Author: Bill Buchanan. Transparent bridge Author: Bill Buchanan CAM

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Slide 1Author: Bill Buchanan
Author: Bill Buchanan









Loops. In this case two redundant/parallel loops have been added. Transparent switches cannot cope with multiple routes to a destination. Requirement for STP (Spanning-tree protocol) – removes loops
Author: Bill Buchanan
Author: Bill Buchanan
STP and BPDUs









After the root switch election, there is a root port section on each switch. It is the lowest accumulated path cost to the root switch. On a tie, choose the neighbouring switch with the lowest bridge ID. If a tie for the ID, select port with the lowest priority. If a tie, select the lowest port number.
Author: Bill Buchanan
Author: Bill Buchanan
STP Enhancements
Portfast. Excludes ports which are not connected to bridges or switches. Reduces the STP data size. Ports do not go through blocking, listening, learning and forwarding phases, but go straight to forwarding. If DHCP is required on a machine, Portfast is needed, as there will be a 30-50 delay as the port goes through the main phases.
(config)# int fa0/1
(config-if)# spanning-tree portfast
spanning-tree extend system-id
STP Enhancements
Portfast. Excludes ports which are not connected to bridges or switches. Reduces the STP data size. Ports do not go through blocking, listening, learning and forwarding phases, but go straight to forwarding. If DHCP is required on a machine, Portfast is needed, as there will be a 30-50 delay as the port goes through the main phases.
# show spanning-tree summary
Root bridge for: none
PortFast BPDU Guard is disabled by default
Portfast BPDU Filter is disabled by default
Loopguard is disabled by default
UplinkFast is disabled
BackboneFast is disabled
Name Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
---------------------- -------- --------- -------- ---------- ----------
# show spanning int fa0/2
---------------- ---- --- --------- -------- --------------------------------
# sh spanning int fa0/3
---------------- ---- --- --------- -------- --------------------------------
Author: Bill Buchanan
Author: Bill Buchanan
STP Enhancements
BPDU Guard. Shuts down the port when it receives a BPDU, and goes into an error disable state.
Switch(config-if)# spanning ?
bpduguard Don't accept BPDUs on this interface
cost Change an interface's spanning tree port path cost
guard Change an interface's spanning tree guard mode
link-type Specify a link type for spanning tree protocol use
mst Multiple spanning tree
portfast Enable an interface to move directly to forwarding on
link up
Switch(config-if)# spanning bpduguard ?
Switch(config-if)#spanning bpduguard enable
with BPDU Guard enabled. Disabling port.
Author: Bill Buchanan
Author: Bill Buchanan
STP Enhancements
BPDU Filter. Filters BPDU packets on a port of a switch. If it receives more than 10 BPDU packets is disables PortFast, and returns to normal.
Switch(config)#int fa0/1
bpduguard Don't accept BPDUs on this interface
cost Change an interface's spanning tree port path cost
guard Change an interface's spanning tree guard mode
link-type Specify a link type for spanning tree protocol use
mst Multiple spanning tree
port-priority Change an interface's spanning tree port priority
portfast Enable an interface to move directly to forwarding on link up
stack-port Enable stack port
Switch(config-if)#spanning portfast ?
trunk Enable portfast on the interface even in trunk mode
<cr>
Switch(config-if)#spanning bpduf enable
Author: Bill Buchanan
Author: Bill Buchanan
STP Enhancements - Uplinks
Uplink. Uses a redundant link connection to reduce the convergence time to less than 4 seconds. Required:
Uplink enabled.
Failure is on the current switch.
Switch(config)# sp ?
extend Spanning Tree 802.1t extensions
logging Enable Spanning tree logging
loopguard Spanning tree loopguard options
mode Spanning tree operating mode
mst Multiple spanning tree configuration
pathcost Spanning tree pathcost options
portfast Spanning tree portfast options
transmit STP transmit parameters
uplinkfast Enable UplinkFast Feature
Author: Bill Buchanan
Author: Bill Buchanan
STP Enhancements - RSTP
Rapid STP (RSTP). 802.1W allows rapid convergence. Standard on many devices. PVST+ used on ISL or 802.1Q links to allow RSTP to work correctly – defined as RPVST+ (enabled by default).
RSTP can converge the spanning-tree instance in less than a second, as apposed to almost 50 seconds for standard 802.1D spanning tree). This type of setup is important in real-time applications such as voice and video traffic.
Author: Bill Buchanan
Author: Bill Buchanan
STP Enhancements - MST
Multiple Spanning Tree (MST). MSTP (Multiple STP – IEEE 802.1S) are used to provide rapid convergence of the spanning-tree protocol. MSTP is used to group VLANs into a single spanning-tree instance. It allows multiple instances of STP, and reduce overhead time for PVST. Advantages: Load balancing and redundant connections. Disadvantages: more complex that standard, and more skill required. MST defines regions, and each switch has the same region name, the same revision number and the same VLAN table content.
(config)# spanning-tree ?
extend Spanning Tree 802.1t extensions
loopguard Spanning tree loopguard options
mode Spanning tree operating mode
mst Multiple spanning tree configuration
pathcost Spanning tree pathcost options
portfast Spanning tree portfast options
uplinkfast Enable UplinkFast Feature
(config)# spanning-tree mst ?
configuration Enter MST configuration submode
forward-time Set the forward delay for the spanning tree
hello-time Set the hello interval for the spanning tree
max-age Set the max age interval for the spanning tree
max-hops Set the max hops value for the spanning tree
(config)# spanning-tree mst configuration
Author: Bill Buchanan
Author: Bill Buchanan
STP Enhancements - MST
Multiple Spanning Tree (MST). Allows multiple instances of STP, and reduce overhead time for PVST. Advantages: Load balancing and redundant connections. Disadvantages: more complex that standard, and more skill required.
MST defines regions, and each switch has the same region name, the same revision number and the same VLAN table content.
(config)# spanning-tree mst configuration
name Set configuration name
private-vlan Set private-vlan synchronization
show Display region configurations
vlan Range of vlans to add to the instance mapping
(config-mst)# instance 1 vlan ?
(config-mst)# instance 1 vlan 1
(config-mst)# name ?
rapid-pvst Per-Vlan rapid spanning tree mode
(config)# spanning-tree mode mst
Author: Bill Buchanan
Author: Bill Buchanan
STP Enhancements - Etherchannels
Etherchannels allow ports to aggregated to be treated as a single channel. They use LACP (Link Aggregation Control Protocol - IEEE 802.3ad). The LACP packets use EtherChannels to intercommunicate, where the neighours and and port group capabilities are learnt and compared with local switch capabilities. In LACP there are roles assigned to the EtherChannel endpoints. Thus the switch with the lowest system priority is then elected to make decisions about what ports are actively participating in the EtherChannel.
(config)# lacp ?
(config)# lacp system-priority ?
<1-65535> Priority value
(config-if)# channel-protocol lacp
(config-if)# channel-group 1 mode ?
active Enable LACP unconditionally
auto Enable PAgP only if a PAgP device is detected
desirable Enable PAgP unconditionally
on Enable Etherchannel only
passive Enable LACP only if a LACP device is detected
(config-if)# channel-group 1 mode active
(config-if)# lacp ?
(config-if)# lacp port-priority ?
<1-65535> Priority value
will be aged out of the
CAM table
Contains: Bridge priority
addresses
the same accumulated
the highest priority wins!
Bridge ID (8 bytes)
Port ID (2 bytes)
Message age (2 bytes)
Max. age (2 bytes)
Hello Time (2 bytes)
Forward delay (2 bytes)
After the root switch election, there is a root port
section on each switch.
·It is the lowest accumulated path cost to the root
switch.
lowest bridge ID.
·If a tie for the ID, select port with the lowest
priority.
Root port on
election. All the paths will then be
measured related to the root switch.
·Lowest identifier wins the election.
·If all the switches have the same priority,
the lowest MAC address wins.
Priority (2 bytes)MAC address (6 bytes)
Switch ID
Root switch
loops have been added. Transparent
switches cannot cope with multiple routes
to a destination.
ports. The ports can be in the
following state.
root. It does not forward any data
frames.
source MAC addresses and puts
into the CAM table. It does not
forward any data frames.
Switch ID
Root switch
extend Spanning Tree 802.1t extensions
loopguard Spanning tree loopguard options
mode Spanning tree operating mode
mst Multiple spanning tree configuration
pathcost Spanning tree pathcost options
portfast Spanning tree portfast options
uplinkfast Enable UplinkFast Feature
(config)# spanning-tree vlan ?
(config)# spanning-tree vlan 1 ?
max-age Set the max age interval for the spanning tree
priority Set the bridge priority for the spanning tree
root Configure switch as root
<cr>
Priority (2 bytes)MAC address (6 bytes)
Switch ID
Root switch
(config)# spanning-tree ?
extend Spanning Tree 802.1t extensions
loopguard Spanning tree loopguard options
mode Spanning tree operating mode
pathcost Spanning tree pathcost options
portfast Spanning tree portfast options
uplinkfast Enable UplinkFast Feature
(config)# spanning-tree vlan ?
(config)# spanning-tree vlan 2
max-age Set the max age interval for the spanning tree
priority Set the bridge priority for the spanning tree
root Configure switch as root
<cr>
primary Configure this switch as primary root for this
spanning tree
(config)# int fa0/1
(config-if)# spanning-tree cost ?
·Fine-tuning of the network performance.
Bridge Protocol Data
Units(BPDUs) are sent
new switch, new route,
on.
forward or blocking
two paths to a
addresses on other side of the bridge, and
forwards data frames that are destined for
other networks.
MAC addresses
each port, and forwards as required.
Src: MAC1Dest: MAC4
Mac Address Table
----------------------------