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Understanding the network.pdf - Back to Home

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classful <strong>network</strong>s. All that matters is that <strong>the</strong> addressing has correct bit boundaries<br />

and that you want <strong>the</strong>m announced. For example, we do not want <strong>the</strong> 12.14.117.0<br />

and 118.0 spaces announced and we are using 12.14.116.0 in various VLSM<br />

address segments. So, we will only announce <strong>the</strong> <strong>network</strong>s we know should be<br />

accessed from <strong>the</strong> Internet:<br />

ASBR-Master(config-router)#<strong>network</strong> 12.14.116.0 mask 255.255.255.252<br />

ASBR-Master(config-router)#<strong>network</strong> 12.14.116.128 mask 255.255.255.128<br />

ASBR-Master(config-router)#<strong>network</strong> 12.14.119.0 mask 255.255.255.0<br />

ASBR-Master(config-router)#<strong>network</strong> 192.168.180.0 mask 255.255.252.0<br />

Now, let's configure our remote neighbors, using <strong>the</strong> BGP configuration subprocess<br />

command :<br />

ASBR-Master(config-router)#neighbor 12.127.40.65 remote-as 46<br />

ASBR-Master(config-router)#neighbor 192.174.36.1 remote-as 67<br />

ASBR-Master(config-router)#neighbor 192.174.36.1 version 4<br />

ASBR-Master(config-router)#neighbor 12.127.40.65 version 4<br />

ASBR-Master(config-router)#neighbor 192.174.36.1 soft-reconfiguration<br />

inbound<br />

ASBR-Master(config-router)#neighbor 12.127.40.65 soft-reconfiguration<br />

inbound<br />

The command forces which version of BGP<br />

will be used, instead of using <strong>the</strong> default negotiation process which starts at version<br />

4 and moves downward until a version match is found. The command indicates that changes <strong>to</strong> <strong>the</strong> inbound<br />

BGP configuration should be enabled au<strong>to</strong>matically. Generally, whenever a change<br />

is made <strong>to</strong> <strong>the</strong> BGP configuration, <strong>the</strong> connection between neighbors needs <strong>to</strong> be<br />

reset. This is accomplished with (<strong>to</strong> reset all sessions) or <strong>to</strong> reset a specific session. With our configuration,<br />

our outbound connections need <strong>to</strong> be reset whenever we make a change.<br />

After BGP routing is established with our Internet access providers, we can also<br />

establish BGP adjacencies with o<strong>the</strong>r ASs, if we desire. To establish a peer session<br />

with BGP neighbors that are not accessible over a direct connection, <strong>the</strong> BGP configuration subprocess command must<br />

added <strong>to</strong> <strong>the</strong> BGP configuration in addition <strong>to</strong> <strong>the</strong> declaration. In this<br />

example, our BGP router is <strong>the</strong> default gateway for <strong>the</strong> inter<strong>network</strong>. Once <strong>the</strong>

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