BGP: Difference between revisions
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= iBGP vs eBGP = |
= iBGP vs eBGP = |
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1. EBGP is peering between two different AS, whereas IBGP is between same AS (Autonomous System). |
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2. Routes learned from eBGP peer will be advertised to other peers (BGP or IBGP); however, routes learned from IBGP peer will not be advertised to other IBGP peers. |
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3. By default, EBGP peers are set with TTL = 1, which means neighbors are assumed to be directly connected, which is not in the case of IBGP. We can change this behavior for EBGP by using command “neighbor x.x.x.x ebgp-multihop <TTL>”. Multihop is the term used in EBGP only. |
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4. EBGP routes have administrative distance of 20, whereas IBGP has 200. |
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5. Next hop remains unchanged when route is advertised to IBGP peer; however, it is changed when it is advertised to EBGP peer by default. |
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This default behavior of IBGP can be changed by the command “neighbor x.x.x.x next-hop-self”; this changes the next hop, while advertising, as a local route. |
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For IBGP peers dont need to be directly connected. |
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Next-hop IP will not be changed when adv prefixes to another IBGP. |
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Also, if you check the way BGP choose the best route to put in the routing table you'll see that EBGP is preferred. |
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And BGP can run in two modes that each has a very different behavior when advertising routing information. |
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EBGP: external BGP runs between routers in different ASs. |
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IBGP: internal BGP runs between routers in the same AS. |
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EBGP: routes received from an EBGP peer can be advertised to EBGP and IBGP peers. |
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IBGP: routes received from an IBGP peer cannot be advertised to another IBGP peer but can be advertised to an EBGP peer. |
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