Let us think about 2 routers, routerA and routerB who want to become BGP neighbors (it might be IBGP or it might be EBGP, same things apply to both). It seems that was not so clear so let me try again from a slightly different perspective. I tried to explain about BGP neighbors using loopback addresses or not in a previous response. I hope to see you continue to be active in the community. This community is an excellent place to ask questions and to learn about networking. It has been a long discussion and I am glad that our explanations have been helpful. By changing the IBGP neighbor address to the vlan interface rather than the loopback interface we remove the requirement for OSPF and make the configuration more simple. But those reasons are not present in this network. There are some good reasons why you might choose to make the IBGP neighbor address be on a loopback interface. This is one example of making things more complex than they need to be. If the neighbor address is the vlan 15 address then the router knows how to reach that address (it is in a directly connected subnet) and there is no need for OSPF. I suggest an alternative: configure IBGP so that the IBGP neighbor address is the vlan 15 address of the peer router (rather than as the loopback address). So OSPF is necessary for this implementation of IBGP. If OSPF did not advertise that address then IBGP would not work. So this is the basis of my statement about OSPF and IBGP. So how does this router know how to reach 10.2.52.240? That address is advertised by OSPF. To form the IBGP peer relationship the router must know how to reach the peer address. This address is the loopback interface address of the peer router. Looking into the configuration of IBGP we find that one router defines the IBGP neighbor as 10.2.52.240. Then let me try to clarify my statement about OSPF and IBGP. (note that the loopback interface address is used both as the OSPF Router ID and used as the IBGP peer address. It is not the vlan 15 address that is advertised but is the loopback interface address that is used. Then let me address this statement that you make " OSPF is having two routes - the vlan 15 interface and ISP address" This is not correct. A vlan interface can not be a loopback and a loopback interface can not be a vlan. A vlan interface is a particular type of virtual interface. A loopback is a particular type of virtual interface. First you ask this question " Cant we use simply the VLAN 15 address as loopback." Perhaps it is simply a confusion about terminology. There are several things I would like to address. Ip prefix-list FILTER-OUT seq 40 permit 10.2.5.0/24 Ip prefix-list FILTER-OUT seq 30 permit 10.2.4.0/24 Ip prefix-list FILTER-OUT seq 20 permit 10.2.3.0/24 Ip prefix-list FILTER-OUT seq 10 permit 10.2.2.0/24 Neighbor 22.2.22.12 prefix-list FILTER-OUT out Neighbor TEST_GROUP soft-reconfiguration inbound Neighbor 10.2.2.11 peer-group TEST_GROUP > this IS router 2 loop back address in DC2 Neighbor TEST_GROUP update-source Loopback0 Neighbor TEST_GROUP password 7 XXXXXXXXXXXXXXXXXX Ip ospf message-digest-key 1 md5 7 XXXXXXXXXXXXXXX In OspF it have defined the redistribute connected and static plus network address for4 subnets also. īoth the router have a default route pointing to their respective ISP. I want to understand how the failover will work in case ISP link goes down. BGP is also configured between two routers. īetween Router 1 and Router 2, we have defined a VLAN 11 where we run OSPF. The DCs are connected over a Physical underground link. Similarly router in DC2 is connected to Core switch in DC 2 ( again L2 connection) The router in DC1 is connected to COre Switch in DC1 > This is a Layer 2 connection FOr one of our customer, they have two router one in each DC
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