Flash to See Spanning Tree Protocol Algorithm
Rules:
1. one ROOT Bridge per broadcast domain;
2. one ROOT PORT per NRB (non-root bridge);
3. one DESIGNATED PORT per segment;
4. non-DESIGNATED PORTS are not used;
Below you can see the STP algorithm in action:
or expand the flash file to see it bigger.
Different Types of Memory That a Computer Uses
The different types of memory that a computer uses, in order of fastest to slowest, are as follows:
- memory inside CPU – L1 cache
- memory in the processor housing – L2 cache
- memory on the motherboard – RAM
- hard drive space that is used as memory – virtual memory
Cache
Cache is a much faster memory that stores copies of the data from the most frequently used main memory locations.
So when the CPU needs to access the data, first it checks the cache to see if it exists there. If so the processor will read the information from the cache, which is much faster than accessing it from the main memory.
There are three three independent caches:
– an instruction cache to speed up executable instruction fetch;
– a data cache to speed up data fetch and store;
– a translation lookaside buffer (TLB) used to speed up virtual-to-physical address translation for both executable instructions and data;
Data cache is usually organized as a hierarchy of more cache levels:
- L1;
- L2;
- L3;
- L4;
- …
Read more at: Wikipedia Multi Level Caches
When to use Straight-Through cable and when to use Crossover cable
Devices Connected with Crossover and Straight-Through cables
On the left hand side are devices that use straight-through cable and on the right hand side are devices that use crossover cable.
These are the devices that use a straight-through cable:
- Switch – Router
- Switch – PC
- Switch – Server
- Hub – PC
- Hub – Server
These are the devices that use a crossover cable:
- Switch – Switch
- Switch – Hub
- Hub – Hub
- Router – Router
- Router – PC
- Router – Server
- PC – PC
But nowadays this standard is becoming obsolete due to the fact that Auto-MDIX (automatic medium-dependent interface crossover) technology let devices to choose between port signals. This means that you don’t need to know anymore what type of cable you must use when connecting two devices.
Commands not supported in Packet Tracer 5.2
- ip router isis
- neighbor A.B.C.D (under router ospf)
- clear ip ospf process
- area x range (under router ospf)
- summary-address (under router ospf, on ASBR)
- show ip ospf virtual-links
- redistribute rip subnets metric 10 (under router ospf)
- auto-cost reference-bandwidth 1000 (under router ospf)
- ip multicast-routing
- ip pim sparse (under interface)
- router bgp AS_NUMBER
- ipv6 address (under interface)
- key chain (under config)
- ip rip (under interface)
- …
OSPF Process in Packet Tracer
When clearing the OSPF process in Packet Tracer instead of using the command clear ip ospf process, because it is not supported by Packet Tracer, save your config using copy ru sta and then reload, wait for the router to reload and the use sh ip o n.
And be patient because the DR election will take more time in Packet Tracer than in real life.
OSPF Network Types
- Non-Broadcast (NBMA) – RFC Standard
- Point-to-Multipoint – RFC Standard
- Point-to-Point – CISCO Proprietary
- Broadcast – CISCO Proprietary (you don’t have to statically configure the neighbs)
- Point-to-Multipoint, Non-Broadcast – CISCO Proprietary (same as P-M, but you have to statically configure the neighbs)
Disable all IP addresses from Router Interfaces
Substitute the interfaces with your own
ena
conf t
int l0
no ip add
int fa0/0
no ip add
int s2/0
no ip add
int s3/0
int s0/0/0
no ip add
int s0/0/1
no ip add
int s0/1/0
no ip add
int s0/1/1
no ip add
no router rip
no router ospf
end
sh ru
copy ru sta
No IP Domain Lookup
If you want to disable DNS resolving when you mistype a command this is what you should do:
ena
conf t
no ip domain-lookup
end
sh ru
copy ru sta
OSPF in Single Area
A router is a DR until it is rebooted.
Default OSPF net type for
- ethernet interface – broadcast
- serial interface – non broadcast
OSPF in Multi Areas
Internal Router – all interfaces are confined in the same area
ABR – Area Border Router – one interface in Area 0 (backbone) and another one in nonbackbone area
ASBR – Autonomous System Boundary Router – A router that connects to outside world
LSA Types
- Type 1 – O – R link LSA – flooded into an area
- Type 2 – O – net link LSA – flooded to whole area
- Type 3 – O IA – net summary link LSA – generated by ABR – sent between areas
- Type 4 – O IA – AS external ASBR summary link LSA – sent from ABR to ASBR
- Type 5 – [O E1|O E2] – external link LSA – flooded throught the AS by ASBRs
- Type 7 – NSSA external LSA – by ASBR residing in NSSA
How to remember what type is used by ABR or ASBR ?
- ABR – 3 letters => LSA Type 3
- ASBR – 4 letters => LSA Type 4
and the other you know them.
Areas
- Ordinary or Standard Area – this area connects to backbone
- Stub Area
- NO EXT SUMMARY Routes = NO Type 5 LSAs
- use of default route
- used in Hub-and-Spoke design
- Totally Stubby Area (or Total Stub Area)
- NO SUMMARY LSAs and NO EXT SUMMARY Routes = NO 3,4,5
- use of default route (network is 0.0.0.0)
- totally Cisco shop
- NSSA
- used when conn to ISPs or when redi is reqed
- NO 4 or 5 LSA, YES for LSA 7
- @NSSA ABR LSA 7 is translated in LSA 5
- RFC 1587 “The OSPF NSSA Option”
- Backbone Area (Area 0)
- can propagate all LSAs except LSA 7
Limitations
- 50 Rs per area;
- 60 Neighbs per R;
- 3 areas per R;
- a R may NOT be a DR or BDR for more than 1 LAN.
STUB and Totally Stubby Areas limitations
- NO EXT routes are allowed;
- NO virtual links are allowed;
- NO redi is allowed;
- NO ASBR Rs are allowed;
- the area is NOT the backbone area;
- All Rs are configed to be STUB Rs.
Commands
default-information originate //+ use of a default route
area range //only on ABRs
summary-address //only on ASBRs
//ASBR performs route redi
I kinda understood what is all about with ABR or ASBR, LSA Types, NSSA, stub and stuff. But it will take me some OSPF configs to understand how it works.
Cisco Packet Tracer Skills Assessment Environment Check
