1. What is error disabled port in switching and what is dynamic desirable mode?
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.
2. Explain the function of a rendezvous point?
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.
3. What is the purpose of the interface command ip multicast spares-dense-mode?
Used with PIMSM Auto-RP and version 2. If the RPs fail, the router reverts to dense mode.
4. What is the range of IP multicast addresses?
224.0.0.0-239.255.255.255
5. Describe the operation of Anycast RP.
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.
6. What protocols do switches use to prevent the broadcasting of multicast traffic?
CGMP and IGMP Snooping
7. Why are the Cisco multicast routing protocols referred to as protocol independent?
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 = 224.0.64.12
1110 0000 1000 0000 0100 0000 1100 = 224.128.64.12
1110 0001 0000 0000 0100 0000 1100 = 225.0.64.12
9. What is the multicast Ethernet address for IP address 227.128.64.12?
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 227.128.64.12 is 01 00 5E 00 40 0C.
10. Explain the difference between dense mode and sparse mode multicast.
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.
12. What are the four general types of BGP attributes?
Well-known mandatory, well-known discretionary, optional transitive, and optional nontransitive.
13. Why is BGP a better choice for Internet routing than the IGPs?
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.
14. What is the major difference between BGP and IGP route summarization?
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.
15. Why does IBGP require a full mesh?
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.
16. Name two methods for reducing the number of IBGP connections.
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.
18. What is the first thing that BGP checks to determine if a prefix is accessible?
BGP checks the NEXT_HOP attribute to determine if the NEXT_HOP is accessible or in the IP routing table.
19. Name all the ways for installing a prefix in the BGP 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
20. What is the order of preference for the BGP attributes AS_PATH, LOCAL_PREF, MED, and WEIGHT?
WEIGHT, LOACL_PREF, AS_PATH, MED
21. What is the purpose of the metric or MULTI_EXIT_DISC attribute?
MED is used to prefer a path into an autonomous system. A lower MED value is preferred.
22. What is the scope of the LOCAL_PREF attribute?
The LOCAL_PREF attribute is advertised throughout the autonomous system.
23. What is the purpose of the LOCAL_PREF attribute?
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).
24. What is the scope of the WEIGHT attribute?
WEIGHT has only local significance and is not advertised to BGP peers.
25. What is the purpose of the WEIGHT attribute?
If a router has more than one route to the same IP prefix, the best path is the one with the highest WEIGHT value.
26. What is the purpose of the AS_PATH attribute?
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).
27. Describe four differences between the operation of IBGP and EBGP.
► 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.
28. What is the difference between an IS-IS narrow and wide metric?
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.
29. Compare IS-IS metrics with OSPF metrics.
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.
31. What is the difference between the types of routes allowed by default into IS-IS and OSPF areas?
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.
32. What is the OSPF counterpart to a Level 1-2 IS-IS router?
An Area Border Router (ABR).
33. In IS-IS, what is the function of a Level 1-2 router?
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.
34. What is the OSPF counterpart to Level 1 routing?
Intra-area routing.
35. In IS-IS, what does Level 1 routing mean?
Level 1 routing is routing between destinations in the same IS-IS area
