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CCNP

Instructions:

Answer 50 questions in 15 minutes.
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Match each statement with the correct term.
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This is a study tool. The 3 wrong answers for each question are randomly chosen from answers to other questions. So, you might find at times the answers obvious, but you will see it re-enforces your understanding as you take the test each time.

1. IOS command to configure a rendezvous point .
Router#(config) ip pim send-rp-announce interface_type scope ttl group-list access-list Multicast
MOSPF DVMRP CBT PIM Dense Mode PIM Sparse Mode PIM Sparse-Dense Mode Multicast
Local preference Atomic Aggregate BGP
'Periodic Flood and Prune.' Initially floods multicast traffic (received on its RPF) to all its PIM neighbors. Traffic that arrives back at the router via a non-RPF is discarded. Prune messages are sent on all non-RPF interfaces and RPF int

2. Describe how PIM-SM operates.
This should only be for ISP's An improperly configured AS (that is not meant to be a transit) could inadvertently become one. BGP
Class D address space First bits are ALWAYS 1110 224.0.0.0 - 239.255.255.255 Multicast
RFC 2362 Pull model - traffic only forwarded to the parts of the network that need it. Sender registers with the RP which is a proxy to group members. Last hop routers to receiver knows the group RP IP address and sends a (* -G) join toward
IGMP is a layer 3 protocol Switches treat multicast just like broadcast (forward out all ports except the one one which is was received) By definition a pure layer 2 devices do not have a mechanism to see IGMP packets or facilitate the rela

3. What is the IBGP Split Horizon rule? What does this accomplish?
Routes learned through IBPG are never propogated to other IBGP speakers. This is a loop prevention mechanism. BGP
Update from client peer - sends update to all non-client peers and client peers except for originating peer. Update from non-client peer - send update to all clients in the cluster. Update from EBGP peer - update sent to all client peers an
Links = n(n-1)/2 BGP
Concatenation of the first (high order) 25 bits of the reserved MAC address range with the last (low order)23 bits of the multicast group IP address. 5 bits of overlap allowing for 32 address (2^5) for each multicast MAC address. 25 bits + 23 bits RR allow the propagation of routes learned by IBGP to other IBGP peers without having a full mesh of IBGP
When not all routers within a transit AS have consistent routing information - due to not running BGP or misconfiguration or BPG speakers. Routing information is advertised but since not all routers within AS can reach the destination traffic is halt
When using the classful method - at least one subnet of the classful range must reside in the IP routing table. When using the classless method the exact subne
Router#(config) router bgp 1 Router#(config-router) neighbor 192.168.1.1 remote-as 1 Router#(config-router) network 192.168.0. mask 255.255.255.0 BGP

5. State how IGMPv1 operates.
* = Best route > = Route has been inserted into the routing table BGP
RFC 1112 Sends membership query every 60 - 120 seconds to 224.0.0.1 Hosts send membership report in response to the query Multicast
Variable length sequence of path attributes Attribute Type -1 byte flag field - 1 byte type code Attribute Length Attribute Value Attribute flag field = 0000 0000 W | O - T | N - P | C BGP
The neighbor expects to see the updates from the source address configured in the neighbor statement. BGP

6. What effect will placing a route to null0 have on BGP?
BPG will find an exact match. BGP
Using a Distribute List to filter outbound routing updates. BGP
224.0.0.1 - All systems 224.0.0.2 - All routers 224.0.0.4 - DVMRP routers 224.0.0.5 - All OSPF 224.0.0.6 - All OSPF DR 224.0.0.9 - RIP v2 routers 224.0.0.10 - EIGRP routers 224.0.0.13 - PIM routers 224.0.0.15 -
Reverse Path Forwarding is the forwarding logic multicast of multicast. It is the opposite of unicast in that is forwards AWAY from source as opposed to towards the receiver. Multicast

7. What are the commands to enable multicast routing on a router?
Router#(config) ip pim send-rp-announce interface_type scope ttl group-list access-list Multicast
Since IBGP learned routes are never propagate to other IBGP peer - full mesh of IBPG peers is required within an AS. THIS IS NOT SCALABLE. RR allow the propagation of routes learned by IBGP to other IBGP peers without having a full mesh of IBGP
Globally: Router(config)# ip multicast-routing Per Interface: Router(config-if)# ip pim dense-mode Enabling PIM on an interface also enables IGMP operation on that interface. Multicast
Local preference Atomic Aggregate BGP

8. What is the solution to establishing neighbor relationships when multiple paths exist? What are the command to establish this? What command to tell R1 to use its loopback0 interface as the update source neighbor 192.168.1.1.
Use loopback interface to establish the neighbor. (i.e. peer to a loopback interface) Tell BGP to use the lookback interface as teh source of updates R1(config-router)# neighbor 192.168.1.1 update-source loopback0 BGP
ISP passes only default route to AS. ISP passes default route and provider owned select routes to AS. ISP passes all routes to AS. BGP
Well-known Mandatory - Must be supported and propagated. Well-known Discretionary - Must be supported; propagation optional. Optional Transitive - Marked as partial if unsupported by neighbor. Option Nontransitive - Deleted is unsuppor
SPT (S -G) consume more memory because there is an entry for each source BUT traffic is sent over optimal path to receiver. Shared distribution tree state entries (* -G) consume less CPU but may take suboptimal path to receiver. Multicast

9. Within the layer 3 multicast address space - name 3 reserved scopes and their purpose.
Language between local router interface and hosts. IGMP - ICMP - similarities TTL is usually 1; RFC states it should never leave local subnet. Creates and maintains group membership for hosts wishing to participate in a multicast grou
Loopback more resilient than physical interfaces. BGP
1. Weight - Administrative preference (Highest) 2. Local Preference - Communicated between peers within AS (Highest) 3. Self-originated - Prefer path originated locally (True) 4. AS Path - Minimize AS hops (Shortest)<
Local scoped: 224.0.0.0 - 224.0.0.255 TTL of 1; Never to leave local network - for routing protocols and other network maintenance. Global scoped: 224.0.1.0 - 238.255.255.255 MBone dynamically allocate throughout Internet Limited/

10. Which IOS command shows what version of IGMP is running?
Router#show ip igmp interface fa0/0 Multicast
Places it in the routing table. BGP
IGMP Snooping - requires special ASICS can degrade performance with it; is supported by multiple vendors. CGMP - Cisco proprietary - only work on Cisco hardware; resource friendly GMRP - Replaced by MRP; obscure Manually - Performance
R1(config-router)# neighbor 192.168.1.1 next-hop-self Cause each routers outgoing interface that the route traverse wihtin the AS (iBPG peers) to annouce itself as the 'next hop' instead of the next hop into the neighboring AS. 

11. Describe 4 multicast application models and give an example of each?
Since IBGP learned routes are never propagate to other IBGP peer - full mesh of IBPG peers is required within an AS. THIS IS NOT SCALABLE. RR allow the propagation of routes learned by IBGP to other IBGP peers without having a full mesh of IBGP
One-to-many: video distribution Many-to-many: Collaboration Many-to-one: auction - polling or data collection Few-to-many: auction - polling or data collection Multicast
Language between local router interface and hosts. IGMP - ICMP - similarities TTL is usually 1; RFC states it should never leave local subnet. Creates and maintains group membership for hosts wishing to participate in a multicast grou
The Source and Share Tree models are the working model of how the tree is built; all multicast routing protocols fit into one or both. This is the 'theory' or model. PIM-DM's operational falls in the source tree model and PIM-SM is classified an

12. How does Source and Shared Distribution Tree models related to PIM-DM and PIM-SM?

13. What are the two multicast distribution tree types models and differences?

14. How does RPF avoid routing loops?
Path Vector - policy based routing protocol. Uses BGP attributes are the 'metric'. Path it decides it based on 'hops' where hop is Autonomous Systems. BGP
Determines upstream and downstream interfaces. Uses the unicast routing table to insure that only one interface is considered to be and incoming interface for the source. RPF makes sure that if data is looped around is not forwarded. 
IANA delegates to Regional Internet Registries (RIRs): ARIN - AfriNIC - APNIC - LACNIC and RIPE NCC BGP
O Cisco only. Routes with higher weight are preferred (0 - 65535) . Paths that the router originates have 32768; other paths have default of 0. BGP

15. Explain the Origin attribute.

16. What is a BGP route reflector - What is it purpose?
AS-Path Next Hop Origin BGP
Determines upstream and downstream interfaces. Uses the unicast routing table to insure that only one interface is considered to be and incoming interface for the source. RPF makes sure that if data is looped around is not forwarded. 
BGP not designed for load balancing (by default). BGP selected the SINGLE best path to a destination and places it in the routing table; the rest are kept in the BGP Table. Paths are chosen based on policy. BGP eliminates paths until one p
Since IBGP learned routes are never propagate to other IBGP peer - full mesh of IBPG peers is required within an AS. THIS IS NOT SCALABLE. RR allow the propagation of routes learned by IBGP to other IBGP peers without having a full mesh of IBGP

17. Explain the Local Preference attribute. 

18. What is one mechanism that GURANTEES the BGP AS path is loop free?
Variable length sequence of path attributes Attribute Type -1 byte flag field - 1 byte type code Attribute Length Attribute Value Attribute flag field = 0000 0000 W | O - T | N - P | C BGP
The router will not accept a routing update that includes its AS number in the path. BGP
Local preference Atomic Aggregate BGP
RFC - 3376 Ability to filter multicast source (can be picky) IGMPv3 membership report goes to 224.0.0.22 and may include the multicast hosts it will accept or deny. Multicast

19. What command will produce the following output and What is it displaying? <img src='5d3c9233dd205ee4319ef0ac2fc07460.jpg' />
Local scoped: 224.0.0.0 - 224.0.0.255 TTL of 1; Never to leave local network - for routing protocols and other network maintenance. Global scoped: 224.0.1.0 - 238.255.255.255 MBone dynamically allocate throughout Internet Limited/
Rule: Router must be known by an IGP before it may be advertised by BGP peers. Prevents 'blackholes' when AS is a transit network and not all speaker are running BGP Should be left on it AS is a transit AS and not all routers run BGP. 
Local preference Atomic Aggregate BGP
The BGP Table Command = show ip bgp BGP

20. What are some of the obstacles with IGMP and multicast in general as it relates to layer 2/switches?
IGMP is a layer 3 protocol Switches treat multicast just like broadcast (forward out all ports except the one one which is was received) By definition a pure layer 2 devices do not have a mechanism to see IGMP packets or facilitate the rela
Dense mode interfaces are always added to the table. Sparse mode interfaces are added to the table only when periodic join messages are received from downstream routers - or when a directly connected member is on the interface Multi
Determines upstream and downstream interfaces. Uses the unicast routing table to insure that only one interface is considered to be and incoming interface for the source. RPF makes sure that if data is looped around is not forwarded. 
The BGP Table Command = show ip bgp BGP

21. What is the full mesh versus partial mesh IBGP and What are the implications of each?
The is the multicast bit. Multicast
<img src='9618cf01b9422f541fc213b74a3bd9de.png' /> Multicast
MOSPF DVMRP CBT PIM Dense Mode PIM Sparse Mode PIM Sparse-Dense Mode Multicast
Partial mesh iBPG is where not all BGP speaks within and AS have an established neighbor relationship. Full mesh is every BGP speaker has a neighbor (peer) with each other. Routing updates are not replcated in iBPG the peers do not pass i

22. What does PIM use for its multicast routing calculations?
Rule: Router must be known by an IGP before it may be advertised by BGP peers. Prevents 'blackholes' when AS is a transit network and not all speaker are running BGP Should be left on it AS is a transit AS and not all routers run BGP. 
Sends a leave message to 224.0.0.2 Router then sends a group specific query Remaining member(s) send a report so group remains active. Multicast
WD Dictates which path is preferred to exit the AS. Higher is is preferred - default is 100 on Cisco. Obviously for this to be relevant there must be multiple exit points for the route. 'Influences outbound traffic for an AS' No routing updates are sent between PIM routers. Multicast

23. What block of multicast MAC addresses belong to multicast?
Router#(config) router bgp 1 Router#(config-router) neighbor 192.168.1.1 remote-as 1 Router#(config-router) network 192.168.0. mask 255.255.255.0 BGP
0100.5e00.0000 - 0100.5e7f.ffff - IANA reserved. Multicast
ON Displayed as metric in Cisco IOS; lower is preferred. Default is 0. Indicated to external AS the preferred path into the AS. 'Influence inbound traffic to an AS' By default ONLY compares if neighbors AS is same for all routes being
Open - Version - AS - Hold Time - BGP Router ID - Optional Parameters Keepalive - Sent every 60 seconds by default; hold time 180 Seconds. Update - Information on only ONE path; Notification - When error condition detected BGP

24. What is the multicast IP address space?
Class D address space First bits are ALWAYS 1110 224.0.0.0 - 239.255.255.255 Multicast
RFC - 3376 Ability to filter multicast source (can be picky) IGMPv3 membership report goes to 224.0.0.22 and may include the multicast hosts it will accept or deny. Multicast
Sends a leave message to 224.0.0.2 Router then sends a group specific query Remaining member(s) send a report so group remains active. Multicast
One-to-many: video distribution Many-to-many: Collaboration Many-to-one: auction - polling or data collection Few-to-many: auction - polling or data collection Multicast

25. What are 2 stipulations of advertising networks BGP?

26. Explain how the multicast routing table is populated.
R1(config-router)#neighbor MyPeers peer-group R1(config-router)#neighbor 10.1.1.1 remote-as 64513 R1(config-router)#neighbor 10.1.1.1 peer-group MyPeers BGP
Dense mode interfaces are always added to the table. Sparse mode interfaces are added to the table only when periodic join messages are received from downstream routers - or when a directly connected member is on the interface Multi
Well know predefined group Directory - sd / SDP Webpage/URL Email link Multicast
Unicast uses a routing table looking and forwards towards the destination address. Multicast forwards out multiple interfaces and away from the source and towards multiple destinations using a distribution tree. Multicast

27. What are some disadvantages of multicast?
Use loopback interface to establish the neighbor. (i.e. peer to a loopback interface) Tell BGP to use the lookback interface as teh source of updates R1(config-router)# neighbor 192.168.1.1 update-source loopback0 BGP
'Periodic Flood and Prune.' Initially floods multicast traffic (received on its RPF) to all its PIM neighbors. Traffic that arrives back at the router via a non-RPF is discarded. Prune messages are sent on all non-RPF interfaces and RPF int
AS-Path Next Hop Origin BGP
Most applications rely on UDP Security issues Out of order delivery & duplicate packets are a possibility during topology changes. Lack of windowing/congestion control. Multicast

28. Describe how and IGMPv2 host leaves. What is the interaction between host and router look like?
Sends a leave message to 224.0.0.2 Router then sends a group specific query Remaining member(s) send a report so group remains active. Multicast
Local preference Atomic Aggregate BGP
Local scoped: 224.0.0.0 - 224.0.0.255 TTL of 1; Never to leave local network - for routing protocols and other network maintenance. Global scoped: 224.0.1.0 - 238.255.255.255 MBone dynamically allocate throughout Internet Limited/
Loopback more resilient than physical interfaces. BGP

29. What config would be used to configured an outbound BGP distribute list to block all routes from being advertised except ones from 192.168.0.0 /24 network to neighbors 10.1.1.1 and 10.1.1.2?
R1(config-router)#neighbor 192.168.1.1 password MyPassword OR R1(config-router)#neighbor MyPeerGroup password MyPassword BGP
Router(config-router)# neighbor 192.168.1.1 remote-as 65000 Router(config-router)# neighbor 192.168.1.1 route-reflector-client BGP
R2(config)# access-list 1 permit 192.168.0.0 0.0.0.255 R1(config-router)# neighbor 10.1.1.1 distribute-list 1 out R1(config-router)# neighbor 10.1.1.2 distribute-list 1 out BGP
(S -G) - 'S comma G'; Source sending to the group. Typically reflect a source tree but can appear on a shared tree. Traffic forwarded via the shortest path from the source. (* -G) - 'Star comma G'; Any source sending to the group. Traffic forwar

30. What are the 4 categories of BGP attributes and what do they mean?
Update from client peer - sends update to all non-client peers and client peers except for originating peer. Update from non-client peer - send update to all clients in the cluster. Update from EBGP peer - update sent to all client peers an
Well-known Mandatory - Must be supported and propagated. Well-known Discretionary - Must be supported; propagation optional. Optional Transitive - Marked as partial if unsupported by neighbor. Option Nontransitive - Deleted is unsuppor
It actually determines which networks are advertised. BGP
R1(config-router)# neighbor 192.168.1.1 next-hop-self Cause each routers outgoing interface that the route traverse wihtin the AS (iBPG peers) to annouce itself as the 'next hop' instead of the next hop into the neighboring AS. 

31. Explain the way RR handles route updates.
Router#(config) ip pim spt-threshold {rate | infinity} [group-list access-list] Multicast
* = Best route > = Route has been inserted into the routing table BGP
Members leave through attrition; no leave group message. This keep traffic flowing for a period of time even with no group members. Multicast
Update from client peer - sends update to all non-client peers and client peers except for originating peer. Update from non-client peer - send update to all clients in the cluster. Update from EBGP peer - update sent to all client peers an

32. What is the command to configure a BGP RR? 
Router(config-router)# neighbor 192.168.1.1 remote-as 65000 Router(config-router)# neighbor 192.168.1.1 route-reflector-client BGP
Sends a leave message to 224.0.0.2 Router then sends a group specific query Remaining member(s) send a report so group remains active. Multicast
EBGP will only peer to direclty connected neighbors and a loopback is considered one hop away. With eBGP peering to a loopback you must enable eBGP Multihop. R1(config-router)# neighbor 192.168.1.1 ebgp-multihop 2 BGP
OT Allows the router to 'tag' and thus implement policy based on this tag. BGP

33. What is the IOS command to check for IGMP group members? What info does it reveal?
RFC 2362 Pull model - traffic only forwarded to the parts of the network that need it. Sender registers with the RP which is a proxy to group members. Last hop routers to receiver knows the group RP IP address and sends a (* -G) join toward
Partial mesh iBPG is where not all BGP speaks within and AS have an established neighbor relationship. Full mesh is every BGP speaker has a neighbor (peer) with each other. Routing updates are not replcated in iBPG the peers do not pass i
Router#show ip igmp group Group address - interface - uptime - expires - and last reporter. Multicast
Most applications rely on UDP Security issues Out of order delivery & duplicate packets are a possibility during topology changes. Lack of windowing/congestion control. Multicast

34. How does a host learn about available multicast streams?
1. Weight - Administrative preference (Highest) 2. Local Preference - Communicated between peers within AS (Highest) 3. Self-originated - Prefer path originated locally (True) 4. AS Path - Minimize AS hops (Shortest)<
Open - Version - AS - Hold Time - BGP Router ID - Optional Parameters Keepalive - Sent every 60 seconds by default; hold time 180 Seconds. Update - Information on only ONE path; Notification - When error condition detected BGP
Bidirection PIM mode - designed for many to many applications. Source Specific Multicast (SSM) ; builds only source specific shortest path trees. Multicast
Well know predefined group Directory - sd / SDP Webpage/URL Email link Multicast

35. Name 6 multicast routing protocols.
Router(config-router)# neighbor 192.168.1.1 remote-as 65000 Router(config-router)# neighbor 192.168.1.1 route-reflector-client BGP
Dense mode interfaces are always added to the table. Sparse mode interfaces are added to the table only when periodic join messages are received from downstream routers - or when a directly connected member is on the interface Multi
BPG will find an exact match. BGP
MOSPF DVMRP CBT PIM Dense Mode PIM Sparse Mode PIM Sparse-Dense Mode Multicast

36. What are the 4 BGP packet types? What do they contain?
Member of a group: Router#(config) ip igmp join-group group-address Statically connected: Router#(config) ip igmp join-group group-address In this mode router forwards (fast switches) group packets but itself does not accept group
Works if router has multiple parallel paths to a destination. ONLY affect number of routes in IP routing table not the route selected at best in the BGP table. Will load balance across equal cost paths in EGP session. BGP
Session description & announcement. Transport session announcement via 224.2.127.254. Creation of new sessions. Multicast
Open - Version - AS - Hold Time - BGP Router ID - Optional Parameters Keepalive - Sent every 60 seconds by default; hold time 180 Seconds. Update - Information on only ONE path; Notification - When error condition detected BGP

37. Name a significant inefficiency with IGMPv1.
Most applications rely on UDP Security issues Out of order delivery & duplicate packets are a possibility during topology changes. Lack of windowing/congestion control. Multicast
Members leave through attrition; no leave group message. This keep traffic flowing for a period of time even with no group members. Multicast
16 bit number 1 to 65535 1-64511: Public AS 64512-6535: Reserved for private AS BGP
Path Vector - policy based routing protocol. Uses BGP attributes are the 'metric'. Path it decides it based on 'hops' where hop is Autonomous Systems. BGP

38. What is the difference between iBGP and eBGP?
ON Displayed as metric in Cisco IOS; lower is preferred. Default is 0. Indicated to external AS the preferred path into the AS. 'Influence inbound traffic to an AS' By default ONLY compares if neighbors AS is same for all routes being
R1(config-router)#neighbor 192.168.1.1 password MyPassword OR R1(config-router)#neighbor MyPeerGroup password MyPassword BGP
Using a Distribute List to filter outbound routing updates. BGP
EBGP is an adjacency between BGP peers in different AS; iBGP peers are in same AS. BGP

39. What are two methods of establishing a gateway of last resort?
MOSPF DVMRP CBT PIM Dense Mode PIM Sparse Mode PIM Sparse-Dense Mode Multicast
The neighbor expects to see the updates from the source address configured in the neighbor statement. BGP
Default-Network Static route BGP
Language between local router interface and hosts. IGMP - ICMP - similarities TTL is usually 1; RFC states it should never leave local subnet. Creates and maintains group membership for hosts wishing to participate in a multicast grou

40. What is the command to enable BPG authentication?
R1(config-router)#neighbor 192.168.1.1 password MyPassword OR R1(config-router)#neighbor MyPeerGroup password MyPassword BGP
BGP peer BGP
The unicast routing table. No routing updates are sent between PIM routers. Multicast
Group of BGP routers being configured that have the same update policy. Similar to a 'template'; members then assigned to the peer group. BGP

41. Explain the AS-Path attribute.

42. What special consideration is there when peering to a eBGP neighbor using a loopback? What is the solution to this?
RFC 2362 Pull model - traffic only forwarded to the parts of the network that need it. Sender registers with the RP which is a proxy to group members. Last hop routers to receiver knows the group RP IP address and sends a (* -G) join toward
Use loopback interface to establish the neighbor. (i.e. peer to a loopback interface) Tell BGP to use the lookback interface as teh source of updates R1(config-router)# neighbor 192.168.1.1 update-source loopback0 BGP
BGP specifies that it can advertise to its peers in neighboring AS's only routes that it uses. BGP cannot influence how a neighboring AS will route your traffic BUT it can influence how your traffic gets to the neighboring AS. BGP
EBGP will only peer to direclty connected neighbors and a loopback is considered one hop away. With eBGP peering to a loopback you must enable eBGP Multihop. R1(config-router)# neighbor 192.168.1.1 ebgp-multihop 2 BGP

43. What is the terminology for BGP route reflector?

44. Explain the contents of the BGP update message.
The BGP Table Command = show ip bgp BGP
Variable length sequence of path attributes Attribute Type -1 byte flag field - 1 byte type code Attribute Length Attribute Value Attribute flag field = 0000 0000 W | O - T | N - P | C BGP
Local scoped: 224.0.0.0 - 224.0.0.255 TTL of 1; Never to leave local network - for routing protocols and other network maintenance. Global scoped: 224.0.1.0 - 238.255.255.255 MBone dynamically allocate throughout Internet Limited/
This will advertise the entire classful network: R1(config-router)# network 10.1.1.0 This will advertise the the classless network: R1(config-router)# network 10.1.1.0 mask 255.255.255.0 BGP

45. What does BGP use for communication? What advantage does it offer?
Use loopback interface to establish the neighbor. (i.e. peer to a loopback interface) Tell BGP to use the lookback interface as teh source of updates R1(config-router)# neighbor 192.168.1.1 update-source loopback0 BGP
Router#(config) ip pim spt-threshold {rate | infinity} [group-list access-list] Multicast
TCP port 179 Reliability; uses sliding window Triggered - incremental updates made very efficient BGP
* = Best route > = Route has been inserted into the routing table BGP

46. What is the command to configure a BGP RR?
Group of BGP routers being configured that have the same update policy. Similar to a 'template'; members then assigned to the peer group. BGP
WD Dictates which path is preferred to exit the AS. Higher is is preferred - default is 100 on Cisco. Obviously for this to be relevant there must be multiple exit points for the route. 'Influences outbound traffic for an AS' Router(config-router)# neighbor 192.168.1.1 route-reflector-client BGP
Using a Distribute List to filter outbound routing updates. BGP

47. What is a neighbor call in BGP?
BGP peer BGP
TCP port 179 Reliability; uses sliding window Triggered - incremental updates made very efficient BGP
Session description & announcement. Transport session announcement via 224.2.127.254. Creation of new sessions. Multicast
The Source and Share Tree models are the working model of how the tree is built; all multicast routing protocols fit into one or both. This is the 'theory' or model. PIM-DM's operational falls in the source tree model and PIM-SM is classified an

48. Explain the Community attribute.

49. Explain the path selection process for BGP? What is the order and what preference does it take?
Works if router has multiple parallel paths to a destination. ONLY affect number of routes in IP routing table not the route selected at best in the BGP table. Will load balance across equal cost paths in EGP session. BGP
1. Weight - Administrative preference (Highest) 2. Local Preference - Communicated between peers within AS (Highest) 3. Self-originated - Prefer path originated locally (True) 4. AS Path - Minimize AS hops (Shortest)<
Determines upstream and downstream interfaces. Uses the unicast routing table to insure that only one interface is considered to be and incoming interface for the source. RPF makes sure that if data is looped around is not forwarded. 
IGMP Snooping - requires special ASICS can degrade performance with it; is supported by multiple vendors. CGMP - Cisco proprietary - only work on Cisco hardware; resource friendly GMRP - Replaced by MRP; obscure Manually - Performance

50. Name the Well-known discretionary attributes.
Local preference Atomic Aggregate BGP
IGMP is a layer 3 protocol Switches treat multicast just like broadcast (forward out all ports except the one one which is was received) By definition a pure layer 2 devices do not have a mechanism to see IGMP packets or facilitate the rela
Must insure loopback is reachable in the routing table. BGP
BGP not designed for load balancing (by default). BGP selected the SINGLE best path to a destination and places it in the routing table; the rest are kept in the BGP Table. Paths are chosen based on policy. BGP eliminates paths until one p