[j-nsp] IBGP via EBGP Default

[Keegan Holley]

You shouldn’t be learning routes via an eBGP peering if they already have your AS number in the path.  Beyond your bouncing peer that could cause a routing loop if the eBGP route took over while the iBGP route was still valid.

That being said, the juniper kit doesn’t treat iBGP routes differently than eBGP routes beyond the normal route selection process.  Technically there is no such thing.  If you think about it your peer’s AS number doesn’t suddenly create two different routing protocols.  It was just an easy way to differentiate between one’s domain and the rest of the internet in the docs. 

I could think of a few places where what you saw could be valid behavior. There are networks using eBGP within a single datacenter for example with no IGP protocol.  Juniper tends not to try and predict how you will use it’s routers when it writes the code.  Some vendors will introduce features that make life easier for most but become cumbersome if presented with a corner case.  That being said juniper router will give you enough freedom to seriously break things if you’re not careful.



On Mar 17, 2014, at 1:55 PM, Christopher Costa <ccosta at gaikai.com> wrote:

> We observe on EX and QFX platforms that their IBGP session is
> maintained (and reestablishes when bouncing the session) when the
> interconnect between them goes down; following an EBGP learned default
> route to reach the peer address.  Juniper says this is expected
> behavior, although my understanding is that the IBGP session should
> not be maintained when the underlying route is known via EBGP.  Am I
> mistaken about that?
> 
> Thanks
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