BGP use case in Dual-homed scenario

[NInja Black]

Need some clarification on BGP use case in a dual-homed scenario.

In the dual-homed scenario depicted below, is there any benefit of using BGP to advertise public networks? Configuring default routes with different metrics should suffice. Please advise

DC-R1 ----------(link)------- ISP-A R1

DC-R2 ----------(link)------- ISP-A R2

[balaji.bandi]

if this is external i prefer to have BGP peering, so you have control on the Traffic Engineering.

Configuring default routes with different metrics should suffice.  <<< - mean static route ? i stay away from static route (i only go with this if i do not have option or ISP offering BGP)

there is pros and cons - depends on use case.

[Sergiu.Daniluk]

Hi @NInja Black 

Not sure if your question is about having dual-homed external connectivity or about routes advertisement (default route vs public prefixes). So I will respond to both of them ^_^

• Dual homed connectivity:

+ redundancy in case a link to one ISP experience problems (latency, drops or goes down)

+ redundancy in case one of the your edge routers goes down or experience a problem

+ higher overall bandwidth/throughput for North South traffic

• Default route vs public prefixes:

+ there is not much of a debate here; usually for a DC, default route is sufficient. Plus, the DC routers (Nexus switches) have a limited amount for IPv4/v6/LPM route entries they can install in TCAM. 

EDIT:  Yes, BGP offers you the advantages of influencing the traffic path, so if the two routers are your exit for your full DC network, and you do not have other connections to main sites or campus, you might want to look at implementing BGP on the edge routers.

Hope it helps,

Sergiu

[NInja Black]

The 2 routers I am referring to are Internet routers (guessing these would be the edge routers) connecting to the same ISP (Dual-home). My understanding was BGP is used in a multi-home scenario connecting to 2 different ISPs. But advertising the public facing network through BGP makes sense in my scenario as routes need to be distributed between the internet and WAN, based on what sergui mentioned "Yes, BGP offers you the advantages of influencing the traffic path".

Extending my question: 

with 2 Data centers, primary and back up, can the internet routers at both DCs have the same public BGP ASN without being iBGP peers? Or do they need to be iBGP peers? All routers in an organization should be iBGP peers. Is this valid across data centers? if yes then all routers should be iBGP peers (full mesh or RR) correct?

I have a basic understanding of how iBGP and eBGP work, but not in a production environment. Hope my questions are clear.

[balaji.bandi]

I would suggest to run BGP between DC Edge routers, so you have ability to detect the failures and route the traffic other path.

Need some clarification is this DC are in One Location ? or different Location ?

For config and reference :

https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13762-40.html

[NInja Black]

The DCs are in different locations. About 300 miles apart.

 Do the edge routers need to be iBGP peers?

[balaji.bandi]

Are these DC are inter connected with Dark Fibre  or MPLS or any other method  ?  or  you use this ISP as Transit ?

Yes i prefer to have peering between Edge Router to Edge Router (in your DC enviroment).

How is your exiting arangement for the Failure Scenario for the DC Failover ?

[NInja Black]

Balaji,

 Sorry for the delayed response. The DCs are interconnected through EMPLS over ASR1000 routers, and also over ISR WAN routers through MPLS.

As of now the same routers work as WAN/internet routers. We are in process of setting up separate internet routers at both DCs and hence the question.

So in conclusion the edge routers do need to be iBGP peers. 

[balaji.bandi]

Sure and i prefer to do that, so you have determine the failures and action.