled output interface, 'B' - unlabeled output interface,
'D' - DS Map mismatch, 'F' - no FEC mapping, 'f' - FEC mismatch,
'M' - malformed request, 'm' - unsupported tlvs, 'N' - no label entry,
'P' - no rx intf label prot, 'p' - premature termination of LSP,
'R' - transit router, 'I' - unknown upstream index,
'l' - Label switched with FEC change, 'd' - see DDMAP for return code,
'X' - unknown return code, 'x' - return code 0
Type escape sequence to abort.
0 12.1.1.1 MRU 1500 [Labels: 200 Exp: 0]
L 1 12.1.1.2 MRU 1500 [Labels: 19 Exp: 0] 16 ms
L 2 23.1.1.2 MRU 1504 [Labels: implicit-null Exp: 0] 12 ms
! 3 34.1.1.2 12 ms Cisco IOS](https://image.slidesharecdn.com/01introductiontompls-200615073213/85/01-introduction-to-mpls-25-320.jpg)
01 introduction to mpls
- 1. Issue Date: Revision: APNIC eLearning: Introduction to MPLS 31 OCTOBER 2018 11:00 AM AEST Brisbane (UTC+10) 20 May 2016 3.0
- 2. Introduction • Presenter/s • Reminder: please take time to fill-up the survey Jessica Bei Wei Training Officer jwei@apnic.net Specialties: Routing & Switching MPLS IPv6 QoS 2
- 3. Overview • Definition of MPLS • Advantages of MPLS • MPLS Application • MPLS Architecture • MPLS Labels • LSP Setup • Forwarding Operations 3
- 4. Definition of MPLS • Multi Protocol Label Switching – Multiprotocol, it supports ANY network layer protocol, i.e. IPv4, IPv6, IPX, CLNP, etc. – A short label of fixed length is used to encapsulate packets – Packets are forwarded by label switching instead of by IP switching 4
- 5. … 128.89/16 171.69/16 Address Prefix I/F 1 0 IP Forwarding Table … 128.89/16 171.69/16 Address Prefix I/F 0 1 IP Forwarding Table Initial Motivation of MPLS 5 A label-swapping protocol was the need for speed. • In mid 1990s, IP address lookup was considered more complex and take longer time. – Longest matching 01 128.89 0 128.89.25.4 Data 128.89.25.4 Data128.89.25.4 Data … 128.89/16 171.69/16 Address Prefix I/F 0 1 IP Forwarding Table 128.89.25.4 Data
- 6. Decoupling Routing and Forwarding 6 • MPLS can allow core routers to switch packets based on some simplified header. • But, hardware of routers became better and looking up longest best match was no longer an issue. • More importantly, MPLS de-couples forwarding from routing, and support multiple service models. 1 0 1 128.89.25.4 Data 128.89.25.4 Data20 128.89.25.4 Data30 128.89.25.4 Data 128.89 01 0
- 7. VPN B Site 1 VPN B Site 3 VPN B Site 2 VPNA Site 2 MPLS VPN 7 • MPLS Layer 3/ Layer 2 VPN MPLS Core CE CE CE CE CE PE PE PE PE P P P VPNA Site 1
- 8. Optimal Traffic Engineering 8 IP TE MPLS TE Shortest path Determines the path at the source based on additional parameters (available resources and constraints, etc.) Equal cost load balancing Load sharing across unequal paths can be achieved. FE FE FE GE GETunnel 1 BW: 300 Mb/s Tunnel 2 BW : 50 M b/s R1 R2 R3 R4 R5 R6
- 9. VPN Site IP Domain MPLS QoS • MPLS does NOT define a new QoS architecture. – Similar parts with IP DiffServ: functional components and where they are used.(such as marking and traffic policing at network edge, etc) – Difference: packets are differentiated by MPLS Traffic Class bits 9 MPLS Domain CE PE PP QoS in MPLS VPN Architecture DSCP MPLS Header Traffic Class IP Packet IP Packet - Packet
- 10. Technology Comparison IP Native Ethernet MPLS Forwarding • Destination address based • Forwarding table learned from control plane • TTL support • Destination address based • Forwarding table learned from data plane • No TTL support • Label based • Forwarding table learned from control plane • TTL support Control Plane Routing protocols Ethernet loop avoidance and signaling protocols Routing protocols Label distribution protocols Packet Encapsulation IP header 802.3 header MPLS Header QoS 8 bit TOS in IP header 3 bit 802.1p in VLAN tag 3 bit TC in label OAM IP Ping, traceroute E-OAM MPLS Ping, traceroute 10
- 11. Evolution of MPLS • Technology Evolution and Main Growth Areas 11 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Complete base MPLS portfolio Optimize MPLS for video Optimize MPLS for packet transport Optimize MPLS for Cloud Today Formation of the IETF MPLS working group First MPLS L3VPN &TE Deployed First MPLS RFCs Released First L2VPN Deployments Large Scale L3VPN Deployments Large Scale MPLS TE Deployed Large Scale L2VPN Deployments First LSM Deployme nts First MPLS TP Deployments 1996, Ipsilon, Cisco and IBM announced label switching plans, till now, there are over 280 RFCs of MPLS tech. Bring MPLS to Market
- 12. MPLS Application Scenario 12 MPLS CORE Enterprise Enterprise Enterprise L3VPN L3VPN L2VPN L2VPN Enterprise L2VPN TE Main Path for PE1-PE3 TE Backup Path for PE1-PE3 PE1 P PE2 PE3 PE4 P P P QoS Operations: Congestion management, congestion avoidance QoS Operations: Traffic marking, police, shaping QoS Operations : Traffic marking, police, shaping
- 13. MPLS Architecture 13 IP Routing Protocols Label Distribution Protocols Control Plane Routing Information Exchange with other routers Data Plane Label Binding and Exchange with other routers Incoming IP Packet Incoming Labeled Packet Routing Information Base (RIB) Forwarding Information Base (FIB) Label Information Base (LIB) Label Forwarding Information Base (LFIB)
- 14. IP Domain MPLS Topology 14 • LSR (Label Switch Router) is a router that supports MPLS. • LER (Label Edge Router), also called edge LSR, is an LSR that operates at the edge of an MPLS network. • LSP (Label Switched Path) is the path through the MPLS network or a part of it that packets take. MPLS Domain Edge LSR LSR LSR Edge LSR IP PacketLabel IP PacketLabel IP PacketLabel IP PacketIP Packet IP Domain
- 15. MPLS Label 15 TC = Traffic Class: 3 Bits; S = Bottom of Stack: 1 Bit; TTL = Time to Live 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 Label - 20bits TC S TTL-8bits MPLS LabelDatalink Layer Header Layer 2/ Layer 3 Packet MPLS Label Encapsulation
- 16. MPLS Label Stacking 16 • Multiple labels can be used for MPLS packet encapsulation. network. This is done by packing the labels into a stack. • Some MPLS applications (VPN, etc.) actually need more than one labels in the label stack to forward the labeled packets. MPLS Label Stack LAN MAC Label Header S=1 Bottom of Stack Bit Set S=0 MAC Header Label S Label S Layer 3 Packet
- 17. LSP Setup Overview • Before forwarding packets, labels must be allocated to establish an LSP. • Protocols for label distribution: LDP, RSVP-TE, MP-BGP. 17 Establishing an LSP Labels are allocated from downstream LSRs to upstream LSRs. R2 To 100.1.1.1/32 Label=100 To 100.1.1.1/32 Label=200 To 100.1.1.1/32 Label=300 R1 R3 R4 LSP DownstreamUpstream 100.1.1.1/32
- 18. Basic Concepts of MPLS Forwarding • FEC – Forwarding Equivalence Class, is a group or flow of packets that are forwarded along the same path and are treated the same with regard to the forwarding treatment. – For example, packets with Layer 3 destination IP address matching a certain prefix. • Push – A new label is added to the packet between the Layer 2 header and the IP header or to the top of the label stack. • Swap – The top label is removed and replaced with a new label. • Pop – The top label is removed. The packet is forwarded with the remaining label stack or as an unlabeled packet. 18
- 19. MPLS Forwarding Operations Prefix: 100.1.1.1/32 Local Label Null Out Interface E1 Out Label 100 Operation Push 19 R2 E0 R3 R4 IP: 100.1.1.1 IP:100.1.1.1100 100.1.1.1/32 IP:100.1.1.1200 IP:100.1.1.1300 IP: 100.1.1.1 R1 E1 E1 E1E0 E0 E0 Prefix: 100.1.1.1/32 Local Label 100 Out Interface E1 Out Label 200 Operation Swap Prefix: 100.1.1.1/32 Local Label 200 Out Interface E1 Out Label 300 Operation Swap Prefix: 100.1.1.1/32 Local Label 300 Out Interface -- Out Label -- Operation POP Push Swap Swap Pop Loopback0
- 20. Why PHP(Penultimate Hop Popping)? Prefix: 100.1.1.1/32 Local Label Null Out Interface E1 Out Label 100 Operation Push 20 R2 E0 R3 R4 IP: 100.1.1.1 IP:100.1.1.1100 100.1.1.1/32 IP:100.1.1.1200 IP:100.1.1.1300 IP: 100.1.1.1 R1 E1 E1 E1E0 E0 E0 Prefix: 100.1.1.1/32 Local Label 100 Out Interface E1 Out Label 200 Operation Swap Prefix: 100.1.1.1/32 Local Label 200 Out Interface E1 Out Label 300 Operation Swap Prefix: 100.1.1.1/32 Local Label 300 Out Interface -- Out Label -- Operation POP Push Swap Swap Pop Review what R4 has done: 1. First, lookup the label in the LFIB; Remove the label 2. Then, IP lookup and forward IP packet. Is the first lookup necessary? Can we simplify it? Loopback0
- 21. Penultimate Hop Popping Prefix: 100.1.1.1/32 Local Label Null Out Interface E1 Out Label 100 Operation Push 21 R2 E0 R3 R4 IP: 100.1.1.1 IP:100.1.1.1100 100.1.1.1/32 IP:100.1.1.1200 IP:100.1.1.1 IP: 100.1.1.1 R1 E1 E1 E1E0 E0 E0 Prefix: 100.1.1.1/32 Local Label 100 Out Interface E1 Out Label 200 Operation Swap Prefix: 100.1.1.1/32 Local Label 200 Out Interface E1 Out Label imp-null Operation Pop Prefix: 100.1.1.1/32 Local Label imp-null Out Interface -- Out Label -- Operation -- Push Swap Pop The implicit NULL label is the label that has a value of 3, the label 3 will never be seen as a label in the label stack of an MPLS packet. Loopback0
- 22. MPLS TTL Processing (1) • MPLS processes the TTL to prevent loops and implement traceroute. • By default, TTL propagation is enabled as above. 22 IP Domain MPLS Domain Edge LSR LSR LSR Edge LSR TTL=250TTL=251 IP Domain TTL=250 TTL=249 TTL=250 TTL=248 TTL=247 Decreased & CopiedDecreased & Copied Only the TTL in the top level decreased
- 23. MPLS TTL Processing (2) • TTL propagation can be disabled to hide the MPLS network topology. • Disabling TTL propagation makes routers set the value 255 into the TTL field of the label when an IP packet is labeled. 23 IP Domain MPLS Domain Edge LSR LSR LSR Edge LSR TTL=255TTL=251 IP Domain TTL=250 TTL=254 TTL=250 TTL=249 TTL=248 DecreasedSet 255 Only the TTL in the top level decreased Decreased After disabled TTL propagation
- 24. MPLS LSP Ping 24 MPLS Domain R2 R3 R4R1 4.4.4.4/32 R1#ping mpls ipv4 4.4.4.4/32 Sending 5, 100-byte MPLS Echos to 4.4.4.4/32, timeout is 2 seconds, send interval is 0 msec: Codes: '!' - success, 'Q' - request not sent, '.' - timeout, 'L' - labeled output interface, 'B' - unlabeled output interface, 'D' - DS Map mismatch, 'F' - no FEC mapping, 'f' - FEC mismatch, 'M' - malformed request, 'm' - unsupported tlvs, 'N' - no label entry, 'P' - no rx intf label prot, 'p' - premature termination of LSP, 'R' - transit router, 'I' - unknown upstream index, 'l' - Label switched with FEC change, 'd' - see DDMAP for return code, 'X' - unknown return code, 'x' - return code 0 Type escape sequence to abort. !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 12/14/16 ms Total Time Elapsed 128 ms MPLS Echo Request MPLS Echo Reply Cisco IOS
- 25. MPLS LSP Trace 25 MPLS Domain R2 R3 R4R1 4.4.4.4/32 R1#traceroute mpls ipv4 4.4.4.4/32 Tracing MPLS Label Switched Path to 4.4.4.4/32, timeout is 2 seconds Codes: '!' - success, 'Q' - request not sent, '.' - timeout, 'L' - labeled output interface, 'B' - unlabeled output interface, 'D' - DS Map mismatch, 'F' - no FEC mapping, 'f' - FEC mismatch, 'M' - malformed request, 'm' - unsupported tlvs, 'N' - no label entry, 'P' - no rx intf label prot, 'p' - premature termination of LSP, 'R' - transit router, 'I' - unknown upstream index, 'l' - Label switched with FEC change, 'd' - see DDMAP for return code, 'X' - unknown return code, 'x' - return code 0 Type escape sequence to abort. 0 12.1.1.1 MRU 1500 [Labels: 200 Exp: 0] L 1 12.1.1.2 MRU 1500 [Labels: 19 Exp: 0] 16 ms L 2 23.1.1.2 MRU 1504 [Labels: implicit-null Exp: 0] 12 ms ! 3 34.1.1.2 12 ms Cisco IOS
- 26. IP MTU • MTU indicates the maximum size of the IP packet that can still be sent on a data link, without fragmenting the packet. 26 IP Domain R2 R3 R4R1 MTU=1500 MTU=1500 MTU=1500 IP Packet size=1500 DF=1 PASS PASS PASS IP Header TCP Header Payload Ethernet MTU IP MTU TCP MSS 20 byte 20 byte 1460 byte
- 27. MPLS MTU Issue 27 MPLS Domain R2 R3 R4R1 MTU=1500 MTU=1500 MTU=1500 Labeled Packet size=1508 DF=1 DROP LDP Label VPN Label IP Header TCP Header Payload Ethernet MTU IP MTU TCP MSS 20 byte 20 byte 1460 byte4 byte 4 byte • In MPLS L3VPN network, 2 labels are added into the packet, the labeled packets are slightly bigger than the IP packets. This would lead to the need to fragment the packet.
- 28. How to Optimize Fragmentation? • Solution 1. Change MPLS MTU: Make sure that you configure this value on all the links in the path so that the packets are not dropped. • Solution 2. Change the TCP MSS to be smaller: 28 R1(config)#interface ethernet1/0 R1(config-if)#mpls mtu 1508 R1#show mpls interfaces Ethernet 1/0 detail Interface Ethernet1/0: IP labeling enabled LSP Tunnel labeling not enabled BGP labeling not enabled MPLS not operational MTU = 1508 R1(config)#interface ethernet 1/0 R1(config-if)#ip tcp adjust-mss 1452 For detailed, please refer to: https://blog.apnic.net/2014/12/15/ip-mtu-and-tcp-mss-missmatch-an-evil-for-network-performance/
- 29. Questions • Please remember to fill out the feedback form – https://www.surveymonkey.com/r/a pnic-20181031-eL1 • Slides are available for download from APNIC FTP. • Acknowledgement to Cisco System. 29
- 31. 31 Thank You!END OF SESSION