BGP confusion

AS 65000 -> ISP -> AS65000

In the above diagram, the customers are using AS 65000 on both sides. The ISP is using the as_override command. In this case, is the customer running IBGP or EBGP? I am confused.

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Comments

Node Man

I'll take a stab at this. BGP neighbors do not need to be adjacent. IBGP and EBGP just depends on same AS or not. The entire internet can be between two IBGP routers.

atorven

The customer is running EBGP with the ISP.

Node Man

The customer could be a layer 2 tunnel across the ISP.

d4nz1g

since there is no mention related to the peering scheme, we could assume that the customer peers with the ISP (eBGP or iBGP - since there is no AS for the ISP as well), or the customer is using the ISP as a transit to reach the other site (l2vpn and a /30 point to point link, or a multihop peering - iBGP)

daveyb

eBGP. As override is used to advertise routes back to a peer with the same origin AS number. Without this, the device on the left would not learn the routes from the device on the right. Usually this is not required as a default route would usually suffice.

As override doesn't apply to an iBGP neighbour as far as I can remember. The rules for redistribution are different.