spanning-tree port cost is of local significance

When you are tuning spanning tree topology, to force a port into blocking or forwarding mode.

Increasing the port cost on a switch makes it less desirable for that switch and if its cost is higher than the current route, this port will move from forwarding to blocking.

p19s3#sh spanning-tree vlan 4 | i Int
Interface Fa0/3 (port 15) in Spanning tree 4 is FORWARDING
Interface Fa0/5 (port 17) in Spanning tree 4 is BLOCKING
Interface Fa0/6 (port 18) in Spanning tree 4 is BLOCKING

p19s3(config-if)#int f0/3
p19s3(config-if)#spanning-tree vlan 4 cost 57

p19s3#sh spanning-tree vlan 4 | i Int
Interface Fa0/3 (port 15) in Spanning tree 4 is BLOCKING
Interface Fa0/5 (port 17) in Spanning tree 4 is LISTENING
Interface Fa0/6 (port 18) in Spanning tree 4 is BLOCKING

By looking at the network topology you can count the hops to the root through the path you prefer, and set the cost of the current port forwarding traffic to a higher value.

Each hop cost is different depending on the link speed.

MST configured switches represent one giant virtual switch so you do not need to count hops inside MST.

MST - IST - CST - PVST all the confusing terms.

PVST - Per VLAN Spanning Tree

• ·         One spanning tree instance per vlan.
• ·         Can achieve load balancing.
• ·         CPU resource intensive, multiple vlans and few logical topologies.

CST – Common Spanning Tree - 802.1q

• ·         One spanning tree for all VLANs.
• ·         No load balancing.
• ·         CPU is spared.

MST - Multiple Spanning Tree – 802.1s

• ·         Combines best of PVST and CST.
• ·         Multiple VLANs mapped to a spanning tree instance.
• ·         Can achieve load balancing and Spare the cpu.
• ·         Mandates that an MST bridge be able to handle IST and one or more MSTIs.

MST Region

·         Maintains the mapping of VLAN to STP instance.

·         Each MST region switches share same config
(MST Region name, revision number, VLAN-to-STP mapping).

·         A digest of the VLAN-to-STP is sent in the BPU if the received digest
matches the local digest the switch port is in the region,
if it differs the switch knows it’s a boundary port.

IST – Internal Spanning Tree

·         Allows for interoperation between MST and CST.

·         IST represents the entire MST region as a virtual switch running CST.

·         Sends BPDU outside of the MST region.

·         IST is MSTI 0

MSTI - MST Instances

·         MSTIs are RSTP instances that run only inside the MST region.

·        Does not send BPDUs outside of the region.


__________________________________________________________________

The relation between them and how trees are formed.

This is intended to be a summary.
for more details refer to Understanding MST

Actual Link speeds

The actual packet per second transmitted goes down as the packet size increases.

At 86 byte packet you can get the expected speed.


At the 1500 byte packet size a 10 Gb/s operates as a 1 Gb/s 
                                               1 Gb/s operates as a 100 Mb/s
                                               100 Mb/s as a 10 Mb/s
                                               10 Mb/s as a 1 Mb/s

What is line rate ?
The interfaces of a network device are said to operate at line rate when the device is capable of forwarding packets, regardless of size.



Ref: http://www.cisco.com/web/about/security/intelligence/network_performance_metrics.html

Traffic is slow in one direction

One thing to look for if network traffic is slow in only one direction, is as you might guess...Duplex mismatch.

Most likely you will find a link that is Half-duplex on one end and Full-duplex on the other.

A possible cause is speed/duplex misconfiguration, that lead to a mis-negotiation.

By consequence you will definitely see a lot of collisions on the interface as well as input or output errors, depending on which side is half/full duplex.

Hope that helps.

Cisco switch naming convention

Hello,

I thought I share this



WS-C3560X-24T-L

WS  -  (C for cisco)Model Name - (Number of ports)(Ports type)-Feature set

WS
for Workgroup Switch
quoting  http://www.avforums.com/forums/networking-nas/545745-what-does-ws-stand-cisco-equipment.html

Ports type:
PF    PoE+ (not sure about the F yet)
P      PoE+
S      SFP
W     wireless
G     Gigabit ports (ex: C2960G vs C2960)


Feature Set :
L     Lan base feature set
S     IP base feature set
E     IP services feature set

Double VLAN tagging ?

If the service provider extends your vlan, can you split it into multiple internal VLANs.

For sure !!

the feature is called Stacked VLAN processing (Cisco)

more info http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/qinq.html

Dell compellent powerconnect

Bizzare !!

the out-of-band interface is how you are supposed to manage these switches.

while specifying the ip address you define the gateway the command goes

(config)#interface out-of-band

(config-if)#ip address 192.168.252.108 255.255.255.0 ?

Press enter to execute the command.
Enter the Gateway.





I was troubleshooting other subnets not able to ping to the out-of-band interface.

looking at the show run it looked perfectly ok.


the solution after a couple of hours was to put the ip address of the out-ofband interface without defining the gateway then putting the whole command !!

I could not believe my eyes !

(config-if)#ip address 192.168.252.108 255.255.255.0 192.168.252.1

(config-if)#ip address 192.168.252.108 255.255.255.0

(config-if)#ip address 192.168.252.108 255.255.255.0 192.168.252.1


and boom

Délai d'attente de la demande dépassé.
Délai d'attente de la demande dépassé.
Délai d'attente de la demande dépassé.
Délai d'attente de la demande dépassé.
Délai d'attente de la demande dépassé.
Délai d'attente de la demande dépassé.
Réponse de 192.168.252.108 : octets=32 temps<1ms TTL=62
Réponse de 192.168.252.108 : octets=32 temps<1ms TTL=62
Réponse de 192.168.252.108 : octets=32 temps=4 ms TTL=62
Réponse de 192.168.252.108 : octets=32 temps<1ms TTL=62
Réponse de 192.168.252.108 : octets=32 temps<1ms TTL=62
Réponse de 192.168.252.108 : octets=32 temps<1ms TTL=62


one thing I found helpful before unclogging the pings is to see the if the switch receives the ICMP echo requests.


show ip traffic does that

show ip traffic


IpInReceives................................... 118177
IpInHdrErrors.................................. 0
IpInAddrErrors................................. 4423
IpForwDatagrams................................ 1412
IpInUnknownProtos.............................. 0
IpInDiscards................................... 0
IpInDelivers................................... 102766
IpOutRequests.................................. 7368
IpOutDiscards.................................. 0
IpOutNoRoutes.................................. 180
IpReasmTimeout................................. 60
IpReasmReqds................................... 0
IpReasmOKs..................................... 0
IpReasmFails................................... 0
IpFragOKs...................................... 1
IpFragFails.................................... 0
IpFragCreates.................................. 3
IpRoutingDiscards.............................. 0

IcmpInMsgs..................................... 176
IcmpInErrors................................... 0
--More-- or (q)uit
IcmpInDestUnreachs............................. 0
IcmpInTimeExcds................................ 0
IcmpInParmProbs................................ 0
IcmpInSrcQuenchs............................... 0
IcmpInRedirects................................ 0
IcmpInEchos.................................... 124 <<<<<<<<<<<<<<
IcmpInEchoReps................................. 52


I hope this helps someone out there.

S