Error disabled when a port is error disabled, it is effectively shut down and no traffic is sent or received on that port. such as, with BPDUGourd you said this port must not send bpdu or receive it as well .. so when this port receive bpdu message it will convert to error disable .. and to make it up again just write (No Shut) command.
Dynamic Desirable:- it is kind or DTP (dynamic trunk protocol) in short, negotiation with front port to be trunk.
A RP is the focal point for multicast traffic. Traffic is forwarded to the RP from multicast sources. The RP then forwards traffic to multicast receivers.
Used with PIMSM Auto-RP and version 2. If the RPs fail, the router reverts to dense mode.
Two or more RPs are configured with the same IP address. The IP addresses of the RPs are advertised using a unicast IP routing protocol. Each multicast router chooses the closest RP. If an RP fails, the routers switch to the next nearest RP after the unicast IP routing protocol converges. The MSDP is used between RPs to exchange active multicast source information.
CGMP and IGMP Snooping
Multicast forwarding decisions are based on the entries in the unicast IP routing table. Multicast is not dependent on how the unicast IP routing table was built; you can use any dynamic interior routing protocol, static routes, or a combination of the two.
The low order 32 bits of the IP address determine the multicast Ethernet address. The first four bits are always 1 1 1 0 and the next five bits can be anything. Therefore, the IP multicast addresses that map to the multicast Ethernet address of 01 00 5E 00 40 0C are
1110 0000 0000 0000 0100 0000 1100 = 18.104.22.168
1110 0000 1000 0000 0100 0000 1100 = 22.214.171.124
1110 0001 0000 0000 0100 0000 1100 = 126.96.36.199
The base Ethernet multicast address is 01 00 5E 00 00 00. The first byte of the IP multicast address is not used. If the second byte is greater than 127, subtract 128, giving a value of 0. The third and fourth bytes of the IP address are used as is after converting to hex. Their values, in hexadecimal, are 40 and 0C. So the Ethernet multicast address for the IP multicast address 188.8.131.52 is 01 00 5E 00 40 0C.
Dense mode multicast assumes all multicast neighbors want to receive all multicast traffic unless the neighbors have specifically pruned the traffic. Sparse mode multicast assumes multicast neighbors do not want to receive multicast traffic unless they have asked for it. Dense mode uses source-based delivery trees while sparse mode uses shared delivery trees where traffic is first sent to an RP.
Unicast IP packets are forwarded based on the destination IP address. Multicast packets are forward based on the source IP address. If a multicast packet is received on the interface used to send a unicast packet back to the source, the multicast packet is forwarded to multicast neighbors. If the multicast packet is received on an interface that would not be used to send a unicast IP packet back to the source, the packet is discarded.
Well-known mandatory, well-known discretionary, optional transitive, and optional nontransitive.
RIP version 1 and IGRP are classful protocols and do not advertise subnet mask information. RIP version 2 has a limited network diameter of 15 hops. EIGRP, OSPF, and IS-IS use computational intensive algorithms for determining a shortest path. BGP relies on simple techniques for best path selection and loop detection, and can handle the number of network prefixes required for Internet routing.
When a summary address is created with an IGP (EIGRP, OSPF, and IS-IS), the specific routes of the summary are not advertised. BGP advertises the summary, and all the specific routes of the summary unless they are specifically suppressed.
BGP uses the AS_PATH attribute for loop detection. If a router sees its own AS number in a BGP advertisement, the advertisement is dropped. IBGP routers have the same AS number so the AS number cannot be used for loop detection. IBGP neighbors will not advertise prefixes learned from one IBGP neighbor to another IBGP neighbor; therefore, a full mesh is required.
Route reflector and confederation.
Synchronization is a property of IBGP. An IBGP router will not accept a prefix received from an IBGP neighbor if the prefix is not already in the IP routing table.
BGP checks the NEXT_HOP attribute to determine if the NEXT_HOP is accessible or in the IP routing table.
► Using the network command to transfer a router from the IP routing table to the BGP routing table
► Redistributing routes from the IP routing table to the BGP routing table
► Learned from a BGP neighbor
WEIGHT, LOACL_PREF, AS_PATH, MED
MED is used to prefer a path into an autonomous system. A lower MED value is preferred.
The LOCAL_PREF attribute is advertised throughout the autonomous system.
If a router has more than one route to the same IP prefix, the best path is the one with the highest LOCAL_PREF (assuming the WEIGHT attribute for the routes is equal).
WEIGHT has only local significance and is not advertised to BGP peers.
If a router has more than one route to the same IP prefix, the best path is the one with the highest WEIGHT value.
If a router has more than one route to the same IP prefix, the best path is the one with the shortest AS_PATH (assuming other BGP attributes are equal).
► IBGP is the protocol used between routers in the same autonomous system. EBGP is the protocol used between routers in different autonomous systems.
► IBGP routes must be synchronized before they can be transferred to the IP routing table (unless synchronization is disabled).
► EBGP sets the next hop attribute to the IP address of the interface used to communicate with the EBGP peer. The next hop attribute is not modified when an IBGP router advertises a prefix to an IBGP peer if the prefix was learned from an EBGP neighbor.
► EBGP advertises all prefixes learned from an EBGP neighbor to all other EBGP neighbors. IBGP routers do not advertise prefixes learned from one IBGP neighbor to another IBGP neighbor.
A narrow metric uses 6 bits for the interface metric and 10 bits for the path metric. A wide metric uses 24 bits for the interface metric and 32 bits for the path metric.
An OSPF interface metric is determined from the interface bandwidth. By default, all IS-IS interface metrics are equal to 10.
Redistribution of Level 2 routes into an area as Level 1 routes.
By default, all routes are advertised into all OSPF areas. This includes interarea OSPF routes and external routes that have been injected into OSPF. By default, IS-IS does not advertise interarea or external routes into an area, but injects a default route.
An Area Border Router (ABR).
A Level 1-2 router has two IS-IS databases. The Level 1 database is used for routing to destinations within the router's configured area. The Level 2 database is used to route between destinations in different areas.
Level 1 routing is routing between destinations in the same IS-IS area
OSPF has a backbone area or area 0. All nonzero areas must be connected to the backbone through a router or a virtual link. IS-IS has a backbone area made up of a contiguous chain of Level 2 capable routers.
The loopback address written in dotted decimal and using three digits for each byte has a value of 135.077.009.254. The system ID is 13.50.77.00.92.54.
An NSAP address has a length of 8 to 20 bytes and consists of three components:
► One to 13 byte area ID
► Six byte system ID
► One byte NSAP selector that is always equal to zero for a router
EIGRP has an administrative distance of 90.
IGRP has an administrative distance of 100.
OSPF has an administrative distance of 110.
RIP has an administrative distance of 120.
Therefore, the EIGRP route is preferred.
The number of OSPF databases on a router is equal to the number of OSPF areas configured on the router.
42. The following OSPF routes originate in OSPF area 1:
What is the command to summarize these routes on the ABR between area 1 and the backbone?
Area 1 range 184.108.40.206 255.255.255.192
By default, the cost of an OSPF interface is 100,000,000/(Interface Bandwidth). The constant 100,000,000 can be changed using the auto-cost reference-bandwidth command.
To connect a nonzero area to the backbone if the nonzero area becomes disconnected from the backbone. A virtual link can also be used if the backbone, or area 0, becomes discontiguous.
First, calculate the shortest path to an ABR.
Second, calculate the shortest path across area 0 to an ABR that is attached to the destination area.
Third, calculate the shortest path across the destination area from the ABR to the destination network.
The router with the highest interface priority will be the router ID. If all the interface priorities on the multi-access network are the same, the router with the highest router ID will be the DR.
If physical interfaces are only used, the OSPF router ID is the highest IP address assigned to an active physical interface. If loopback interfaces are used, the OSPF router ID is the highest IP address assigned to a loopback interface. If the router-id command is used with the OSPF configuration, the address used with this command will be the router ID.
OSPF routes are summarized on an ABR. External routes are summarized on an ASBR.
Intra-area, interarea, E1, E2, N1, and N2.
ABR, internal router, and ASBR.
An E1 route contains the OSPF cost to reach the ASBR plus the cost from the ASBR to the external route. An E2 route contains only the cost from the ASBR to the external route.
OSPF intra-area routes and a default route. External routes from ABRs are blocked, and external routes from ASBRs are converted to N1 or N2 routes.
OSPF intra-area and interarea routes, and possibly a default route. External routes from ABRs are blocked, and external routes from ASBRs are converted to N1 or N2 routes.
OSPF intra-area routes and a default route. OSPF interarea and external routes are not advertised into a totally stubby area.
OSPF intra-area and interarea routes, and a default route. External routes are not advertised into a stub area.
OSPF databases on routers in the same area must be identical. If route summarization was allowed within an area, some routers would have specific routes and some routers would have summary routes for routes in the area. If this were allowed, the databases for the area would never agree.
Areas allow the design of a hierarchical network. Routes can be summarized or blocked in an area to reduce the amount of routing information on internal OSPF routers.
You need to examine the third byte because that is the byte where the four prefixes differ:
0 = 0 0 0 0 0 0 0 0
32 = 0 0 1 0 0 0 0 0
64 = 0 1 0 0 0 0 0 0
96 = 0 1 1 0 0 0 0 0
The last 7 bits are irrelevant, so the mask is 1 0 0 0 0 0 0 0 and the EIGRP command is ip summary-address eigrp 1 10.1.0.0 255.255.128.0.
The reported distance to a route that is sent to another router is the feasible distance on the reporting router. Feasible distance is the reported distance plus the metric between the receiving and reporting routers. The route with the lowest feasible distance is the successor. Any routes with a reported distance that is less than the feasible distance are feasible successors.
The passive state means that a router has a successor for a route. The active state means that a router does not have a successor or feasible successor for a route and is actively sending queries to neighbors to get information about the route.
Classless routing protocols advertise subnet mask information along with the network prefixes. Classful routing protocols do not. Therefore, for a classful protocol, all subnets for the major network number being used must be the same length. Also, classful protocol cannot support discontiguous networks prefixes.
64 because 2 bits are needed for the hosts on the network, leaving 6 bits for the subnet.
172.16.53.97 through 172.16.53.126
65. Using the following routing table, determine the best route to reach the host at address 220.127.116.11.
Network Output Interface
18.104.22.168/8 Serial 0
22.214.171.124/11 Ethernet 1
126.96.36.199/22 Ethernet 2
188.8.131.52/11 because it matches more network bits than 184.108.40.206/8. Network 220.127.116.11/22 and 18.104.22.168/22 do not match on the network address.
22.214.171.124/27 and the subnets are:
0111 0011 0100 0010 0001 0101 2
111 011 100 010 001 101
Convert each octal digit into three binary digits, and then convert the binary result to hexadecimal.
001 010 011 100 101 110 111 000
0010 1001 1100 1011 1011 1000
Answer is True
Convert to dotted hexadecimal first, and then convert each hexadecimal number pair to decimal.
A2.F5.9D.8B then 126.96.36.199
Answer: FA 16 = 250 10, CE16 = 20610, 1216 = 18 10, and 34 16 = 52 10
FACE1234 16 = 250.206.18.52 dotted decimal
224, 252, 128, 240, and 63 (64 - 1)
The last four digits are the used at the access layer to identify a particular telephone. The next three numbers are used at the distribution layer to identify an exchange that services several phone numbers. The area code is used at the core level for routing between different regions.
The street name and number are the access layer components. The city name is the distribution layer component. The state name is the core layer component.
The source address is not used unless the letter needs to be returned to the sender. Using the destination address, the access level post office in New York examines the state, city, and street information to determine if it is directly connected to the destination. If not, the letter is sent to the distribution layer post office using a default route. The distribution layer post office also examines the state, city, and street information to determine if it is directly connected to an access layer post office servicing the particular street. If it isn't, the letter is routed to the core level using a default route. The core level post office examines the state name, and if the state name does not equal New York, the letter is delivered to the core post office for the state of California. The California core post office delivers the letter to the distribution post office that handles the city of San Diego. The San Diego distribution post office delivers the letter to the access post office that handles the destination street. Finally, the access level switch delivers the letter to the proper destination.
The airport system. At the core routing level, there are major hub airports such as Denver, Chicago, New York, and Atlanta. The core airports are responsible for routing people and cargo to major geographical areas. Core airports connect with regional airports that serve a specific area; regional airports are at the distribution layer. Finally, to reach your final destination, you can take a bus, a cab, a train, or rent a car. This can be considered the access layer.
Using multiple protocols is modular and allows changes to one protocol without affecting the others. For example, if the addressing protocol is dependent on the delivery protocol, changes to one would imply changes need to be made to the other.
If a delivery system is not divided into access, distribution, and core layers, every point in the system needs to maintain every possible destination address to make a delivery decision. The use of a layered system means each layer needs only the information necessary to deliver to the next layer, either above or below.
At the core layer in the postal system, the only information that is needed to make a routing decision is the state or city/state information. The specific street names and street numbers are hidden, the core layer does not need this information. At the core layer in the telephone system, the area code is used to make a routing decision. The specific exchange or last four digits of the phone number are not needed, or hidden, from the core layer.
Routing moves a letter or telephone call to the access layer (as in a street or telephone exchange). Switching makes the final delivery. A switching decision is made on the part of the address that is not used in routing (as in the street number or last four digits of a phone number).
A default route is used if there is not a specific entry in the routing table for the destination.
A postal address has three components that can be used to deliver mail: state, city, and street. A phone number has an area code and exchange. At the core layer, mail can be delivered to the next post office based on only the state or city and state information. A phone number is delivered at the core layer based on the area code.