1 / 17

MPLS

MPLS. H/W update Brief description of the lab What it is? Why do we need it? Mechanisms and Protocols. Multi-Protocol Label Switching (MPLS). A mechanism for building tunnels Label Switched Path (LSP) Forwarding based on “labels” 20 bits for label Packet contains MPLS header Label

kapono
Download Presentation

MPLS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. MPLS • H/W update • Brief description of the lab • What it is? • Why do we need it? • Mechanisms and Protocols

  2. Multi-Protocol Label Switching(MPLS) • A mechanism for building tunnels • Label Switched Path (LSP) • Forwarding based on “labels” • 20 bits for label • Packet contains MPLS header • Label • 3 EXP (experimental) bits • 8 bits for TTL • 1 bit for bottom of stack • EXAMPLE • LSPs are unidirectional

  3. Label Operations • PUSH • Add a label on the packet • At the entry point of the tunnel • Packet may already have a label • Label stack • POP • Remove a label from the packet • At the exit point of the tunnel • SWAP • Exchange the label on the packet with another one • During forwarding inside the tunnel

  4. LSP • Has an “ingress” • Entrance • Egress • Exit • It goes over some transit nodes • What traffic does it carry • Forwarding Equivalence class (FEC) • Anything that matches some rules that use the IP header information • We not have the “EDGE” where information is put into the LSP • Edge classifies packet into a FEC and there is no need to do it again inside the network

  5. MPLS forwarding • Routers than can do MPLS forwarding are called Label Switch Routers (LSRs) • Both a router and an LSR • Before we had the RIB and FIB • Now we (also) have the LIB and the LFIB • Lookup incoming label in LFIB • Determine where the packet goes and • What label it should carry • SWAP labels and send the packet

  6. Label Stack • Can have tunnel hierachies • Push another label on a labeled path • I have a label stack • Forwarding decisions are always based on the label at the top of the stack • Swap operations apply to the label at the top of the stack

  7. Signaling • In order to create the LSP somebody has to setup the labels • They are put in the LFIB – Label FIB • MPLS signaling protocols • Label Distribution Protocol (LDP) • RSVP-TE • Even BGP (for VPNs) • They distribute labels and establish tunnels

  8. Reserved Labels • 0 – IPv4 explicit NULL • 1 – Router Altert • 2 – IPv6 explicit NULL • 3 - Implicit NULL • What are these NULLs? • Determine what the Penultimate hop (PHP) will do • May pop the label completely • Or may keep an empty label in the packet

  9. PHP • Penultimate Hop Popping • The egress scales better • But does not know that it was an MPLS packet • Potentially useful information (e.g. EXP bits) are lost

  10. Label Distribution modes • Ordered vs. Independent • Will I wait for the downstream nodes to give me their label? • Unsolicited vs. on-demand • Will I wait for a neighbor to ask me for a label or I will send my labels to them anyway? • Label Space • Per platform • Per interface • Labels have link-local scope • They are unique for the same link only

  11. What is the big deal • Initially people though MPLS forwarding will be faster than IP forwarding • Not an issue anymore • Now people like MPLS because it can be used to setup tunnels • Tunnels for Traffic Engineering • Tunnels for Recovery from failures • Tunnels for VPNs

  12. How can I use the tunnels • Use them if I am their ingress • Can have a static route pointing to a tunnel next-hop • Share traffic • Between IGP • Between IGP/LSPs • Between LSPs • Can share with unequal weights • Advertise them in IGP and use them as links • “forwarding adjacencies” • I already can do things that I could not do with IGP • Can control quite well where my traffic goes • EXAMPLE

  13. Intro to TE • An ISP has a number of core routers that attach to PoPs • ISP usually knows the traffic matrix • Traffic demands between PoPs • ISP would like to control exactly how this traffic moves around in his network • Can setup a full mesh of LSPs and control exactly what is going on • Of course scalability is a issue

  14. RSVP-TE • Based on Resource Reservation Protocol • Extended to carry labels (TE) • It is a signaling protocol • Sets up network state • Does not have anything to do with routing/forwarding • Basic Idea • I am telling RSVP the path I want and it will setup an LSP over this path • Specify the whole path • Loose of strict source route • RSVP calls it Explicit Route object (ERO)

  15. PATH and RESV messages • Ingress sends a PATH message downstream • Follows the route we specified until it hits the egress • ERO or simply IP forwarding towards the destination • Egress sends a RESV message upstream • Until it hits the ingress • Intermediate routers install state • Labels are allocated • Downstream ordered mode

  16. Soft state • PATH and RESV messages create state in RSVP routers • PATH and RESV messages are send periodically to refresh this state • If state is not refreshed in time it expires and it is cleared • Simpler • Do not need to worry about reliable messages etc • Do not need to check with hellos if my neighbor is alive • But I have the overhead of state refreshes

  17. A big example • How messages are sent • How labels are allocated

More Related