Show Posts
This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.
Your screenshots look weird. Why not using carp and connect both units on both wans without a routing protocol
CARP presents a unique address to LAN clients. The clients will use one of the two nodes as their default gateway.
BGP to external peers tell each node where "the Internet" is.
iBGP - which is just BGP (not an IGP!) between two systems in the same AS - tells each node all routes the other node learned about "the Internet".
iBGP has a lower priority as the routes learned from external peers - also called eBGP.
So a packet gets to the CARP primary for e.g. destination the AS of German Telekom. If the AS path it received from external peer is shorter than the one it received from its partner node, it will send the packet through its uplink. Otherwise - even with both WAN links up and running - it will send the packet to its partner which will in turn send it along its WAN uplink.
The two nodes work in tandem.
If one WAN link fails all routes received from that external peer vanish.
If that was the WAN link of the active CARP primary, it will still receive the packets from the clients but now simply send all of them to its partner to use the other WAN uplink.
No failover for the clients ever (!) takes place as long as bot your nodes are up and running. The two nodes decide in a coordinated way if a packet for "the Internet" shall go "left" or "right" and act accordingly. The WAN links are completely opaque to the clients.
That's what you do with BGP.
Now OSPF is what you need if you have local networks inside your AS that should also be routed redundantly. So you have a remote office with VPN or leased lines and one connection to each of your nodes. That's where OSPF comes into play. Completely separate from all the BGP routing. The external BGP is only interested in a single route/prefix covering your entire AS.
Some people ditch OSPF altogether and use (i)BGP for internal routing, too. Leaner design but you must be careful not to leak more specific routes into the Internet.
Repeating myself: there is no failover ever for CARP if both nodes are running. Clients always send to the CARP primary. The primary then sends to the secondary in case it does not have an active uplink - or the secondary announces as better (i.e. shorter) route.
CARP is in place only for the case that one of your nodes explodes. In that case the secondary can take over.
The routes learned via iBGP from the partner node will take over, and all the traffic received from clients on the CARP address will be handed over to the partner node.