12 - Implementing eBGP Flashcards
What protocol port does BGP use?
TCP 179
What is Single Homed?
1 Connection to 1 ISP
What is Dual Homed?
2 Connections to 1 ISP
What is Single Multihomed?
1 Connection each to 2 ISPs
What is Dual Multihomed?
2 or more connections to 2 ISPs
How do you pre-define neighbors in BGP?
neighbor remote-as ‘
What 3 ways are routes added to the BGP table?
1.) BGP network cmd 2.) Route Redistribution 3.) Learning prefixes from a neighbor
What is NLRI?
Network Layer Reachability Information
What is the AS_Path?
The list of ASNs a route must go through to reach its destination. The shorter that list is the better.
What routes should an enterprise router advertise to an ISP BGP peer?
Public address blocks only.
What route should an ISP BGP peer advertise to the enterprise router?
Default route
What BGP commands verify the peer relationship?
show tcp brief’ and ‘show ip bgp summary’
How can you tell whether a peer relationship is an eBGP or iBGP peer?
show ip bgp peer summary’ and if the ASNs are different then it’s eBGP. If same, then iBGP.
What are the 6 neighbor states in BGP?
- Idle * Connect * Active * Opensent * Openconfirm * Established
What does the IDLE state mean?
The router has been administratively disabled or its waiting for the next retry.
What does the CONNECT state mean?
The TCP connection is being attempted but has not completed.
What does the ACTIVE state mean?
The TCP connection has been completed but no BGP messages have been sent yet.
What does the OPENSENT state mean?
The TCP connection exists and the router has sent the first message to establish the BGP neighbor relationship. (a BGP Open message)
What does the OPENCONFIRM state mean?
The TCP connection exists and the local router has received an OPEN message from the other router. The neighbor relationship may still be rejected.
What does the ESTABLISHED state mean?
The router are now neighbors/peers and can exchange update messages.
What command administratively shuts down a neighbor?
neighbor 198.51.100.2 shutdown
What command brings an adminstratively shutdown neighbor back up?
no neighbor 198.51.100.2 shutdown
What command lists the BGP neighbor state?
show ip bgp summary’
What does the BGP ‘network’ command do?
Put this prefix/ length into the BGP table, ASSUMING that prefix/ length is in the IP ROUTING TABLE.
What is the format of the BGP ‘network’ command?
network mask
How do you verify a route is in the BGP table?
show ip bgp’
What does the command ‘show ip route 192.0.2.0 255.255.255.0 longer-prefixes’ do?
Shows all the routes in that range.
A network engineer subnets a /24 into a /25 and a /26. ISP just wants the /24. How does the engineer get the /24 into the ip routing table?
Configure a static route for the /24 with an outgoing interface of null0.
What is a route called that has an outgoing interface of null0?
Discard route.
What is an Autonomous System?
An internetwork that is managed by a single organization.
What is the Internet Edge?
The connection between an ISP Customer and the ISP.
What is the BGP Table?
The table in each router, maintained by the BGP process, that holds prefixes and path attributes known to BGP.
What is a Discard Route?
A static route with an outgoing interface of null0, which causes a router to discard packets that, when forwarded, happen to match that route.
