The static routes were configured in this case in order to achieve connectivity between the BGP peers. Remember, in order for BGP to operate, BGP peers must be able to find each other. That means that routing between those BGP peers must already be established, either by using IGPs or by using static routes.
This might sound a little bit strange because BGP is a routing protocol. Why do you need other routing protocols to enable communication between BGP peers, in order to exchange routes? Take a look at this NetworkLessons note on why we need an IGP for BGP to work, and if you have any further questions, please let us know.
When configuring eBGP peering between two routers with two redundant connections using their Loopback interfaces, is it better to configure it like this
neighbor x.x.x.x ebgp-multihop 2
or
neighbor x.x.x.x disable-connected-check
Since in both situations, the adjacency would establish successfully.
Great work as always. I had a question. I see this type of redundancy creating static routes with BGP. In this example what if there were 6 routers to hop? I understand you configure the multi hop to 6 but would I then also have to create a static for all the routers so I can achieve connectivity and be able to reach each other? Or is there a more simple and easy way for this.
If there were 6 routers/hops between the two eBGP peers, then yes you would configure the multihop value to 6 or larger. But the other prerequisite is that the two eBGP routers must be reachable to each other. In other words, the two eBGP peers must have routing established between them, over those 6 hops, to be able to achieve an eBGP peering.
That routing can be established using any method you like, static routing, or some dynamic routing protocol such as OSPF, EIGRP, or IS-IS. As long as routing is established between them, they will be able to create the eBGP peering. Does that make sense?
When using the ebgp multihop to peer with loopbacks, I want to see if I understand. This may not be bgp multipath but wouldnât the next hop for all prefixâs be the other neighbors loopback? If so then wouldnât this end up in a load balancing situation for all advertised prefixâs (because of the statics) even if its technically not using bgp multipath? An L3 channel should give the same result as well correct?
To quickly answer your question, yes, you will see load balancing across the links BUT thatâs due to the static routes delivering equal cost load balancing. BGP plays no role whatsoever in this behavior. In this lesson, the only thing that is being done with BGP is creating BGP peerings. There are actually no routes being advertised or exchanged between BGP peers in this lesson.
The purpose of the lesson is to show how BGP peerings behave and the related best practices when using eBGP multihop to deal with using loopbacks as the source of BGP messages, and with multiple links between routers.
Now if BGP were to use this peering to advertise routes, by default it would advertise only a single path. This is because the best path algorithm ensures that only a single path is advertised by definition. In this case, for both links the router ID is the same (since both links lead to the same router), so the very last tie breaker is the Neighbor IP address. From the point of view of R1, the neighbor IP address of R2 for the first link is 192.168.12.2 and for the second link is 192.168.21.2. This attribute CANNOT be equal, thus it will always break the tie, thus you will never have load balancing.
Take a look at the BGP attributes and path selection lesson for more information:
Do you mean EtherChannel? Hmm, well actually no, because an L3 EtherChannel would be seen by all processes as a single logical link, so the mechanisms for load balancing across the two physical links will not be applied by the equal cost static routes, but via the EtherChannel load balancing algorithms. Similarly, BGP would see this as a single link, so there would be no BGP best path algorithm process taking place.
Hello Guys.
Big question here. If I want to use my interfaces loopbacks for ebgp peering I need to use ebg Multihop right? If I want to use interface loopbacks for ibgp I can omitted multihop?
Yes, you are absolutely correct. By default, eBGP requires that peerings take place between sources on the same subnet and that is why the multihop feature is necessary.
iBGP has no such restriction. Remember that within a single AS, all iBGP routers within that AS must have a full mesh peering. In other words, all iBGP speakers within an AS must be peered with all other iBGP speakers in the AS. And this means even iBGP peers that are several hops away. So, iBGP peerings donât need the multihop feature because they can inherently peer with iBGP routers that are several hops away, as long as their IP addresses are reachable. This is also why we need an IGP within the AS for BGP to work.
