lec1 lan switching
DESCRIPTION
TRANSCRIPT
Session 1
COMP 1161: Adv. Network and Security
Switching Technologies
OverviewAddress learningForwarding or filteringLooping avoidance – Spanning
Tree ProtocolLAN switch types
Switching Technologies
Overview – layer 2 switchAdvantages
Hardware based (ASIC)Wire speedLow latencyLow cost
DisadvantagesCan not break up broadcast domainPerformance issueNetwork size limitation
Switching Technologies
Comparison between switches & bridgesBridge – software based, one STP
per bridge, up to 16 portsSwitch – hardware based, many
STP, hundreds of ports
Switching Technologies
Switching functionsAddress learningForward/filter decisionsLoop avoidance
Switching Technologies
Address learning - Layer-2 switches and bridges remember the source hardware address of each frame received on an interface and enter this information into a MAC database.
Forward/filter decisions - When a frame is received on an interface, the switch looks at the destination hardware address and finds the exit inter-face in the MAC database.
Switching Technologies
Switching Technologies
Loop avoidance - If multiple connections between switches are created for redundancy, network loops can occur. The Spanning-Tree Protocol (STP) is used to stop network loops and allow redundancy Broadcast storm Multiple frame copies Thrashing(constantly updating the MAC filter table with same
SA) Multiple loops(generating throughout an internetwork)
Switching Technologies
Switching Technologies
Switching Technologies
STP (Spanning Tree Protocol)Root bridge – reference point, the
lowest bridge ID Root port – the port with the
lowest cost to the root bridgeDesignated port – root bridge
ports and non root bridge forwarding ports
Non root bridge
Switching Technologies
STP ruleOne root bridge per network
subnet/VLANOne root port per non-root bridgeOne designated port per segmentAll ports of root bridges are
designated ports
Switching Technologies
Election rule – through BPDURoot bridge – highest priority
(lowest priority value), lowest MAC address
Root port – lowest cost to the root bridge
Designated port – all root bridge ports, lowest cost to the root bridge, bridge ID
Switching Technologies
Switching Technologies
Switching Technologies
STP port statesBlocking – not forward frames but
listen to BPDU (stable state)Listening - only receive BPDULearning – learning MAC
addresses, build MAC tableForwarding – send and receive
data (stable state)
Switching Technologies
Switching Technologies
LAN switch types Store and forward - the complete data frame is received
on the switch’s buffer, a CRC is run, and then the destination address is looked up in the MAC filter table.
Cut through - the switch only waits for the destination hardware address to be received and then looks up the destination address in the MAC filter table.
Fragment free - the default for the Catalyst 1900 switch, it is sometimes referred to as modified cut-through. Checks the first 64 bytes of a frame for fragmentation (because of possible collisions) before forwarding the frame.
Switching Technologies
Switching Technologies