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	<title>Cisco Networking Answers &#187; bgp</title>
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		<title>BGP Configuration for Cisco Routers</title>
		<link>http://cisco-network.com/hands-on/bgp-configuration-for-cisco-routers/</link>
		<comments>http://cisco-network.com/hands-on/bgp-configuration-for-cisco-routers/#comments</comments>
		<pubDate>Wed, 03 Oct 2007 20:21:46 +0000</pubDate>
		<dc:creator>MustafaAksu</dc:creator>
				<category><![CDATA[Hands-on]]></category>
		<category><![CDATA[bgp]]></category>
		<category><![CDATA[cisco 3845]]></category>
		<category><![CDATA[cisco router]]></category>

		<guid isPermaLink="false">http://cisco-network.com/hands-on/bgp-configuration-for-cisco-routers/</guid>
		<description><![CDATA[I want to show a basic BGP configuration for Internet access. In our case, we have two carriers (Sprint &#038; Level3) and we act as an enterprise company, which needs reliable Internet access. As a precondition we need an Autonomous System Number (ASN) and an IP address block assigned to us. We have to apply [...]]]></description>
			<content:encoded><![CDATA[<p>I want to show a basic BGP configuration for Internet access. In our case, we have two carriers (Sprint &#038; Level3) and we act as an enterprise company, which needs reliable Internet access.<br />
As a precondition we need an Autonomous System Number (ASN) and an IP address block assigned to us. We have to apply ARIN / RIPE / APNIC / LACNIC / AFRINIC for this purpose. We assume that we have 6767 as our AS number and 193.93.93.0/24 as our official IP block.<br />
<a href='http://cisco-network.com/wp-content/uploads/2007/10/bgp_configuration_sample.GIF' title='bgp_configuration_sample.GIF'><img src='http://cisco-network.com/wp-content/uploads/2007/10/bgp_configuration_sample.thumbnail.GIF' alt='bgp_configuration_sample.GIF' /></a></p>
<p>To show some different conditions, our connected Level3 router is also the BGP router, but Sprint BGP router has been located 3 hops away.</p>
<blockquote><p>! We are starting with router command with our ASN like EIGRP/OSPF configuration<br />
<strong>router bgp 6767</strong><br />
! We have one router in our case and we don’t need IGP / BGP synchronization it is default in newest IOSes<br />
 <strong>no synchronization</strong><br />
! To have some idea about our peering history we are recording events<br />
 <strong>bgp log-neighbor-changes</strong><br />
! We are announcing our network<br />
 <strong>network 193.93.93.0 </strong><br />
! Our first neighbor is Sprint, we have to define neighbor ASN<br />
 <strong>neighbor 122.22.33.1 remote-as 1239</strong><br />
! Descriptions are always helpful<br />
 <strong>neighbor 122.22.33.1 description Sprint </strong><br />
! Our bgp neighbor in Sprint 3 hops away<br />
 <strong>neighbor 122.22.33.1 ebgp-multihop 3</strong><br />
! Sprint will use our Loopback IP (193.93.94.1) for us as the neighbor<br />
 <strong>neighbor 122.22.33.1 update-source Loopback 0</strong><br />
! If we have enough memory, we can prevent BGP session resets on inbound updates<br />
 <strong>neighbor 122.22.33.1  soft-reconfiguration inbound</strong><br />
! We won’t announce any network other than ourselves<br />
 <strong>neighbor 122.22.33.1 filter-list 1 out</strong><br />
! Now the Level 3<br />
<strong> neighbor 111.11.11.1 remote-as 3356<br />
 neighbor 111.11.11.1 description LevelThree<br />
 neighbor 111.11.11.1 soft-reconfiguration inbound<br />
 neighbor 111.11.11.1 filter-list 1 out<br />
 no auto-summary</strong><br />
!<br />
! Sprint BGP bridgehead is not directly connected to our router<br />
! We must add necessary routing<br />
<strong>ip route 122.22.33.1 255.255.255.255 122.22.22.1</strong><br />
!<br />
! This filter means we are not announcing Sprint networks to Level3 or vice versa.<br />
<strong>ip as-path access-list 1 permit ^$</strong><br />
!</p></blockquote>
<p>In the end, if you are not on the middle of the Internet, BGP configuration is not a big issue.</p>
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