RSTP(Rapid Spanning Tree Protocol)
IEEE 802.1w , \u65bc2001\u5e74\u63d0\u51fa
ps:
RSTP includes features equivalent to Cisco PortFast, UplinkFast, and BackboneFast for faster network reconvergence.<\/p>\n\n\n\n
convergence much faster<\/strong> RSTP\u5c0dSTP\u7684\u6539\u9032<\/strong>\u3000 RSTP\u76f8\u5bb9\u6027<\/strong> ………………………………………………………………<\/p>\n\n\n\n root bridge<\/strong> RSTP port roles<\/strong> RSTP port states<\/strong> ……………………………………………………<\/p>\n\n\n\n BPDU<\/strong> some previously unused bits in the Message Type field are used.<\/strong> BPDU\u904b\u4f5c<\/strong> BPDU\u907a\u5931<\/strong> \u4e0d\u540c\u7248\u672cBPDU\u8655\u7406<\/strong> \u6539\u8b8aSTP\u6642\u7684\u904b\u4f5c<\/strong> ………………………………………<\/p>\n\n\n\n RSTP Convergency<\/strong> …<\/p>\n\n\n\n Point-to-point ports\u7684\u7522\u751f\u65b9\u5f0f<\/strong> PA handshake<\/strong> Synchronization process<\/strong> \u63a5\u6536agreement message\u7570\u5e38\u6642 …<\/p>\n\n\n\n TC(topology change)<\/strong> TC\u7684\u8655\u7406<\/strong> TC\u7684\u6b65\u9a5f<\/strong> RSTP(Rapid Spanning Tree Proto …<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"fifu_image_url":"","fifu_image_alt":"","_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[26],"tags":[],"class_list":["post-813","post","type-post","status-publish","format-standard","hentry","category-osi-layer2"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/posts\/813","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/comments?post=813"}],"version-history":[{"count":0,"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/posts\/813\/revisions"}],"wp:attachment":[{"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/media?parent=813"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/categories?post=813"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/tags?post=813"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
1. \u6536\u6582\u901f\u5ea6\u6700\u5feb\u53ef\u52301sec
2. \u5728Blocking state port\u4e0d\u9808\u75282\u500d\u7684Forward Delay\u6642\u9593\u5373\u53ef\u76f4\u63a5\u8b8a\u6210Forward state
ex:
1. edge port\u53ef\u4ee5\u76f4\u63a5\u8fdb\u5165forward state and no delay
2. \u7576root port\u70baBlocking status,\u4e14new root port\u6240\u63a5\u4e4bdesignated port\u70baForwarding status\uff0c\u5247new root port \u53ef\u7acb\u5373\u6210\u70baForwarding status
3. non-edge port\u7684designated port\uff0c\u53ef\u8207neighbor bridge\u9032\u884cPA handshake\u800c\u5feb\u901f\u6210\u70baForwarding status<\/p>\n\n\n\n
1
STP\u6536\u6582\u4e3b\u8981\u4f9d\u8d56port status
RSTP\u6536\u6582\u4e3b\u8981\u4f9d\u8d56port type
2
STP port state\u6539\u8b8a,\u9700\u4f9d\u8cf4timer\u8d85\u6642
RSTP port state\u6539\u8b8a,\u662f\u4e3b\u52d5\u5354\u5546
3(\u5f85\u78ba\u8a8d)
STP\u4e2d\u7684non-root bridge\u53ea\u80fdrelay\u7684hello bpdu
RSTP\u4e2d\u7684non-root bridge\u6703\u4e3b\u52d5\u767chello bpdu\u3000<\/p>\n\n\n\n
RPVST+(Rapid PVST+)
\u3000by using RSTP as the underlying mechanism for the Cisco-proprietary PVST+
MST(Multiple Spanning Tree)
\u3000RSTP also is used as part of the IEEE 802.1s MST operation.
\u3000RSTP operates consistently in each, but replicating RSTP as multiple instances requires different approaches.<\/p>\n\n\n\n
The root bridge in a network using RSTP is elected just as with 802.1D(by the lowest Bridge ID) <\/p>\n\n\n\n
After all switches agree on the identity of the root, the following port roles are determined:
Root port<\/strong>(This is identical to 802.1D)
\u3000\u4fdd\u6301forward state
Alternate port<\/strong>
\u3000A port that has an alternative path to the root, different from the path the root port takes.
\u3000This path is less desirable than that of the root port.
ex:
an access-layer switch with two uplink ports; one becomes the root port, and the other is an alternate port.
Designated port<\/strong> (This is identical to 802.1D)
\u3000\u4fdd\u6301forward state
Backup port<\/strong>
\u3000\u5099\u63f4\u7684designated port
\u3000A port that provides a redundant (but less desirable) connection to a segment where another switch port(deesignated port) already connects.<\/p>\n\n\n\n
1. After the role is determined, each port can be given a state that determines what it does with incoming data.
2. RSTP defines port states only according to what the port does with incoming frames.
(Naturally, if incoming frames are ignored or dropped, so are outgoing frames.)
Any port role can have any of these port states:
Discarding<\/strong>(=Disabled, Blocking,Listening states)
\u30001.Incoming frames simply are dropped;
\u30002.no MAC addresses are learned.
Learning<\/strong>(\u66ab\u6642\u6027\u5b78\u7fd2)
\u30001. Incoming frames are dropped,
\u30002. but MAC addresses are learned.
Forwarding<\/strong>(\u53ea\u89816\u79d2\u5373\u53ef\u9032\u5165\u6b64\u72c0\u614b)
\u30001. Incoming frames are forwarded
\u30002. according to MAC addresses that have been (and are being) learned
ps:
discarding state combines the 802.1D Disabled, Blocking,Listening states because all three did not effectively forward anything.
ps:
The Listening state is not needed because RSTP quickly can negotiate a state change without listening for BPDUs first.<\/p>\n\n\n\n
1. RSTP uses the 802.1D BPDU format for backward compatibility.
2. The sending switch port identifies itself by its RSTP role and state
3. RSTP BPDU is ver2 ,802.1D BPDUs is ver0<\/p>\n\n\n\n
stp:flags(1byte):
\u300000000000:topology change(\u6709\u67b6\u69cb\u8b8a\u66f4\u65d7\u6a19)
\u300010000000:topology change ack(\u67b6\u69cb\u8b8a\u66f4\u56de\u8986\u65d7)
rstp:flags(1byte):
\u300000000000:\u540cstp
\u300000000001\u70baProposal message
\u300000000[00]0:\u70baport role\u5982\u4e0b
\u3000\u3000[00] unknown
\u3000\u3000[01] alternate\/backup port
\u3000\u3000[10] root port
\u3000\u3000[11] designate port
\u300000010000:\u70baLearning state
\u300000100000:\u70baforwarding state
\u300001000000:\u70baagreement message
\u300010000000:\u540cstp<\/p>\n\n\n\n
BPDUs are sent out every switch port at Hello Time intervals, regardless of whether BPDUs are received from the root.
ps:
any switch anywhere in the network can play an active role in maintaining the topology\u3000<\/p>\n\n\n\n
When 3 BPDUs(3 Hello intervals) are missed in a row (default 6sec)
\u30001. neighbor switch is presumed to be down,
\u30002. all information related to the port leading to the neighbor immediately is aged out.
ps:
the Max Age timer interval (default 20 seconds) for 802.1D,\u624d\u80fd\u66f4\u65b0BPDU<\/p>\n\n\n\n
RSTP can coexist with switches still using 802.1D
Each port attempts to operate according to the STP BPDU that is received.
ps:
802.1D STP\u7121\u6cd5\u8fa8\u8b58RSTP\u7684BPDU
ex:
when an 802.1D BPDU is received on a port, that port begins to operate according to the 802.1D rules.<\/p>\n\n\n\n
each port has a measure that locks the protocol in use, in case BPDUs from both 802.1D and RSTP are received within a short time frame.
This can occur if the switches in a network are being migrated from one STP type to another. Instead of flapping or toggling the STP type during a migration, the switch holds the protocol type for the duration of a migration delay timer.
After this timer expires, the port is free to change protocols if needed.<\/p>\n\n\n\n
When a switch first joins the topology (perhaps it was just powered up) or has detected a failure in the existing topology, RSTP requires it to base its forwarding decisions on the type of port
ps:
RSTP\u900f\u904eport type\u53ef\u5feb\u901f\u6536\u6582\u4e0d\u4f9d\u8cf4timer,\u4f46STP\u8981\u5feb\u901f\u6536\u6582\u53ea\u80fd\u4f9d\u8cf4timer
ps:
RSTP takes a different approach when a switch needs to decide how to participate in the tree topology.<\/p>\n\n\n\n
Port Types<\/strong>
Every switch port can be considered one of the following types:
Edge port:\u53ef\u5feb\u901f\u8f49\u79fb,\u4e0d\u6703\u6536\u5230\u4efb\u4f55bpdu,\u4e5f\u5c31\u662f\u63a5\u5230hub\u6216pc
nonedge port:\u5728\u9019\u88e1\u6307\u5168\u96d9\u5de5\u7684switch\u9593\u9023\u7dda
\u3000Root port
\u3000Point-to-point port:\u53ef\u5feb\u901f\u8f49\u79fb<\/p>\n\n\n\n
Edge port<\/strong>
1.A port at the “edge” of the network, where only a single host connects.
ps:this has been identified by enabling the STP PortFast feature. RSTP keeps the PortFast concept for familiarity.
2.the port cannot form a loop as it connects to one host, so it can be placed immediately in the Forwarding state.
ps:
if a BPDU ever is received on an edge port
\u30001.the port immediately loses its edge port status
\u30002.topology change be triggered(a nonedge port transitions to the Forwarding state)
Root port<\/strong>
1. The port that has the best cost to the root of the STP instance.
2. Only one root port can be selected and active at any time, although alternative paths to the root can exist through other ports.
3. If alternative paths are detected, those ports are as alternative root ports and immediately can be placed in the Forwarding state when the existing root port fails.
Point-to-point port(designated port)<\/strong>
1. Any port that connects to another switch and becomes a designated port.
2. A quick handshake with the neighboring switch, rather than a timer expiration, decides the port state.
3. BPDUs are exchanged back and forth in the form of a proposal and an agreement.
4. One switch proposes that its port becomes a designated port; if the other switch agrees, it replies with an agreement message.<\/p>\n\n\n\n
automatically be determined by the duplex mode in use
Full-duplex ports
\u30001 point to point port(p2p)
\u3000because only two switches can be present on the link.
\u30002.STP convergence can occur quickly over a p2p link through RSTP handshake messages
Half-duplex ports
\u30001 not point-to-point ports\/shared port.
\u3000because a shared medium with possibly more than two switches present.
\u30002.the traditional 802.1D style convergence must be used. This results in a slower response<\/p>\n\n\n\n
RSTP\u6536\u6582\u539f\u7406<\/strong>
propagation of handshakes over point-to-point links
step1
When a switch needs to make an STP decision,a handshake is made with the nearest neighbor.
step2
When that is successful, the handshake sequence is moved to the next switch and the next, as an ever-expanding wave moving toward the network’s edges.<\/p>\n\n\n\n
Synchronization concept<\/strong>
To participate in RSTP convergence, a switch must decide the state of each of its ports.
1. Nonedge ports begin in the Discarding state.
2. After BPDUs(PA handshake) are exchanged between the switch and its neighbor, the Root Bridge can be identified.
3. If a port receives a superior BPDU from a neighbor, that port becomes the root port<\/p>\n\n\n\n
For each nonedge port, the switch exchanges a proposal-agreement handshake(a configuration BPDU) to decide the state of each end of the link
ps:\u7576non-edge port\u5f9eblocking\u6210\u70baforwarding\u72c0\u614b,\u624d\u6703\u904b\u4f5cPA handshake<\/p>\n\n\n\n
Each switch assumes that its port should become the designated port for the segment, and a proposal message is sent to the neighbor suggesting this.
\u6b65\u9a5f\u5982\u4e0b
1
switch(DP)\u50b3\u9001Proposal message(BPDU flag 00000001)\u5230neighbor switch(root port)
ps:switch all Nonedge ports begin in the Discarding state.
2
neighbor switch\u505a\u4ee5\u4e0b\u4e8b
All nonedge ports immediately are moved into the Discarding (blocking) state
neighbor switch(root port)\u50b3\u56deagreement message(BPDU flag 01000000)\u7d66switch(DP)
3
switch\u7684designated port\u548cneighbor switch\u7684root port\u9032\u5165Forwarding state,\u53ef\u958b\u59cbforwarding
4
\u82e5neighbor switch\u9084\u6709\u5c1a\u672a\u505aPA\u4ea4\u63e1\u4e4bswitch,\u5247neighbor switch\u505a\u70ba\u6b65\u9a5f1\u4e2d\u7684switch
ps:
This creates a moving “wave” of synchronizing switches, which quickly can decide to start forwarding on their links only if their neighbors agree
ps:
the entire convergence process happens quickly, at the speed of BPDU transmission,without the use of any timers<\/p>\n\n\n\n
Suppose that the neighboring switch does not understand RSTP or has a problem replying.
The sending switch then must become overly cautious and must begin playing by the 802.1D rules – the port must be moved through the legacy Listening and Learning states (using the Forward Delay timer) before moving to the Forwarding state.<\/p>\n\n\n\n
RSTP detects a topology change only when a nonedge port transitions to the Forwarding state.
topology changes are detected only so that bridging tables can be updated and corrected as hosts appear first on a failed port and then on a different functioning port.<\/p>\n\n\n\n
a switch must propagate news of the change to other switches in the network so that they can correct their bridging tables, too.
This process is similar to the convergence and synchronization mechanism;
TC messages propagate through the network in an ever-expanding wave<\/p>\n\n\n\n
1.
The switch send BPDUs(with their TC bit set) out all the nonedge designated ports
This is done until the TC timer expires, after 2 intervals of the Hello time
\u7528\u9014:This notifies neighboring switches of the new link and the topology change.
2.
The swich all MAC addresses associated with the nonedge designated ports are flushed from the CAM table.
\u7528\u9014:This forces the addresses to be relearned after the change, in case hosts now
appear on a different link
3.
All neighboring switches that receive the TC messages,\u505a\u4ee5\u4e0b\u5169\u4ef6\u4e8b
\u30003.1 flush the MAC-addr learned on all ports except the one that received the TC message
\u30003.2 \u6210\u70bastep1\u4e2d\u7684switch , send TC messages out their nonedge designated ports, and so on.<\/p>\n","protected":false},"excerpt":{"rendered":"