Term
| Describe the local preference attribute used in BGP. |
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Definition
| The local preference attribute indicates to the routers within the same AS which path is preferred to exit the AS. The path with the higher local preference is preferred. It is also a well-known distretionary attribute. |
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Term
| Describe the community attribute used in BGP. |
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Definition
| BGP communities allow routers to tag routes with an indicator (the community) and allow other routers to make decisions based on that tag. Communities are optional transitive attributes. |
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Term
| Describe the multi-exit distriminator (MED) attribute used by BGP. |
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Definition
| The MED (also called the metric) indicates to external neighbors the preferred path into an AS. The lower metric will always be preferred. The MED is an optional nontransitive attribute . |
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Term
| What is the difference between the MED and local preference attributes? |
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Definition
| The MED attribute influences inbound traffic to an AS, whereas the local preference influences outbound traffic from an AS. |
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Term
| Describe the weight attribute used by BGP. |
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Definition
| The weight attribute provides local routing policy used for the path-selection process. Routes with a higher weight are preferred when multiple routes to the same destination exist. |
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Term
| In what order are the attributes considered in selecting the best path for BGP? |
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Definition
1. Highest weight 2. Highest local preference 3. The route that was originated be the local router 4. Shortest AS-path 5. Lowest origin code 6. Lowest MED 7. Prefer EGP over IGP paths 8 Closest IGP neighbor 9 Oldest route 10. Lowest neighbor router ID 11. Lowest neighbor IP address |
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Term
| How is a peer group used in BGP? |
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Definition
| A BGP peer group is group of BGP neighbors of the router being configured that all have the same update policies. |
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Term
| How can a configuration from a peer group be overridden on a BGP router? |
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Definition
| The router can be configured to override options from a peer group, but only if these options do not affect outbound updates. Only options that affect the inbound updates can be overridden. |
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Term
| What commands can be used to create a BGP peer group? |
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Definition
neighbor peer-group-name peer-group or neighbor ip-address peer-group peer-group-name |
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Term
| What command is used to reset the BGP connections for all members of a BGP peer group? |
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Definition
| clear ip bgp peer-group peer-group-name |
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Term
| What command is used to enter BGP global configuration mode? |
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Definition
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Term
| How many autonomous systems can a router be a part of when running BGP? |
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Definition
| Only one instance of BGP can be configured on a router at a time. |
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Term
| What command is used to activate a BGP session for external or internal neighbors? |
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Definition
| neighbor [ip-address | peer-group] remote-as AS |
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Term
| What command is used to disable (administratively shut down) an existing BGP neighbor or peer group? |
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Definition
| neighbor [ip-address | peer-group] shutdown |
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Term
| What command is used to cause a router to use the address of the specified loopback interface as the source address for BGP connections to a neighbor? |
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Definition
| neighbor {ip-address | peer-group} update-source loopback interface-number |
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Term
| What command allows the router to accept and attempt BGP connections to external peers residing on networks that are not directly connected? |
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Definition
| neighbor {ip-address | peer-group} ebgp-multihop [ttl] |
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Term
| What command is used to force BGP to use the source IP address of the update as the next hop for each network it advertises to the neighbor? |
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Definition
| neighbor {ip-address | peer-group} next-hop-self |
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Term
| What command is used to permit BGP to advertise a network if it is present in the IP routing table? |
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Definition
| network network-number [mask network-mask] [route-map tag] |
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Term
| What is the difference between the neighbor command and the network command in BGP? |
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Definition
| The neighbor command tell BGP where to advertise, and the network command tells other routing protocols what to advertise. |
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Term
| What must be in the IP routing table in order for BGP to advertise a specific route? |
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Definition
| An exact match to the network (both address and mask) must exist in the routing table for the network to be advertised by BGP. |
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Term
| What command is used to enable MD5 authentication on a TCP connection between 2 BGP peers? |
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Definition
| neighbor {ip-address | peer-group} password string |
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Term
| What command enables synchonization on a BGP router? |
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Definition
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Term
| What happens when a new policy is applied to a BGP router, and an update is not triggered? |
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Definition
| The new policy is applied only on routes received or sent after the change. |
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Term
| What command is used to cause a hard reset of the BGP neighbor(s)? |
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Definition
| clear ip bgp {* | neighbor-address} |
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Term
| What command is used to cause BGP to do a soft reset for outbound updates? |
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Definition
| clear ip bgp {* | neighbor-address} [soft out] |
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Term
| What command is used to inform BGP to save all updates that were learned from a specified neighbor? |
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Definition
| neighbor [ip-address] soft-reconfiguration inbound |
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Term
| What command is used to cause the router to use the stored unfiltered table to generate new inbound updates? |
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Definition
| clear ip bgp {* | neighbor-address} soft in |
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Term
| What command is used to preform a soft reconfiguration of both inbound and outbound updates? |
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Definition
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Term
| What command is used to display the BGP topology datebase? |
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Definition
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Term
What do the following status codes mean when seen inthe BGP topology table? - s - d - h - r - S |
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Definition
- s - indicates that the specified routes are suppressed (usually because routes have been summarized and only the summarized route is being sent) - d - indicates that the route is being dampened (penalized) for going up and down too ofter. - h - indicates that the route is unavailable andis probably down, but historic information exist. - r - indicates that the route was not installed inthe RIB. - S - Indicates that the route is stale (this is used in a nonstop forwarding-aware router) |
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