MPLS_VPN培训汇.pptx

MPLS培训CISCO AS XiaKeWeiLabelLabel Header for Packet Media0 1 2 30 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 1LabelEXPSTTLLabel = 20 bitsCOS/EXP = Class of Service, 3 bitsS = Bottom of Stack, 1 bitTTL = Time to Live, 8 bitsCan be used over Ethernet, 802.3, or PPP linksFixed length label – 4 bytes per label (32 bits)Uses two new Ethertypes/PPP PIDsContains everything needed at forwarding timeOne word per labelMPLS LabelsTCPHeaderDATASegmentIPHeaderTCPHeaderDATAPacketLabels imposedon the IP packet(4 bytes each)IPHeaderTCPHeaderFrameHeaderMPLSLabelDATAFrameFCS011010101MPLSLabelIPHeaderTCPHeaderFrameHeaderBitsDATAFCS标签分发协议LDPMPLSUnicast Routing ProtocolsOSPF, IS-IS, BGP are needed in the network They still provide reachability between devices in the networkLabel distribution protocols distribute labels for prefixes advertised by unicast routing protocols using Label Distribution Protocol (LDP,TDP) RSVP-TE for Traffic Engineering Extending existing protocols like BGP (MP-BGP address-families) to distribute Labels (inter-AS) *TDP LDPTag Distribution Protocol—Cisco proprietary Pre-cursor to LDP Used for Cisco Tag Switching (port 711)TDP and LDP supported on the same device Per neighbor/ link basis Per target basis TDP is the default on most Cisco devices, go figure?LDP is a superset of TDPUses the same label/ tagLabel Distribution ProtocolDefined in RFC 3035 and 3036Port 646(TCP or UDP )Used to distribute Labels in an MPLS networkAdvertise Labels per FEC －Reach destination a.b.c.d with label x单跳 LDP 多跳LDPLabel Distribution Modes（标签分发模式）Downstream unsolicited(下游主动分发式) Downstream node just advertises labels for prefixes/FEC reachable via that deviceDownstream on-demand（上游请求式） Upstream node requests a label for a learned prefix via the downstream node标签分发（下游主动分发模式）LFIB on BFIB on ALFIB on D目的网络出标签目的网络入标签出标签接口接口目的网络入标签出标签接口XE025XS02550XE080 -X = 25X = 25X = 50S1E0E0S0AS0S1DBCX = 50X = 80E1E0LFIB on CN